关键词: 林火, 时空分布, 自组织, 火频度

Abstract:

The spatial and temporal dynamics and statistical distribution of forest fires in Heilongjiang province was studied here based on fire data of the province during 1980～1999 by means of GIS software. The results showed that the 20 years fire history can be divided into two phases: low fire occurrence stage before 1987 and high fire occurrence stage after 1987 The annual fire number and anthropogenic fire number are positively correlated with similar spectrum cycles of 2.3, 4.6 and 16 years and a size spectrum cycle of 6 years. Annual areas burned by lightning caused fires is irrelevant to its number, the former cycles every 9.1 years and the later every 9.1 and 3.0 years in each spectrum. Fires occur mainly in April and May with more burned areas in March and April for anthropogenic fires and May for lightning caused ones. The fires spatially distributed as a belt from northwest to southeast with 5 high fire occurrence regions and few burns in the west, southwest and northeast parts of the province. The fire size, averaged area expanding rate and burning time follow lognormal distribution with a self organizing character with respective fractal dimensions of 0.86、1.045 and 0.68 Discussion is made on fire cycles, self organizing characters and suitable frequency and intensity of human introduced fires in ecosystems. It is emphasized that although self organizing function links the spatial characters of fire with temporal ones, a lower limit exits when describing self organizing character with negative power functions and a formula for calculating the limit is presented here. Comparison is also made between fire fractals of different regions.

Key words: Forest fire, Spatial and temporal dynamics, Self organizing, Fire frequency