Diversity did not influence soil water use of tree clusters in a temperate mixed forest

摘要

Compared to monocultures, diverse ecosystems are often expected to show morecomprehensive resource use. However, with respect to diversity–soil-water-userelationships in forests, very little information is available. Weanalysed soil water uptake in 100 tree clusters differing in tree speciesdiversity and species composition in the Hainich forest in central Germany.The clusters contained all possible combinations of five broadleaved treespecies in one-, two- and three-species clusters (three diversity levels),replicated fourfold (20 one-species, 40 two-species and 40 three-species clusters).We estimated soil water uptake during a summer dry period in 0–0.3 m soildepth, based on throughfall and soil moisture measurements with a simplebudgeting approach. Throughout the whole vegetation period in 2009, soilwater uptake was additionally determined at a higher temporal resolution andalso for a greater part of the soil profile (0–0.7 m) on a subset of 16intensive clusters. During the dry spell, mean soil water uptake was1.9 ± 0.1 mm day−1 in 0–0.3 m (100 clusters) and 3.0 ± 0.5 mm day−1in 0–0.7 m soil depth (16 clusters), respectively.Besides a slightly higher water use of Fraxinus clusters, we could not detect anyeffects of species identity or diversity on cluster water use. We discussthat water use may indeed be a conservative process, that differences intree-species-specific traits may be compensated for by other factors such asherb layer coverage and tree spatial arrangement, and that diversity-drivendifferences in water use may arise only at a larger scale. We furtherconclude that with respect to stand water use "tree diversity'' alone isnot an appropriate simplification of the complex network of interactionsbetween species traits, stand properties and environmental conditions thathave varying influence on stand water use, both in space and time.