Will Russell

Landscape scale vegetation-type conversion and fire hazard in the San Francisco bay area open spaces

Successional pressures resulting from fire suppression and reduced grazing have resulted in vegetation-type conversion in the open spaces surrounding the urbanized areas of the San Francisco bay area. Coverage of various vegetation types were sampled on seven sites using a chronosequence of remote images in order to measure change over time. Results suggest a significant conversion of grassland to shrubland dominated by Baccharis pilularison five of the seven sites sampled. An increase in Pseudotsuga menziesii coverage was also measured on the sites where it was present. Increases fuel and fire hazard were determined through field sampling and use of the FARSITE fire area simulator. A significant increase in biomass resulting from succession of grass-dominated to shrub-dominated communities was evident. In addition, results from the FARSITE simulations indicated significantly higher fire-line intensity, and flame length associated with shrublands over all other vegetation types sampled. These results indicate that the replacement of grass dominated with shrub-dominated landscapes has increased the probability of high intensity fires.

The relative importance of fire and watercourse proximity in determining stand composition in mixed conifer riparian forests

Abstract Factors related to the composition of riparian forest stands on three streams in the northern Sierra Nevada mixed conifer forest type were related to proximity to the water course and years since fire. Using a linear regression analysis 46 variables were correlated to the natural log of distance from the thalweg “ln(distance)” including a highly significant positive correlation to dominance and percent canopy cover of conifers, and a significant negative correlation to the same variables when applied to hardwoods. Twenty six variables were correlated to years since fire “years” including similar correlations to the dominance and cover of hardwood and conifer species. However, the significance of the correlation and the degree of sample variability described by fire age was relatively low in comparison to that found for distance from the thalweg. In addition the relative frequency of fire scars increased in a linear fashion with distance from the watercourse. The results of this study indicate that the importance of fire as a determining influence on forest composition declines in proximity to the riparian zone.

Stand Development on a 127-yr Chronosequence of Naturally Regenerating Sequoia sempervirens (Taxodiaceae) Forests

Abstract Understanding the natural patterns of regeneration following human disturbance is essential for effective restoration and management of second-growth forests. Despite their unique ecological character, little is known about these patterns in Sequoia sempervirens (D. Don) Endl. (Coast Redwood) forests. We examined the composition and structure of naturally regenerating stands with 360 randomly located sample plots across a chronosequence of five replicated age-classes (18 to 127 yr) and three old-growth reference sites. Results indicate a progression of stand characteristics towards old-growth conditions, with several measures reaching old-growth equivalence within the timeframe of the chronosequence. Stand density, canopy cover, and species richness reached old-growth equivalence within 41–80 yr; Shannon-diversity reached old-growth equivalence between 80–100 yr; and the density of redwood seedlings and shrub cover reached old-growth equivalence between 100–130 yr. Basal area, herb cover, and the relative dominance of S. sempervirens progressed toward, but did not reach, old-growth equivalence. Size-class analysis indicated an increase in the density of large diameter trees, with no change in the density of smaller size-classes after forty yr. Coast redwood associated understory species were favored on the older sites with the cover of Calypso bulbosa (L.) Oakes, Trillium ovatum Pursh, and Viola sempervirens Greene reaching old-growth equivalence, while Iris douglasiana Herb., Tiarella trifoliate L., and Achlys triphylla (Sm.) DC. did not. No non-native species were recorded in stands older than 60 yr. We conclude that coast redwood forests are resilient to human disturbance, though some old-growth characteristics may require more than a century to develop.

Evaluating wildlife response to coastal dune habitat restoration in San Francisco, California.

The vast dune system that once dominated the entire western half of the San Francisco peninsula in California has been reduced to a few fragments that conserve locally threatened plant and animal species. We measured the effects of ongoing restoration efforts on wildlife abundance and diversity on one of the largest of these fragments, Fort Funston in the Golden Gate National Recreation Area. Efforts included removal of non-native species, active restoration of native dune vegetation, and restricted visitor use. We collected data regarding the composition and abundance of vegetation, birds, and ground-dwelling vertebrates on four treatments including an actively restored area with restricted visitor use, an unrestored area where visitor use had been restricted for ten years, an unrestored area where visitor use had been restricted for two years, and an unrestored area with unrestricted visitor use. Results indicated that the diversity and abundance of wildlife species, as well as the richness and cover of native plant species, were greater in the restored area than in all other sampled areas. Restricted visitor use alone had only modest positive effects on the abundance and diversity of wildlife and the richness and cover of native plant species.

The Effects of Revetment on Streamside Vegetation in Sequoia sempervirens (Taxodiaceae) Forests

Abstract Stream-bank stabilization structures, or revetment, can impact riparian systems by confining watercourses to the point where natural functions are limited. Removal of existing revetment may have considerable impacts to stream-bank stability however. The effects of revetment and revetment removal on vegetation and stream-bank morphology were measured on three streams in forests dominated by Sequoia sempervirens (Coast Redwood) in northern California. Data were collected using randomly located transects on three treatments; “no-revetment,” “revetment-intact,” and “revetment removed.” Results were compared between treatments using ANOVA at a 0.05 level of significance. On all three sites, species richness, vegetation cover, and tree seedling density were found to be highest where no revetment existed compared to where revetment was intact. Stream depth and stream-bank slope were highest where revetment was intact. Recovery of vegetation following removal of revetment was more site specific being most pronounced where recovery time was greatest and stream-bank restoration efforts were highest.