Global and local variations in tropical montane cloud forest soils

Abstract

Although soil resources are widely considered as a major factor that reduces the productivity, stature, and diversity of tropical montane cloud forests (TMCF), systematic comparisons of soil resources within and between TMCF are lacking. This study combines published reports on TMCF soils with new data on the soils and forest structure of the Luquillo Mountains in Puerto Rico to assess the current state of knowledge regarding global and local-scale variation in TMCF soils. At the global scale, soils from 33 TMCF sites and over 150 pedons are reviewed. Compared to soils in humid lowland tropical forests, TMCF soils are relatively acidic, have higher organic matter content, and are relatively high in total nitrogen and extractable phosphorus. Across all sites, significant correlations also exist between mean annual precipitation and soil pH and base saturation, but not between any soil chemical factor and canopy height, site elevation, or air temperature. Although comparisons between TMCF are limited by inconsistent sampling protocols, analysis of available data does indicates that lower montane cloud forests (LMCF) have taller canopies, higher soil pH, lower soil nitrogen, and higher C/N ratios than upper montane cloud forests (UMCF). Within an UMCF in NE Puerto Rico, the abundance of soil nitrogen, carbon, and potassium accounted for 25% to 54% of the variation in canopy height. However, as much as 68% of the variation in stand height could be accounted for when site exposure, slope gradient, and the percent coverage of surface roots were also included in the analysis. […]