Lightning Fires in North Dakota Grasslands and in Pine-Savanna Lands of South Dakota and Montana

Abstract

Lightning strike fires which occurred between 1940 and 1981 were studied in mixed-grass prairie grasslands and in pine-savanna lands in the Northern Great Plains region. A majority (73%) of ignitions occurred during July and August, while a lesser number was recorded in April, May, June, and September. The AprilSeptember period is also the average time of the freeze-free period and approximates the average distribution period for thunderstorm activity in this region. The area burned by each of 293 lightning fires (most of which were suppressed) ranged from 0.0041158.3 ha (X = 10.8 ha). The frequency of lightning fires in mixedgrass prairie grasslands averaged 6.0/yr per 10,000 km2 in eastern North Dakota, 22.4/yr per 10,000 km2 in southcentral North Dakota, 24.7/yr per 10,000 km2 in western North Dakota, and 91.7/yr per 10,000 km2 in pine-savanna lands in northwestern South Dakota and southeastern Montana. The ecological role of lightning-set fires is discussed relative to the development of resource research and management plans and to the interpretation of historical records of natural fire occurrence in the Northern Great Plains region. Climate and fires are strongly supported in recent reviews as primary agents affecting the origin and development of native grasslands in North America (Vogl 1974, Wright and Bailey 1980). Lightning has for many years been recognized as an important cause of forest fires (Komarek 1966, 1968; Stokes and Dieterich 1980) but there is less agreement about its importance as a natural cause of grassland fires. Rowe (1969) and Vogl (1974) summarized historical perspectives of the arguments relative to the purported unimportance or absence of lightning fires in North American grasslands. However, authentic instances of lightning-caused fires have been reported in grasslands or steppes in Alberta (Nelson and England 1971), Saskatchewan (Raby 1966, Rowe 1969, Coupland 1973), Kansas (Brock 1925, Malin 1956), Nebraska (Kirsch and Kruse 1973, Wolfe 1973, Westover 1977, Bragg 1978), and Washington (Uresk et al. 1976). Komarek (1966) reported lightning-caused fires for South Dakota and Nebraska, all of which were associated with forest or forest-savanna vegetative types. Thus, lightning-caused fires are a natural phenomenon in the Central and Northern Great Plains grasslands but there is a paucity of information about their seasonality, frequency, and extent. The present paper summarizes and characterizes the events of 294 known occurrences of lightning-caused fires in grasslands in North Dakota and in pine-savanna lands of nearby South Dakota