Download NSDNR Forest Disturbance Report

Forest Disturbance Ecology
in Nova Scotia
Draft Report
February 7, 2007
Renewable Resources Branch, Forestry Division
Ecosystem Management Group, Truro
by
P. D. Neily, E. J. Quigley,
B. J. Stewart and K. S. Keys
Table of Contents
1
2
Introduction
Disturbance Ecology
2.1
Natural Disturbance Defined
2.2
Natural Disturbances in Nova Scotia
3
Natural Disturbance Regimes
3.1
Frequent Stand Initiating Disturbances
3.2
Infrequent Stand Initiating Disturbances
3.3
Gap Dynamics Disturbances
3.4
Stand Maintaining Disturbances
3.5
Open Seral Maintaining Disturbances
4
Forest Disturbance Agents
4.1
Fire
4.1.1 Fire Caused By Lightning
4.1.2 Regional Fire History
4.1.3 Fire Suppression
4.2
Insects and Diseases
4.3
Hurricanes and Windstorms
4.4
Other Natural Disturbances
5
Anthropogenic Disturbances
6
Natural Disturbances and Forest Structure
7
Forest Management and Natural Disturbances
7.1
Emulation Silviculture
7.1.1 Fire Disturbances and Forest Management
7.1.2 Wind Disturbances and Forest Management
8
Closing
9
Literature Cited
10
Additional Reading and Sources of Information
Appendix I Significant post-settlement forest disturbances in Nova Scotia.
Appendix II Natural disturbance regimes by ecodistrict.
Appendix III Methodology for assigning natural disturbance regimes to ecosections.
1.
Introduction
Ten thousand years ago all remaining ice from the Wisconsin glaciation had melted from
Nova Scotia and the climate had warmed rapidly (Stea et al 1992). Plants began the migration inland
and northward onto the newly exposed land areas. Roland and Smith (1969) write that data from
pollen analysis of peat bogs suggest that tundra and steppe conditions prevailed for a considerable
time, perhaps a thousand years or more. Grasses, sedges and pteridophytes (ferns, club mosses and
horsetails) became common and trees such as poplars, then birches, fir, spruce and pines increased
gradually in abundance. Sugar maple, elm, beech and oak followed with their typical herbaceous
flora. During this period natural disturbances varied only as vegetation responded to climate
fluctuation, which has not changed drastically since the first trees appeared (Roland and Smith,
1969).
The development of Acadian forest communities has continued in a more or less steady state
with plants distributed according to the ecological conditions to which they were best adapted. For
example, as sites became more leached and acidic, heath plants increased in abundance. Roland and
Smith (1969) suggest that plants of richer habitats may possibly be still moving into the region as
the deciduous forests become longer established and conditions more suitable for them to develop.
At the time of European arrival in the 1500's the forests of Nova Scotia had evolved to include large
tracts of shade tolerant hardwood and softwood trees under natural processes that reflected the
climate and physical environment and included disturbances to the forests by wildfire, hurricanes,
insects and diseases. By 1900 over 2.2 million acres (20% of the province) of forested land had been
cleared for agriculture (Fernow 1912). In addition, extensive harvesting had occurred in the forests
with the timber shipped to France and England as both had depleted their own forests. Fernow
(1912) estimated that only .68 million acres (5.6%) of the provincial forest was still in a virgin state
and most of that (.425 million acres) was comprised of extensive balsam fir forests on the Cape
Breton Highlands. As well harvesting practices, such as high-grading, and uncontrolled fires
following land clearing and harvesting, created large areas of poorly stocked stands of low quality
timber.
However, after Fernow’s report, both industry and government became concerned about the
health of the forest and the supply of forest products. The wanton destruction by fire, in particular,
would no longer be tolerated and in 1926 legislation created the Department of Lands and Forests
and assigned to the Minister, the conservation and protection of all forests and timber lands, and to
the Chief Forester, the Forest Ranger Service, to conserve the forests and to protect them from fire
(Creighton 1988).
The intent of this report is to provide information on the disturbances that have created the
current composition and extent of forests in Nova Scotia. The report attempts to place in one
document the available literature and data on forest disturbances in Nova Scotia.
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2.
Disturbance Ecology
- the larger message is that there was no fixed “original landscape”
David A. Foster, Director, Harvard Forest
Foster (2000), an ecological historian in Massachusetts suggests there is a pattern of long
term, ongoing dynamics in which multiple factors drive population, ecosystem, and landscape
changes in complex ways and that there is an absence of established baseline conditions
(unchanging “primeval” or “natural” conditions). Since forest composition was changing due to
natural causes prior to European arrival, for example, both beech and hemlock were in decline about
500 years ago, the post-settlement changes were “clearly a consequence of multiple factors” - natural
disturbance, European settlement, and environmental change. He concludes that we should expect
future change to our landscapes and that there is no true ability to re-create or preserve the past.
Kay et al (2000) suggest that it is not about maintaining the ecosystem in a specific state or
even configuration - rather it is about maintaining the process of self-organization. Frelich (2002)
continues this point by saying that if the forest experiences a series of unique disturbances over time,
so that type, frequency, severity and size cannot be characterized, then there is no stable regime.
However, he reports that apparent stability of the regime is a function of the length of time and size
of area observed, for example, paleoecologists may view the temperate forest of eastern North
America as unstable since there have been at least three major vegetation shifts in the forest since
the last glaciation (spruce; pine-oak; hemlock-hardwood) during which the forest experienced a
series of unique climatic and disturbance events that resulted in major changes. From the forester’s
point of view, however, there may have been periods of stable disturbance regime at time scales of
decades to centuries between major changes. Frelich (2002) believes it is becoming increasingly
obvious that forest change over time exhibits a punctuated stability phenomenon, and those who
view the vegetation as stable and those who view it as unstable may both be right. This is however
dependent on the scale of observation.
McRae et al (2001) raise an interesting point when they suggest that the forests before
European colonization were not in a condition of near-equilibrium with climate and the natural
disturbance regime and that post-glacial equilibrium landscapes had not fully developed (studies
show wide variations in species composition and abundance in pre-settlement forests). They suggest
that the abundance of old growth forest in pre-Columbian times should not be used as proof that the
forests had reached a state of ecological equilibrium. They further suggest that since anthropogenic
disturbances have greatly modified the forests, the changed ecosystems may make it impossible and
even undesirable to fully restore the primeval landscapes.
2.1
Natural Disturbance Defined
Naturaldisturbances in the temperate forests of North America can usually be divided into
two types based on the amount of overstory removed . Those which remove or kill all the exisiting
trees above the forest floor vegetation are referred to as major disturbances or stand-replacing
disturbances. Those which leave some of the predisturbance trees alive are referred to as minor
disturbances (Oliver and Larson, 1996). In forests, major disturbances generally favour colonizing
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species, while minor disturbances favour the competitive species. Typically, diversity in the
landscape is greater with major disturbances at infrequent intervals while minor but frequent
disturbances create high diversity at the stand or ecosystem level (Dunster and Dunster 1996). Since
disturbances exert a strong control over the species composition and structure of forests Frelich
(2002) gives as a general rule of thumb that landscapes with frequent, severe disturbances (stand
replacing) are dominated by young even-aged stands of shade-intolerant species such as aspen
[white birch, jack pine, red pine]. Conversely, old stands of shade-tolerant species such as hemlock
[red spruce, sugar maple, yellow birch] dominate where severe disturbances are rare. Frelich (2002)
continues to say that every conceivable mixture between these two extremes can be created by the
various combinations of disturbance and that forest development depends upon the intensity of the
disturbance described as follows:
i) a high severity disturbance kills most of the understory and overstory, leaving only
scattered survivors and portions of the seedbank. Examples: crown fires, clearcutting
followed by slash burning.
ii) a moderate severity disturbance kills some of the overstory and understory, leaving a
partial canopy layer and portions of the seedling/seedbank layer intact. Examples:
windstorms and clearcutting, surface fires.
iii) a low severity disturbance kills small pieces of the forest understory or overstory (or
both). Examples: treefall gaps, individual tree mortality, selection harvesting.
2.2
Natural Disturbances in Nova Scotia
In Nova Scotia natural disturbances in the forest result from fire, wind and ice, insects,
animal predation, disease, flooding, downslope creeping or fast destructive slides and senescence.
After four hundred years of European colonization the activity associated with settlement has
affected the frequency, intensity, and magnitude of natural disturbance processes in the Acadian
forest region. New disturbances have been introduced as a result of human activity including the
clearing of forests for agriculture, increased frequency of forest fires, timber harvesting, urbanization
and development, introduction of exotic animals, plants, insects, and pathogens, fire
suppression/exclusion in the forest and changes in the chemical and physical characteristics of the
atmosphere. The extent to which it is possible to fully restore the pre-European condition to Nova
Scotia has been compromised by human actions- exotic (non-native) pests have been introduced
resulting in irreparable changes to forest communities, e.g. beech canker, Dutch elm disease; there
have been species extinctions, e.g. woodland caribou; climate (global warming) and acid
precipitation reflect the human presence, and overall, the impact of natural disturbances on forests
has been exacerbated by human interventions.
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3.
Natural Disturbance Regimes
Natural disturbance in the forest can be described by 1) the amount of existing forest removal
above the forest floor; 2) frequency of the disturbance; 3) size and shape of the area disturbed; and
4) amount of forest floor vegetation, forest floor, and soil removed. Many disturbances vary in the
amounts of vegetation removed and the reoccurrence interval of the disturbance. Combinations of
the amount of vegetation removed - whether major (stand replacing) or minor - and the recurrence
interval could be considered as disturbance regimes (Oliver and Larson, 1996). Disturbance regimes
are one of the major forces that structure the mosaic of forest communities across the landscape,
therefore, landscape characteristics are sensitive to changes in disturbance regimes (Frelich 2002).
