The Holdridge life zones of the conterminous United States in relation to ecosystem mapping

Aim Our main goals were to develop a map of the life zones for the contermi nous United States, based on the Holdridge Life Zone system, as a tool fur ecosystem mapping, and to compare the may of Holdridge life zones with othe r global vegetation classification and mapping efforts. Location The area of interest is the forty-eight contiguous states Of the U nited Starts, Methods We wrote a PERL program for determining lift: zones from climatic d ata and linked it to the: image processing workbench (IPW). The inputs were annual precipitation (Pann), biotemperature (T-bio), sea-level biotemperat ure (Tbio), and the frost line. The spatial resolution chosen for this stud y (Lj are-minute for classification, 4-km for mapping) was driven by the av ailability of current state-of-the-art, accurate and reliable precipitation data. We used the Precipitation-elevation Regressions on independent Slope s Model, or PRISM, output fur the contiguous United States downloaded from the Internet. The accepted standard data for air temperature surfaces Ir-er e obtained from the Vegetation/Ecosystem Modelling and Analysis Project (VE MAP). This data set along with station data obtained from the National Clim atic Data Center for the US, were used to develop all temperature surfaces at the same resolution as the Pann. Results The US contains thirty-eight life zones (34% of the world's life zo nes and 85% of the temperate ones) including one boreal, twelve cool temper ate, twenty warm temperate, four subtropical, and one tropical. Seventy-fou r percent of the US falls in the 'basal belt', 18% is montane, 8% is subalp ine, 1% is alpine, and < 0.1% is nival. The US ranges from superarid to sup erhumid, and the humid province is the largest (45% of the US). The most ex tensive life zone is the warm temperate moist forest, which covers 23% of t he country. We compared the Holdridge lift: zone map with output from the B IOME model, Bailey's ecoregions, Kuchler potential vegetation, and land sev er, all aggregated to four cover classes. Despite differences in the goals and methods for all these classification systems, there was a very good to excellent agreement among their for forests but poor for grasslands, shrubl ands, and nonvegetated lands. Main conclusions We consider the life zone approach to have many strengths for ecosystem mapping because it is based on climatic driving factors of ec osystem processes and recognizes ecophysiological responses of plants; it i s hierarchical and allows fur the use of other mapping criteria at the asso ciation and successional levels of analysis; it can be expanded or contract ed without losing functional continuity among levels of ecological complexi ty; it is a relatively simple system based on few empirical data; and it us es objective mapping criteria.