Effects of Silvicultural Management on Coast Redwood Forest Composition, Density and Structure in Santa Cruz and San Mateo Counties

Author

Michael J. Papa, California Polytechnic State University, San Luis ObispoFollow

DOI: https://doi.org/10.15368/theses.2012.198
Available at: https://digitalcommons.calpoly.edu/theses/647

Date of Award

12-2012

Degree Name

MS in Forestry Sciences

Department/Program

Natural Resources Management

Advisor

Walter Mark

Abstract

The multiple-objective exploratory study investigates effects of various silvicultural management regimes commonly applied to coast redwood (Sequoia sempervirens [D. Don] Endl.) forests in Santa Cruz and San Mateo Counties, California, USA. A temporary forest inventory was installed in 24 harvest origin stands and 4 natural origin stands throughout the study area (sample area = 1189 acres). Data from the systematic sample of 233 one-quarter acre nested cluster plots (sample intensity = 4.9%) rendered overall forest descriptions in terms of species composition, density, and structure. The common forestry measures of trees per acre (TPA), basal area per acre (BA), and quadratic mean diameter (QMD) were calculated from the "snapshot" data and stratified by species groups and diameter ranges/canopy layers.

Forest components were derived from the dataset by selecting specific groups within the forest as defined by the California Forest Practice Rules, literature, and common forestry groups (refer to the table below). An example of a forest component would be TPA of conifers from 2.1-14.0 inches DBH. In all, 162 forest components were analyzed through three research objectives: (1) general forest components, (2) small stem density and distribution, and (3) large stem density. The driving question behind the analysis is whether forest management is creating significantly different forest structure. If so, in which components of forest composition, density, and structure do those differences reside?

A mixed-effects linear model tested overall significance and Fisher's Least Significant Difference (LSD) method tested pairwise comparisons among the six management regimes. Each model was tested with a significance level of alpha = 0.05 (pairwise and experimentwise).

A fourth objective compared two methods of late successional forest (LSF) classification based on QMD measures of canopy layers and diameter ranges. The methods were compared via a paired-sample t-test. The two methods are significantly different, but the investigation of LSF classification led to an examination of the validity of current LSF policy. It is suggested that the minimum overstory QMD for LSF classification be increased from 24.0 to at least 30.0 inches DBH. Furthermore, it is recommended that landowner incentives should be implemented by the State of California to encourage promotion of LSF and its functional elements.

An underlying theme of all research objectives in this study is an examination of forest restoration management. Restoration management is intentional treatments that begin or accelerate recovery of a degraded ecosystem in regards to its integrity and sustainability relative to a reference condition, often defined culturally, historically, or ecologically (Society for Ecological Restoration 2004, Hobbs 2004, Hobbs and Norton 1996, Stanturf 2005). Results and conclusions were synthesized to discuss current restoration efforts in the redwoods. Recommendations for target stand densities and silvicultural methods are presented.