The distribution of tree species and forest types is closely related to the topographic and soil
conditions of the land (Rowe 1972). The change in forest structure and/or composition is
accomplished through disturbances in forest ecosystems - individually distinct forces that cause
significant change through natural events such as fire, flood, wind or earthquake; mortality caused
by insect or disease outbreaks; or by human-caused events such as the harvest of a forest (Dunster
and Dunster 1996). Thus landscape structure and pattern are essentially a product of the underlying
or inherent geomorphological pattern and the overlying or induced disturbance pattern (Methven and
Kendrick 1995). The former exerts its control on species distribution and development rates, while
the latter controls age class patches and their distribution over space and time. Therefore
disturbances are necessary for maintaining species richness and biodiversity. By changing existing
forest conditions and initiating secondary succession, natural disturbances create new ecological
communities such as can be achieved through the complete removal of vegetation from an area as
a consequence of an intense fire, or by the partial removal of a particular species or individual as a
result of insect infestation or senescence.
Disturbances vary from very infrequent and at irregular intervals to very frequent and at
regular intervals (Oliver and Larson, 1996). With several major disturbance types, each of which
could occur with many different levels of severity, different frequencies, different sizes, and all the
types interacting on a forested landscape, the problem of classification into disturbance regimes may
seem complex. However, the following five disturbance regimes are described for the forest
ecosystems of Nova Scotia1.
3.1
Frequent Stand Initiating Disturbance Regime
When the interval between stand initiating events is shorter than the longevity of the climax
species the disturbance regime is considered frequent. This disturbance regime is of an intensity that
results in the rapid mortality of an existing forest stand to the extent that a new forest of relatively
even-age is able to become established and dominate the site. These stands develop usually with
some retention of unharmed, older cohorts that have survived the disturbance in pockets and/or as
scattered individuals with insufficient numbers to dominate the structure of the newly developing
forest. Stand development is interrupted with another disturbance before the stand becomes old
1
Ecological Technical Committee, N.S. Dept. of Natural Resources, 1997.
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enough to display many uneven-aged characteristics such as canopy gap dynamics and understory
recruitment. The size and severity of the event is mitigated by several factors including climate,
species mix, and the agent. Examples of this type of disturbance include spruce budworm
infestations on the balsam fir dominated Cape Breton Highlands Ecoregion or the fire dependent jack
pine ecosystems of Cumberland County.
Black spruce forests in Nova Scotia are found primarily on imperfectly to poorly drained
soils. The stands are usually even-aged since the disturbance agents, fire and wind, result in a
significant portion of the canopy being destroyed. Black spruce are naturally shallow rooting which
makes this forest susceptible to blowdown. As well many of the imperfect to poorly drained sites
occur on shallow soils which during the summer months experience a moisture deficit. The dry soils
combined with the flammable make-up of the lesser vegetation, usually ericaceous shrubs (kalmia,
huckleberry, blueberry, rhodora), creates sites susceptible to fire. In the absence of stand initiating
disturbances site conditions will eventually lead to stand level senescence in black spruce due to the
accumulated effects of poor site, pathogens, insects, drought and excessive moisture. These
conditions lead to overstory mortality which becomes more pronounced as trees age, especially if
the vigour of the overstory species is diminished by site as may occur if the forest floor organic
matter increases, tying up nutrients, moisture and oxygen (Oliver and Larson 1996).
3.2
Infrequent Stand Initiating Disturbance Regime
When the interval between stand initiating events is longer than the longevity of the climax
species the disturbance regime is considered infrequent. Subsequently many stands develop unevenaged characteristics, i.e. multi-cohort, as trees from the understory are recruited into the overstory
as a result of frequent but low severity disturbances in the canopy. Under this disturbance regime the
opportunity for multiple successional steps/stages en route to the climax condition can occur. After
a catastrophic disturbance forest communities develop as even-aged stands and as the interval
between disturbances lengthens and the stand matures uneven-aged stand structure develops as a
result of individual or small patch tree mortality. The longer the disturbance interval the more
uneven-aged the stand becomes. Depending on the severity of the gap disturbances that will occur
as these stands develop and mature stands can either have the trees of all cohorts evenly distributed
throughout the stand or as a mosaic of small single-cohort stands. The spruce-pine-hemlock
ecosystems of the Western, Eastern and Central ecoregions could be considered examples of this
disturbance regime.
3.3
Gap Dynamic Disturbance Regime
Forest communities that are rarely exposed to stand initiating disturbances characteristically
develop overstories that are sustained by processes of canopy gap formation followed by understory
development and overstory recruitment, leaving an essentially intact forest canopy with a few gaps.
Gap dynamic disturbance regimes of small scale, continuous, incremental disturbances may favour
the development of fully uneven-aged stand structure and a sense of stability. Mortality is commonly
by animal or insect predation, disease, lightning, blowdown, and senescence due to old age.
Regeneration occurs under openings (gaps) created in the canopy after the death of individual or
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small patches of trees. Usually shade tolerant species regenerate in the openings and as more gaps
are created in the over-story this regeneration is released into the canopy and shares the space with
surviving older trees. With sufficiently long intervals between disturbances the stand develops a
“shifting mosaic” structure of mixed-aged trees all younger than the time since the last stand
initiating disturbance. In Nova Scotia the tolerant hardwood forests of the Uplands Ecoregion reflect
a forest maintained through the dynamics of gap disturbances. Lorimer and Frelich (1994) suggest
that gap formations in mesophytic (average sites) hardwoods cause nearly complete turnover in the
canopy in less than 250 years and that the mere existence of northern hardwoods on a site cannot rule
out severe disturbance as a factor in stand establishment since these species are adaptable to many
types of disturbances and that while intense fires in hardwood stands are relatively uncommon, this
disturbance agent cannot be excluded. An old growth study by Stewart et al (2003), indicates that
the canopy turnover in the Acadian hardwood climax forest is approximately 300 years.
Event-driven gap disturbances occur when uneven-aged climax forests experience mortality
or decline of an entire species or cohort over a wide area creating an influx of coarse woody debris
and extensive canopy gaps. In Nova Scotia recent examples of event-driven gap disturbances in the
climax sugar maple/yellow birch/beech forests occurred with the spread of the beech bark disease
in the early 1900's and the yellow birch dieback in the 1940's. During an event-driven gap
disturbance changes in the climax forest leave the post-disturbed stand different in species
composition and structure than the pre-disturbed one, and often favours the formation of two-aged
and multi-aged stands with distinctive age classes (Oliver and Larson, 1996).
3.4
Stand Maintaining Disturbance Regime
These low intensity disturbances occur at frequent intervals, an example being understory
or surface fires in pine, oak and hemlock stands in the Western Ecoregion. Surface fires cause light
to moderate damage to mature fire-adapted species, kill or injure flame intolerant trees, shrubs and
lesser vegetation, and reduce the build-up of slash and litter on the forest floor. These fires appear
to promote self-seeding or sprouting in red oak, black and red spruce, white pine and red pine forests.
The removal of flame intolerant species can shift the overall species composition, and favour fireadapted species (Kimmins 1997, Oliver and Larson 1996). The abundance of white pine, red pine
and red oak in pre-settlement forests may have been an indication of the dominance of fire in the
disturbance ecology of those forests. Basquill et al. (2001) found multiple scarred stems in
Kejimkujik National Park, some dating back to 1803, suggesting repeated under-story fires with an
average return interval of 25 years.
3.5
Open Seral Maintaining Disturbance Regime
Many terrestrial ecosystems have site conditions that restrict or limit tree growth creating
sparse or non-existent forest cover. Some of these ecosystems have developed site limitations to tree
growth after repeated site disturbances, especially fire. On these sites loss of fertility, hardpan
formation in the soil profile, and the allelopathic effect of ericaceous vegetation (heath-like) on
coniferous species create open woodland ecosystems with stunted trees, for example, the barrens of
southwest Nova Scotia. Gray (1956) concluded from his studies on the southwest barrens that once
8
heath plants and bracken fern are established in a dominant position, they become a serious limiting
factor to tree regeneration. Catling et al (2004) concludes that natural fires contributed to the
maintenance of the Annapolis Valley heathlands. Other areas in Nova Scotia have inherent
limitations to tree growth through natural processes such as extreme exposure to wind (e.g. coastal
krummholtz), seasonal flooding (floodplains along rivers) and adjacency to tidal waters (salt
marshes). And still others are wetland ecosystems (bogs and fens) where tree growth is restricted due
to excessive moisture, site conditions such as thick organic peat layers, and ericaceous vegetation.
Rowe (1972) states that the combination of moist climate and gentle relief has produced considerable
areas of non-forested bogland in the western and eastern ecoregions.
4.
Forest Disturbance Agents
Disturbances can vary in intensity and impact on the affected forest. Their variability can be
a function of the climate and weather, topography and landforms, soil properties, forest composition
and age class, wildlife populations, and other factors. The following provides some characteristic
features of the common disturbances in Nova Scotia.
Forest fires occur in late spring prior to green-up and throughout the summer, especially
during periods of lower humidity and dryness. Human activities during these periods increase the
probability of wild fires. Most fires kill both overstory and understory species with damage to the
forest floor dependent on ground moisture conditions and the amount of fuel buildup.
Winds from hurricanes and storms can cause both uprooting and stem breakage. Tree
susceptibility is dependent on site conditions (soil drainage, slope position/exposure, rooting depth),
tree physiology (crown size, crown/diameter ratio), time of year (leaves on or off, snow loads, soil
moisture), stand conditions (stocking, openings, edge exposure), and tree vigour (stem rot, disease
cankers, root rot). In Nova Scotia forest stands are exposed to hurricanes during the late summer and
early fall. Damage from storms associated with the provinces’s Maritime locale is a year round
threat.
Ice storms occur generally from late November to late March. Most damage, because of the
weight of the ice, occurs from breakage of limbs or whole trees and is particularly evident in the
hardwood forests. In Nova Scotia the situation is aggravated by strong winds which accompany these
ice storms or follows shortly thereafter with additional breakage, uprooting and snapping of the stem.
