Multiaged redwood responds well to partial harvest and herbicide treatments

Abstract

Chemical control of unwanted trees can be a cost-efficient tool for forest management and restoration. In California, United States, the response of merchantable conifers to hardwood control is poorly understood. We studied the tree growth of coast redwood (Sequoia sempervirens (Lamb. ex D. Don) Endl.) following herbicide frill treatment of competing tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, C.H. Cannon, & S. Oh), coinciding with a partial harvest of conifers. The radial growth of 420 redwoods in 45 plots was measured using increment cores. With or without partial harvesting, herbicide treatment of tanoak enhanced growth of most redwoods: 23% of redwoods in herbicide-only plots and 34% of redwoods in herbicide + harvest plots had ≥100% higher posttreatment basal area increment (BAI). In untreated plots, 67% of redwoods displayed declining BAI. The response of redwoods (the ratio of 8-year postharvest BAI to 8-year preharvest BAI) was 59% higher in herbicide-only plots and 108% higher in herbicide + harvest plots compared with untreated control plots over the same period. Redwoods with long crowns maintained rapid growth with or without treatment. Trees growing slowly before treatment exhibited the greatest response, provided that they had relatively long crowns and were not left in suppressed crown positions. Forest managers implementing partial harvesting and (or) chemical control of hardwoods can expect to maintain or promote rapid growth of most residual redwoods.