| Abstract: |
Background: Monitoring vegetation dynamics and their responses to climate change has been the subject of considerable
research. This paper aims to detect change trends in grassland activity on the Tibetan Plateau between 1982 and 2006 and
relate these to changes in climate.
Methodology/Principal Findings:Grassland activity was analyzed by evaluating remotely sensed Normalized Difference
Vegetation Index (NDVI) data collected at 15-day intervals between 1982 and 2006. The timings of vegetation stages (start
of green-up, beginning of the growing season, plant maturity, start of senescence and end of the growing season) were
assessed using the NDVI ratio method. Mean NDVI values were determined for major vegetation stages (green-up, fast
growth, maturity and senescence). All vegetation variables were linked with datasets of monthly temperature and
precipitation, and correlations between variables were established using Partial Least Squares regression. Most parts of the
Tibetan Plateau showed significantly increasing temperatures, as well as clear advances in late season phenological stages
by several weeks. Rainfall trends and significant long-term changes in early season phenology occurred on small parts of the
plateau. Vegetation activity increased significantly for all vegetation stages. Most of these changes were related to
increasing temperatures during the growing season and in some cases during the previous winter. Precipitation effects
appeared less pronounced. Warming thus appears to have shortened the growing season, while increasing vegetation
activity.
Conclusions/Significance: Shortening of the growing season despite a longer thermally favorable period implies that
vegetation on the Tibetan Plateau is unable to exploit additional thermal resources availed by climate change. Ecosystem
composition may no longer be well attuned to the local temperature regime, which has changed rapidly over the past three
decades. This apparent lag of the vegetation assemblage behind changes in climate should be taken into account when
projecting the impacts of climate change on ecosystem processes. |
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