Improving the behaviour of forest gap models along drought gradients

Recent applications of forest gap models have shown weak perfomance along drought gradients. Using the gap model FORCLIM, examines two possible explanations for this: the parameters denoting the drought tolerance of the tree species need to be estimated more accurately, the soil water balance estimation schemes used in most gap models are not capable of tracking soil moisture content under dry conditions sufficiently well to reflect its influence on tree growth. The behaviour of the model along two drought gradients in Europe and eastern North America, respectively, is used as a test case. Concludes that the Thornthwaite and Mather model of soil water balance should not be used in forest gap models any more.