Abstract
BackgroundMonitoring 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 FindingsGrassland 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/SignificanceShortening 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.
Highlights
Vegetation has an essential function in regulating carbon and energy exchange through phenology [1,2,3,4], photosynthetic activity [5,6], autotrophic and heterotrophic respiration [6]and other processes
Vegetation Dynamics on the Tibetan Plateau Based on the means of phenological dates for the green-up phase over 25 years, greening of the Tibetan Plateau typically occurs between April and May in most places
The growing season ended in October in most grassland regions of the Tibetan Plateau (Fig. 3)
Summary
Vegetation has an essential function in regulating carbon and energy exchange through phenology [1,2,3,4], photosynthetic activity [5,6], autotrophic and heterotrophic respiration [6]and other processes. Several studies have considered changes in vegetation productivity as the primary cause of variation in terrestrial net carbon uptake [6,7,8,9]. Vegetation growth in mid to high latitudes of the Northern Hemisphere is very sensitive to temperature changes [12,13], and a climate-driven greening trend has been well-documented since the 1980s [14,15,16]. With its Northern Hemisphere mid-latitude position and high elevation, the Tibetan Plateau is experiencing even faster temperature increases than the global average [17]with net primary productivity (NPP) increasing remarkably, especially in alpine meadows [18]. 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
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