Chapter 4 - Water Relations of Forest Fuels

Abstract

This chapter begins with a review of the influence of moisture on the combustion of forest fuels and how fuel characteristics determine the moisture content level of these fuels. It summarizes current understanding of the amount of water these fuels can hold, gain and loss of this water, and how the governing processes have been described mathematically. Only fuels associated with or originating from vascular plants (grasses, shrubs, and trees as opposed to mosses and worts that lack internal structure for transporting water) are considered. The discussion of live fuels emphasizes the physiological aspects of water transfer, but only a few studies related to mechanisms of water transport in these fuels are discussed. For example, the effects of photosynthesis, respiration, and growth on water potential and water movement are not described. Brief mention is made of soil water transport, which has been a prominent topic in many soil physics and hydrology texts. In the case of dead fuels, a description of what the author believes in the more relevant studies is given. Only a few of the published studies of moisture content change in wood and forest fuels have dealt with diurnal change; a glimpse at prediction models for diurnal moisture variation is provided. Near the end of the chapter, several methods of measuring the moisture content of live and dead forest fuels are briefly discussed, and the reader is referred to works related to the fuel moisture aspects of current fire behavior and fire danger rating systems.