DOI: 10.6073/pasta/2d47b8de393940ef6c0de730b01b3cf5
title: Landscape-Scale Forest Dynamics in the Luquillo Experimental Forest in Puerto Rico 1936-1989

description: This study examined landscape-scale forest dynamics in the Luquillo Experimental Forest (Puerto Rico). The analysis was based on vegetation maps created from aerial photographs taken in 1936 and 1989. For details on methods and results, please see the published paper (Foster, D. R., M. Fluet and E. R. Boose. 1999. Human or natural disturbance: landscape-scale dynamics of the tropical forests of Puerto Rico. Ecological Applications 9: 555-572). The Abstract from the paper is reproduced below. "Increasingly ecologists are recognizing that human disturbance has played an important role in tropical forest history and that many assumptions concerning the relative importance of natural processes warrant re-examination. To assess the historical role of broad-scale human versus natural disturbance on an intensively studied tropical forest we undertook a landscape-level analysis of forest dynamics in the Luquillo Experimental Forest (LEF; 10,871 ha) in eastern Puerto Rico. Using aerial photographs (1936 and 1989), GIS, a model of topographic exposure to hurricane winds, and historical data, we sought to: (1) document historical changes in extent, cover and type of forest vegetation, (2) evaluate the distribution of land-use and hurricane impacts, (3) assess the contributions of these processes in controlling current vegetation patterns, and (4) relate these results to ongoing ecological, conservation and natural resource discussions. "With over 1000 m of relief in the LEF, the broad vegetation zones of Tabonuco (below 600 m a.s.l.), Colorado (600-900 m), Dwarf (above 900 m), and Palm forest are determined by environmental gradients. However, over the past 60-100 years forest extent, cover, and type have been transformed: in 1936, 40% of the LEF was unforested or secondary forest and less than 50% had continuous canopy (more than 80% cover); in 1989, less than 97% was continuous forest. Secondary forest and agricultural lands in 1936 were replaced largely by Tabonuco and Colorado forest, which increased from 8% and 28% (1936) to 26% and 45% (1989). "These broad-scale vegetation dynamics are best explained by a gradient of human land use, intense at low elevations and decreasing on steep, high terrain, which peaked historically around 1900 followed by a gradual decline in agriculture. GIS analysis and historical sources suggest that essentially all of the LEF was affected by human activity and that Tabonuco forest, which is the focus of LTER research, has been most substantially altered and is largely of secondary origin. Rapid reforestation following agricultural decline has obscured much of the past land use and confirms the resiliency of some tropical forests to intensive human disturbance. Impacts of earlier hurricanes (e.g., in 1928 and 1932), though not evident in the broad forest pattern in 1936, may be significant in explaining the distributions of Colorado and Palm forest. Damage from Hurricane Hugo in 1989 indicates that natural disturbance is increasingly important as land use declines and forest cover and height increase. However, this study and post-Hugo studies emphasize that land-use legacies are long-lasting and need to be considered in modern ecological studies and natural resource management. The subtle though persistent effects of historical human activities may have profound consequences for modern forest ecosystems in the tropics."