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LANDSCAPE CHANGE AND PROCESSES IN
NATURAL AREA MANAGEMENT AT LIMEHOUSE
CONSERVATION AREA
Authors:
ROBERT MILNE AND LORNE BENNETT
Abstract: The Niagara Escarpment can be considered as a combination
of land systems, composed of uplands, slopes and valleys. In
management of these components, it is important to consider them as
functioning systems interconnected by ecosystem processes that cause
change or flux in the structure and diversity of the landscape. In past
papers, the role of geomorphic processes in shaping the forest dynamics
and avifauna populations has been explored for slope systems of the
Escarpment. In this paper, this concept is expanded to examine the
larger landscape of the Escarpment, at the scale of land use identified in
the Niagara Escarpment Plan. A broader model for these land systems is
presented that describes the relationships between disturbance regimes,
geomorphic processes and landforms, and forest and bird associations,
in the Central region of the Escarpment from Mono Cliffs to
Georgetown. In planning for land system attributes such as biodiversity,
it is critical to consider the role of ecosystem processes, including fluxes
from human and natural disturbance. By altering the disturbance
regime, human or natural land systems will disappear and consequently
alter the ecological structure of the landscape. These concepts will be
considered for natural area management for sites within the Niagara
Escarpment Plan.
1. LANDSCAPE CHANGE AND THE NIAGARA ESCARPMENT
Managers of parks and natural areas have been facing new challenges with the introduction of
management units such as biosphere reserves, where human activities are integrated across
protected areas and the lands surrounding them (Price 1996; Daniels 2000). Within the
framework of the Niagara Escarpment Plan, and more recently the Niagara Escarpment Biosphere
Reserve, there has been an amalgamation of a diverse collection of ecosystems experiencing
different levels of land use and human disturbance (Niagara Escarpment Commission 1991).
These lands have been subject to varying levels of human impact over the past two centuries and
since the implementation of the Niagara Escarpment Plan are experiencing new directions of
change as many areas revert to a more natural environment. One of the directives of the Reserve
is to preserve and maintain natural diversity through habitat continuity and integrity (NEC 2002).
Achieving this goal requires an understanding of how the Escarpment land systems function, such
as the processes of energy and matter fluxes and the directional changes of the flora and fauna
initiated by human and natural disturbance (Milne and Moss 1996; Moss and Milne 1998).
An emerging issue in the management of human-modified landscapes is facilitating the return of
natural areas to the landscape. This can require making decisions on preserving the anthropogenic
landscape as it is, allowing landscapes to return to their pre-disturbed state or renewing the land
by adding species through restoration and re-introduction. There are important ecological
consequences arising from each of these paths. For instance, allowing the land to naturalize could
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be at odds with other conservation directives such as maintaining biodiversity and functioning of
the ecosystem, especially where there has been a long history of human impact on the land.
Across the Escarpment, forest cover is changing as abandoned lands are regenerating naturally or
through human intervention. However, this change is at the expense of other ecosystems such as
abandoned agricultural fields and coniferous plantations. These land units can play an integral
role in the Escarpment but are threatened by current land use and resource demands (Milne 2002).
The decline in these ecosystems will also constitute a loss of critical habitat for a number of bird
species. Many species found in the coniferous plantations are more northern in nature but have
maintained populations in Southern Ontario in these plantations established during the past
century (Cadman et al. 1987).
Of even greater concern is the decline of old field and thicket species. Eastern North America is
experiencing a loss in early successional species as abandoned agricultural land returns to a
forested state. The clearing of the forests for European settlement led to the co-existence of a
diversity of successional habitats, but the recent decline in anthropogenic disturbance and related
habitat is leading to significant declines and local extirpations of many species (Askins 2000;
Hunter et al. 2001). The neglect of these land units and reduced habitat creation in Niagara
Escarpment land systems could put associated avian species at risk.
2. LANDSCAPE CHANGE AT LIMEHOUSE CONSERVATION AREA
To illustrate this situation, habitat change and bird populations will be described for Limehouse
Conservation Area, a protected area in the mid-region of the Halton Hills land system (Moss and
Milne 1998). This area is currently responding to several types of human disturbance that have
created a diverse combination of natural and human land units. The dynamics and consequences
of the succession of a thicket-meadow complex will be described and the significance of this land
change will be considered for populations of avian species.
