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| Titel |
Global changes in dryland vegetation dynamics (1988-2008) assessed by satellite remote sensing: comparing a new passive microwave vegetation density record with reflective greenness data |
| VerfasserIn |
N. Andela, Y. Y. Liu, A. I. J. M. Dijk, R. A. M. Jeu, T. R. McVicar |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 10 ; Nr. 10, no. 10 (2013-10-24), S.6657-6676 |
| Datensatznummer |
250085374
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| Publikation (Nr.) |
 copernicus.org/bg-10-6657-2013.pdf |
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| Zusammenfassung |
| Drylands, covering nearly 30% of the global land surface, are
characterized by high climate variability and sensitivity to land management.
Here, two satellite-observed vegetation products were used to study the
long-term (1988–2008) vegetation changes of global drylands: the widely used
reflective-based Normalized Difference Vegetation Index (NDVI) and the
recently developed passive-microwave-based Vegetation Optical Depth (VOD).
The NDVI is sensitive to the chlorophyll concentrations in the canopy and the
canopy cover fraction, while the VOD is sensitive to vegetation water content
of both leafy and woody components. Therefore it can be expected that using
both products helps to better characterize vegetation dynamics, particularly
over regions with mixed herbaceous and woody vegetation. Linear regression
analysis was performed between antecedent precipitation and observed NDVI and
VOD independently to distinguish the contribution of climatic and
non-climatic drivers in vegetation variations. Where possible, the
contributions of fire, grazing, agriculture and CO2 level to vegetation
trends were assessed. The results suggest that NDVI is more sensitive to
fluctuations in herbaceous vegetation, which primarily uses shallow soil water,
whereas VOD is more sensitive to woody vegetation, which additionally can
exploit deeper water stores. Globally, evidence is found for woody
encroachment over drylands. In the arid drylands, woody encroachment appears to
be at the expense of herbaceous vegetation and a global driver is
interpreted. Trends in semi-arid drylands vary widely between regions,
suggesting that local rather than global drivers caused most of the
vegetation response. In savannas, besides precipitation, fire regime plays an
important role in shaping trends. Our results demonstrate that NDVI and VOD
provide complementary information and allow new insights into dryland vegetation
dynamics. |
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