CONTROLS OF PRIMARY PRODUCTIVITY - LESSONS FROM THE LUQUILLO MOUNTAINS IN PUERTO-RICO

The Luquillo Mountains of eastern Puerto Rico are used as a case study to evaluate possible single-or multiple-factor controls of productivi ty in montane forests. A review of published studies from the Luquillo Mountains revealed that canopy height, productivity, and species rich ness decline while stem density increases with elevation, as is typica l of other montane forests. A mid-elevation floodplain palm stand with high levels of productivity provides a notable exception to this patt ern. Previous basic and applied studies of productivity in the Luquill o Mountains have consistently considered the overall gradient in produ ctivity to be important in understanding forest structure and function . Recent observational and experimental studies have determined that d isturbance of all types is an important factor mediating productivity in both low-and high-elevation (cloud) forests, For example, low-eleva tion forest recovers more quickly :From hurricane disturbance and is m ore responsive to nutrient additions than is cloud forest. All of the factors proposed for limiting productivity are supported in one way or another by research in the Luquillo Mountains. What is critically lac king is both an appreciation for the way that these factors interact a nd experiments appropriate to evaluate multiple controls acting simult aneously.