5 | CONCLUSIONThe interannual vegetation activity on the Tibetan Plateau shows an overall increasing trend, but there is strong spatial heterogeneity. The NDVI of the alpine desert increased the most significantly of all studied vegetation types. The NDVI values of four types of vegetation, namely, alpine meadow, subalpine scrub, needleleaf forest and broadleaf evergreen forest, showed a decreasing trend, but their NDVI values were typically larger than those of the other vegetation types.The responses of vegetation to temperature, precipitation and relative humidity have certain lag periods. The alpine meadow, alpine desert, temperate desert steppe and temperate desert respond more significantly to temperature than to other climate factors, and the length of the lag period varies greatly in different vegetation ecosystems and growth stages. Desert vegetation is the most sensitive to precipitation, followed by grassland vegetation and finally shrubs. The response of vegetation activity to precipitation generally occurs with a lag period of 1 or 2 months. During the whole growing season, the correlation between vegetation activity and precipitation first increased to reach a peak and then decreased.At the start of the growing season, temperature is the main climatic factor that affects the activity of most vegetation. After that, precipitation begins to have an effect on vegetation. The duration of sunshine has a relatively important impact on the vegetation activity in the alpine meadow, alpine sparse vegetation, subalpine scrub, needleleaf forest, and broadleaf evergreen forest. At the end of the growing season, many climatic influencing factors simultaneously affect vegetation activity.This study mainly provided an overview of how different climate factors affect domain types of vegetation on the Tibetan Plateau. These findings will provide a better understanding of the climate change trends and contribute to the general knowledge of the drivers and mechanisms of ecosystem-dependent vegetation degradation on the Tibetan Plateau. For further study, high spatial and temporal resolution data are required for more accurate analyses of the lag effects and ecological mechanisms.