The change in vegetation over the past 40 years at Limehouse Conservation Area is highlighted
by the airphotographs presented in Figure 1. Figure 1a shows the landscape in 1960. Figure 1b,
taken from the most recent airphotograph, shows the landscape in 1990. In 1960, 75 percent of
the conservation area was field or in an early successional stage. Mature forest, including older
white pine (Pinus strobus), is evident along the steep slopes adjacent to the floodplain of Black
Creek. In addition, a mature sugar maple (Acer saccharum) - beech (Fagus grandiflora) forest is
found on the thin soils and rugged karst topography characteristic of the rim and slope of the
Escarpment. It is evident from Figure 1b that the dominant land cover has been reversed with the
forest now occupying a considerable portion of the Conservation area. By 2002, the fields and
early successional vegetation occupied just 28 percent of the landscape. Mid to late successional
forests, mature forests and small areas of conifer plantations occupy much of the remaining
landscape. Thus nearly 50 percent of Limehouse Conservation Area has changed from field and
early successional thicket-meadow to mid and late successional forest.
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Many areas on the Escarpment are in a state of succession between agricultural fields and mature
forests. These cultural meadows and savannas will experience a decline as abandoned fields
return to a forest cover. This process is often assisted by human involvement through programs
such as tree plantings and habitat restoration. Just as it has been important to develop an
understanding of the role of ecosystem change and biophysical processes for natural slope
systems, it is critical to establish the direction and composition of this human-generated flux to
assist in management decisions (Moss and Milne 1998). A descriptive model of vegetation
change is presented in Figure 2, based on fieldwork at Limehouse Conservation Area and several
other sites along the central region of the Escarpment (Milne 2002). Old agricultural fields are
reverting to a forest cover through a shrub-tree layer to a mixed open forest and are predicted to
return to a predominant deciduous or mixed closed forest.
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3. AVIAN RESPONSE TO LANDSCAPE CHANGE
As the fields fill in, there is a corresponding shift in dominant avian populations. Coniferous
species in the plantations such as Black-capped Chickadee (Parus atricapillus) and Pine Warbler
(Dendroica pinus) will be joined by deciduous forest-interior birds such as Red-eyed Vireo
(Vireo olivaceus) and Eastern Wood-Pewee (Contopus virens). The fields experience a shift from
thicket-meadow species such as Indigo Bunting (Passerina cyanea) and Gray Catbird (Dumetella
carolinensis) to the deciduous forest interior species.
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The patterns of change for two sets of species in the old fields at Limehouse are presented in
Table 1. Common species were determined by a combined measure of frequency and abundance
during the breeding seasons of 1997-2000 (Milne and Bennett 1998; Milne 2002). Species of
Conservation Concern were identified by Credit Valley Conservation based on a set of criteria
including habitat, rarity and expert evaluation (CVC 1998; Milne et al. 2000). Many of the
common species found in this area of Limehouse Conservation Area are typical of regenerating
fields, including Indigo Bunting, Song Sparrow (Melospiza melodia), Field Sparrow (Spizella
pusilla), Common Yellowthroat (Geothlypis trichas), Northern Cardinal (Cardinalis cardinalis)
and two species of concern, Blue-winged Warbler (Vermivora pinus) and Gray Catbird. All of the
species of concern identified at this site can be linked to disturbance habitats. These include
species associated with small disturbances within forests (<4 ha), such as American Redstart
(Setophaga ruticilla), and those associated with large patches (>5 ha) with thicket-meadow and
forest edge conditions such as Mourning Warbler (Oporornis philadelphia) (Hunter et al. 2001).
Table 1. Lists of species for thicket-meadow habitats at Limehouse Conservation Area. This
includes the top 10 common species determined as a measure of abundance and frequency
and Species of Conservation Concern recognized by Credit Valley Conservation (CVC,
1998). Predicted change in the status of each species is indicated as the landscape reverts
to a mixed forest cover.
Common Species *
Species of Conservation Concern
Indigo Bunting G
American Redstart Song Sparrow Bobolink G
Black-capped Chickadee Chestnut-sided Warbler Field Sparrow G
Eastern Kingbird G
Common Yellowthroat G
Eastern Towhee G
Northern Cardinal Golden-winged Warbler G
American Crow Mourning Warbler American Robin Nashville Warbler Blue-winged Warbler** G
Gray Catbird** G
*
**
G
In descending order of combined abundance and frequency
Species of Conservation Concern (CVC, 1998)
Species that will persist with conversion to Escarpment mixed forest
Species that will persist with conversion to mixed forest with local disturbance
Species that will not persist in the mixed forest
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Table 1 also provides a prediction of how these species will respond to habitat change based on
population patterns from other sites on the Escarpment (Milne 2002). When the fields fill in and
are replaced by either a mixed or deciduous forest (see Figure 1), most species of concern and
habitat-specific species will disappear from this system, producing a substantial change in the
composition of the avifauna. Only several of the common species such as American Robin
(Turdus migratorius) will make the transition to mature, undisturbed forests. The field species,
including all the species of concern, will leave the system. For example, both Blue-winged and
Golden-winged Warbler (Vermivora chrysoptera) were present at the beginning of the study, but
Golden-winged Warbler did not reappear after the second season and Blue-winged Warbler was
not present by the fourth year (Milne 2002). Those identified as gap-specialists, such as Chestnutsided Warbler (Dendroica pensylvanica) or American Redstart, could make the transition to the
forest habitat if there are local disturbances within the forest structure.
