Responses of alpine grassland to climate warming and permafrost thawing in two basins with different precipitation regimes on the Qinghai-Tibetan Plateau

摘要

Alpine grassland and permafrost occupy about two thirds and one half of the total area of the Qinghai-Tibetan Plateau (QTP), respectively. Soil water, which can be affected by permafrost thawing and precipitation, is important for vegetation growth in this region. It is therefore vital to consider the effects of both thawing and precipitation when studying the effect of climate warming on alpine grassland on the QTP. In this study, we examined two adjacent basins, one semiarid and the other semihumid, in the northeastern section of the QTP. We used remote sensing data to compare fractional vegetation cover (FVC) and the relationships between FVC and land surface temperature (LST) in different types of frozen ground; the samples were analogous to a chronosequence of climate warming and permafrost thawing. Our analysis produced three significant results: (1) the FVCs of the semihumid basin were significantly greater than those of the semiarid basin for most types of frozen ground (p < 0.05); (2) the changes in FVC along the climate warming and permafrost thawing chronosequence were different in the two basins, with the maximum FVC occurring on the transition permafrost zone in the semiarid basin and on the seasonal frost zone in the semihumid basin; and (3) at the peak of the growing season, only the three warmest types of frozen ground in the semiarid basin had a negative relationship between FVC and LST, suggesting that vegetation growth was limited by water. Therefore, we concluded that the responses of alpine grassland to climate warming in the permafrost regions are complicated by precipitation and permafrost thawing; specifically, grasslands will not necessarily simply degrade as the climate warms, as suggested by previous plotscale studies.