Understory bees and floral resources in logged and silviculturally treatedCosta Rican rainforest plots

Natural forests managed for timber production conserve tropical biodiversit y, but how much? In a lowland wet forest of northeastern Costa Rica, we stu died bees and understory flowers in regenerating forest plots logged 6-8 ye ars previously, including silviculturally refined plots where non-timber sp ecies were removed. The experiment had a complete randomized block design w ith 3.24 ha plots (n = 3 per treatment) surrounded by 40 m buffer strips. O ur four-month comparative study covered the major flowering period. Overall , 69 species monitored for visitors at 629 individuals demonstrated bees vi sited and likely pollinated 55 to 80% of understory plants-a mixture of pri mary forest species in shaded microsites (e.g., palms) and pioneers associa ted with relatively high insulation (e.g., certain Melastomataceae, Rubiace ae and Solanaceae). Small Halictinae predominated among the bees at flowers , 62% of the 21 species were undescribed. Few notable differences were found among plots of forest drastically altere d by culling of non-timber species, and naturally regenerating forest. Such control and refined plots were similar in numbers of species flowering, ri chness of bees, visitor species per plant, and insolation. Both plot groups had similar complements of halictine species, as well as relatively low le vels of foraging specialization by bees evidently nesting, as well as forag ing, within plots. Bees were mainly active in shaded microhabitats of close d forest, but the small proportion of relatively insolated plants was heavi ly visited. Rarity of both native bees frequent in sunny, exposed sites (e. g., Megachile, Centris, Xylocopa) and of African honey bees, is evidence fu r existence of both a distinctive guild of understory bees and their percep tion of conditions in logged forests as similar to those of mature forest.