Download Ecosystem Restoration on the California Channel Islands

The Fourth Califorllia Islallds Symposium: Update 011 the Status of Resources
Edited by W. L. Halvorson and G. J. Maender. 1994. Santa Barbara Museum of Natural History, Santa Barbara, CA.
Ecosystem Restoration on the California Channel Islands
William L. Halvorson
National Biological Survey, Cooperative Park Studies Unit, 125 Biological Sciences East,
The University of Arizona, Tucson, Arizona 85721
Tel. (602) 670-6885: Fax (602) 670-5001
Abstract. Restoration of natural habitat has become
increasingly important over the last 2 decades, first as
mitigation for development (especially in wetlands), and
more recently in natural areas. This latter restoration has
come about as land managing agencies have seen the
need to reverse the impact of past land uses, and agencies
like the National Park Service have taken on the responsibility for less-than-pristine lands. Restorations have
typically been carried out with little prior study and with
no follow-up monitoring.
On the Channel Islands, the need for restoration is
great, but this restoration should be based on a sound ecological understanding. By conducting surveys, implementing long-term research and monitoring, and by
conducting population and community dynamics
research, we can obtain the necessary data to arrive at
such an understanding. Once management actions have
been taken to effect restoration, monitoring should be
conducted to determine the success of those actions. The
intention is to gain enough of an understanding of the
islands' ecosystems that we can manage to restore not just
populations of native plants and animals, but also the
processes of a naturally functioning ecosystem.
Keywords: California; California Channel Islands; island biogeography; vegetation; population dynamics; restoration.
Introduction
Ecosystem restoration is a lofty ideal, but the question is still very open as to whether it is possible. A great
deal of work is currently being done in the name of
restoration, rehabilitation, and re-creation, especially at
the boundary between developed lands and the natural,
unimpacted world (Halvorson 1993). There are many barriers to complete restoration; 3 of the most important are
(1) there is insufficient information on what was there
before disturbance (i.e., restore to what?); (2) there is
insufficient information on the kinds of disturbances
affecting a particular area, and exactly what are the
effects of those disturbances (e.g., timing and intensity of
disturbance, specific changes caused by disturbance); and
(3) all ecosystems are much too complex for us to deal
with comprehensively (most projects deal with major
macro-species and ignore other components such as
micro-flora and fauna, and soil).
Historical degradation
On the Channel Islands, a number of management
agencies are dealing with the issue of reversing the trend
of more than 150 yr of overgrazing and over-utilization of
the islands' natural resources. Historical accounts of past
land uses have been documented in a number of publications (Philbrick 1972; Clark and Halvorson 1987;
Halvorson et al. 1988; Clark et al. 1990; O'Malley 1991).
The situation is that the islands were used for sheep grazing from the 1840s to approximately the tum of the century (depending on the island) when, for the most part, a
period of more active farming or ranching occurred,
including the change on some of the larger islands to cattle grazing. On many of the islands, nineteenth- and early
twentieth-century sheep grazing left the land scarred,
eroded, and devoid of much of its vegetation.
While the twentieth century has seen some recovery,
many of the regressive trends started by sheep grazing are
still in evidence today. In addition, military activities and
large scale fires have also taken their toll, exacting new
impacts to recovering natural systems. One of the military
impacts was the introduction of European rabbits onto
Santa Barbara Island and the subsequent devastation of
native shrubs and succulents, and, in some areas, removal
of all plant cover (Sumner 1959; Halvorson et al. 1988).
Besides sheep, cattle, and goats, other large herbivores
that have been introduced to the islands include bison
(Santa Catalina), deer (Santa Catalina, Santa Rosa), elk
(Santa Rosa), donkeys (San Miguel), and pigs (Santa
Catalina, San Clemente, Santa Cruz, Santa Rosa).
Along with the introductions of animals came the
introduction of many plants. Today nonnative species
comprise, on average, about 25% of the islands' flora.
The most seriously impacted of the islands are Santa
Barbara and San Nicolas with 30% and 40% nonnative
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Halvorson, W. L.
plant species. Even these numbers do not really tell the
whole story, however. The plant community cover of the
islands is even more dominated by nonnative plant
species. For instance, Santa Barbara and Santa Rosa have
some two-thirds of the land surface covered by an annual
grassland community with mostly introduced European
grasses. If eroded areas me added to the land cover that
has something other than a native species-dominated plant
community, the impact on some islands is more than 75%.
