Helm Norbert, Essl Franz, Mirtl Michael, Dirnböck Thomas
Division of Conservation, Vegetation and Landscape Ecology University of Vienna Vienna Austria.
Department for Ecosystem Research and Data Information Management Environment Agency Austria Vienna Austria.
Ecol Evol. 2017 Mar 1;7(7):2155-2168. doi: 10.1002/ece3.2801. eCollection 2017 Apr.
Human-induced changes of the environment and their possible impacts on temperate forest understory plant communities have been examined in many studies. However, the relative contribution of individual environmental factors to these changes in the herb layer is still unclear. In this study, we used vegetation survey data covering a time period of 21 years and collected from 143 permanent plots in the Northern Limestone Alps, Austria. Data on soil chemistry (49 plots), light condition (51 plots), soil temperature and moisture (four and six plots), disturbance (all plots), climate (one station in a clearing area), and airborne sulfur (S) and nitrogen (N) deposition (two forest stands) were available for analyses. We used these data together with plot mean Ellenberg indicator values in a path analysis to attribute their relative contributions to observed vegetation changes. Our analysis reveals a strong directional shift of the forest understory plant community. We found strong evidence for a recovery of the ground-layer vegetation from acidification as response to decreased S deposition. We did not observe a community response to atmospheric N deposition, but we found a response to altered climatic conditions (thermophilization and drying). The path analysis revealed that changes in the light regime, which were related to small-scale disturbances, had most influence on herb layer community shifts. Thermophilization and drying were identified as drivers of understory community changes independent of disturbance events.
许多研究已经探讨了人为引起的环境变化及其对温带森林林下植物群落可能产生的影响。然而，各个环境因素对草本层这些变化的相对贡献仍不明确。在本研究中，我们使用了涵盖21年时间段、从奥地利北部石灰岩阿尔卑斯山143个永久样地收集的植被调查数据。可用于分析的有土壤化学数据（49个样地）、光照条件数据（51个样地）、土壤温度和湿度数据（分别为4个和6个样地）、干扰数据（所有样地）、气候数据（空旷区域的一个站点）以及空气中硫（S）和氮（N）沉降数据（两个林分）。我们在路径分析中结合样地平均埃伦贝格指示值使用这些数据，以确定它们对观察到的植被变化的相对贡献。我们的分析揭示了森林林下植物群落的强烈方向性转变。我们发现有力证据表明，随着硫沉降减少，地被层植被从酸化中恢复。我们未观察到群落对大气氮沉降的响应，但发现了对气候变化（变暖和干燥）的响应。路径分析表明，与小规模干扰相关的光照状况变化对草本层群落转变影响最大。变暖和干燥被确定为林下群落变化的驱动因素，且与干扰事件无关。
