Mechanistic modeling of landscape fire patterns

Fire as a landscape process is of broad interest to ecologists and land managers. Fires alter forest age-distributions (Heinselman, 1973; Van Wagner, 1978), are sensitive to climate (Balling et al., 1992, Swetnam and Bettancourt, 1990; Swetnam, 1993; Timoney and Wein, 1991), can be manipulated by fire suppression (Baker, 1992; Barrett, 1994), and affect directions for land management policy (Hunter, 1993; Lesica, 1996; Huff et al., 1995; Johnson et aI., 1995; Omi, 1996). Fire models are used for ecological research into spatial disturbance and recovery patterns (Turner et al., 1989; Green, 1989; Ratz, 1996; Boychuk et al., 1997), forest landscape dynamics (Keane et al., 1996; Mladenoff et al., 1996; Boychuk and Perera, 1997; Li et al., 1997), and fire planning (Kessell, 1976; Methven and Feuenkes, 1988; Beer, 1990). For ecological modeling, fire or disturbance patterns have usually been simulated by directly applying stochastic algorithms to modify spread directions and rates (Turner et al., 1989; Green, 1989; Baker et al., 1991; Mladenoff et al., 1996; Gardner et al., 1996), or to bum a proportion of the landscape area (Ratz, 1996; Li et al., 1997). Another approach is to focus on simulating the fire processes so that the cause-and-effect relationships for a given pattern can be studied. There is great interest in analyzing landscape patterns that result from fire to determine how those patterns relate to ecological theories (Romme, 1982; Baker, 1992; Suming et al., 1988) . Because many landscape patterns are produced by variation in fire behavior, a mechanistic simulation of fire behavior and fire growth is useful for explaining how, why, and when such patterns can form. Mechanistic simulation models (e.g., process models) try to represent a system as a set of fundamental processes that each describe cause and effect relationships between physical variables. Often, empirical relationships must substitute for individual processes that are not understood well enough for a more detailed description. The general mechanistic approach is useful for studying fire patterns because it allows an evaluation of: (i) the role of specific envirorunental factors in creating