Mapping gains and losses in woody vegetation across global tropical drylands

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

Abstract

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 MODerate 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 (VODwood) in 35% of the areas characterized by a nonsignificant trend in the leaf component (VODleaf 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 VODwood and changes in ground observed woody cover (r2 = 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.

Detaljer

Författare
  • Feng Tian
  • Martin Brandt
  • Yi Y. Liu
  • Kjeld Rasmussen
  • Rasmus Fensholt
Externa organisationer
  • University of Copenhagen
  • University of New South Wales
Forskningsområden

Nyckelord

Originalspråkengelska
Sidor (från-till)1748-1760
Antal sidor13
TidskriftGlobal Change Biology
Volym23
Utgåva nummer4
StatusPublished - 2017 apr 1
PublikationskategoriForskning
Peer review utfördJa
Externt publiceradJa