Dense canopies browning overshadowed by global greening dominant in sparse canopies

Bingwen Qiu; Zhiyan Ye; Chongcheng Chen; Zhenghong Tang; Zuoqi Chen; Hongyu Huang; Zhiyuan Zhao; Weiming Xu; Joe Berry

doi:10.1016/j.scitotenv.2022.154222

Dense canopies browning overshadowed by global greening dominant in sparse canopies

Sci Total Environ. 2022 Jun 20:826:154222. doi: 10.1016/j.scitotenv.2022.154222. Epub 2022 Feb 28.

Authors

Bingwen Qiu¹, Zhiyan Ye², Chongcheng Chen², Zhenghong Tang³, Zuoqi Chen², Hongyu Huang², Zhiyuan Zhao², Weiming Xu², Joe Berry⁴

Affiliations

¹ 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. Electronic address: qiubingwen@fzu.edu.cn.
² Key Laboratory of Spatial Data Mining &Information Sharing of the Ministry of Education, Academy of Digital China (Fujian), Fuzhou University, Fuzhou 350116, Fujian, China.
³ Community and Regional Planning Program, University of Nebraska-Lincoln, Lincoln 68558, NE, USA.
⁴ Department of Global Ecology, Carnegie Institution for Science, Stanford, CA 94305, USA.

PMID: 35240174
DOI: 10.1016/j.scitotenv.2022.154222

Abstract

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 (R² = 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.

Keywords: Climatic changes; Density-dependent; Global greening; Peak growth of vegetation; Spatial heterogeneity; Time series images.

MeSH terms

Climate Change*
Ecosystem*
Environment
Plants