Lightning detection rates and wildland fire in the mountains of northern Baja California, Mexico

Abstract

Chaparral and conifer forest ecosystems in northern Baja California are subject to recurrent fire owing to the regions's mediterranean climate. The high frequency of burns has been attributed to deliberate burning. However lightning from summer thunderstorms are a frequent source of natural ignitions. The US lightning detection (LD) data system records and locates lightning discharges in this region. These data were entered into the ARC-INFO geographic information system (GIS) in which were calculated LD rates within vegetation types. LD densities are greatest in updraft zones along the eastern escarpments of the Sierras Juarez and San Pedro Martir. From 1985 to 1990, there were 17 to 46 times as many lightning discharges as burns occurring in both sierras. The fire refractory periods -the time between consecutive burns- are long (70-82 yr). An area of 1000 ha, which is the average size of burns in northern Baja California, receives a number of lightning strikes every few years. Consequently, few lightning strikes give rise to fire due to the scarcity of combustible biomass. The long refractory periods of the vegetation provide evidence of an inverse relation between the number and the size of burns. Given the high rates of lightning detection, ignitions provoked by man would have little impact on fire regimes.