Microenvironmental effects on growth response of Pinus massoniana to climate at its northern boundary in the Tongbai Mountains, Central China

The Tongbai Mountains is an ecologically sensitive region and the northern boundary of Pinus massoniana Lamb. To analyze the effect of different microenvironments on tree growth response to climate factors, we developed standard chronologies for earlywood width (EWW), latewood width (LWW), and total ring width (TRW) of P. massoniana at two sampling sites on slopes with different orientations, then analyzed characteristics of the chronologies and their correlations with climate variables from five stations in the region and with a regional normalized difference vegetation index (NDVI). Statistical results showed that the TRW/EWW/LWW chronology consistency and characteristics (mean sensitivity, signal to noise ratio, expressed population signal) for trees growing on the southeastern slope were much higher than for trees on the northeastern slope. Correlations indicated that temperature in current March and August has a significant positive effect on TRW/EWW/LWW formation, and the effect on the northeastern slope was weaker than on the southeastern slope. Compared to temperature, precipitation has more complicated effects on tree growth, but the effect on the northeastern slope was also generally weaker than on the southeastern slope. Stepwise linear regression analyses showed that temperature in August was the main limiting factor at the two sampling sites. Similarly, the response of tree growth on the southeastern slope as determined by the NDVI is better than on the northeastern slope, and the TRW/EWW/LWW chronologies for the southeastern slope explained over 50