Remote Sensing Laboratories, University of Zurich, Wintherthurerstrasse 190, 8057, Zurich, Switzerland.
Glob Chang Biol. 2013 Jun;19(6):1953-64. doi: 10.1111/gcb.12193. Epub 2013 Apr 3.
Vegetation forms a main component of the terrestrial biosphere and plays a crucial role in land-cover and climate-related studies. Activity of vegetation systems is commonly quantified using remotely sensed vegetation indices (VI). Extensive reports on temporal trends over the past decades in time series of such indices can be found in literature. However, little remains known about the processes underlying these changes at large spatial scales. In this study, we aimed at quantifying the spatial relationship between changes in potential climatic growth constraints (i.e. temperature, precipitation and incident solar radiation) and changes in vegetation activity (1982-2008). We demonstrate an additive spatial model with 0.5° resolution, consisting of a regression component representing climate-associated effects and a spatially correlated field representing the combined influence of other factors, including land-use change. Little over 50% of the spatial variance could be attributed to changes in climatologies; conspicuously, many greening trends and browning hotspots in Argentina and Australia. The nonassociated model component may contain large-scale human interventions, feedback mechanisms or natural effects, which were not captured by the climatologies. Browning hotspots in this component were especially found in subequatorial Africa. On the scale of land-cover types, strongest relationships between climatologies and vegetation activity were found in forests, including indications for browning under warming conditions (analogous to the divergence issue discussed in dendroclimatology).
植被是陆地生物圈的主要组成部分，在土地覆盖和气候相关研究中发挥着关键作用。植被系统的活动通常使用遥感植被指数（VI）来量化。在文献中可以广泛地找到关于过去几十年时间序列中这些指数的时间趋势的报道。然而，对于这些变化在大空间尺度下的潜在过程，我们知之甚少。在这项研究中，我们旨在量化潜在气候生长限制（即温度、降水和入射太阳辐射）变化与植被活动变化（1982-2008 年）之间的空间关系。我们展示了一个具有 0.5°分辨率的附加空间模型，该模型由一个代表气候相关影响的回归分量和一个代表其他因素（包括土地利用变化）综合影响的空间相关场组成。超过 50%的空间方差可以归因于气候的变化；值得注意的是，阿根廷和澳大利亚的许多绿化趋势和褐变热点。非相关模型分量可能包含大规模的人为干预、反馈机制或自然影响，这些因素没有被气候模式所捕获。在这个分量中，褐变热点尤其出现在亚热带非洲。在土地覆盖类型的尺度上，在森林中发现了与气候模式和植被活动之间最强的关系，包括在变暖条件下的褐变迹象（类似于在树木年代学中讨论的发散问题）。
