LAND USE HISTORY, ENVIRONMENT, AND TREE COMPOSITION IN A TROPICAL FOREST

Thompson, J., N. Brokaw, J.K. Zimmerman, R.B. Waide, E.M. Everham III, D.J. Lodge, C.M. Taylor, D. Garcia-Montiel, and M. Fluet.  2002. 
 Land Use History, Environment, and Tree Composition in a Tropical Forest.  Ecological Applications:  12(5): 1344-1363

Abstract. The effects of historical land use on tropical forest must be examined to understand present forest characteristics and to plan conservation strategies. We compared the effects of past land use, topography, soil type, and other environmental variables on tree species composition in a subtropical wet forest in the Luquillo Mountains, Puerto Rico. The study involved stems ≤10 cm diameter measured at 130 cm above the ground, within the 16-ha Luquillo Forest Dynamics Plot (LFDP), and represents the forest at the time Hurricane Hugo struck in 1989. Topography in the plot is rugges, and soils are variable. Historical documents and local residents described past land uses such as clean-felling and selective logging followed by farming, fruit and coffee production, and timber stand improvement in the forest area that now includes the LFDP. These uses ceased 40 – 60 yr before the study, but their impacts could be differentiated by percent canopy cover seen in aerial photographs from 1936. Using these photographs, we defined four historic cover classes with the LFDP. These ranged from cover class 1, the least tree-covered area in 1936, to cover class 4, with the least intensive historic land use (selective logging and timber stand improvement). In 1989, cover class 1 had the lowest stem density and proportion of large stems, whereas cover class 4 had the highest basal area, species richness, and number of rare and endemic species. Ordination of tree species composition (89 species, 12 167 stems) produces arrays that primarily corresponded to the four cover classes (i.e., historic land uses). The ordination arrays corresponded secondarily to soil characteristics and topography. Natural disturbances (hurricanes, landslides, and local treefalls) affected tree composition, but these effects did not correlate with the major patterns of species distributions on the plot. Thus, it appears that forest development and natural disturbance have not masked the efforts of historical land use in this tropical forest, and that past land use was the major influence on the patterns of tree composition in the plot in 1989. The least disturbed stand harbors more rare and endemic species, and such stands should be protected.

Key words: biodiversity; conservation; disturbance; land use history; Luquillo Experimental Forest; Puerto Rico; soil; species diversity; topography; tree community; tropical forest.