Effects of selective logging on the abundance, regeneration and short-term survival of Caryocar costaricense (Caryocaceae) and Peltogyne purpurea (Caesalpinaceae), two endemic timber species of southern Central America

Abstract

In this study, we determined the effects of selective logging on the abundance of the last remnant populations of two tropical timber species with a restricted distribution, Caryocar costaricense and Peltogyne purpurea. We conducted a census of adult tree densities for these species on 94 selectively logged sites located in a tropical rain forest on the Osa Peninsula, Costa Rica. We compared the abundance of juveniles and seedlings for both tree species on 11 logged and unlogged sites. In addition, we analyzed the growth and mortality rates of adult trees of P. purpurea (>10 cm dbh) in a 4 ha permanent plot that was selectively logged once in 1992. Both species presented a heterogeneous density distribution over the Osa Peninsula (166,668 ha) and the highest density of both species is located in the region of the highest logging activity. For C. costaricense, seedling (height < 50 cm) and juvenile (height > 50 cm, dbh < 2 cm) abundance was greater in unlogged areas, while trees 2–10 cm dbh were more abundant in logged areas. For P. purpurea, seedlings were more abundant in unlogged areas, but small and large juvenile abundance did not differ between selectively logged treatments. The density of P. purpurea adult trees remained constant 15 years after selective logging but the density of trees 10–30 cm dbh decreased in the same period. We predict that recurrent 15 year cutting cycles of 50% of timber trees with restricted distribution, as it is practiced by conventional logging in Costa Rica, may lead a significant reduction of the main reproductive individuals, decreasing the regeneration of the populations subjected to exploitation and fragmentation.