Transitional responses of vegetation activities to temperature variations: Insights obtained from a forested catchment in Korea

Vegetation activities sensitively response to topological conditions and a changing climate. To better understand vegetation dynamics under varying environmental conditions, we analyze observations of vegetation indices, Land Surface Temperature (LST), air temperature, and precipitation of a Korean forest over an 11. year period from year 2000 to 2010. While a positive relationship between EVI (Enhanced Vegetation Index) and LST is established for all seasons, independent of elevation, the EVI-LST relationship exhibits a threshold above which the rate of EVI increase over LST increase changes significantly. This transitional point is associated with the condition that the air temperature triggers the start of the growing season. The EVI-LST relationship above the threshold exhibits a hysteresis loop, i.e., rising limb differs from falling limb. We identify two types of hysteresis patterns, i.e., a single loop and a twisted loop. The variation in loop width between the ascending and descending paths contains a signature in annual precipitation of concurrent year. In our analysis, annual precipitation above 1600. mm is associated with LST difference more than 5. °C in the loop width.