Impacts of climate extremes on vegetation dynamics in a transect along the Hu Line of China

Abstract

Climate projections infer increasing frequency of extreme events in the future which would alter terrestrial hydrologic functioning and ecosystem services. Understanding the responses of vegetation to extreme events can provide prerequisite knowledge to mitigate climate change impacts. The relationships between climate extremes and vegetation phenology and productivity were examined for a transect along the Hu Line across China during 1988–2014. Results show that high frequency and severity of droughts existed in the mid-latitude regions where happened to be mostly occupied by grassland and cropland with relatively low productivity compared to trees. Prolonged growing seasons (4.3 days/decade) resulted mostly from advanced green-up were observed over the transect. No strong impact of extreme droughts on vegetation was observed for any plant functional types, due to the timing of drought occurrences primarily in pre- and post-growing seasons while water supply was likely not so limited during growth indicated by a drought index. Non-woody plants in the mid-to-high latitudes (37-54°N) were identified more sensitive to climate extremes than woody plants in the low latitudes. Meanwhile, grassland in the relatively low-elevation areas (<1000 m.a.s.l) was more responsive than that in the high-elevation areas. Productivity above 45°N increased with drought severity attributable to an intensified favorable environment during frequent and mild droughts with warmer temperature and increased solar radiation. The results may suggest the generally relative stability of the ecosystems along the Hu Line, however, with further deteriorating climate, the stable relationships between climate and ecosystems may be shifted, likely starting from low-elevation grassland.