Perspektiven historischen Denkens 1

Background: To improve the understanding of consequences of climate change for annual plant communities, I used a detailed, grid-based model that simulates the effect of daily rainfall variability on individual plants in five climatic regions on a gradient from 100 to 800 mm mean annual precipitation (MAP). The model explicitly considers moisture storage in the soil. I manipulated daily rainfall variability by changing the daily mean rain (DMR, rain volume on rainy days averaged across years for each day of the year) by ± 20%. At the same time I adjusted intervals appropriately between rainy days for keeping the mean annual volume constant. In factorial combination with changing DMR I also changed MAP by ± 20%. Results: Increasing MAP generally increased water availability, establishment, and peak shoot biomass. Increasing DMR increased the time that water was continuously available to plants in the upper 15 to 30 cm of the soil (longest wet period, LWP). The effect of DMR diminished with increasing humidity of the climate. An interaction between water availability and density-dependent germination increased the establishment of seedlings in the arid region, but in the more humid regions the establishment of seedlings decreased with increasing DMR. As plants matured, competition among individuals and their productivity increased, but the size of these effects decreased with the humidity of the regions. Therefore, peak shoot biomass generally increased with increasing DMR but the effect size diminished from the semiarid to the mesic Mediterranean region. Increasing DMR reduced via LWP the annual variability of biomass in the semiarid and dry Mediterranean regions. Conclusion: More rainstorms (greater DMR) increased the recharge of soil water reservoirs in more arid sites with consequences for germination, establishment, productivity, and population persistence. The order of magnitudes of DMR and MAP overlapped partially so that their combined effect is important for projections of climate change effects on annual vegetation. Background Drylands are characterized not only by low water availability but also by great variability of water supply, which play important roles in structuring ecosystems and maintaining biodiversity [1-3]. However, our knowledge about the effects of climate change on vegetation with regard to changes in daily precipitation patterns is still limited [4]. In this paper I use a simulation approach to systematically examine the effect of daily rainfall variability on the growth of annuals in the Middle East along a climatic gradient from arid to mesic Mediterranean. Published: 27 March 2008 BMC Ecology 2008, 8:4 doi:10.1186/1472-6785-8-4 Received: 8 December 2006 Accepted: 27 March 2008 This article is available from: http://www.biomedcentral. com/1472-6785/8/4 © 2008 Kochy; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. BMC Ecology 2008, 8:4 http://www.biomedcentral. com/1472-6785/8/4