Second log branch analysis of redwood and Douglas-fir

Thesis (M.S.)--Humboldt State University, Natural Resources: Forest, Watershed, and Wildland Sciences, 2014We studied branching in Sequoia sempervirens (coast redwood) and Pseudotsuga menziesii var.menziesii (coastal Douglas-fir) because of their widespread commercial and ecological value to coastal northern California. We focused our research on branching in the second log, located immediately above the 16-foot-long (~5 m long) butt log, which constitutes an important part of a tree???s wood volume and potential value. Our first goal was to quantify branch size and branch growth in uneven-aged stands in Mendocino County, California in response to topographic, silvicultural, and stand and tree-related variables. Our second goal was to test for differences in branch size between even-aged and uneven-aged Douglas-fir in Humboldt County, California. \ud Using regression analysis we found that branch size correlated negatively with stand density. In Humboldt County, branches were smaller in multiaged stands of Douglas-fir than even-aged stands except in the case where the tree in the even-aged stand was suppressed. Branch diameters were more sensitive to competition from their nearest neighbor trees than overall stand density. In Mendocino County, branch growth response to the treatments of (i) partial conifer harvest and (ii) herbicide hardwood control were quite different. Residual overstory conifer branches in harvested plots responded almost immediately with increased growth but this ???release??? was short-lived. Conifer branches in herbicide-treated plots had more moderate response, and release was delayed giving more consistent branch growth throughout the two five-year periods after herbicide treatment of hardwoods growing among the conifers. \ud Although we found that branches were smaller for understory trees in multiaged stands, partial harvesting in these stands creates gaps and openings that will promote growth of live branches on residual trees, especially on the edges of gaps with no neighboring trees to control branch development. If large branch size within the second log is a concern, managers may consider more dispersed patterns of retention so that edges are minimized. Harvesting could be delayed until the live crown base has risen above the second log. Managers may also want to leave Douglas-fir on the inside of stands since it had greater branch growth response to silvicultural treatments than redwood, and the increase in knot size may be more detrimental to the value of structural Douglas-fir lumber than redwood used for exterior applications