Variation in old-growth Sequoia sempervirens (Cupressaceae) stands in Mendocino County, California

Background/Question/Methods

Unmanaged stands of old-growth coast redwood (Sequoia sempervirens (D. Don) Endl.) are increasingly rare, particularly in the central part of the range. An understanding of variability within, and between, old-growth stands can provide a template for restoration and management of this forest type. We compared basal area, tree density, canopy cover, shrub cover, herbaceous cover, and cover of two old-growth indicator species, Trillium ovatum Pursh and Oxalis oregana Nutt., in three old-growth coast redwood sites. The three sites selected for study include a coastal site with high topographic diversity: the Russell Unit of Mendocino Headlands State Park, and two alluvial inland sites: Montgomery Woods State Natural Reserve and Hendy Woods State Park, all managed by California State Parks. These sites represent the largest remaining unharvested redwood stands in Mendocino County, although additional old-growth sites in this region have yet to be identified. We conducted nonmetric multidimensional scaling, perMANOVA, and indicator species analysis for each old-growth stand. Qualitative comparisons were also made between edaphic and climate variables for each site.

Results/Conclusions

Results based on multivariate statistical analyses illustrated significant differences between the coastal site of the Russell Unit, and the more inland sites of Montgomery Woods State Natural Reserve and Hendy Woods State Park. Percent cover of understory species O. oregana, tree density, and percent herbaceous cover were lowest in the Russell Unit and highest in Hendy Woods, with slightly lower values in Montgomery Woods. Percent canopy cover exhibited only slight differences, although basal area, influenced primarily by the dominant species S. sempervirens, reached highest values in Montgomery Woods. Percent shrub cover, percent cover of understory indicator species T. ovatum, and species richness were highest at the coastal Russell Unit, reached lowest values in Hendy Woods, and illustrated higher values in Montgomery Woods. Based on these results, a qualitative matrix was developed of potential indicators that may characterize different old-growth forests. A more comprehensive understanding of the suite of characteristics that can exist within old-growth communities will aid in the conservation of this unique forest type.