4. LANDSCAPE MANAGEMENT
It is important for the manager to identify these land units and be aware of the expansion of forest
and the rate of forest re-establishment within human-altered land units. Wildlife management
strategies could consider long-term renewal of land units such as plantations or abandoned fields
to maintain their place within the landscape. This could require thinning of forest tree species in
the fields and plantations. By maintaining the open nature of these sites, bird species adapted to
field and edge habitats will remain in the landscape. This may be desirable if there is a large
number of target species, such as species of conservation concern, identified at the site. These
decisions have to be tempered with recognizing the natural processes that maintain the landscape
and ensuring they continue to keep adjacent natural areas functioning properly. Consequently,
more information is required on the rate and extent of natural and human processes that create
change in the Escarpment landscape.
REFERENCES
Askins, R.A. 2000. Restoring North America’s Birds: Lessons from Landscape Ecology. New
Haven: Yale University Press.
Cadman, M.D., Eagles, P.F.J. and Helleiner, F.M. 1987. Atlas of the breeding birds of Ontario.
Waterloo, Ontario: University of Waterloo Press.
Credit Valley Conservation (CVC). 1998. Credit Watershed Bird Species of Conservation
Concern. Meadowvale, Ontario: CVC.
Daniels, T. 2000. Integrated working landscape protection: the case of Lancaster County,
Pennsylvania. Society and Natural Resources 13:261-271.
Hunter, W.C., Buehler, D.A., Canterbury, R.A., Confer, J.L. and Hamel, P.B. 2001. Conservation
of disturbance-dependent birds in eastern North America. Wildlife Society Bulletin 29(2):440-455.
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Milne, R.J. 2002. The Relationships of Vegetation and Bird Communities with Landforms and
Geomorphic Processes on the Central Niagara Escarpment. Unpublished Ph.D. thesis,
Department of Geography and Environmental Studies, Wilfrid Laurier University, Waterloo.
Milne, R.J. and Bennett, L.P. 1998. Seasonal patterns of avian populations on the central Niagara
Escarpment. . Paper in Leading Edge ’97: The Edge and The Point Conference Proceedings, ed.
S. Carty et al. Georgetown, Ontario: Niagara Escarpment Commission.
Milne, R.J. and Moss, M.R. 1996. Natural area boundaries and the dynamics of biophysical
processes on the Niagara Escarpment. Paper in Leading Edge ’95: A Conference Exploring The
Connections and Interrelationships Between Environment, Use and Culture in the Niagara
Escarpment Biosphere Reserve. Georgetown: Ontario Ministry of Energy and Environment.
Moss, M.R. and Milne, R.J. 1998. Biophysical processes and bioregional planning: The Niagara
Escarpment of Southern Ontario, Canada. Landscape and Urban Planning 40:251-268.
Milne, R.J., Bennett, L. and Puddister, M. ‘Species of Conservation Concern’ and their role in
landscape assessment on the Central Niagara Escarpment. Paper in Leading Edge '99: Making
Connections Conference Proceedings. Toronto: Ontario Ministry of Natural Resources.
Niagara Escarpment Commission. 1991. Five-Year Review: Niagara Escarpment Plan. Niagara
Escarpment Parks System. Georgetown: Niagara Escarpment Commission, Ontario Ministry of
Environment.
Niagara Escarpment Commission. 2002. A Cooperation Plan for the Niagara Escarpment
Biosphere Reserve. Georgetown: Niagara Escarpment Commission, Ontario Ministry of
Environment.
Price, M.F. 1996. People in biosphere reserves: an evolving concept. Society and Natural
Resources 9:645-654.
CONTACT
Rob Milne
Department of Geography and Environmental Studies
Wilfrid Laurier University
75 University Avenue
Waterloo, Ontario
N2L 3C5
Telephone: (519) 884-0710, ext. 3470
Fax: (519) 725-1342
Email: [email protected]
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