Approximation of Fire-Return Intervals with Point Samples in the Southern Range of the Coast Redwood Forest, California, USA

Gregory A Jones,Will Russell

doi:10.4996/fireecology.1103080

Gregory A Jones, Will Russell

Open Access

https://doi.org/10.4996/fireecology.1103080

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Abstract

AbstractA legacy of past fires is evident in the form of blackened basal hollows found throughout the southern range of the coast redwood (Sequoia sempervirens [D. Don] Endl.) forest. A deeper look reveals cambial scars dating back centuries, telling a story of low- to moderate-intensity fires that burned periodically across California’s Central Coast bioregion. While attempts have been made to reconstruct the fire history of this forest type, estimates of the fire-return interval vary widely, and the relationship of the fire-return interval to varying cultural influences is not fully understood. We analyzed 373 fire scars from 70 cross-sections removed from stumps, downed logs, and live trees in the coastal Santa Cruz Mountains of California, USA, in order to estimate fire-return intervals (FRI) for individual trees, mean FRI across samples, and seasonality of historical fires. The mean FRI, averaged across point samples, was 60.6 yr with a median of 40.1 yr. Fire scars were most prevalent in the dormant and latewood portions of annual growth rings. A sub-sample of 19 cross-sections, for which we were able to determine approximate fire years, exhibited a high degree of variation between samples with individual tree FRIs ranging from 10.4 yr to 128 yr. The mean FRI of 43.3 yr was marginally higher for the pre-settlement period (1352 to 1849) compared to 30.7 yr for the settlement period (1850 to 1924) and 32.3 yr for the recent period (1925 to 2013). While our results suggest a longer estimate of fire-return intervals than previously documented for this forest type, high variation within and between samples clouded distinctions and illustrates a culturally constructed fire regime characterized by temporal and spatial heterogeneity.

Highlights

Recent wildfires in California’s Central Coast bioregion have revived interest in the fire ecology of coast redwood
While our results suggest a longer estimate of fire-return intervals than previously documented for this forest type, high variation within and between samples clouded distinctions and illustrates a culturally constructed fire regime characterized by temporal and spatial heterogeneity
Both of these studies focused on areas where Sequoia sempervirens tends to grow in isolated groves and are not necessarily representative of southern coast redwood forest as a whole, as fire frequencies found in these two studies are likely influenced by the fire regimes of adjacent grassland or chaparral communities (Stephens and Fry 2005)

Summary

Introduction

Recent wildfires in California’s Central Coast bioregion have revived interest in the fire ecology of coast redwood Short mean FRIs (6.2 yr to 23.0 yr) were found by Finney and Martin (1992) on individual stumps, and mean FRIs ranged from 12.4 yr to 16.3 yr in a study by Stephens and Fry (2005). Both of these studies focused on areas where Sequoia sempervirens tends to grow in isolated groves and are not necessarily representative of southern coast redwood forest as a whole, as fire frequencies found in these two studies are likely influenced by the fire regimes of adjacent grassland or chaparral communities (Stephens and Fry 2005). Both of these studies focused on areas where Sequoia sempervirens tends to grow in isolated groves and are not necessarily representative of southern coast redwood forest as a whole, as fire frequencies found in these two studies are likely influenced by the fire regimes of adjacent grassland or chaparral communities (Stephens and Fry 2005). Brown et al (1999) found relatively short composite mean FRIs (7.7 yr to 13.0 yr) where coast redwood mixed with Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco var. menziesii) in Point Reyes National Seashore, while a longer mean FRI of 21.7 yr to 27.1 yr was reported for Muir Woods National Monument in southwestern Marin County, where redwood is more contiguous across the landscape (Jacobs et al 1985). Greenlee (1983) estimated a composite mean FRI of 45.4 yr in a more representative coastal redwood stand in Big Basin Redwoods State Park, but the estimate was based on scars from only two stumps

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