Habitat Quality
Habitat quality is rarely uniform in landscapes because of natural variation in
topography, soils, and vegetation (Foster 1980). Habitat quality is a critical
feature of corridor effectiveness because, irrespective of the mobility of species,
survival rates are predicted to be much greater in high-quality habitats than in
marginal or poor habitats (Henein and Merriam 1990). Although the diversity of
species and their needs make it impossible to focus on individual species, there
do appear to be some general patterns. For tropical rainforests, high-quality habi-
tat is that which most closely resembles primary forest. Structural features such as
canopy height, canopy connectivity, canopy and understory structure, and floris-
tic composition may all be important, depending on the dispersing species.
In a study of 36 rainforest corridors or linear remnants in northern Aus-
tralia, for example, Laurance and Laurance (1999) found that only corridors
of primary rainforest supported the entire assemblage of arboreal mammals.
Mature (tall and floristically diverse) regenerating forests supported more
arboreal mammal species than young or less diverse regrowth, but they still did
not support the sensitive forest species that were at greatest risk of extinction
in forest fragments (Laurance and Laurance 1999).
Yet even a little forest cover is significantly better for wildlife movement
than none. At the Biological Dynamics of Forest Fragments Project near Man-
aus, Brazil, the deleterious effects of fragmentation on some faunal communi-
ties were significantly alleviated once the pasture areas that surround the frag-
ments were abandoned to forest regrowth (Gascon et al. 1999). For example,
the abundances of many understory bird species recovered significantly in
small fragments when forest regrowth provided continuous cover to undis-
turbed rainforest (Stouffer and Bierregaard 1995).
In Indonesia and Central America, the traditional agroforestry systems
often are refuges for high biological diversity (Thiollay 1995; Perfecto et al.
1996). A number of comparative studies have demonstrated that traditional
rubber and coffee plantations harbor more species than the more simplified
commercial plantations (Thiollay 1995; Perfecto et al. 1996; see also Chapters
9 and 10, this volume). The higher structural complexity of these plantations
supports many forest species (Thiollay 1995), including rare forest trees
(Purata and Meave 1993 in Perfecto et al. 1996), orchids (Nir 1988), inverte-
brates (Perfecto et al. 1996), and migrant birds (Greenberg et al. 1997).
Similarly, the floristic diversity of both natural habitat corridors (Laurance
1996) and agroforestry plantations (Perfecto et al. 1996) has been found to be
an important contributing factor to high biodiversity. A diverse array of flow-
ering and fleshy-fruited plant species in the canopy and understory can sup-
port many resident and dispersing wildlife species. Furthermore, the presence
of plant species (e.g., fig trees and palms) that offer fruit for long periods or
- Landscape Connectivity and Biological Corridors 57