Restoration Activities
The major thrust of reversing this pattern of human
use of the islands started in the 1970s when the Catalina
Conservancy was started (1972), and active management
of natural resources began at Channel Islands National
Monument (the islands of Anacapa and Santa Barbara).
Since that time, Channel Islands National Park and
Channel Islands National Marine Sanctuary were created
(1980), The Nature Conservancy bought most of Santa
Cruz Island, and the U.S. Navy, which manages the
islands of San Clemente, San Nicolas, and San Miguel,
became much more conservation oriented. Santa Catalina
Island is a very good example of the change in thinking
relative to the islands. As reported by O'Malley (1991),
since 1950, management of the island evolved through 3
major changes: (1) initial efforts to maintain the island as
an economic resource (1950-1970), (2) more aggressive
preservation efforts that recognized the value of the natural history of the island (1970-1985), and (3) active
restoration of existing resources combined with informational and educational programs (1985-present).
InventOlY and monitoring
When Channel Islands National Park was created in
March 1980, 2 major resource issues needed to be dealt
with. Unlike most National Park Service areas, the land
purchased for this park was heavily impacted and anything but pristine. Further, there was very little known
about the natural resources of the islands.
The decision was made very early that the highest
priority was to inventory the islands and begin a process
of monitoring natural resource conditions (Davis and
Halvorson 1988). This information would then be used to
develop long-term data sets essential to the rehabilitation
and perpetuation of unimpaired natural resources, ideally
characteristic of national parks (Davis et al. 1988; Davis
et al. 1994).
At Channel Islands National Park, a step-down diagram was used in the development of the monitoring program. Managers and scientists worked together using a
Delphi approach to identify all of the steps needed in the
program and arrayed these in a logical hierarchy in the
diagram. Park ecosystems were divided into an exhaustive list of mutually exclusive taxonomic groups, such as
seabirds, vegetation, mammals, and invertebrates.
Priorities were then set on all the steps needed, including
16 research projects to design protocols.
Design studies were conducted by research scientists
to devise new ways of tracking population dynamics and
assessing ecosystem health. Based on literature reviews
and field experience, individual species were selected for
their importance to each community, sampling techniques
were developed and standardized, and protocols were
defined to analyze and report results for each taxonomic
group. Handbooks were then written to assure that continuity and quality would be maintained through many
generations of resource managers who would actually be
monitoring ecosystem health.
Restoration initiation
Surveys conducted during the initial inventory phase
located nonnative species (human-caused introductions)
destructive to native species and communities (Erickson
and Halvorson 1990; Halvorson 1992). In some cases,
these could be eradicated without extensive planning and
research (Halvorson and Koske 1987; Schuyler 1987;
Erickson et ai. 1990). In other situations, it was necessary
to develop native species-management techniques in
order to protect and enhance these natives in a milieu of
grazing destruction (Clark and Halvorson 1987;
Halvorson 1990; O'Malley 1991). It was also necessary
to gain an understanding of soil characteristics and of
plant/soil relationships (Halvorson, et ai. 1988;
D' Antonio et ai. 1992; Belnap 1994). The initiation of
restoration, therefore, was the control and eradication of
nonnative species, both plant and animal, and the protection of the more seriously impacted native species.
Examples of programs already accomplished or
underway include the eradication of feral pigs on Santa
Rosa Island and their control on Santa Cruz Island, the
eradication of sheep from Santa Cruz and San Miguel
islands, rabbits from Santa Barbara Island, and donkeys
from San Miguel Island. Programs dealing with nonnative
plant species (weeds) tend to be longer term than those
dealing with animal species because of the tendency of
plants to remain as seeds for long periods. Some of these,
like thistles, Australasian fireweed, and fennel can be very
invasive and dismptive to native communities. Natural
resource managers have tended to wait until the animal
problems that they could deal with were solved before
starting on the plant problems. Currently, most of the
islands have some nonnative plant species removal underway. Fortunately, the Channel Islands do not have many
invasive woody species to contend with like some regions
of the world, such as south Florida and Hawaii, where nonnative woody species are an extremely serious problem.
