Initial Floristic Response to High Severity Wildfire in an Old-Growth Coast Redwood (Sequoia sempervirens (D. Don) Endl.) Forest

Abstract

Climate driven increases in fire frequency and severity are predicted for Mediterranean climatic zones, including the Pacific coast of California. A recent high severity wildfire that burned in the Santa Cruz Mountains affected a variety of vegetation types, including ancient coast redwood (Sequoia sempervirens (D. Don) Endl.) stands. The purpose of this study was to characterize the survival and initial recovery of vegetation approximately six months after the fire. We sampled thirty randomly selected points in an old-growth coast redwood forest to examine and compare survival, crown retention, and post fire regeneration of trees by species, and the recovery of associated understory plant species. Sequoia sempervirens exhibited the highest post-fire survival (95%), with lower survival rates for subcanopy hardwood associates including tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos) (88%), coast live oak (Quercus agrifolia Nee.) (93%), Pacific wax myrtle (Myrica californica (Cham. & Schltdl.) Wilbur) (75%), Pacific madrone (Arbutus menziesii Pursh) (71%), and the lowest survival recorded for the canopy codominant Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) (15%). Canopy retention and post fire regeneration were also highest for S. sempervirens and lowest for P. menziesii, indicating that S. sempervirens had a competitive advantage over P. menziesii following high severity crown fire. Both canopy survival and regeneration were greater for larger height and diameter trees; and basal sprouting was positively associated with tree height and diameter for S. sempervirens and N. densiflorus. Observed recovery of understory species was modest but included the reemergence of coast redwood associated herbaceous species. The robust nature of survival and recovery of S. sempervirens following this extreme fire event suggest that the removal of scorched, and the seeding or planting of trees, following this type of fire is contraindicated. The decline of P. menziesii is of concern, however, and suggests that repeated high severity fires driven by climate change could eventually lead to vegetation type conversion.

Reproduction of a Serotinous Conifer, the Giant Sequoia, in a Large High-Severity Fire Area

“…Similar to recent results regarding natural regeneration of a related species, the coast redwood (Sequoia sempervirens) [23,24], the results here are encouraging for the conservation of giant sequoias. Further research will be needed in other sequoia groves through which large fires have spread recently to determine how broadly applicable our results here may be.…”

“…However, the results ofSoderberg et al (2024) [17] were based on field surveys conducted in 2022 at one year post-fire. We conducted our field surveys in 2023, two years post-fire, and 41% of our plots had sequoia seedlings exclusively from 2023.Our results and previous work[11,13,14] suggest several mechanisms that work to provide advantageous conditions for giant sequoia reproduction in high-severity fire areas, including (a) intense heat that facilitates the release of a super-abundance of seeds; (b) consumption of all duff and litter, which allows sequoia seedlings to sink their roots into soil, and which provides a layer of mineral ash that aids growth over time; (c) mortality of most or all canopy trees, which provides high levels of sunlight to sequoia seedlings; (d) a competitive advantage over non-sequoia conifers in terms of the proportion of total species composition, at least in the earlier stages of natural succession; and (e) an extraordinary growth rate.Similar to recent results regarding natural regeneration of a related species, the coast redwood (Sequoia sempervirens)[23,24], the results here are encouraging for the conservation of giant sequoias. Further research will be needed in other sequoia groves through which large fires have spread recently to determine how broadly applicable our results here may be.…”

Forest Fuel Bed Variation in Tropical Coastal Freshwater Forested Wetlands Disturbed by Fire

“…Thus, the conservation and management of these coastal ecosystems are important for the C cycle at the local and regional scales. Therefore, Mahdizadeh and Russell [94] pointed out the need not only to estimate degraded areas, but also to quantify the amount of C lost in the most disturbed areas in a given year, which can vary greatly.…”