Long-term improvement of coast redwood (Sequoia sempervirens) growth following thinning in second growth forests of northern California

van Mantgem, Phillip; Teraoka, Jason; LaFever, David; Lalemand, Laura

In second growth forests at Redwood National and State Parks (RNSP) and the Bureau of Land Management’s Headwaters Forest Reserve (HDWT) managers promote the development of late seral forest characteristics using mechanical thinning, where competing vegetation is removed to promote growth of residual trees. Yet the ability to quantify and reliably predict outcomes of treatments such as these is hindered by the long time scales at which forests respond to thinning. Here we present analyses of tree growth at RNSP and HDWT from sites that have had >10 years to respond to thinning treatments. Compared to untreated stands, thinned stands had lower stem density (trees ha-1) and basal area (m2 ha-1) (permutation tests, P < 0.05), primarily due to removal of Douglas-fir (Pseudotsuga menziesii). Individual tree growth (basal area increment, BAI, m2 yr-1) was related to tree size (basal area, m2) and treatment history, with the highest growth observed in large trees in thinned stands. The positive growth response to thinning was more pronounced in coast redwood (Sequoia sempervirens) compared to Douglas-fir [i.e., BA*TreatmentThin interaction term (95% CI), redwood = 0.011 (0.007 to 0.015), Douglas-fir = 0.004 (0.000 to 0.007)], indicating a long-term advantage in growth following thinning for coast redwood. Future work will focus on identifying site-level differences (site quality, local competition, slope, aspect, stand age, distance from the ocean) to improve our understanding of the growth response. Early results suggest a large degree of variation among sites, but without regular patterns in growth responses between RNSP and HDWT.

Long-term improvement of coast redwood (Sequoia sempervirens) growth following thinning in second growth forests of northern California

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