Second-growth redwood forest responses to restoration treatments
Kevin R. Soland, Lucy P. Kerhoulas, Nicholas J. Kerhoulas, Jason R. Teraoka
Abstract
Following 20th century logging, much of the natural coast redwood (Sequoia sempervirens [D.Don.] Endl.) range consists of dense second-growth stands with slow tree growth and low biodiversity. There is a landscape-scale effort in much of coastal northern California to increase tree growth rates and ecosystem biodiversity via thinning treatments, thereby hopefully accelerating the development of old-growth forest characteristics. Redwood National Park has been experimenting with thinning in these forest types since the 1970s. This study investigated short- (1 year post-thinning) and long-term (40 years post-thinning) responses of redwood physiology (water potential and stomatal conductance), redwood growth (via tree-rings), and forest biodiversity (understory plants, birds, and mammals) to restoration thinning treatments. We found that thinning second-growth redwood forests with 40% basal area reduction treatments 1) did not meaningfully influence tree water potential, 2) increased tree stomatal conductance in the short-term, 3) increased tree growth in the long-term, 4) increased understory plant diversity, and 5) did not affect bird or mammal diversity. Collectively, these findings demonstrate that thinning second-growth redwood forests has the potential to accelerate the development of old-growth characteristics. This verification of the efficacy of restoration treatments is important information for land managers, as plans are currently underway to apply these treatments at the landscape-scale. This study can provide useful baseline data to aid future assessments of long-term forest responses to contemporary restoration efforts.