Abstract
Net primary productivity (NPP) and precipitation-use efficiency (PUE) are crucial indicators in understanding the responses of vegetation to global change. However, the relative contributions of climate change and human interference to the dynamics of NPP and PUE remain unclear. During the past few decades, the impacts of climate change and human activities on alpine grasslands on the Qinghai-Tibet Plateau (QTP) have been intensifying. The aims of the study were to investigate the spatiotemporal patterns of grassland NPP and PUE on the QTP during 2000–2017 and quantify how much of the variance in NPP and PUE can be attributed to the climatic factors (precipitation and temperature) and grazing intensity. The results showed that: (1) grassland NPP significantly increased with a rate of 0.6 g C m−2 year−1 over the past 18 years, mainly induced by the increased temperature and the enhanced precipitation. The temperature was the dominant factor for NPP interannual variation in mid-eastern QTP, and precipitation restrained vegetation growth most in the southwest and northeast. (2) The PUE was higher on the eastern and western parts of the plateau, but lower at the center. Regarding grassland types, the PUE of alpine steppe (0.19 g C m−2 mm−1) was significantly lower than those of alpine meadow (0.31 g C m−2 mm−1) and desert steppe (0.32 g C m−2 mm−1). (3) Precipitation was significantly and negatively correlated with PUE and contributed the most to the temporal variation of grassland PUE on the QTP (52.7%). (4) Furthermore, we found that the grazing activities had the lowest contributions to both NPP and PUE interannual variation, compared to temperature and precipitation. Thus, it is suggested that climate variability rather than grazing activities dominated vegetation changes on the QTP.
Highlights
Due to climate change and human activities, terrestrial ecosystems have undergone unprecedented changes, including the changes of carbon sources and sinks [1], land cover and land use [2,3,4], and loss of biodiversity [5]
This study aimed to reveal the relative contributions of climate factors and grazing to interannual Net primary productivity (NPP) and precipitation-use efficiency (PUE) variations on the Qinghai-Tibet Plateau (QTP)
We found that the relative contributions of temperature, precipitation, and grazing to growing-season NDVI (GSNDVI) were similar to those to NPP (Figure S1), suggesting that the autocorrelations between NPP and climate factors had no significant effects on the conclusions
Summary
Due to climate change and human activities, terrestrial ecosystems have undergone unprecedented changes, including the changes of carbon sources and sinks [1], land cover and land use [2,3,4], and loss of biodiversity [5]. In arid and semi-arid regions, anthropogenic activities and climate change can cause ecosystem degradation [8]. The grassland ecosystem is one of the most widely distributed vegetation types, accounting for about one-fifth of the world’s surface area [9]. It plays a vital role in maintaining biogeochemical cycles, protecting biodiversity, and supporting animal husbandry and food production [10].
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