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| Fire and Sequoia Reproduction |
While advanced imaging and computer technology can help predict fire behavior in the future, tree ring analysis reveals fire patterns of centuries past. At Sequoia and Kings Canyon National Parks, WERC researchers and collaborators from the University of Arizona's Laboratory of Tree-Ring Research have put together the longest and most detailed fire histories anywhere. The records, assembled from fire scars in the annual growth rings of giant sequoias, extend back over 2,000 years, and show that fire typically burned on the floor of sequoia groves every 3 to 8 years.
The record shows how sequoias have responded to what has been, on a scale of centuries, an ever-changing climate and fire regime. The historical record shows a shifting matrix of low to moderate-intensity fires, with occasional hot spots of severe fire that open gaps in the forest and clear the way for sequoia regeneration. The hot spots reduce competition for sequoia seedlings. Sequoia seeds require contact with bare soil to germinate, and this is possible only when fire has cleared away the layers of leaf litter and debris. A century of fire exclusion in sequoia groves has had a greater effect on sequoia populations than the preceding several millennia of changing climate and fire regimes. Fire exclusion prevents sequoia reproduction. In most sequoia groves today, even the youngest trees are over a century old. Most areas in most groves have not burned for 100-130 years. To determine what would restore sequoia reproduction, WERC scientists have extensively studied the effects of prescribed burning on sequoia groves. Unlike some other forest systems, sequoia groves have responded extremely well to prescribed burning alone, with no other treatment needed.
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