Modeling Coast Redwood Variable Retention Management Regimes

Variable retention is a flexible silvicultural system that provides forest managers with an alternative to clearcutting. While much of the standing volume is removed in one harvesting operation, residual stems are retained to provide structural complexity and wildlife habitat functions, or to accrue volume before removal during subsequent stand entries. The residual overstory trees and the new understory cohort will have different growth rates, and should therefore be modeled as distinct stand components. We used the redwood MASAM (multiaged stocking assessment model) to predict the growth of overstory and understory cohorts within pure coast redwood (Sequoia sempervirens) stands managed under dispersed variable retention management regimes. A range of overstory densities were simulated, and compared with an even-aged stand in terms of stand growth, and the growth and yield of each stand component. Results showed that overstory density had a minor influence on stand volume production, and a major influence on volume increment within overstory and understory cohorts. As overstory density increased, less growing space was available to the understory cohort. Too few data were available to model a combination of redwood and Douglas-fir. The redwood MASAM does not consider the spatial arrangement of stems, preventing comparison of aggregated and dispersed variable retention. Key words: coast redwood, growth and yield, leaf area, variable retention