Qiu Bingwen, Ye Zhiyan, Chen Chongcheng, Tang Zhenghong, Chen Zuoqi, Huang Hongyu, Zhao Zhiyuan, Xu Weiming, Berry Joe
Key Laboratory of Spatial Data Mining &Information Sharing of the Ministry of Education, Academy of Digital China (Fujian), Fuzhou University, Fuzhou 350116, Fujian, China; Department of Global Ecology, Carnegie Institution for Science, Stanford, CA 94305, USA.
Key Laboratory of Spatial Data Mining &Information Sharing of the Ministry of Education, Academy of Digital China (Fujian), Fuzhou University, Fuzhou 350116, Fujian, China.
Sci Total Environ. 2022 Jun 20;826:154222. doi: 10.1016/j.scitotenv.2022.154222. Epub 2022 Feb 28.
Greening, an increase in photosynthetically active plant biomass, has been widely reported as period-related and region-specific. We hypothesized that vegetation trends were highly density-dependent with intensified browning in dense canopies and increased greening in sparse canopies. We exploited this insight by estimating vegetation trends in peak growth from dense to sparse canopies graded from 1 to 20 using the non-parametric Mann-Kendall trend test based on the 500 m 8-day composite MODIS Near Infrared Reflectance of terrestrial vegetation (NIRv) time series datasets in the past two decades (2001-2019) at the global scale. We found that global greening increased by 1.42% per grade with strong fit before grade 15 (R = 0.95): net browning (11% browning vs 9% greening) exhibited in high-density canopies (NIRv > 0.39) in contrast to 32% greening in low-density canopies (NIRv ≈ 0.15). While the density-dependent greening was evidenced across different biomes and ecosystems, the steepest gradient (changes per grade) in cropland highlighted the increasingly intensified agricultural activities globally. Greening gradients declined in the dryland, but enhanced in the High-latitude ecosystems driven by warming, especially in the shrubland. Density-dependent vegetation trends were accounted for by the disproportionately impacts from climate changes and the unequal contributions of Land Cover Changes (LCC) among dense and sparse canopies. Vegetation trends and greening gradients could be extensively facilitated by Wetting or Decreasing solar Radiation (WDR), especially in sparse grassland and shrubland. Browning was dominant in dense canopies, which was further aggravated by Drying and Increasing solar Radiation (DIR), especially woody vegetation. This study implied the widespread degradation or mortality of highly productive vegetation hidden among global greening dominant in open ecosystems, which might be further exacerbated by the predicted increasing drought under global warming.
植被变绿，即光合活性植物生物量的增加，已被广泛报道具有周期性和区域特异性。我们假设植被趋势高度依赖于密度，密集树冠中褐变加剧，稀疏树冠中绿化增加。我们利用这一见解，通过基于过去二十年（2001 - 2019年）全球尺度的500米8天合成中分辨率成像光谱仪（MODIS）陆地植被近红外反射率（NIRv）时间序列数据集，使用非参数曼 - 肯德尔趋势检验来估计从密集到稀疏树冠（从1级到20级）的峰值生长期间的植被趋势。我们发现，全球绿化每级增加1.42%，在15级之前拟合度很高（R = 0.95）：高密度树冠（NIRv > 0.39）中出现净褐变（11%褐变对9%绿化），而低密度树冠（NIRv ≈ 0.15）中绿化率为32%。虽然在不同生物群落和生态系统中都证明了密度依赖性绿化，但农田中最陡峭的梯度（每级变化）突出了全球农业活动日益加剧。旱地的绿化梯度下降，但在高纬度生态系统中，受变暖驱动绿化梯度增强，尤其是在灌丛中。密度依赖性植被趋势是由气候变化的不成比例影响以及密集和稀疏树冠中土地覆盖变化（LCC）的不平等贡献所导致的。湿润或减少太阳辐射（WDR）可以广泛促进植被趋势和绿化梯度，特别是在稀疏草地和灌丛中。褐变在密集树冠中占主导地位，干燥和增加太阳辐射（DIR）会进一步加剧褐变，尤其是木本植被。这项研究表明，在开放生态系统中以全球绿化为主导的情况下，高产植被存在广泛的退化或死亡，而在全球变暖预测的干旱加剧情况下，这种情况可能会进一步恶化。