Populations of native insects and diseases are usually present at low levels causing minor
amounts of mortality. However, populations will reach epidemic proportions when trees and stands
are weakened by other agents such as wind, fire, senescence, or site conditions and forest losses can
be extensive. Insects such as bark beetles, budworms and several species of defoliators have a long
history in the province. Pathogens such as the beech canker, Dutch elm disease, and balsam woolly
adelgid have been recently introduced and have caused extensive changes in the forest ecosystem
which may not be mitigated.
There are many references available which document the historic forest conditions in Nova
Scotia. The journal of Nicolas Denys (1672) describes the coastal forest encountered by the early
French settlers which seems to differ little from what is present today. His description of the inland
9
forests relied on what he learned from the Native population and suggests an older forest but of
similar species. Denys’ descriptions support a fire origin forest over parts of the Maritimes given the
abundance of oak, white birch and pine in his accounts. There is also enough reference to beech and
other long-lived species to suggest large tracts of less frequently disturbed forests (Neily 2006). Later
Simeon Perkins (Champlain Society, 1948) writes in his diaries about the horrific forest fires
experienced in south-western Nova Scotia in the 1790's. But perhaps one of the more enlightening
documents is the account of the travels of Titus Smith in 1801-1802 throughout mainland Nova
Scotia as he described the natural history (Clark, 1954; Gorham, 1955; Hawboldt, 1955). More
recently pollen studies of lake sediments and tree ring analysis (dendrochronology) have provided
insight to the composition and disturbance history of the forests before European settlement. As
research continues using sediment cores from lakes, bog analysis and tree ring analysis a more
thorough understanding of our natural disturbance ecology will result. The following descriptions
of the natural disturbances is based on the literature and available data.
4.1
Fire
From the end of the spring and during the summer and autumn, the thunder falls sometimes
in fire and strikes in the woods, where everything is so dry that it continues there some three
weeks or a month. Unless rains fall sufficiently to extinguish it, the fire will burn sometimes
10, 12, and 15 leagues of country. At evening and at night, one sees the smoke 10 and a
dozen leagues away. In the places where that occurs all the animals flee from it 15 and 20
leagues. If this happens upon the border of the sea, where the water from the rains can wash
down into it, all the fish flee from it, and there will be no fishery the following year, nor
waterfowl on the coast.
Nicolas Denys describing forest fires in Acadia (New France), 1672
The Heavens appear to Brass and the rain of our Land, Powder and Dust.
Simeon Perkins describing the forest fires near Liverpool, 1792
Fire has been a disturbance agent in the forests of Nova Scotia since the last glaciation and
it has been a dominant disturbance at least since European settlement; Denys (1672), Perkins (17661812), Smith (1802), Fernow (1912), Loucks (1962), Strang (1969), Wein and Moore (1977, 1979),
Johnson (1986), Basquill et al (2001). Research by Green (1981) suggests that based on pollen and
charcoal analyses in cores of sediment taken from large lakes in southwestern Nova Scotia, large
intense fires occurred 11 000 to 6 000 years before present (BP) with a resultant instability in forest
community composition. Wein and Moore (1979) report that almost all paleoecologists who have
examined lake sediments or bog profiles in the Maritime Provinces and New England have found
evidence of fire in the form of charcoal. This has recently been supported by the work of Foster et
al (2002) in north central Massachusetts who have concluded from palaeoecological analyses of
wetlands that the pre-European period (3500 BP) in New England was marked by two 1000+ year
periods of remarkably stable forest composition (attributed to on-going disturbance by fire and
10
windstorm), separated by an abrupt compositional shift (an apparent cooling and increase in moisture
availability, ca 1500 BP). Parshall and Foster (2002) report that the major factor influencing the
distribution of fires across New England is climate, which has a direct effect on the physical
conditions conducive to fire ignition and spread and an indirect effect on fire through its influence
on the distribution of vegetation at this spatial scale. Other factors that exert control over the local
fire regimes includes the impact of landforms on vegetation composition, firebreaks and prevailing
winds.
The role of fire, both pre- and post-settlement, in forming the forests of the province has been
contentious. Some believe that much of the provincial forest reflects the extensive use of fire by
settlers to clear the unwanted forest for agricultural pursuits and the perpetuation of crops of wild
berries. There are others who suggest that the native peoples used fire to encourage berry production
and to maintain browse for the moose and caribou (the historical presence of caribou indicates that
fires created enough open habitat to support viable population levels) . While researching the history
of fires in the Kejimikujik National Park, Basquill et al (2001) report that they could find little
conclusive information in the literature to confirm the use of fire, by first nations people, outside
their encampments. And in New England, Parshall and Foster (2002) concluded that native
Americans likely influenced the local occurrence of fire but their impact on regional fire regimes is
not apparent from this or other studies.
Generally the barrens of southwestern Nova Scotia have been considered the product of
frequent fires, many of them human caused, and the subsequent impoverishment of the soils.
Basquill et al (2001) and other researchers have concluded that these barrens originated well before
European colonization. Strang (1972) notes that “although fire is undoubtedly a potent factor in
maintaining shrub cover, pollen analyses indicate that an open woodland developed many centuries
ago in response to the soil conditions and the prevailing climate. The present shrubby vegetation is
thus an expression of inherent site factors as well as of the effects of burning.” Strang (1972)
described the barrens as underlain by a coarse, infertile soil characterized by a massive pan layer
which restricts rooting to within a few centimeters of the surface and is impervious to water
movement. Since this hardpan layer is so common in the soils of the Southwest barrens Strang
hypothesized two possibilities; 1) compaction of a shallow soil layer by glaciers or 2) percolation
of dissolved humic nutrients once vegetation had been established after the glaciation. There are
similar barrens on the Chebucto and Chedabucto Peninsulas.
Large fires have been recorded by several authors including Simeon Perkins who described
a fire south of Lake Rossignol in 1800 that covered an estimated 175,000 ha. Another fire reported
in the travels of Titus Smith occurred in Queens and Lunenburg counties, east of Rossignol, where
an estimated 150,000 ha burned in 1720. In this case the fire was preceded by a hurricane.
Throughout his traverse of western Nova Scotia, Smith repeatedly draws attention to the fire barrens
and the extensive areas of burned forest. The most notable fire in the Maritimes was the Mirimichi
fire of 1825 which destroyed three million acres in four days earning this fire the distinction of North
America’s largest post-settlement fire (Repap 1995). Johnson (1986) states that “although most
settlers tried to be careful with fire, burning only at what they considered to be safe times, fires often
got out of control and burnt extensive areas”. Perkins (1766-1812) described many fires around
Liverpool in June and July 1792, with nothing done to stop them. Again in 1800, another dry
summer resulted in continuous burning with most of the area burned south of Lake Rossignol and
11
Jordan Lake from the Liverpool (Mersey) River to the Roseway River. And in 1803, Perkins enters
in his diary that “smoak [from the Port Mouton and Beech Hill fires] is come down upon us so thick
as to darken the air to such a degree that one can scarcely see acrost the street”. Wein and Moore
give an account of the pre-suppression fires between 1500-1914 reporting that most of the fires
occurred as a result of land clearing. The authors assume that settlers permitted land-clearing fires
to escape because few resources were required from the land by the maritime-oriented society. The
first legislation to control this type of fire was passed in 1761 ( Johnson 1986) and subsequent
legislation continued to be introduced as the province began to derive more of its income from
timber harvesting.
In his 1912 report on the Forest Conditions of Nova Scotia, B.E. Fernow devotes an entire
chapter to ‘Forest Reproduction and Soil Conditions on Burned Areas’. In this chapter he details the
location of recent burns and old fire barrens, of which most occurred on the Southern Upland, an
area of the mainland from Canso to Yarmouth with watercourses draining into the Atlantic ocean.
He did not speculate as to the origin of these fires although reference is made to barrens caused by
man. However, he did try to date many of the fires and forests which occurred on the old burns
dating some of the forest stands to the 1830's thus indicating that fire was not always used year after
year to maintain habitat for wildlife or conditions necessary for berries or pasture. Fernow closes this
chapter by stating “approximately one-fourth of the present forest area of the Province is semi-barren
of commercial trees. This condition has been brought about by repeated fires in situations possessing
naturally the coarser soils. If the fires were excluded and if these areas were thoroughly seeded with
merchantable species, it would take Nature at least one hundred years to produce a marketable forest
on these fire barrens.”
Another study by Gray (1956) indicated that repeated heavy cuttings and light fires on the
poorer soils of the Southern Upland encourage the invasion of heath plants, which when abundant,
result in serious limitations for tree regeneration.
Wein and Moore (1979) used provincial fire records from 1915 to 1975 to calculate a fire
rotation of 1000 -2500 years. All burns recorded were used in the calculations to determine a mean
annual burn or median annual burn respectively. In contrast, calculations of burned areas on maps
produced at the turn of the century (Fernow, 1912) gave pre-suppression fire rotation periods of just
over 200 years. Green(1981) who studied charcoal particle abundance in cores taken from lakes in
southwestern Nova Scotia, found that the fire rotation period was about 400 years for the years 6600
to 2200 BP. With the advent of fire suppression and the improvement of response times and
equipment the fire rotation period continues to increase. From 1915 to 1994 a total of 371,000 ha
of forest had been burned by fire. This 80 year time period covers the post suppression era. excluding
Cape Breton, with an average of 4600 ha burned each year, it would take about 900 years to burn the
entire mainland assuming all areas were only burnt once. Wein and Moore (1979) suggest a fire
return interval of approximately 2000 years for the more recent period between the years 1958 and
1975.
