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Incorporating metapopulation dynamics of greater gliders into reserve design in disturbed landscapes
Ecology, March, 1999 by Michael A. McCarthy, David B. Lindenmayer
If the conservation of greater gliders were based solely on the reservation of existing old-growth patches in wood production areas, there would be a high probability of extinction of the species in the next 300 yr. Unreserved areas will be logged on a rotation time that prohibits the development of habitat that is suitable for greater gliders. In addition, old-growth patches will eventually burn, reducing the habitat quality of these areas for a period of time. Excluding timber harvesting from areas of regrowth forest can reduce the risk of extinction of greater gliders within timber production forests. Our simulations indicated that concentrating reserved regrowth forest around the largest areas of old growth had the greatest effect on reducing risks of extinction [ILLUSTRATION FOR FIGURE 7 OMITTED]. This is because the large areas of old growth were most likely to support animals that could colonize the regrowth areas once they became suitable habitat. Therefore, the largest remaining areas of old-growth mountain ash should act as nuclei for the establishment of reserve systems within timber production forests, if the aim is to reduce the risk of extinction of greater gliders. Thus, our findings strongly support the present actions by the Government of Victoria to exclude logging from remaining areas of old-growth forest (Macfarlane and Seebeck 1991). Our simulations indicate that to reduce the risk of extinction within the Ada Forest Block to [less than]0.10 within the next 300 yr, an additional 600 ha reserve of regrowth forest would need to be added to the 159 ha of old growth. This is different from the recommendation of Lindenmayer and Possingham (1995), who suggested that several (12-20) small reserves established within each forest block would minimize the risk of extinction of Leadbeater's possum, another species of arboreal marsupial that occurs in mountain ash forests. The difference is due, in part, because different species with different life history attributes were being considered (Lindenmayer and Lacy 1995), but also because of the different way that fire was modeled.
TABLE 3. Results of a sensitivity analysis to determine effects of
parameters on the number of reserves needed to minimize the
predicted risk of extinction of greater gliders within 300 yr in
old-growth mountain ash forest. The optimum number of reserves when
reserving a total of 256 ha is shown in parentheses below each
parameter value. The optimum number of reserves for the unchanged
set of parameters was 8.
Parameter Low value High value
Annual fecundity 0.176 0.324
(1) (8)
Annual survival rate 0.80 0.90
(1) (8)
Maximum population density 1.5 3.0
(no./ha) (8) (8)
Spatial correlation strength halved doubled
(2) (8)
Mean tire interval (yr) 75 200
(2) (16)