Restoration research
After the initiation of field surveys, natural resource
inventories, and implementation of long-term monitoring,
it became evident that full ecosystem restoration, inclucling both the pieces of the ecosystems ancl their interactions (processes and function), would require an
exhaustive research program. Research programs are now
being developed on most of the islands. The programs are
well-thought-out, integrated stuclies; not just financial
support for unrelated research projects that are brought to
management agencies individually and encl up as final
reports resting on some office shelf.
At Channel Islands National Park, tlus program has
developed along a number of lines of investigation: (1)
general community structure and distribution (Clark and
Halvorson 1990); (2) population biology of, and management techniques for, native species that need recovery
(Clark and Halvorson 1987; Danielsen and Halvorson
1990,1991; Fellers and Drost 1991); (3) population biology of, and eradication techniques for, nonnatives for
which better information is needed on their impacts and
on methods for removal (Erickson and Halvorson 1990;
Erickson et al. 1990); and (4) rehabilitation of completely denuded or nonnative species-dominated areas
(Halvorson 1984; Halvorson et al. 1988; D' Antonio et al.
1992). Many of these same sorts of studies are now being
conducted by The Nature Conservancy on Santa Cruz
Island, by the U.S. Navy on San Nicolas ancl San
Clemente Islands, and by the Catalina Conservancy on
Santa Catalina Island.
Community structure. Our work on general community structure and distribution has included lists of flora
and fauna. The flora of the islands is highly impacted with
introduced species. In Channel Islands National Park,
approximately 25% of the plants are nonnative species
(Halvorson 1992). Chain-wide, the islands with the highest percentages are Santa Barbara with 31 % and San
Nicolas with 44%. Exact percentages keep changing
because the lists per island are not static-most survey
trips result in new species fmds. It is bad enough that the
list of plants contains such a high percentage of nonnatives, but the situation worsens when looking at the composition of communities and landscape-level distributions.
The importance of nonnative species to community
stmcture is such that on many islands, nonnative speciesdominated communities cover as much as two-thirds of
the island surface (Clark et al. 1990). This is a problem
whose solution requires an understanding of long-term
species and community dynamics in order to effect a shift
in species dominance over time. This will require a longterm monitoring program aimed at determining community composition changes over time and their causes. For
instance, given protection from disturbance and normal
rainfall, shrub species such as coreopsis, buckwheat, and
coastal sage increase regularly in the annual grassland.
487
Coreopsis especially will recover noticeably under these
conditions, and no restoration management actions are
needed to accomplish this. When, however, the islands
experience a drought sequence such as the one in the late
1980s, the shrub species do not increase in population
numbers; in fact, population densities decline.
Understanding these types of population dynamics
and ecological relationships is necessary to develop a
strategy for long-term restoration of native species-dominated plant communities. An understanding of other ecological relationships is also needed to understand the
function ancl stability of native islancl ecosystems. Belnap
(1994) has shown the importance of cryptobiotic soil
crusts to nutrient flow and soil stability. Other stuclies
have investigated the importance of mycorrhizae to island
plants (Halvorson and Koske 1987; Koske ancl Halvorson
1989, 1990). Knowing what is going on at the boundary
between the various levels of ecosystem structure is
important, but arriving at a fuller understanding of the
interrelationships of many levels of island ecosystems
(see, for example, Drost and Fellers 1991) will allow for
better management of the natural resources of the islands
and for restoring naturalness.
Native species ecology. Many of the native species
thought to be threatened or endangered on the islands have
been found to be so because of past land use or current
impacts from introduced grazing animals (Clark and
Halvorson 1990; Halvorson et al. 1992). Once these conditions have changed, most of the species studied thus far have
shown improvement rather quickly; some, however, have
not and have been recommended for active management.
Fellers and Drost (1991) concluded from their study
on island night lizards on Santa Barbara Island that the
lizards were able to survive episodes of goats (last on the
island in 1922), sheep (1937), feral cats (1979), and rabbits (1981). They also survived 10 yr of farming, the
establishment of 40 species of nonnative plants, 5 yr of
annual burning of crop land, and at least I major grass
fire. They found that night lizards on Santa Barbara
Island maintained a stable population through the 1980s
at a density greater than ground-dwelling lizards in any
other area for which there are such reports.
Clark and Halvorson (1987) found that the Santa
Barbara Island live-forever, a federally listed endangered
plant species, was recovering, but not yet out of danger.