4.1.1
Fires Caused by Lightning
Based on the records of the Nova Scotia Department of Natural Resources (1929-1999), 240
forest fires (1%) of forest fires were attributed to lightning strikes (3.4 forest fires per year). Early
12
fire records were inconsistent and no fire records were kept during the 1931-36 Depression. In New
Brunswick lightning is the cause of seven percent of the province’s forest fires based on data from
1929 to 1975 (Wein and Moore 1977). Environment Canada weather data for 1998-1999 indicates
that most of Nova Scotia receives .25 to 0.5 lightning to ground strikes per square kilometer per year
with two thirds of all strikes occurring during June, July and August and most of these in the
afternoon (Lanken 2000). Based on 40 years of records, Figure 1 illustrates the occurrence of fires
in ecodistricts (Neily et al, 2003) caused by lightning. Fifty one percent of these fires have occurred
in the ecodistricts of the western ecoregion. A summary of lightning caused forest fires in Nova
Scotia is presented in Table 1.
4.1.2
Regional Fire History
Basquill et al (2001) describe Western Nova Scotia as one of the more fire prone areas in the
Acadian forest using several accounts to support this assumption including Denys (1672), Perkins
(1776-1812), Smith (1802), Fernow (1912), and more recently Candy (1951), Martin (1956) and
Gimbarzevsky (1975). Fire has had a dominant influence on the regional forest ecosystems. Areas
that were repeatedly burned often created fire barrens even preventing seed germination of flame
tolerant species (Smith 1802, Hardy 1869, Fernow 1912, Strang 1972, Gimbarzevsky 1975). The
presence of fire in Kejimkujik National Park was readily apparent by Basquill et al (2001) who noted
abundant charcoal at 87% of their sampling sites and using bark and tree ring chronology found
evidence of understory fire dating back to 1803. These researchers also determined that overstory
fires in Kejimukujik National Park initiated 100% of sampled red pine stands and 60% of both white
pine and white birch stands; to a lesser extent, these fires were shown to initiate the development of
black spruce, red spruce and red maple stands. This lead them to suggest an average overstory fire
return interval of 78 years in the Park. In New Brunswick Methven and Kendrick (1995) conclude
from their study that the presence of jack pine through the region indicates a fire cycle of from 50
to 100 years; red and white pine require stand maintenance fires every 30 to 50 years for control of
competition and cone insects with stand replacing fires every 200 to 300 years and black spruce has
a fire cycle of 200 years.
Throughout Nova Scotia both Loucks (1962) and Rowe (1972) reiterate the presence of fire
origin species such as jack, red and white pine, red maple, wire and white birch, and red oak as proof
of the role of fire in regional forest composition. Although both authors state that the occurrence of
fire and its frequency has probably increased since European settlement the conditions conducive
to fire are a product of the topography, soils and climate and that these conditions exist mainly in the
lowland ecodistricts and western ecoregion. In the Atlantic Coastal ecoregion fires have been
common but they appear to have been started by settlers to extend their pasture land (Loucks 1962).
However, the presence of jack pine in several places on the Canso peninsula, and on Madame Island,
suggests that the constant winds may create a droughtiness that is conducive to fire.
13
Table1. Lightning-caused forest fires, 1929-1999 (Compiled from fire records of the Nova
Scotia Department of Natural Resources, Shubenacadie).
Fire
Period
# of Fires
Area
(hectares)
M onth
# of
Fires*
1929-38
13
264
May
15
1939-48
18
894
June
39
1949-58
22
271.8
July
78
1959-68
82
688.8
August
78
1969-78
25
16.2
September
4
1979-88
43
31.3
1989-98
100
61.6
1999
26
16.4
* Month of fire was not
always recorded.
Selected Lightning-caused Forest Fires 1929-1999
Year
Location (county)
Area (ha)
Year
Location
Area (ha)
1939
Crossburn (Annapolis)
85
1965
Sixth Lake (Queens)
114
1942
Tobeatic (Shelburne)
370
1968
Cape Dauphin (Victoria)
14
1944
Cherryfield (Lunenburg)
283
1984
Tidney River (Queens)
15
1946
Peskawesk Lk. (Queens)
62
1991
Laura Lake (Guysborough)
6
1952
Kelly’s Mtn. (Victoria)
61
1997
Mosher Lk. (Guysborough)
17
1961
First W . Brook Lk. (Queens)
517
1998
Hayden’s Lk. (Kings)
9
4.1.3
Fire Suppression
In 1761 the Nova Scotia legislative assembly passed an Act designed to reduce the
unseasonable burning or firing of the woods and from the preamble to this Act there was little
concern apparent for damage to the woods, but rather for damage to settlers’ buildings and crops due
to the fire spreading from the woods (Creighton 1988). Various annual reports of the Commissioner
of Crown Lands between 1869-1925 include comments on a variety of efforts being made by the
provincial government to reduce the loss of forests to fire. As early as 1864 legislation was passed
to imprison anyone convicted of unlawfully setting fires. Basquill et al (2001) suggest that as the
frequency of anthropogenic fire increased in the 19th century and since there was no technology
available at the time for extinguishing large blazes, errant fires were abandoned for they rarely
threatened the settlers and the extent of the timber resources seemed inexhaustible. In 1904 an Act
14
of considerable importance was passed entitled The Protection of Woods Against Fire (Creighton
1988). It put in place Chief Rangers for each municipality with all fire fighting costs paid by the
municipalities and as well set in place permits, penalties, taxes and education programs. Several of
the Chief Rangers reported support from landowners, fishermen and hunters, and railway and timber
companies for efforts to reduce forest fires.
Both Creighton (1988) and Johnson (1986) detail the passage of the Lands and Forests Act
in 1926 which legally placed the responsibility for the suppression of forest fires directly with the
Province. In the first report of the Chief Forester to the Minister of Lands and Forests (Anon. 1926)
both the extent of forest losses and the cause of past forest fires was outlined. It was reported that
in the three counties of Yarmouth, Digby and Shelburne, fire barrens covered 540,000 acres with
67.5% of Shelburne County consisting of fire barrens. In these counties the cause of fires was
attributed to persons who repeatedly set fire to the barrens “under the supposition that it is necessary
for the growth of blueberries”. The new Act also put in place a requirement for permits to burn
brush. In his second report (Anon.1927) the Chief Forester concluded that the increase in issued
permits, 847 in 1926 and 2573 in 1927, “shows a willingness of the people of Nova Scotia to cooperate with the Ranger service”.
The popularity of the small transportable sawmill was increasing as well in the early 1900's
and the activity associated with these mills was contributing to the loss of forests from fire. In the
1880's Johnson (1986) reports that most of the sawmills were stationary, usually on rivers where the
wood could be floated from the forests upstream. However, the advent of portable steam mills, light
enough to be moved on sleds and wagons to the woods allowed lumbermen access to more remote
areas of the province and increased the potential for forest fires. The Lands and Forests Act required
these operators to obtain a permit if the mill was within 60 rods (5.03 m) of the forest.
But perhaps the most significant development in the early efforts to control forest fires was
the arrival of the motorized fire pump. In his 1927 annual report the Chief Forester noted the
effectiveness of such pumps - “one reliable forest fire pump will do as much effective work on a fire
as a crew of 25 men working with hand tools”- and by 1929 fire pumps were available to the
Department’s fire fighting crews. In addition the fire tower network expanded rapidly during the
1926-29 period and 51 towers were located throughout the province. And on June 21, 1929 the first
closure of the woods to travel under the Lands and Forest Act was proclaimed due to a significant
dry period blamed in part on “one of the most open winters in the Province’s history (Anon.1929).
The construction of the railways throughout the province between 1858-1890 (Table 2)
resulted in significant burning of the woods. Creighton (1988) reports that “for the first time the
Department of Crown Lands was given some little authority to protect the woods against fire” with
the passage of legislation in 1883. Apparently the “appalling waste of the forests” in the early days
of railway construction incited the legislature to pass regulation outlining precautions required when
locomotives passed through wooded areas and the duties of the engineer. Johnson (1986) reports that
during the first eight years of operation 20 times as much wood was destroyed by fire as was hauled
out by the railway.
Although fires originating along railways were mentioned in the Chief Forester’s reports
between 1926-29 as the greatest [known] cause of fires he also reported that the railway companies
had by this time “developed an excellent fire protective system so that in all 31 fires of 1926 only
27 acres of forest had been destroyed”. Another report, this time by the assistant provincial fire
15
inspector to the Chief Forester concluded that “the small number of forest fires caused by
locomotives and right of way burnings during 1928 shows the healthy co-operation of the railway
officers with the officers of the Department of Lands and Forests (Anon.1928).
Table 2. Construction periods for provincial railways (from Johnson 1986).
Halifax -W indsor
1858
Dominion Atlantic Railway (1894)
W indsor - Annapolis Royal
1872
“
Yarmouth - Digby
1879
“
Digby - Annapolis Royal
1891
“
Halifax - Truro
1858
Truro - New Glasgow
1865
New Glasgow - Antigonish
1879
“
Antigonish - Mulgrave
1880
“
Point Tupper - Sydney
1890
“
Middleton - Lunenburg
1889
Nova Scotia Central Railway
Truro - New Brunswick
1872
Intercolonial Railway
Springhill - Parrsboro
1873
Cumberland Railway & Coal Co
Sydney - Louisbourg
1894
Dominion Coal Company
Point Tupper - Inverness
ca 1894
Dominion Coal Company
Yarmouth - Halifax
1900
Halifax & Southwestern Railway
Dartmouth - Upper M usquodoboit
ca 1900
Guysborough Railway Project (Province of N.S.)
New Glasgow - Sunnybrae
ca 1900
Guysborough Railway Project (Province of N.S.)
Halifax - Cape Breton Railway & Coal Co.
