AbstractsBiology & Animal Science

The purpose of this study was to investigate basal area growth in coast redwood (Sequoia sempervirens) along a ten mile east-west gradient in Mendocino County, California, USA, following herbicide treatment of tanoak (Notholithocarpus densiflorus) and partial harvest of conifers. We hypothesized that coast redwood basal area (BA) growth after treatment would be related to location, species composition, stand density, tree size, vigor, tanoak removal, and partial harvesting of conifers. Growth data were taken from increment cores of 472 redwood trees in 45 plots, and analyzed for response to treatment. Redwood tree BA growth was 23 percent greater within stands that were treated with herbicide and had additional conifers removed when compared to untreated stands. Mean annual BA growth of residual redwood trees was 18 percent greater within stands where herbicide was applied to tanoak compared with untreated stands. Among the three treatments, redwood trees in stands treated with herbicide and partial harvesting of conifer exhibited the greatest annual radial growth and had the largest growth ratios (comparison of basal area growth before and after treatment at equal time intervals). Total value of standing merchantable volume of redwood per acre added to live trees via (enhanced) growth over 8 years since treatment was 37 percent greater in herbicide-only and 47 percent greater in herbicide and partially harvested stands compared to no treatment, based on standard volume equations. Mean annual BA increment of redwood trees was significantly correlated with tree size, age, live crown ratio, species composition, treatment prescription and intensity, location, stand structure, site quality, and canopy position. Over the first five years since treatment, 34 percent of redwood trees in herbicide and partial harvest stands had ??? 200 percent greater BA growth, while 23 percent of redwoods in herbicide-only stands showed the same response over that period. When left untreated, 67 percent of redwood trees had declining diameter growth. Removing tanoak enhanced growth of most coast redwood trees, especially younger, larger redwood with longer crowns, so these factors should be considered when marking stands to retain redwoods depending on the desired response to treatments. The discount cashflow analysis indicated that herbicide injection of tanoak was a cost-effective silvicultural treatment that promoted redwood tree growth with or without partial harvesting under multiaged forest management in multiaged stands.