Variable-Density Thinning and a Marking Paradox: Comparing Prescription Protocols to Attain Stand Variability in Coast Redwood

Variable-density thinning (VDT) is an emerging thinning method to enhance stand structural heterogeneity by deliberately thinning at different intensities within a stand. Subsequent stand development forms a more varied structure than is common in many even-aged forest stands. A primary difficulty with VDT treatments is systematically attaining heterogeneity. Instead, tendencies seem to be to apply a uniform treatment across a stand that enhances structural homogeneity. In coast redwood (Sequoia sempervirens), VDT has become the primary restoration treatment for young stands in state parks in the Humboldt and Del Norte Counties of northern coastal California. These stands are young and even-aged following clearcutting by previous industrial landowners. VDT is being used to increase structural heterogeneity, increase the proportion of redwood or other conifers, and accelerate development toward old forest structures. Six marking prescriptions have been used to date to achieve VDT objectives. These marking prescriptions were compared with regard to (1) ease of use; (2) effectiveness in achieving spatial heterogeneity; (3) capability to approach density/species composition targets; and (4) qualitative assessments of potential for bear damage, potential costs, and long-term stand development trends. Generally, prescriptions that were most complex achieved the greatest heterogeneity and vice versa. This creates a paradox with VDT: Finding simple ways to create complex structures.