“
Since the inception of the Department of Lands and Forests the area of forest lost to fire has
decreased substantially (Figure 2) although the number of fires per year has not (Figure 3). This
reduction in burned forest land can be attributed to the constantly improving fire detection and
suppression capabilities of the Department such as the availability of motorized fire pumps, better
fire surveillance using a network of fire towers, airplanes and helicopters and quick response by
helitak crews and local fire brigades. However, in many parts of Nova Scotia fire has had a major
role in shaping natural successional patterns, e.g. pure red pine and red oak stands at Kejimukujik
National park (Basquill et al 2001), pure jack pine stands in Cumberland County and black
spruce/white pine stands in the St .Mary’s River Ecodistrict. Basquill et al (2001) conclude that fire
suppression will serve to maintain the trend towards a reduced representation of forest community
diversity. They also suggest that altered fire regimes can shift patterns of nutrient cycling and
hydrology and change soil constitution and ecology.
16
Figure 2. Annual area burned by forest fires in Nova Scotia 1919-1999 (NSDNR).
Figure 3. Annual number of forest fires in Nova Scotia 1919-1999 (NSDNR).
17
4.2
Insects and Diseases
The severity and frequency of insect and disease epidemics in pre-settlement forests were
largely influenced by climate, age class and species composition (successional stage) and genetics.
However, forest harvesting and fire suppression have altered the patterns of natural disturbance on
the landscape and the literature can be used to support this thesis. Nonetheless native insect
populations and disease infestations in Nova Scotia still create considerable changes to forest
ecosystems in very short time periods.
Several pests, for example, the spruce beetle (Dendroctonus rufipennis (Kirby)), whitemarked tussock moth caterpillar (Orgyia leucostigma (J.E.Smith)) and spruce budworm
(Choristoneura fumiferana (Clemens)), have the capability to destroy entire stands. Such population
explosions can be responsible for large scale disturbances especially in ecosystems that are
comprised, almost entirely, of the preferred food group. The historical records of insect outbreaks
are not well recorded since in many cases the susceptible trees, for example, balsam fir (Abies
balsamea (L.) Mill.) and eastern larch (Larix laricina (Du Roy) K. Koch.), were of little or no use
to the early settlers and infestations were ignored. However, parts of the Maritimes have been
ravaged by the spruce budworm and there have been several outbreaks recorded according to federal
scientists at the Canadian Forestry Service in Fredericton, three in the 1700's, four in the 1800's and
three in the 1900's (Johnson 1986). With the advent of dendrochronology and cross referencing of
growth patterns historic trends of insect infestations are coming to light.
The spruce budworm and the recurring cyclic nature of infestations has a significant influence
on the successional stages and composition of the spruce-fir forests in Nova Scotia. Mature and
overmature balsam fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss.)
are its preferred food source, so are the most susceptible to defoliation. Red spruce (Picea rubens
(Sarg.) and black spruce (Picea mariana (Mill.) BSP.) are less susceptible to defoliation but not
immune.
Spruce budworm outbreaks
have been documented for over 200
years as an integral disturbance in the
spruce-fir forest on the Cape Breton
Highlands. Evidence of and outbreaks
confined to Cape Breton Island have
been recorded in 1846, 1891-1896,
1911-1915 and 1922-1927 (NSDLF
1977). Between 1927 and 1950 the
budworm remained active only in
localized areas of northern Cape Breton
Island but between 1951-1955 a major
infestation occurred in the mainland
counties of Cumberland, Colchester,
Pictou, Antigonish and Guysborough
and throughout Cape Breton Island. By
1956 all populations had plummeted
18
with the only recorded infestation in
1960-1963 on Cape Breton.
The collapse of the fir on Cape
Breton Island and throughout the
eastern mainland started again in 1967
when defoliation was recorded in
Inverness and Victoria counties and a
moth migration, presumably from
across the Bay of Fundy from southern
New Brunswick, resulted in egg-mass
infestation in Annapolis and Kings
counties. By 1974 the insect had
caused widespread mortality
throughout the province. On Cape
Breton Island the population crashed
in 1982 but defoliation and mortality
continued on the mainland until 1987
(Guscott 2001; NSDLF 1977). The area affected by the latest spruce budworm epidemic on Cape
Breton Island covered 629,910 hectares, reduced the growing stock of spruce and fir by 70% or 31
million m3 and increased the hardwood covertype from 16% pre-budworm to 36% post-budworm
(NSDNR 1994). Losses in Cumberland County were estimated at 3.2 million m3 softwood or 20%
of the merchantable volume (NSDLF 1982).
Methven and Kendrick (1995) noted that the return interval between budworm infestations
in New Brunswick had increased in the twentieth century and attributed human activity in terms of
fire and insect suppression that increased the availability and distribution of the host species - mature
balsam fir. They suggest that the natural rotation cycle for budworm disturbances would be linked
to the life span of balsam fir and at a spatial scale of thousands of square kilometers in which the
forest would be a single age class of fir that would advance over time until the next outbreak
(Methven and Kendrick 1995). In Nova Scotia pure balsam fir ecosystems are found primarily in the
upland and highlands ecoregion (Appendix III) and occupy approximately 235,000 hectares (2350
square kilometers).
The larch sawfly (Pristiphora erichsonii Htg.) has defoliated extensive areas of larch forests
in Nova Scotia often causing mortality. Not only does the sawfly attack pure stands of larch but it
also has the ability to locate isolated trees. Defoliation in a given year is usually of little
consequence, but repeated damage over several years will kill the tree. There is uncertainty as to
whether this insect is native to North America but the first recorded outbreak in Canada occurred at
Bury, Quebec, in 1878 and by the late 1880's much of the mature larch through North America was
dead. The Chief Forester for Nova Scotia reported (Anon.1927) that the larch sawfly and its partner,
the larch casebearer, which had completely killed off the larches in the 1880's was back again in
1927. There have been several attacks since that time with considerable losses attributed to the larch
sawfly in 1936. Between the years 1974 - 1977 severe damage occurred in much of Nova Scotia.
The white-marked tussock moth (Orgyia leucostigma (J.E. Smith)) was first reported in 1937
and recently caused extensive mortality to balsam fir trees in the central and the eastern mainland
19
counties in 1999. Broad leaved trees
are the preferred food of this species
but when populations are high,
balsam fir, white spruce and larch
are susceptible.
The spruce beetle is a
primary disturbance in unevenaged
forest of spruce creating many of the
gaps associated with this disturbance
type. This insect attacks the tree
bole, living between the bark and the
wood. First identified in Canada in
1923 this beetle prefers over mature
or unhealthy trees however during
epidemics all spruces regardless of
age or health are susceptible. In the
1940's mortality due to the beetle
was observed on the islands near Argyle, Yarmouth County with estimated losses of 10-15 %.
Following the spruce budworm outbreak of the 1980's weakened red spruce in many parts of the
province succumbed to the beetle. In the 1990s beetle mortality was widespread in mature stands of
old field white spruce, especially in eastern Nova Scotia and along the North Mountain of the
Annapolis Valley.
Other native insects capable of inflicting serious damage include the hemlock looper
(Lambdina fiscellaria Gn.), balsam fir sawfly (Neodiprion abietis (Harr.), blackheaded budworm
(Acleris variana Fernald), and the pale winged grey (Iridopsis ephyraria (Wlk.).
Forest pathogens in Nova Scotia’s forests seldom cause mortality in mature forests but can
significantly affect tree growth and development. The numerous blights, rusts and fungal infections
present in the forests only cause mortality with repeated infection over several years. Forest
pathogens generally follow other agents such as insects, environmental and site stresses, or animal
predation which have weakened the tree and created conditions that will eventually lead to mortality.
As such forest diseases are significant in gap disturbed forests where individual tree mortality creates
opportunities for a younger cohort to enter the canopy.
The introduction of non-native forest insects and diseases to Nova Scotia has had disastrous
impacts by removing significant components from the natural forest such as beech and elm. Most
of these pests have arrived in the last century along the eastern seaboard in shipments from Europe.
Most notably the beech bark disease and the Dutch elm disease have had the most significant effect
on our forest. The beech, once the dominant species of the hardwood forests has been relegated to
the understory, no longer providing the quantity of nuts it once did for wildlife forage and no longer
the dominant tree in the canopy. The elm has been all but eliminated from the interval locations
along rivers. The loss of this species although not of significant timber value did fulfill a vital role
in the ecology of these habitats by providing shade, acting as a nutrient pump cycling soil nutrients,
and providing habitat for a variety of cavity nesting species of birds and small mammals. Some of
the more serious introductions include;
20
White pine blister rust
Beech bark disease
Balsam woolly adelgid
European winter moth
European spruce sawfly
Gypsy moth
Dutch elm disease
Mountain-ash sawfly
Spruce longhorn beetle
Year
1929
1890's
1910's
1950
1922
1981
1969
1926
2000
Location
Chester
Halifax
Western N.S.
Nova Scotia
Ottawa
Yarmouth
Liverpool
New York
Halifax
Preferred Host
Eastern white pine
American beech
balsam fir
oak
spruce
hardwoods
American elm
mountain ash
red spruce
The impact of introduced and native forest pests on the forest ecology of the province is
determined by the adaptability, natural control mechanisms and genetics of the tree species. In the
future the extent and influence of climate change on tree growth will be a significant factor in
determining the level of severity of disturbance and renewal in the forest. While the degree of change
is uncertain forest managers should strive to ensure that a satisfactory level of natural biodiversity
is preserved on the landscape in order to ensure that natural ecological functioning can occur in order
to adapt to this changes as best as possible. Of recent note has been the advance of the balsam woolly
adelgid (aphid) (Adelges piceae Ratzeburg) eastward. This pest and most other introduced species
are vulnerable to cold winters, especially when temperatures persist in the -30 C range or when snow
cover is not excessively deep. In the past the intensity of this pest has been restricted in central and
eastern Nova Scotia due to colder winter temperatures. However, the past several winters have been
milder with deep snow cover resulting in noticeable damage to balsam fir trees on the eastern
mainland. If winters become less severe in Nova Scotia several forest pests that may increase their
destructive activities include the gypsy moth, balsam woolly adelgid, European shoot moth and
winter moth.
