Land Use History, Environment, and Tree Composition in a Tropical Forest

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 rugged, and soils are variable. Historical documents and local residents described past land uses such as clear‐felling and selective logging followed by farming, fruit and coffee production, and timber stand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 within 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, 13 167 stems) produced 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 effects 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.

Emerging forests on abandoned land: Puerto Rico’s new forests

“…Stand management has favored tree species that have commercial value. Consistent with this finding are research results that show that previous land use has a significant effect on present forest structure and species composition (García Montiel and Scatena, 1994;Zimmerman et al, 1995;Foster et al, 1999;Molina Colón, 1998;Chinea, 2002;Thompson et al, 2002). The percentage of a stand's density or basal area attributed to alien species was higher than expected from the percent of the total number of species classified as alien (Table 2).…”

Plant functional traits have globally consistent effects on competition

“…The data sets collated fell into two broad categories: (1) national forest inventories (NFI), in which trees above a given diameter were sampled in a network of small plots (often on a regular grid) covering the country (references for NFI data used [39][40][41][42][43][44][45][46][47][48] ); (2) large permanent plots (LPP) ranging in size from 0.5 to 50 ha, in which the x-y coordinates of all trees above a given diameter were recorded (references for LPP data used refs [49][50][51][52][53][54][55][56]. LPP were mostly located in tropical regions.…”

Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

“…at the northern end of the LFDP to 428 m at the south (Thompson et al 2002). There are two permanent streams running through the plot from east to west and several small ephemeral stream channels.…”

“…The soils are clays formed from volcaniclastic sandstone (USDA Soil Survey Staff 1995) with small amounts of Fluaquents in and along the stream channels. The distribution of the soil types across the plot, have little impact on forest composition when compared with the effects of previous land use history (Thompson et al 2002).…”

“…Canopy cover class 4 will, hereafter, be described as undisturbed. More details of the land use history and species composition of the LFDP can be found in Thompson et al (2002); for introduced species see Table 1.…”