A model of arctic tundra vegetation derived from topographic gradients

We present a topographically-derived vegetation model (TVM) that predicts the landscape patterns of arctic vegetation types in the foothills of the Brooks Range in northern Alaska. In the Arctic there is a strong relationship between water and plant structure and function and TVM is based on the relationships between vegetation types and slope (tan beta) and discharge (delta), two independent variables that can be easily derived from digital terrain data. Both slope and discharge relate to hydrological similarity within a landscape: slope determines the gravitational hydrological gradient and hence influences flow velocity, whereas discharge patterns are computed based on upslope area and quantify lateral flow amount. TVM was developed and parameterized based on vegetation data from a small 2.2 km(2) watershed and its application was tested in a larger 22 km(2) region. For the watershed, TVM performed quite well, having a high spatial resolution and a goodness-of-fit ranging from 71-78%, depending on the functions used. For the larger region, the strength of the vegetation types predictions drops somewhat to between 56-59%. We discuss the various sources of error and limitations of the model for purposes of extrapolation.