Forests and woodlands resistant to drought revealed in remotely sensed foliar moisture content using probabilistic models

Foliar moisture content (FMC) is of primary importance in many biological and ecological processes of forests and woodlands, including herbivory and fire dynamics. The role of FMC, which is the mass of moisture on a dry matter basis, in such processes is increasingly important due to changes in length and severity of climate extremes, like drought. Here we studied the sensitivity of forest and woodland FMC to climatic water balance, i.e. Standardised Precipitation and Evapotranspiration Index (SPEI), across five landscapes in temperate and sub-tropical south-eastern Australia. To do this we used copula-probabilistic modelling, including consideration of drought (i.e. SPEI) length. We used an FMC dataset over eight years of Sentinel-2 satellite reflectance (2015-2023), based on the inversion of a radiative transfer model at 20m resolution. We found the spatial variation of FMC within landscapes to be large and that the spatial variation in response to drought was very large, particularly within the more arid landscapes. The areas of lesser response to extreme drought are revealed to be drought resistant forests and woodlands that are potential climate refugia for animals, and natural breaks in the contiguity of fire fuels.