Forest fire characteristics in China: Spatial patterns and determinants with thresholds

Forest fire characteristics and their determinants are important considerations for forest management. However, the interaction among natural and anthropogenic factors and their impacts on the occurrence and distribution of forest fires in China, a vast country with enormous variation in its environmental and social contexts, has remained a lasting challenge in science and forest management. In this study, ground-based data of forest fires at the county level in China's forest fire hazards survey (1989-1991) were applied in studying forest fires and five relevant factors: climate, fuel, topography, human activity, and firefighting facilities at national and provincial scales. During the study period, the county-level number of forest fires in China increased with decreasing latitude, and the burnt area was larger in the subtropical region and some counties of Northeast China. Industry fires and recreation fires showed contrasting latitudinal patterns, and cultural fires dominated in North China. Lightning fires constituted less than 1% of forest fires, and dominated in only six counties. Results of a random forest model indicated that spring temperature and forest stocking level were respectively the most critical variables affecting the fire number and burnt area across China, and overall threshold values of mean spring temperature of 15 degrees C and forest stocking of 500 million were suggested respectively for abrupt changes in fire frequency and burnt area. Climatic conditions generally dominated the variation in human-caused fires, but lightning fires were primarily influenced by fuel load. However, the most important factors for fire features varied substantially at the provincial scale, highlighting the complexity in the roles of climate or fuel conditions and their combinations for fire risk. Our results provided a first ground-based snapshot of forest fire patterns in China at a high spatial resolution, revealed contrasting features of natural- and human-caused forest fires, and highlighted the spatial variation of fire drivers. The potential uncertainty indicated the necessity of long-term monitoring with multiple approaches for better understanding of forest fire activities and optimal practice in forest fire management in China, both at national and provincial scales.