Giant sequoia regeneration in grovesexposed to wildfire and retention harvest

Abstract

Both wildland fire and mechanical harvest have been proposed to achieve ecological restoration goals in giant sequoia (Sequoiadendron giganteum [Lindl.] Buchholz) groves of the southern Sierra Nevada, but their effectiveness on giant sequoia regeneration has received little attention. In the summer of 2010, we examined giant sequoia regeneration in four groves subjected to: 1) moderate- to high-severity wildfire in 1987 (Case Mountain, Redwood Mountain groves), 2) low-severity wildfire in 2008 (Black Mountain grove), 3) retention harvest (removal of all trees except large-diameter giant sequoia) followed by prescribed burning in the mid-1980s (Black Mountain, Bearskin groves), and 4) nearby unburned and un harvested (control) stands in all groves. Density of giant sequoia regeneration was greater in the moderate- and high-severity wildfire stands than control stands, but there was no difference in giant sequoia regeneration between low-severity burned and control stands. Stands thinned by retention harvest and prescribed burning had greater giant sequoia regeneration than control stands. Across all control and low- to moderate-severity wildfire stands, giant sequoia regeneration was positively associated with canopy gaps. In wildfire and retention harvest stands, giant sequoia regeneration was positively associated with distance to gap edge, direct and indirect solar radiation, and soil moisture. Our results corroborate previous studies in finding that giant sequoia regeneration benefits from fire. Both wildfire and prescribed fire (preceded by harvest or not) can serve to promote giant sequoia regeneration, providing that fire intensity is sufficient to create canopy gaps, increase understory light, and remove surface litter.