Phenological observations of grass curing in Germany

The degree of grass curing, i.e. the proportion of dehydrated dead grass per unit grassland area, is one of the most important parameters affecting grassland fire risk and fire behaviour. The objective of the present study was to develop a simple relationship between grass moisture and grass curing to use as an input into the next-generation fire-danger rating models of the Deutscher Wetterdienst. Seasonal changes in yellow and green portions of grass plots were estimated visually at weekly intervals. At the same time, the grass-moisture content was measured gravimetrically after destructive sampling. Regression analysis revealed an exponential relationship between decreasing leaf moisture and increasing yellowing level, in rough agreement with findings reported from Australia and North America.