Coast redwood seedling regeneration following fire in a southern coast redwood forest
| Authors: | Rachel Lazzeri-Aerts, Will Russell |
| Year: | 2017 |
| Type: | General Technical Report |
| Station: | Pacific Southwest Research Station |
| Source: | Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 99-101 |
Abstract
It has been hypothesized that individuals adapted to conditions near the species’ range edge, may increase the likelihood that the species will persevere under changing climatic conditions (Rehm et al. 2015). The southern coast redwood (Sequoia sempervirens (D. Don) Endl.) forests vary from more northern redwood forests in terms of stand size, genetics, forest associates, and have less annual precipitation (Noss 2000). Redwoods regenerate through both seed and basal sprouting, with sprouting being the dominate regeneration method (Douhovnikoff et al. 2004). A study of three recent fires in the Santa Cruz Mountains, California found that one site had significantly more redwood seedlings 1 year post-fire than the other two sites (Lazzeri-Aerts and Russell 2014). Our objectives were to: 1) quantify seedling germination and size, and 2) characterize environmental conditions on this site 8 years post-fire. Prolific seedling recruitment and growth may help the species persist under changing climate conditions. As conditions become drier and warmer in the southern part of the redwood range, the increased ability to regenerate through seed germination may be an advantage.
The Whitehurst Fire burned 103 ha (256 ac) within the Mt. Madonna County Park, Santa Clara County, California in June 2008 within a mixed coast redwood forest. Twenty-six plots were sampled in 2009 and 2016 for number of seedlings in three size classes (small: < 0.05 m (< 1.64 ft), medium: 0.5 to 1.0 m (1.64 to 3.28 ft), and large: > 1.0 m (> 3.28 ft)), height of tallest seedling, canopy cover, shrub cover, duff depth, soil moisture, slope, and aspect.
On average, more redwood seedlings were found than seedlings of three other common forest associates—madrone (Arbutus menziesii Pursh), tanoak (Notholithocarpus densiflorus (Hook. & Arn.) P.S. Manos, C.H. Cannon, & S.H. Oh), and mixed oak (Quercus agrifolia Née, Q. chrysolepis Liebm., Q. wislizeni A. DC.)—in both 2009 and 2016. There were fewer redwood and madrone seedlings per square meter in 2016 than 2009, but more tanoak and oak seedlings per square meter in 2016 (fig. 1). The difference in mean number of seedlings was significantly lower for redwood (p = 0.03) and significantly higher for tanoak (p = 0.0004).