Abstract: Alpine timberline of Qinling Mountains is sensitive to climate change, providing an-ideal place for studying climate change. Based on the MODIS NDVI (normalized difference vegetation index) and air temperature data over the span of 2000 to 2015, the characteristics of response of Larix chinensis to air temperature variation were investigated and the mechanism of response was explored in this paper. The results showed that: (1) The average annual NDVI of L. chinensis was positively correlated with the annual average temperature, and 96.30% of the correlations were positive with 31.42% being significant. It meant that the annual temperature was conductive to the growth of L. chinensis. (2) On the monthly scale, the monthly mean NDVI response of L. chinensis distribution region to monthly mean air temperature was mostly positive, with the characteristics of synchronism and hysteretic nature, and the lag time was around 1-3 months. The NDVI in August was negatively correlated with the temperature of previous period, the current temperature and accumulated temperature, and most of the correlations were significantly negative. (3) The annual maximum NDVI of L. chinensis was negatively correlated with the air temperature in different periods, which indicated that the rise of temperature was not conducive to the maximum NDVI growth of L. chinensis to a certain extent. (4) The analysis of correlation between annual maximum NDVI and the mean air temperature from August of previous year to current July showed that the number of negative pixels was much more than that of positive pixels. Furthermore, when the annual mean temperature from previous August to current July was within the range of -0.4-0.8 ℃, the response of maximum NDVI to air temperature reached the peak. On the other hand, if the temperature was lower than -0.4 ℃ or higher than 0.8 ℃, the percentage of negative pixel number increased and the growth of L. chinensis would be inhibited somewhat.

Key words: Robinia pseudoacacia, light condition, photosynthetic parameter, Quercus variabilis, gas exchange parameter