Equilibrium moisture content of dead fine fuels of selected central European tree species

Abstract

Fine fuel moisture content is a key parameter in fire danger and behaviour applications. For modelling purposes, equilibrium moisture content (EMC) curves are an important input parameter. This paper provides EMC data for central European fuels and adds methodological considerations that can be used to improve existing test procedures. Litter samples of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) were subjected to three different experiments using conditioning in a climate chamber and above saturated salt solutions. Climate chamber conditioning yielded the best results and can generally be recommended, however saturated salt solutions are able to produce lower relative humidities, which are relevant to forest fire applications as they represent the highest fire danger. Results were within the range of published sorption isotherms for forest fine fuels. A fairly clear gradation was present with higher EMC values in leaf litters than in needle litters. These differences are in accord with values from the literature and suggest general differences in the sorption properties of leaves and needles, which may be caused by differing chemical and physical properties. The influence of temperature on EMC described in the literature could be confirmed.