Applying dendrochronology and remote sensing to explore climate-drive in montane forests over space and time

Both radial growth and canopy dynamics of trees play a critical role in terrestrial carbon cycle. Yet, it is still not very clear about how climate variability influences radial growth and canopy dynamics. To help bridge the knowledge gap in this field, we combined Tree Ring Width Index (TRWI, radial growth) and Normalized Difference Vegetation Index (NDVI, canopy dynamic), to quantify how forests responded to climatic variability across altitudinal gradients in Hengdaun Mountain, China. We applied TRWI of Pinus yunnanensis at nine sample sites and NDVI from 2000 AD to 2016 to analyze how these two indicators respond to temperature and precipitation. The results showed that the radial growth of P. yunnanensis was mainly limited by precipitation at low altitudes (≤1700 m). But the limited factor transformed into temperature at high altitudes (≥2200 m). NDVI presented significantly positive correlation with temperature and negative correlation with precipitation at annual scale. Relationship between TRWI and NDVI showed significantly positive correlation in July but negative correlation during dry season, indicating that both indicators had consistent response to climate during growing season, while the response was heterogeneous in dry season. Our comprehensive study helps to elucidate the unique contributions of foliar and radial growth to terrestrial carbon cycling and to explore the difference of these two indicators response to climate change.