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Mapping gains and losses in woody vegetation across global tropical drylands
Author(s) -
Tian Feng,
Brandt Martin,
Liu Yi Y.,
Rasmussen Kjeld,
Fensholt Rasmus
Publication year - 2017
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.13464
Subject(s) - vegetation (pathology) , environmental science , biome , normalized difference vegetation index , woody plant , moderate resolution imaging spectroradiometer , tropical savanna climate , enhanced vegetation index , herbaceous plant , leaf area index , climatology , ecosystem , satellite , ecology , vegetation index , geology , medicine , pathology , engineering , biology , aerospace engineering
Woody vegetation in global tropical drylands is of significant importance for both the interannual variability of the carbon cycle and local livelihoods. Satellite observations over the past decades provide a unique way to assess the vegetation long‐term dynamics across biomes worldwide. Yet, the actual changes in the woody vegetation are always hidden by interannual fluctuations of the leaf density, because the most widely used remote sensing data are primarily related to the photosynthetically active vegetation components. Here, we quantify the temporal trends of the nonphotosynthetic woody components (i.e., stems and branches) in global tropical drylands during 2000–2012 using the vegetation optical depth ( VOD ), retrieved from passive microwave observations. This is achieved by a novel method focusing on the dry season period to minimize the influence of herbaceous vegetation and using MOD erate resolution Imaging Spectroradiometer ( MODIS ) Normalized Difference Vegetation Index ( NDVI ) data to remove the interannual fluctuations of the woody leaf component. We revealed significant trends ( P < 0.05) in the woody component ( VOD wood ) in 35% of the areas characterized by a nonsignificant trend in the leaf component ( VOD leaf modeled from NDVI ), indicating pronounced gradual growth/decline in woody vegetation not captured by traditional assessments. The method is validated using a unique record of ground measurements from the semiarid Sahel and shows a strong agreement between changes in VOD wood and changes in ground observed woody cover ( r 2 = 0.78). Reliability of the obtained woody component trends is also supported by a review of relevant literatures for eight hot spot regions of change. The proposed approach is expected to contribute to an improved assessment of, for example, changes in dryland carbon pools.