How does a Sierran Forest Grow? Fire, Thinning, and Regenerating Trees

How does a Sierran Forest Grow? Fire, Thinning, and Regenerating Trees

Read nineteenth century travelers’ descriptions of wandering through open groves of trees in Sierra Nevada forests, and you will do more with your imagination than picture waistcoats, horses, and pocket watches. Along with dress, transportation and technology, mixed-conifer forests, the most common forest type of the Sierra Nevada, have experienced dramatic changes. Harvesting the largest pines over the last century allowed more plants to grow in the understory and midstory, creating opportunities for shade-tolerant and fire-intolerant firs and incense cedars to multiply and reduce gaps in the forests. The patchy tree canopy filled in. As the structure of the mixed-conifer forest has changed since earlier travelers’ tales, and the kinds of tree species present, so has the way the forest behaves. Thick mats of needles and leaves increase on the forest floor. Shrubs, bushes, and small trees, crowded together, create ladder fuels—places where fire can climb from the forest floor, up to the midstory, and into the dense canopy above. With fewer gaps in the canopy, fire can roar into high-intensity crown fires, and spread easily through the nearly continuous upper story.

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