Section for Ecoinformatics and Biodiversity, Department of Bioscience, Aarhus University, Aarhus C, Denmark.
Department of Bioscience, Center for Biodiversity Dynamics in a Changing World (BIOCHANGE), Aarhus University, Aarhus C, Denmark.
Glob Chang Biol. 2018 Dec;24(12):5789-5801. doi: 10.1111/gcb.14451. Epub 2018 Oct 9.
The satellite record has revealed substantial land surface "greening" in the northern hemisphere over recent decades. Process-based Earth system models (ESMs) attribute enhanced vegetation productivity (greening) to CO fertilisation. However, the models poorly reproduce observed spatial patterns of greening, suggesting that they ignore crucial processes. Here, we explore whether fine-scale land cover dynamics, as modified by ecological and land-use processes, can explain the discrepancy between models and satellite-based estimates of greening. We used 500 m satellite-derived Leaf Area Index (LAI) to quantify greening. We focus on semi-natural vegetation in Europe, and distinguish between conservation areas and unprotected land. Within these ecological and land-use categories, we then explored the relationships between vegetation change and major climatic gradients. Despite the relatively short time-series (15 years), we found a strong overall increase in LAI (i.e., greening) across all European semi-natural vegetation types. The spatial pattern of vegetation change identifies land-use change, particularly land abandonment, as a major initiator of vegetation change both in- and outside of protected areas. The strongest LAI increases were observed in mild climates, consistent with more vigorous woody regrowth after cessation of intensive management in these environments. Surprisingly, rates of vegetation change within protected areas did not differ significantly from unprotected semi-natural vegetation. Overall, the detected LAI increases are consistent with previous, coarser-scale, studies. The evidence indicates that woody regrowth following land abandonment is an important driver of land surface greening throughout Europe. The results offer an explanation for the large discrepancies between ESM-derived and satellite-derived greening estimates and thus generate new avenues for improving the ESMs on which we rely for crucial climate forecasts.
卫星记录显示，近几十年来北半球陆地表面“绿化”现象显著。基于过程的地球系统模型（ESMs）将植被生产力的提高（绿化）归因于 CO2 施肥。然而，这些模型并不能很好地再现观测到的绿化空间模式，这表明它们忽略了关键过程。在这里，我们探讨了精细尺度的土地覆盖动态变化，即通过生态和土地利用过程进行的变化，是否可以解释模型与基于卫星的绿化估算之间的差异。我们使用 500 米卫星衍生的叶面积指数（LAI）来量化绿化。我们专注于欧洲的半自然植被，并区分保护区和未受保护的土地。在这些生态和土地利用类别中，我们进一步探讨了植被变化与主要气候梯度之间的关系。尽管时间序列相对较短（15 年），但我们发现所有欧洲半自然植被类型的 LAI 均呈现出强劲的总体增长（即绿化）。植被变化的空间模式确定了土地利用变化，特别是土地废弃，是保护区内外植被变化的主要启动因素。在气候温和的地区观察到最强的 LAI 增加，这与这些环境中停止密集管理后木质再生更加旺盛的情况一致。令人惊讶的是，保护区内植被变化的速度与未受保护的半自然植被没有显著差异。总体而言，检测到的 LAI 增加与以前更粗糙尺度的研究一致。这些证据表明，土地废弃后的木质再生是欧洲整个地区陆地表面绿化的重要驱动因素。研究结果为 ESM 衍生和卫星衍生的绿化估算之间存在的巨大差异提供了一种解释，从而为我们赖以进行关键气候预测的 ESM 提供了新的改进途径。
