Coast Redwood Responses to Pruning

A large-scale pruning study was established in the winter of 1999 to2000 at seven different sites on Green Diamond Resource Company forestlands in Humboldt County. The objective of this study was to determine the effects of pruning on increment, epicormic sprouting, stem taper, heartwood formation, and bear damage on these young trees. Pruning treatments varied pruning severity and were usually applied in conjunction with thinning treatments. Trees were assessed six years after pruning. Basal area increment decreased with increasing pruning severity but results were inconsistent from one study site to another. Height increment was unaffected by pruning. Six-year volume increment results resembled those for basal area increment: heavier pruning sometimes resulted in lower increment. Additionally, the negative effects of pruning on tree increment were probably short-lived in redwood because of the fast growth rates of this species. The number of epicormic sprouts was generally unaffected by pruning severity with the notable exception of the most severe pruning treatments. By year six, the number of sprouts was no different in the unpruned treatments than in most pruned treatments. The exception was the severe crown removal that left only approximately 15 percent residual live crown length. Epicormic sprouting does not appear to be a deterrent to pruning in redwood. Tree stem taper was also unaffected by pruning severity. Heartwood formation was expected to increase with pruning severity. However, no effects were evident in these data. Apparently, the greater heartwood expected in more severely pruned treatments was obscured by the same factors that minimized treatment effects on increment: in the six years following treatment, the pruned trees had rebuilt crown foliage and required similar sapwood for water transport as unpruned trees. Bear damage was observed at four of the seven study sites and was severe in several plots. However, no trends were evident relative to pruning treatment. In summary, pruning that leaves residual crown lengths of 40 to 60 percent should result in minimal levels of epicormic sprouting and no effects on tree increment.