Fire-vegetation feedbacks in a Southeast Asian forest-savanna mosaic

Abstract

Fire-vegetation feedbacks are critical to the dynamics of forest-savanna mosaics. Differences in fire potential between savanna (high fire potential) and forest (low fire potential) drive distinct fire regimes that enable their coexistence as landscape mosaics. In Southeast Asia, forest-savanna mosaics are vital for regional biodiversity, natural resources, and ecosystem services, yet they remain poorly documented and are increasingly threatened by degradation and homogenization. To better understand fire dynamics across Southeast Asian forest-savanna mosaics, we collected data on fuels, microclimate, and canopy cover within a mosaic in northern Cambodia. Data were gathered during both the early and late dry seasons from 46 sites representing a range of canopy cover, fuel conditions, and times since fire. These data were then used to parameterize BehavePlus6 fire behavior prediction software to model fire potential across the mosaic and over the season. Canopy cover moderated fire potential in two key ways: (1) the probability of ignition decreased gradually along the canopy cover gradient, and (2) the rate of spread, fireline intensity, and flame length declined sharply, reaching a fire-suppression threshold at approximately 2.2 LAI. This threshold coincided with grass exclusion, underscoring the central role of grass biomass in shaping fire dynamics within these systems. Between 1.2 LAI and 2.2 LAI, grass loads were highly variable, indicating a large influence of site-specific factors, other than canopy cover, in determining fire within this range. Fire potential increased from the early to the late dry season, driven primarily by leaf litter accumulation—a finding that contrasts with patterns observed in other mesic savannas and emphasizes the high tree cover and deciduousness of Southeast Asian savannas. Fuel moisture also contributed to intraseasonal variation in fire potential. We recommend against indiscriminate fire suppression policies, which risk promoting high-severity fires or facilitating forest encroachment, both of which threaten mosaic stability and heterogeneity. Adaptive management strategies that consider local dynamics and the ecological role of fire are essential for maintaining the resilience and diversity of SE Asian forest-savanna mosaics.Arts, Faculty ofGeography, Department ofGraduat