Landscape units of Puerto Rico: influence of climate, substrate, and topography

Abstract

The landscape units map of Puerto Rico represents climatic, substrate, and topographic variation by integrating six climatic zones (Ewel and Whitmore 1973), six distinct substrates (Bawiec 2001, USGS 2005), five topographic positions or landforms (Martinuzzi et al. 2007), and prominent lakes and rivers (USGS 2005). Substrates were a simplified set of Bawiec’s (2001) twelve geologic terrane units and include cretaceous and tertiary limestone deposits, alluvium and other unconsolidated quaternary deposits, intrusive and extrusive volcanic formations and volcaniclastic sedimentary deposits (reworked sediments of volcanic origin – may or may not be calcareous), and ultramafic serpentine and amphibolite formations (low quartz content – typically high pH). We also deliniated saline and nonsaline wetlands (USGS 2005). The resulting map displays a set of 57 landscape units for the islands. The map builds on earlier work by Figueroa (1996) mapping geoclimatic variation in Puerto Rico and was developed for the purpose of understanding and modeling variation in vegetation. Natural variation in vegetation has a hierarchy of environmental controls, including controls, including climate, geochemical substrates, topography, and disturbance. Geospatial information on these controls is useful for modeling potential variation in vegetation cover and associated ecosystem properties. (?) Climatic controls include the range, mean, and variability of air temperatures and precipitation regulated by latitudinal gradients, global atmospheric patterns, orographic patterns, and feedbacks with landcover (Chapin et al. 2005). (?) Substrate characteristics (geochemistry) include soil pH, nutrient availability, and texture, which strongly affect plant species composition (Gould et al. 2006). Geochemistry is related to exposed bedrock, quaternary deposits, land use history, and biological processes. (3) Topography affects plant species composition by influencing soil moisture, development, texture, and chemistry (Birkeland 1984). Slope position is also related to disturbance and particular landforms may be more or less influenced by flooding, storms, landslides, fire, or human development. The most abundant landforms in Puerto Rico are the moist and wet slopes on volcanic substrates of the Central and Luquillo Mountains, which include 40% of the area. Moist and wet slopes on limestone substrates make up 10% of the area. Dry hills and slopes make up 6% of the area, with 30% of these on limestone and the remaining 70% on volcanic and ultramafic serpentine substrates. Nearly 12% of the landscape is made up of ridges and 90% of these are in the moist and wet climatic regions. Moist plains include 16% of the area and dry plains include 8% of the area. Wetlands and depressions, not including open water bodies, make up 5% of the area. Nearly 70% of these are in moist climatic regions and just under 30% in dry climatic regions.