Crown Fire Regimes

California chaparral shrublands and Northern Rocky Mountain lodgepole pine forests typically burn as crown fires, where fire spread is through the canopy of the dominant life forms. In these ecosystems fires burn much of the aboveground biomass leaving what often appears as denuded landscapes. Recovery of these ecosystems is largely endogenous, meaning the regeneration stock is still present on the completely burned landscape and there is limited dependence on survival of outside stock, as in the case of ponderosa pine forests. In chaparral the vast majority of species regenerate rapidly by resprouting new shoots from the base of burned stems. In addition, many of the dominate species possess dormant seed banks that have accumulated for decades in the soil. These seeds are triggered in unison to germinate after fire by cues such as intense heat or smoke. Both of these regeneration modes are favored by the fact that there are relatively limited fuels on the soil surface and most of the intensity of the fire is held aloft in the canopies of the shrubs, thus, limiting the mortality of seeds and rootstocks.

One important ecosystem property of this fire regime is that regeneration is independent of the pattern of burning. Recovery after fire is not affected by the size of the fire and these ecosystems recover well after massive landscape burns that consume thousands of hectares of shrubland. Indeed, in some cases small localized burns are detrimental to recovery because the unburned landscape harbors many herbivores that can decimate post-fire regeneration.

In northern latitudes forest growth is often stunted due to a very short growing season and these forests have many similarities to chaparral shrublands. Examples include Rocky Mountain lodgepole pine and forest jack pine forests. Under these conditions of lower growth rates, coupled with typically very high lightning fire density, the trees seldom can outgrow the surface fuels and thus succumb to crown fires. Some of the dominant trees have developed dormant seed banks much like in chaparral, but rather than being stored in the soil they are held in the canopy in serotinous cones that remain closed until heated by fire.

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