Köchy, M., K. Tielbörger, and M. Sternberg (2002)
Contrary to climate change predictions, extreme rainfalls in southern Israel have become rarer since the 1930s, making the distribution of annual precipitation more normal. I used a spatially explicit model to simulate the effect of rainfall distribution on a common desert annual, Filago desertorum (Asteraceae). The model tracks soil moisture, germination, and plant growth in five-day steps. The seedbank is updated annually. Germination depends on the number of available seeds and a rain threshold. Plant growth including seed production is controlled by soil moisture and intraspecific competition. Daily rainfall is taken in sequence from random years of data sets. I manipulated rainfall intensity to create data sets with skewed or normal distribution in combination with higher (104 mm), average (88 mm), and lower (70 mm) annual volume compared to a reference site. Further, I included unmanipulated records of one moister, one average, and one drier site. I compared the effects of distribution and volume using a factorial analysis of variance. Shoot mass, seed production, and seedbank varied significantly with the interaction of distribution and volume due to low survival (3-21%) in the low-volume treatments with normal or actual rainfall distribution. Apparently, the replenishment of the seedbank depends on high seed production in years with very high rainfalls. Thus, the model predicts that the species will decline in its southern range if the normalization of rain distribution continues.