Forest fire in the tropical montane forests of northern Vietnam

Thanh T Pham

In recent decades, forest fires of increasing frequency and severity, attributed to both human activity and climate change, have become one of the most important threats to tropical forest ecosystems in Northern Vietnam. Tropical rainforests are not typically adapted to fire; trees are typically killed and forest regeneration depends largely on dispersal of seeds from neighbouring unburned forest areas. Thus, fire is becoming a crucial challenge for forest management and conservation. This PhD research used remote sensing and field surveys to investigate the drivers of forest fire occurrence and severity, and post-fire regeneration patterns in the tropical montane rainforests of Northern Vietnam. Evaluations of the spatiotemporal patterns of fire occurrence found that most fires occurred in the dry season from January to May, with highest frequency in natural forests and lowest in plantation forests. Maximum Entropy (Maxent) modelling suggested that assessment of multiple drivers (weather conditions, topography, fuel condition, and human activities) better predicts fire occurrence than a fire danger rating system based on weather alone, and may support improved fire management in northern Vietnam. Remote sensing was then used to map fire boundaries and estimate fire severity, which was related to the driver variables with multilevel mixed effects regression analyses. While topography (especially elevation, followed by slope and aspect) and vegetation fuel availability (measured as EVI2) were significantly correlated to burn severity, weather conditions were not. Finally, analyses of field survey data of forest composition and structure found that density, basal area and species richness and diversity were greater in unburned than recently burned plots and with increasing time since fire. Ordination and classification analyses found that species composition was more similar to unburned communities for plots experiencing low than high severity fire, and for areas closer to unburned forest edges. Plots burned twice at short interval showed the largest difference from unburned forest. Thus, while burned forests are recovering towards unburned forest composition, recovery is likely to be markedly slowed where fires are large (distance from edge effects) and/or of high severity, and forests may shift towards a different state if more than one fire affects the same area over short time intervals. The findings of this thesis should enhance the future integration of fire management into forest ecosystem conservation in Vietnam and more broadly for other tropical forest regions.

Forest fire in the tropical montane forests of northern Vietnam

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