The problem presented to natural resource managers was
that successful recruitment of this species depends on a
rather narrow range of moisture conditions over 2 to 3 yr to
allow appropliate seed set, germination, and establishment.
This live-forever, like many species of the genus, suffered
during the drought of 1986-1991 (Clark 1989) increasing
both the need for and difficulty of recovery efforts.
Many woody species on the islands have been shown
to need active management in addition to protection and
monitoring. The 2 subspecies of island ironwood, island
oak, and island pine are all examples of this. O'Malley
488
Halvorson, W. L.
- Ecosystem Restoration -
Crystalline Iceplant Lifecycle
(Soil Salinity)
(
Germination
(High)
\
Growth
(Decreasing)
Death
(Increasing)
Maturity
(Low)
Figure 3. Effect of iceplant life cycle on soil salinity in the
immediate area.
mumtles consisted of, the first phase of the iceplant
removal study was to determine the effect of iceplant on
the soil characteristics; phase 2 was to study removal and
revegetation techniques. With help from earlier studies on
the species (Vivrette and Muller 1977), we were able to
determine that increased density of foliage and increased
soil salinity were major factors in maintaining dominance
over the area. These factors were taken into account in
determining that the plants needed to be removed during
the growing season when they were at their largest and
held the most amount of water and salt (Fig. 3).
Revegetation benefited from tilling the soil and covering
it with some type of erosion-control blanket. The process
of removing iceplant and revegetating the area turned out
to be very labor intensive.
Figure 1. Isolation of island oak stand on Santa Rosa Island.
reports on efforts to refurbish the ironwood groves on
Santa Catalina Island. Channel Islands National Park is
currently planning projects for restoration work in ironwood, island oak (Fig. 1) and island pine stands on Santa
Rosa Island (Halvorson 1990). These projects to date
have been primarily aimed at stopping erosion and restoring cover of native species; no one has yet made a determined effort to restore an ecosystem of these woodland
types because we do not yet have enough information to
attempt it.
Rehabilitation. In 1984, we initiated a series of studies aimed at restoring areas on Santa Barbara Island that
were either devastation areas (completely denuded of
vegetation and highly eroded) as seen in Figure 2, or that
were dominated by a cover of the nonnative annual, crystalline iceplant.1n 1994, San Nicolas Island was added to
this research program. These studies are being conducted
because it is clear that natural recovery is not occurring
and that active management is required to halt erosion,
recontour the land, and reestablish a native plant community. The study of the devastation area started with an
analysis of the vegetation and soils surrounding the area
(Halvorson et ai. 1988) and went on to study revegetation
techniques (D'Antonio et al. 1992). Future work will be
needed to discover all the connections necessary for
restoring a functioning ecosystem in the area.
Conclusion
Figure 2. Eroded devastation area on Santa Barbara Island.
The invasion of the crystalline iceplant onto Santa
Barbara and San Nicolas islands was facilitated by
human-related disturbance, and it does not appear that
iceplant decreases in abundance when the disturbance is
removed. This is another example of a situation in which
active management is needed in order to return a specific
site to a natural (i.e., native species- dominated) habitat.
After determining what the surrounding native plant com-
We have found on the Channel Islands that current
management by protection and removal of introduced
grazers is encouraging a trend toward recovery of native
plant communities and, thereby, a recovery of native animal species. However, there are situations in which managers must use a relatively heavy hand to reverse a
destructive trend toward loss of native vegetation cover,
loss of top soil, and continued erosion.
Whenever we set out to restore or rehabilitate a natural habitat, we should be very cognizant of the fact that,
if we mean to restore whole, functioning ecosystems, it is
not simply a matter of developing a vegetative cover with
489
the right species mix. Ecosystem restoration or rehabilitation requires a great deal of understanding of species and
how they relate to each other and their environment. This
will require expertise from a diverse group of people, as
well as continued commitment to go beyond inventory
and monitoring work to more intensive ecological
research. Knowledge gained from this research can be
appropriately applied to the management of the islands'
native systems.
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The Fourth California Islands Symposium: Update on the Status of Resources
Edited by W. L. Halvorson and G, J. Maender. 1994. Santa Barbara Museum of Natural History, Santa Bm'bara, CA.