4.3
Hurricanes and Windstorms
“the occurrence at times of furious gusts of wind, which overthrow trees, but they are not of long
duration (Denys , 1672).”
As a peninsula jutting out into the Atlantic Ocean, Nova Scotia’s forest are especially
vulnerable to storms and hurricanes tracking up the eastern seaboard of North America (Figure 4 ).
As a natural disturbance these winds are a vital process in the ecology of the provincial forests. Stand
renewal is initiated after catastrophic wind events such as hurricanes whereby a significant portion
of the stand has been destroyed. At other times small, gap-type disturbances in the canopy remove
a single or patch of trees creating an opportunity for a younger cohort of trees to develop.Hurricane
winds may be expected at almost any season of the year, and are a threat to all classes of forest
(Loucks 1962). In the western and eastern ecoregions wind damage is of frequent occurrence (Rowe
1972). Even the late fall and early winter gales which are not categorized as hurricanes can cause
extensive damage and disturbance. Shallow rooted softwood forests on soils saturated with the fall
rains and still unfrozen are particularly vulnerable to extensive blowdown. Such a storm devastated
21
30,000 hectares of mature balsam fir on the Christmas Mountains, New Brunswick on November
7, 1994 with patches of complete blowdown of up to 400 hectares. Many other stands were partially
destroyed. Other winter storms associated with the freezing and thawing cycles of the Maritime
climate and the accompanying freezing rain and snow can cause extensive damage to hardwood
forests, especially those at the higher elevations. Such an event occurred on the north slopes of the
Cobequid and Cumberland hills in 2003 (Figure 4).
Titus Smith witnessed extensive blowdown on his western tour in 1802 - “in some places,
particularly north of St. Margaret’s Bay, there were miles of country where nearly all the trees had
been blown down in the Great Storm of September 25, 1798. At times it took Smith and Carter [his
assistant] a half hour to travel a hundred yards because of these fallen trees. The storm had blown
Figure 4. Damage assessment of the ice storm of February 2-5, 2003 in Cumberland and
Colchester Counties, Nova Scotia (Guscott 2003)
ships ashore and caused great damage in Halifax and along the south shore as far west as Liverpool.
The forest destruction from this hurricane covered an area of over a million acres, stretching from
Porter’s Lake, Halifax County on the east to Shelburne County on the west and north as far as
22
Windsor” (Johnson 1986). Smith also reported of an area 20 miles by 30 miles (east of Rossignol
to east of Middle River, Lunenburg County) of even-aged hardwoods, chiefly beech, yellow birch,
sugar maple, ironwood and ash. According to the local settler, as told to him by the natives, there
had been an extensive blowdown 80 years earlier followed by a large fire the following year. This
is an early verification that fire hazard following blowdown is exacerbated by the heavy fuel loads
of downed material that dry quickly and become susceptible to ignition during extended periods of
summer dryness.
Hurricanes and winter storms also played a prominent role in shaping the coastal forests
along the Atlantic Ocean. Tannehill (1956) reported that the frequency of hurricanes originating in
the West Indies and subsequently moving up along the eastern seaboard of North America has not
changed since the days of Columbus. Over the past couple of centuries more than 20 major storms
of hurricane intensity have affected Nova Scotia, (Figure 3). The tracks of these hurricanes can
include a width of as little as 50 - 75 miles or as wide as 400 miles (Dwyer 1958). Unlike fire and
insect damage, wind uproots trees and mixes the soil and is therefore both a vegetational and a
pedological disturbance agent (Schaetzl et al. 1988). Moisture availability and movement is
influenced by the severity of the uprooting. The exposure of mineral soil or the mixing of humus and
mineral soil creates a variety of seedbed conditions for both trees, shrubs and herbaceous vegetation.
As well the intensity of destruction in the canopy can create variable light conditions on the forest
floor and thus influence the species and type of vegetation that will establish after the event. The
intensity of the uprooting is evident in the resulting pit and mound microtopography which remains
visible for many years (centuries) after the event. Evidence of blowdown on Crowdis Mountain,
Victoria Co., caused by the August Gale of 1873 is still visible (Hanham 1991) and “the 95-110 year
old, even-aged, second growth stands (distinguished by dominance of balsam fir, red maple and
white birch mixed with yellow birch) on the northern branch of the Trout Brook correlate very well
with this storm.” Even on the Cape Breton Highlands, Loucks (1962) observes that the characteristic
inverted soil profiles indicate that old growth forests are normally destroyed by wind, if not by insect
attack
Dwyer (1958) concluded that the susceptibility of forest stands to hurricanes and the
subsequent damage is related to a variety of site and stand factors and that aspect and tree dominance
were the important factors (Table 5) in determining the extent of blowdown in the red spruce forests
of the St. Margaret’s Bay area after hurricanes Carol (1953) and Edna (1954). Six million board feet
were destroyed by Hurricane Carol followed by an additional 700 million board feet in 1954 during
Hurricane Edna (Dwyer 1958). Approximately half of the area affected by the hurricanes received
blowdown damage between 20-60% of the stand. However, blocks of over 240 hectares, where
practically all trees are down (Johnson 1955), were extensive over much of western Nova Scotia.
Trees affected by uprooting and snapping off included red spruce, hemlock and maples with white
pine also subject to breakage as opposed to uprooting. Both Dwyer (1958) and Johnson (1955) report
damage in both previously undisturbed forests and in those partially cut. The risk of blowdown in
areas partially harvested, silviculturally treated, along the edges of harvested areas, or in riparian
zones has always been a management concern, especially on sites where rooting depth is restricted
due to shallow soil depth and/or excessive soil moisture. Shortly after Hurricane Juan (Sept.29,
2003) battered the forests in central Nova Scotia blowdown damage in commercial thinnings was
examined by Jan Ellingsen, a forest consultant, and the N.S. DNR (Lindsay 2005). Data revealed an
23
increasing level of damage correlation between removal rates and height diameter ratios - where
when one factor was higher, the other had to be lower in order for the stand to survive. Other factors
such as soils, aspect, slope and stand condition were not evaluated.
The following is an abridged excerpt from Frelich (2002) describing the impacts of wind on
tree damage. Wind is more likely to topple larger trees than smaller ones. Large trees (> 46.0 cm
dbh) are 1.5 times more likely to topple than are mature trees (26.0-45.9 cm dbh), which in turn are
1.5 times more likely to topple than are pole-sized trees (11.0-25.9 cm dbh). There are three reasons
for this. First, the larger a tree’s diameter is, the less flexible the trunk will be. If a tree trunk is able
to bend in the wind, the force is uniformly distributed over the length of the trunk. With a stiff trunk,
all the force of the wind on the entire tree is applied at the base of the tree, which can result in
uprooting or snapping off at a weak point. Second, large trees are much more likely to have decay
of some sort and this decay is most likely to be located near the base or in the root crown, causing
a weak spot just where the force of the wind is applied. The third reason that large trees are more
susceptible is that wind speeds are higher in the upper canopy where the crowns of large trees reside
than in the understory.
Soil type and rooting depth have a major effect on chance of windthrow. Sandy soils provide
the greatest stability, probably because of greater depth of root penetration, followed by loams, silts,
clays, and peat. Root diseases such as fungal rots and variable depth to bedrock or water table blur
this ranking of soil stabilities.
Hurricane and windstorm damage can be quite varied on the landscape and provide a mosaic
of forest ecosystems. Stand destruction ranging in size from 400 hectares to individual trees will
create a mottled appearance to the landscapes where forests are sensitive to hurricanes and winds.
After reviewing the literature for the Lakes States region and New England, Methven and Kendrick
(1995) suggest that the wind cycle or rotation appear to be in excess of one thousand years for New
Brunswick. Using hurricane reports and records dating back to 1635, Dwyer (1979) shows that Nova
Scotia’s occurrence of storm and storm-free periods could be an 80 year cycle with the most current
period starting with Hurricane Carol in 1953. In this period several hurricanes have impacted the
province’s forest including Edna (1954), Daisy (1962), Blanche (1975), Hortense (1996) and Juan
(2003). This does not imply that there is an 80 year rotation of the forest due to hurricanes but that
perhaps the province experiences storm cycles during which there is an increased chance of damage
by hurricanes.
24
Table 3. Forest stand and site attributes contributing to blowdown (from Dwyer 1958).
Site and Stand Attributes
Level of Blowdown Damage
W ind velocity
> 80 mph
60 - 80 mph
<60 mph
Topography
- wind velocity build-up in narrow valleys and at windward shores of lakes
& large rivers increases wind damage
- ridges and hills can offer protection from wind
Aspect
- excessive on heights of land, windward slopes, margins of swamps, along
road-right-of-ways
- severe on south-facing slopes and heights of land
Soil depth
6-18 inches over
bedrock
Soil moisture
shallow rooting due to excessive moisture increases blowdown
Tree species
spruce, fir, maple, hemlock - shallow rooted & susceptible
white pine - deep rooted & less susceptible although root system becomes
shallow with age
Tree dominance
co-dominants and intermediates susceptible to blowdown
Stand type
even-aged
overmature & mature susceptible
uneven-aged
less susceptible as stands reduce wind velocity
build-up
Stand health
root, butt & trunk rot
increased susceptibility to breakage
Stand management
partial harvests with
>20 -30 % basal area
removed
increased susceptibility to uprooting and breakage
4.4
most trees
overmature & exposed trees
partially stocked stands
blowdown increases with shallowness of soil
Other Natural Disturbances
Landslides involve mass movements of materials down steep sided slopes and may occur in
the form of a rapid rock fall along a cliff, a gradual slide or slump and as an almost imperceptible
creep where movement occurs at a rate of about 1 cm per year. This disturbance is particularly
common in Cape Breton where the well drained steep slopes of the Cape Breton Highlands
Ecodistrict are frequently found covered with talus. The Grande Falaise, just North of Cheticamp,
is a prime example of slumping. Other areas of talus slope can be noticed along the North Mountain
(Annapolis Valley) and throughout the Cobequid Mountains.
