Abstract: Fire is a critical disturbance factor in forests, with consequences on ecosystem structure and function. Based on the satellite fire point data in Heilongjiang and Jiangxi provinces of China from 2005 to 2017, we analyzed the spatial-temporal variations of fire occurrences and fire risk period using Mann-Kendall test and sliding t test methods. The annual variation of forest fire occurrences in both provinces showed a trend of first rising and then falling. The mutation year of forest fire occurrences in Heilongjiang was around 2011 and that in Jiangxi was around 2016. The statutory fire risk period in Jiangxi was more reasonable than that in Heilongjiang. Forest fire in Heilongjiang mainly occurred in spring and autumn. The occurrence period of forest fire in spring shifted to early spring, and the occurrence period of forest fire in autumn shifted to summer and extended, the mutation years of spring, summer, and autumn were 2010, 2014, and 2011 respectively, and there was no mutation year in winter. Forest fire in Jiangxi mainly occurred in winter, the occurrence period of forest fire tended to shift to winter and shortened, and the mutation years of spring, summer, autumn and winter were around 2010, 2015, 2014 and 2016, respectively. The density of forest fires in both provinces showed an opposite increasing trend in the spatial perspective. In Heilongjiang, the density of forest fires increased from southeast to northwest, dominantly distributed in Heihe (a northern city of the province) and Daxinganling (a northwest part of the province). In contrast, the density of forest fires increased from northeast to southwest in Jiangxi, concentrated in Ganzhou (a southern city of the province) and Ji’an (a southwest city of the province). The overall number of forest fires showed a downward trend in both provinces. The number of forest fires in Daqing, Jiamusi and Daxing’an Mountains in Heilongjiang had a significant downward trend, while the number of forest fires in Yichun and Jixi during the statutory fire danger period was on the rise. This study demonstrated the temporal and spatial variations of forest fires in two provinces located in north and south China and the shifts of fire risk period in both provinces. These findings can provide support for revealing forest fire impacts on regional environment and effective management of forest fires.

Key words: forest fire, temporal and spatial distribution, fire risk period, Mann-Kendall test, sliding t test, Heilongjiang, Jiangxi.