Lengthening of the growth season, not increased water availability, increased growth of Picea likiangensis var. rubescens plantations on eastern Tibetan Plateau due to climate change

On the eastern Tibetan Plateau, the growth of trees is strongly affected by climate change. Previous researchers have found that climate warming changes thermal and hydraulic conditions, lengthening the growing season and promoting tree growth. Some studies have analyzed the effects of drought, precipitation, and temperature on tree growth. However, previous studies have mainly focused on natural forests, with few studies on the response of plantations to climate change. Therefore, we studied the relationship between dendrochronology (basal area increment, BAI), normalized difference vegetation index (NDVI), and climate factors to explore the response of Picea likiangensis var. rubescens plantations to climate change. The results showed that from 1990 to 2018, the temperature in the study area increased significantly; the rate of increase was 0.39 degrees per decade. Among the climate factors, self-calibrated Palmer drought severity index (scPDSI) had the most significant impact on BAI. From P_May (P_represents the month of the previous year) to December, BAI was always negatively correlated with the scPDSI, with 9 months being significantly negatively correlated. BAI was significantly positively correlated with the minimum 2m temperature (TMN) in P_July, P_September, July, and September. BAI was significantly positively correlated with the maximum 2 m temperature (TMX) in P_October, P_December, and July. BAI was significantly positively correlated with the mean 2 m temperature (TMP) in P_July, P_December, and July. There is a significant positive correlation between BAI and annual NDVI (NDVIa), which means that NDVI can be used to study the response of plantations to climate change. Our study contributes to a better understanding of the response of plantation growth in high-altitude areas to climate change, which is needed by forest managers.