Disturbance to trees caused by animals is usually confined to individual trees. Beaver are
probably the most recognizable example of a animal induced natural disturbance on a forest stand.
Their cutting of trees and flooding of land creates scattered pockets of disturbance across most of
North America. Other animals frequently causing damage to individual or small patches of trees
25
include porcupines, bear, hare and woodpeckers. While damage is not always life threatening it may
create a situation where a secondary agent could kill the tree.
Other forms of natural disturbance on forested ecosystems include - environmental stresses
such as drought, temperature extremes, geological disturbances such as sinkholes, earthquakes and
climatic disturbances such as flooding, snow and ice. Edaphic climax forests are also subjected to
extremes of moisture which eventually lead to stand level mortality and renewal.
5.
Anthropogenic Disturbances
Ecologists have been want to document and interpret the shifts in ecosystem structure and
function that occurred as the landscape changed from Native American to European dominance
(Foster 2000). Bellemare et al (2002) conclude that distribution patterns for many plant species still
reflect the open, agricultural environment of the nineteenth century in New England. Foster et al
(2002) also suggest that in response to 260 years of human activity, the vegetation has changed rather
continuously, producing stand, landscape and regional patterns that are novel as well as recent in
origin. Foster (2000) reports that stands in New England recovering from Hurricane Hugo (1989)
continue to differ in their response according to their prior land-use - “the legacies of history strongly
persisted in the face of catastrophic natural disturbance”.
In Nova Scotia data from Statistics Canada indicates that there has been a loss of almost
371,000 hectares of improved land for agriculture between 1901 and 1991. This has resulted in
extensive forests of old-field white spruce, especially in northern and eastern Nova Scotia and in the
west, old field stands of white pine. Foster (2000) concludes from the work of other research
ecologists that a legacy of former use as either woodlot, pasture or plowed field has exerted a strong
influence on modern forest composition. Even after 100-150 years, formerly plowed sites have
naturally reforested and now resemble natural forests, however, the soil still retains a distinctive
signature of the past in its structure, appearance and chemical composition.
By 1912 Fernow warned of possible lumber shortages in Nova Scotia unless remedial
measures were taken, including the control and prevention of forest fires which had up to that time
exacerbated the wood supply situation. In his report Fernow indicated that there was just 86,000
hectares (2.2%) on the mainland that had not been harvested or burned over. Since that time the
harvest of forest fibre in the province has increased from 2,000,000 m3 in 1929 to over 6,000,000
m3 in 2003. This reflects not only the benefits of fire control and forest management, but includes
additions to the forest land base from reforested farmlands and fire barrens, silviculture investments,
and improved harvesting technology.
6.
Natural Disturbances and Forest Landscape Structure
A knowledge of ecosystem dynamics, particularly how communities renew themselves after
natural disturbances, is a prerequisite to designing appropriate silvicultural systems (Seymour &
Hunter, 1999) for old growth, age class distribution, patch sizes and species composition in order
26
to maintain the natural ecology of a forested landscape. McRae et al (2001) suggest that the
recognition that natural forests are maintained by periodic events of stand-replacing disturbance
caused by fire, windstorms, irruptive insects, or pathogens is a cornerstone of ecological
management. A report from New England (Gerhardt and Foster 2002) ranked the factors controlling
forest structure and composition in the landscape as follows:
landform > agricultural history > elevation > hurricane = fire = logging
If this ranking was applied to Nova Scotia the challenge for ecological planners is to suggest how
the natural disturbances arranged the forests upon the landscape (Table 4).
Stewart et al (2003) applied natural disturbance regimes and climax forest types to the Nova
Scotia ecological land classification (NSDNR 2001) and determined that 52% of the landbase (Table
5, Appendix II and III) could support climatic climax forests of tolerant softwoods (red spruce,
hemlock, white pine) and hardwoods (sugar maple, yellow birch, beech). These forests would
originate or be renewed from infrequent and gap type disturbances, the longevity of these species
creating uneven-aged forests where gap and patch dynamics maintain a continuous forest canopy on
the landscape. Another 42% of the province supports forests of balsam fir, black spruce, jack pine,
red pine, red maple, aspen, white birch and red oak which originated from frequent disturbances such
as fire, blowdown and insect epidemics. These forests occur on the landscape where soils,
geomorphology and climate create the conditions that permitted the frequent disturbance of the
ecological processes. Thus at any one time in history the majority of the province’s forests could
have been comprised of uneven-aged climax species or conversely, even-aged forests.
Table 4. Ecosystem disturbance regimes and the age structure of developing forest stands.
Natural Disturbance
Regime
Disturbance Agents
Forest Age
Structure
Climax Species
1. Frequent Stand Initiating
Fire, Insects, W ind,
Senescence
Even-age
black spruce, jack
pine, red pine, white
pine, balsam fir, red
oak
2. Infrequent Stand Initiating
Fire, Insects, W ind
Even-age to Unevenage
red spruce, white
pine, hemlock
3. Gap Dynamics
Fire, Insects, Disease, W ind,
Fungi, Senescence
Uneven-age
sugar maple, yellow
birch, white ash,
beech
4. Stand Maintaining
Fire
Two-age
white pine, red pine
5. Open Seral
Site factors
Bogs, marshes,
barrens
27
Seymour and Hunter (2002) developed a natural disturbance comparability index for gap and
frequent natural disturbances in the tolerant softwood and hardwood forests in northeastern North
America. Adapting this index for use in the Acadian forest of Nova Scotia would enable forest
managers to determine if the recommended silviculture system would have a natural precedent
within the landscape. Combined with the requirement to match stand boundaries with large-scale,
enduring and edaphic features, not simply on the basis of the present age structure and species
composition, early successional and multi-aged communities can be planned to create a naturally
diverse landscape comparable to the pre-settlement era.
7.
Forest Management and Natural Disturbances
Loucks (1962) identified several forest management issues related to natural disturbances.
In the western ecoregion two problems in forest management are [due to] frequent wind damage
from hurricanes and the high hazard of fire. Further he concluded fire to be a dominant factor in
forest ecosystem renewal and subsequent forest management activities on much of the lowlands in
the province. Adopting a policy of ecosystem-based management enhances our ability to maintain
natural successional and climax forest communities reflective of the Acadian forest. By adapting
forest management practices to create the structures and processes that would mimic natural
disturbance regimes we create natural looking landscapes while conserving and maintaining native
biodiversity. Foster (2000) concludes that the best management option is to provide opportunities
for ecosystems to adapt.
Forest biodiversity in Nova Scotia has increasingly become a reflection of human
interventions upon the landscape rather than of the processes and structures created by natural
disturbances. McLachlan et al (2000) conclude that the vast majority of forests in New England have
direct anthropogenic origins, and all forests are subject to such indirect human influences as
atmospheric deposition of nutrients and changing herbivore populations. The long term [stand]
dynamics, dominated by anthropogenic disturbance and environmental change, are more likely to
represent the character of forest change in the future than any model based on a static environment.
They conclude that the ecological features considered to indicate development under an unchanging
environment, such as large and old late successional trees, open understories, and accumulations of
coarse woody debris, are in fact the legacy of repeated, intense, often anthropogenic disturbances.
McRae et al (2001) state that anthropogenic disturbances associated with timber harvesting,
agriculture, urbanization, and other activities have greatly modified the forests, and the changed
ecosystems may make it impossible and even undesirable to fully restore the primeval landscapes.
Nonetheless, in many areas of Nova Scotia forest biodiversity still reflects the natural disturbances
of the pre-settlement past and by providing the structures and processes as best we can through forest
management, the existing level of biodiversity has a better chance to be conserved and maintained
into the future.
7.1
Emulation Silviculture
Many approaches to forest ecosystem management have focused on the need to mimic natural
disturbances when prescribing forest management treatments in order to preserve biodiversity.
28
Emulation silviculture, as described by McRae et al (2001), is the use of silvicultural techniques that
try to imitate natural disturbances such as wildfire, and is becoming increasingly popular in Canada
because it may help circumvent the political and environmental difficulties associated with intensive
forest harvesting practices. The success of these attempts has been questioned but perhaps they have
been more successful than at first thought.
The intensity of a disturbance refers to the amount of energy released by the physical process
of disturbance, and severity refers to the amount of mortality that occurs among tree and plant
populations in a disturbed area (Frelich 2002). Frelich and Reich (1998) suggest that the severity of
the natural disturbance regime changes so dramatically from one disturbance to the next, that
Table 5. Natural disturbance regimes by ecoregion for Nova Scotia.
Ecoregion
Predominant Natural Disturbance Regime
Frequent
I nfrequent
ha
%
ha
100
Taiga
30 862
72
200
C. B. Highlands
162 494
50
173
300
N. S. Uplands
179 757
19
156 907
400
Eastern
328 108
55
500
Northumberland
Bras d’Or
476 746
600
Central Lowlands
Gap Dynamics
%
ha
%
Open Seral
Total Area*
ha
%
ha
12 285
28
43 147
113 513
35
49 065
15
325 245
16
610 878
64
6 086
1
953 628
139 261
23
107 145
18
20 342
4
594 856
59
57 148
7
253 032
31
20 452
3
807 378
157 783
41
175 706
46
41 826
11
8 638
2
383 953
700
W estern
569 227
37
653 118
42
215 074
14
112 146
7
1 549 565
800
Atlantic Coastal
312 263
72
28 521
7
91 525
21
432 309
900
Fundy Coastal
13 783
10
35 957
26
8 8 204
63
1 025
1
138 969
Total*
2 231 023
43
1 246 791
24
1 429 672
27
321 564
6
5 229 050
* Total area does not include salt marshes, coastal beaches, dykelands, urban Halifax or inland water
such as lakes, rivers and ponds.
