RESPONSE OF ALPINE TUNDRA TO A CHANGING CLIMATE - A HIERARCHICAL SIMULATION-MODEL

The present paper describes an alpine tundra simulation model that has been developed within a hierarchical framework based primarily on data from Niwot Ridge and adjacent areas of the Colorado Front Range. Our objective is to simulate the response of alpine tundra to climatic change. The model consists of three hierarchically nested submodels. The level i submodel represents the alpine zone of the Front Range of Colorado (16.6 km2) and operates on a time scale of centuries. The Level ii submodel represents Niwot Ridge alpine (6.8 km2) and operates on a time scale of decades. The Level iii submodel, which is itself divided into six submodels, represents each of the six major soil-plant communities that occur on Niwot Ridge (several hectares each) and operates on a time scale of years. Simulations were run representing tundra system dynamics under (a) constant environmental temperatures and (b) a cooling trend of 0.07°C per year. Simulation results show shifts in the elevation of treeline (Level i), shifts in the proportion of tundra occupied by each of six different soil-plant communities (Level ii), and changes in rates of primary production and decomposition in each community type (Level iii). © 1990.