Cyanobacterial-Lichen Soil Crusts of San Nicolas Island
Jayne Belnap
National Biological Survey, 125 W 200 South Moab, UT 84532
Tel. (801) 259-3911; Fax (801) 259-8628
Abstract. CymlObacterial-lichen soil crusts are a dominant
feature on the soils of San Nicolas Island. These crusts can
play many important roles in ecosystems in which they
occur. These roles can include contribution of nitrogen to
soil nitrogen pools, enhancement of element uptake in vascular plants, increase in vascular plant seedling establishment and survival, and stabilization of soil surfaces. Species
composition of crusts on San Nicolas Island are discussed,
along with the roles the crusts play in the different habitat
types found on the island, and the effects of disturbance on
the crusts, including successional sequences, nitrogenase
activity, and recovery rates.
Keywords: Nitrogen cycles; Microcoleus vaginatus; Collema; soil
stabilization; revegetation; arid lands; semi-arid lands.
Introduction
Cryptobiotic soil crusts, consisting of cyanobacteria,
mosses, and lichens, are an important component of semiarid and arid ecosystems. These crusts represent up to 70%
of the living ground cover in many of these areas. Many
roles have been ascribed to these crusts, including stabilizing soils (Harper and Marble 1988; Belnap and Gardner
1993); increasing water infiltration and nutrient status of
soils; contributing to nitrogen fixation (West and Skujins
1977; Skujins and Klubek 1978; Belnap 1991; Belnap et
al. 1993; Evans and Ehlringer 1993; Harper and Pendleton
1993); and enhancing seedling establishment (Belnap
1993a). Data suggest that these crusts are slow to recover
from severe disturbance, requiring 40 yr or more to recover on even small areas (Belnap 1993a). This paper discusses the role of cryptobiotic soil crusts in the
functioning of desert ecosystems in general, and 2
Channel Islands (Santa Barbara and San Nicolas) more
specifically. Data are drawn from several different studies
conducted over the past 5 yr by Belnap (1991, 1993a,
1993b), Belnap and Gm'dner (1993), Belnap and Harper
(1993), Belnap et al. (1993), Harper and Pendleton (1993),
and recent work by Belnap on the Channel Islands.
Methods
Crust surveys were done on 2 of the Channel Islands,
Santa Barbara Island and San Nicolas Island. The survey
of Santa Barbara Island was brief, and only general conclusions of that survey are discussed in this paper. Crust
surveys on San Nicolas Island were extensive. All soil
map units as defined by the Soil Conservation Service
were sampled. In addition, sites with varying disturbance
histories were sampled. Lichen and moss species were
identified, and unusual specimens collected. Collections
were made to identify cyanobacterial mld green algal components of the major crustal types encountered. These samples were cultured on agm' in media with and without
nitrogen to separate cyanobacteria and green algae. Cultures
were then exmnined microscopically, and species identified.
Nitrogenase activity of crustal organisms on San
Nicolas Island was measured. Samples were collected dry
from heavily crusted areas and flown to a portable laboratory located at Point Mugu, arriving within an hour of collection. Samples were wetted equally with distilled water
and injected with sufficient acetylene to create a 10%
acetylene atmosphere. After injection, samples were incubated for 4 hr at 26° C in 2.5-cm diameter, clear, gas-tight
tubes. Incubation occun'ed in a chamber lighted with
Chrom050 (5,000 K) and cool white fluorescent bulbs.
Subsamples (0.25 ml) of the head space within the tubes
were then analyzed for acetylene and ethylene content on
a Carle FID gas chromatograph equipped with an 8-ft column (8% NaCI on alumina), using helium as carrier gas
(30 ml/min). Units reported are gas chromatographic units
and are not convertible to kg/ha of N without calibration
by N15, which was not done. Measurements obtained were
used to determine relative rates of fixation between sample sites, sample dates, and geographic locations. There
were 20 replicates per site. Statistical analyses were done
using analysis of variance and a multiple range test.
Results and Discussion
Results of survey
Minimal crustal development was seen on Santa
Barbara Island. This is probably attributable to the high
shrink-swell potential of most soils found on this island.
Areas with these types of soils supported a minimal
cyanobacterial flora. Sandy, rocky soils on the north and
east portions of the island supported lichenaceous crusts;
however, these areas represented only a small portion of