Eastern Arc Mountains and Coastal Forests of Tanzania and Kenya ...

2. Restore and increase connectivity among fragmented forest patches in the hotspot,especially in Lower Tana River Forests, Taita Hills, East Usambaras/Tanga andUdzungwasIt is a well-established principle in ecology that species richness is positively correlated witharea. When a forest is fragmented, each fragment of forest contains fewer species than did theintact forest and large fragments contain more species than small fragments (Laurance et al.2001 and references therein; Newmark 2002). Some species are lost immediately throughsampling effects, while others are lost because they need large areas to sustain their populations.Local extinctions continue well after the fragmentation event, as genetic diversity decreases andisolated populations become more inbred and vulnerable to diseases and random events. Somespecies disappear because they depend on others that are lost. Edge effects become moreimportant as fragment size decreases, affecting microclimates, exposing trees to winds and otherconditions that exceed their physiological tolerance and further reducing the amount of habitatfavoured by forest-dependent species. Some species do well in such conditions and there may belocal increases in biodiversity, with edge-tolerant species thriving and matrix species penetratingthe forest fragments. But for most of the forest-dependent species and these include many of theRed List species in this hotspot, fragmentation further threatens their survival. For example, inthe Taita Hills, fragmentation is associated with adverse effects on sex ratios and developmentalstability in threatened bird species, including the Critically Endangered Taita thrush (Lens & VanDogen 1999; Lens et al. 1998, 1999a, b, 2001, 2002).Reconnecting recently fragmented forest patches can save species from extinction. Gene flowcan be restored among isolated populations, locally extinct species can be reintroduced throughimmigration and ecologically complex processes that sustain diversity can be re-established. Thisis an important research front and the hotspot is an ideal location for such work. There are manyopportunities for implementation and investigation in both conservation science and communityconservation. Best practices could be replicated over larger areas. The hotspot is also a treasurehouse for evolutionary biology. A wide variety of taxa, at various levels of speciation, areavailable to examine issues of genetic divergence and isolation in relation to distance, mobilityand vagility. The sites chosen for this strategic direction were assessed from a biologicalperspective and were determined to present the greatest opportunity for successful connectivityefforts.2.1 Assess potential sites in the hotspot for connectivity interventions. Not all forestfragments should be reconnected. Where fragmentation is natural and long established, anynegative effects will have already been expressed and, over evolutionary time, new subspeciesand species will have evolved. There is little doubt that this process of fragmentation andisolation has been responsible, for example, for the extraordinary diversity of some of theinvertebrates (millipedes, linyphiid spiders, opilionids and carabid beetles) in the Eastern ArcMountains, where single site endemism exceeds 80 percent (Scharff et al. 1981; Scharff 1992,1993; Hoffman 1993, 2000; Burgess et al. 1998). The most suitable sites for connectivityinterventions are, therefore, those in which (1) fragmentation is relatively recent, where (2)detailed scientific background data are available, where (3) this is considered to be a priorityconservation action and where (4) this is a realistic activity. It will also be important to identifyaltitudinal forest corridors, which are, or could be, used for seasonal altitudinal migration.58