29
oscillations in composition [in the boreal forest] over time are likely to be individualistic and
irregular, rather than stable. Thus the frequency and severity of natural disturbances that affect the
successional trends of forest stands changes constantly over time. For example, forest fire intensity
is very dependent on the quantity and dryness of the fuel load. If forest stands are extremely dry and
of a large volume then the intensity of the fire will create different conditions for renewal than if the
fire had been less intense due to wetter fuels. Methven and Kendrick (1995) concluded that patch
sizes [due to fire] varied from a few hectares to as high as ten thousand or more hectares, and that
complexity in terms of islands and strings of resistant vegetation, and the nature of the perimeter,
increased with size. Windstorms are also variable and the degree of blow down is dependent on the
intensity of the storm and the condition and location of the stands hit by the wind. In all disturbances,
either natural or anthropogenic, the legacy of seeds and seedlings left after the disturbance is
especially important in determining the future of stand development. And perhaps the greatest and
most difficult unknown to predict and adapt or mitigate is climate change. Research and historical
records in this province, indicate that climate change has been affecting the type, frequency and
intensity of natural disturbances for the last several millennia creating conditions that have caused
the loss of or reduction of several species, for example, basswood, cedar and grapes.
Methven and Kendrick (1995) state - “ there is no need to copy or mimic the natural or
undisturbed landscape [in sustainable forest management activities]; only to reflect some of its
essential features or characteristics. Human use and need are a reality and must be accommodated the only question is how to do it.” Exact duplication of natural disturbance regimes will not likely
be possible - however, the forest structure these disturbances produce, for example, age class
distribution, patch size, species composition and habitat can be approximated through forest
management.
7.1.1
Fire Disturbances and Forest Management
Fire on the landscape creates unburned areas resulting from sheltering terrain features, higher
site moisture or chance. Unburned patches of mature forest that are missed by fire provide seed
sources for regeneration of the burned areas and habitat for some species until the forest has been
restored. But in forest ecosystems where fire is an important disturbance agent, fire suppression and
its replacement with a different stand initiating agent may have important consequences for some
characteristic elements of the ecosystem.
Frelich (2002) suggests that fire regulates the distribution of species across the landscape
and that fire is important for maintaining the diversity of tree species even in landscapes where fire
is rare. The difficulty in reconciling that fire - a chemical process, and harvesting - a mechanical
process, is often suggested by opponents of emulation silviculture that it is not representative of the
natural process (Table 6). However, McRae et al 2001 suggest that the time necessary for the
combustion of much of the biomass of an ecosystem, which is measured in minutes or hours, is much
smaller that the temporal scale of post-fire succession, which is measured in decades or centuries.
They conclude that emulation silviculture should focus on the ecological processes (chemical,
physical, and biological) occurring during the post-disturbance recovery, rather the ephemeral
processes taking place during combustion.
In Ontario, direction has been provided in guidelines and standards (OMNR 2001) for forest
30
managers to use in the development and implementation of forest management plans so that
managed forest landscapes will resemble more closely the landscapes created naturally by fire. The
objective is to conserve biological diversity through the location and size of disturbances, residual
stand structure, species composition of the forest and its age class distribution. Over time it is
expected that application of these guidelines will create a landscape that appears more natural than
the one developed with the application of many of the species-specific wildlife habitat guidelines.
Table 6. Differences and similarities between wildfire and forest harvesting (OMNR 2001).
Disturbance feature
Fire
Forest harvesting
Process
Chemical
Mechanical
Rapid nutrient recycling
Yes
No
Pathogen control
Yes
Limited
Size control
No
Yes
Favours fire dependent species
Yes
No
Produces islands & peninsulas of residuals
Yes
Yes (under regulation)
Facilitates forest renewal
Yes
Yes
Protects areas of wildlife habitat
No
Yes
Soil compaction
No
Yes
Fine organic material in soil
Reduces
Increases
Forest managers incorporating natural disturbances in their ecosystem-based approach must
be aware how stand manipulation may not yield the desired results. Frelich (2002) concludes that
forest managers often assume that fires can be mimicked by logging without taking into account that
harvesting may be lower in severity than crown fires. By changing the severity of the disturbance
regime changes in forest composition will occur, even if rotation periods and sizes of disturbance
are purposely made the same as the natural disturbance regime. McRae et al 2001 suggest the
proponents of emulation silviculture believe that the ecological effects of wildfire are natural and
therefore ecologically acceptable, whereas those of forest harvesting are less so. It is debatable that
wildfire for example had positive impacts at the broad scale of regions and landscapes and over long
periods of time, however, wildfire can have damaging effects on the environment and to human
interests. Moreover, although natural aesthetics are sometimes invoked as a reason to promote
natural disturbances instead of anthropogenic ones not all people regard the effects of wildfire to be
aesthetically pleasing. They conclude that wildfire and harvesting may differ considerably in their
ecological effects, but it is still possible to promote emulation silviculture by tailoring forestry
operations after desirable effects of fire in forest ecosystems.
31
7.1.2
Wind Disturbances and Forest Management
Frelich (2002) reports that disturbance regimes dominated by wind are generally comprised
of late-successional species and wind creates a very complex web of stands in many stages of
development. However, wind does not easily regulate the distribution of species across the
landscape, a task more suited to fire.
In gap disturbed forests continuous mature tree cover maintains an ecological continuity and
temporal connection. Well established, old, ecological processes and structures that would be broken
and otherwise lost by a stand initiating event are maintained by this ‘legacy’ or ‘ecological memory’.
For instance, some fungal networks may be older than the oldest trees, an indication that these and
other species depend upon a temporal connection for site occupation and survival. In terms of
forestry practices this implies that in gap disturbed ecosystems a provision must be made to maintain
old trees, ecological legacy, temporal connectivity, and upper canopy presence.
8.
Closing
Natural and anthropogenic disturbances create structural and functional differences in the
forest that subsequently affect biodiversity. However, natural disturbances have impacted our forests
for a considerably longer period of time and natural biodiversity has developed through the
evolutionary process to reflect the randomness of these disturbances to allow individual or suites of
species to share some structural or functional characteristic of the forest. We can learn from natural
disturbances and use them to guide our forest management planning and silviculture treatments to
maintain and conserve the structures and functions that native biodiversity has developed upon. Aldo
Leopold (1949) concluded that “the hope for the future lies not in curbing the influence of human
occupancy - it is too late for that - but in creating a better understanding of the extent of that
influence and a new ethic for its governance”. A Royal Commission on Forestry in Nova Scotia
(Connor et al, 1984) suggested that forests ought to be seen as part of a dynamic environment subject
to biological, industrial and social changes. Some of these changes occur consistently, others
unpredictably. Nonetheless, they conclude that the impact of human activities on much of the forest
is continuous, but, in all but the most extreme cases, nature restores itself and eradicates the traces
of man’s presence. More recently Nova Scotia’s Code of Forest Practices (NSDNR 2004) outlined
the principles of ecosystem management required to ensure a sustainable forest for the future and
for the maintenance of biodiversity in forests under management. The focus is on managing forest
ecosystems to sustain or restore their natural patterns and attributes by incorporating disturbance
ecology into forest management practices. Implementation of this strategy into forest management
planning will strive to provide habitat for all organisms, maintain diverse gene pools, and maintain
the processes that support biodiversity and healthy ecosystems. The application of forest
management practices at the landscape and stand level will utilize both the ecological land
classification and the forest ecosystem classification as tools to apply forest management treatments
reflective of natural disturbances.
32
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Spicer, M. 1970 ca. The history of the Chignecto Game Sanctuary. N. S. Dept. of Lands and Forests,
Parrsboro, N.S.
St.Clair, James. 1999. Personal communication. Mull River, Inverness
County, N.S.
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Stea, R.R., H. Conley and Y. Brown. 1992. Surficial geology of the province of Nova Scotia. N. S.
Dept. of Nat. Res., Mines & Energy Br., Map 92-3
Stewart, B. J., P. D. Neily, E. J. Quigley, A. P. Duke and L. K. Benjamin. 2003. Selected Nova
Scotia old-growth forests: age, ecology, structure, scoring. For. Chron. 79(3): 632-644
Strang, R.M. 1969. Ecology and afforestation: a study on the barrens of Southwestern Nova Scotia.
Can. For. Serv., For. Res. Lab., Fredericton, N.B., Int. Rep. M-50, 77 pp. + Illus.
Strang, R.M. 1972. Ecology and land use of the barrens of western Nova Scotia. Can. J. Forest Res.
2, 276-290.
Tannehill, I.R. 1956. Hurricanes. Ninth Edition. Princeton Univ. Press. In: Dwyer, G.D. 1958. A
study of blowdown in Nova Scotia. Unpublished. Univ. of New Brunswick, 57 pp. +
Append. & Illus.
Wein, R.W. and J.M. Moore. 1977. Fire history and rotations in the Acadian Forest of New
Brunswick. Can. J. For. Res. 7: 285-294.
Wein, R.W. and J.M. Moore. 1979. Fire history and recent fire rotation periods in the Nova Scotia
Acadian Forest. Can. J. For. Res. 9: 166-178.
10.
Additional Reading and Sources of Information
Harvey, D.C. 1935. Holland’s description of Cape Breton Island and other documents. Public
Archives of Nova Scotia, Publ. No.2, Halifax. 135 pp. + Appendices.
Lindenmayer, D.B. and J.F Franklin. 2002. Conserving forest biodiversity: a comprehensive
multiscaled approach. Island Press, Washington. 351 pp.
Perera, A.H., L.J. Buse and M.G. Weber (Editors). 2004. Emulating natural forest landscape
disturbances: concepts and applications. Columbia University Press, New York. 315 pp.
Ecological Land Classification:
http://www.gov.ns.ca/natr/forestry/ecosystem/elcpg1.htm
Historical References (e.g. Denys, Perkins):
http://www.champlainsociety.ca/index.htm
Hurricanes:
http://www.gov.ns.ca/natr/juan/
Lightning:
http://www.msc.ec.gc.ca/education/lightning/index_e.html
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