2000: Comparing the correlative Holdridge model to mechanistic biogeographical models for assessing vegetation distribution response to climatic change

Abstract. A well-established and widely used correlative climate-vegetation model (Holdridge Life Zone model) was compared to three mechanistic simulation models (BIOME2, Dynamic Global Phytogeography Model (DOLY), and Mapped Atmosphere-Plant-Soil System (MAPSS)) for the conterminous United States under contemporary climate and a set of future climates prescribed by three Global Circulation Model experiments. Output from the mechanistic models were from the Ve-getation/Ecosystem Modeling and Analysis Project (VEMAP) intercomparison. Holdridge modeling approaches, using a ‘Simple ’ implementation (vegetation distribution based on biotemperature and precipitation alone) or a ‘Full ’ implementation (vegetation distribution based on biotemperature, pre-cipitation, altitudinal region, latitudinal belt, and transitional vegetation zones), represented current potential natural U.S. vegetation poor to fair, respectively. The more sophisticated mechanistic mod-els were superior at reproducing potential vegetation under current climate compared to Holdridge, although there was significant variability among these models. The Holdridge implementations gen-erally showed similar or greater climate sensitivity with respect to spatial redistribution of vegetation compared to the mechanistic models run both with and without doubled CO2 levels; however, the sensitivity of the Holdridge model depended on the implementation. Reduced sensitivity of the mech