Since people arrived in Madagascar some 2,000 years ago, an estimated 97 percent of the island's dry deciduous western forests have been destroyed and those that remain are extremely fragmented. Restoring these forests is one of the highest conservation priorities worldwide, according to a 1995 United Nation's Development Program workshop. Ganzhorn and his colleagues studied regeneration in both contiguous and fragmented primary forest. The fragments ranged from about seven to 1,500 acres. The researchers found 177 tree species at study sites and determined that 20 trees or about 10 percent of the trees were dispersed largely or entirely by lemurs.
Lemurs act as seed dispersers for trees with seeds that are larger than a half an inch in size.
Fecal analysis showed that these 20 tree species are dispersed primarily by the brown lemur. Of the eight lemur species living in these forests, the brown lemur is the only one that ingests and excretes intact seeds larger than half an inch. Seven of the 20 tree species have seeds this size or bigger. Ganzhorn and his colleagues compared regeneration in forest fragments with and without brown lemurs and found that without lemurs there was significantly less regeneration of the 20 lemur-dispersed trees. In contrast, there was no difference in regeneration for the 157 tree species that do not depend solely on lemurs for dispersal.