Post-fire regeneration and fuel succession patterns in Hesperocyparis bakeri forests

Author

Bret Anthony McNamaraFollow

Graduation Date

Spring 2018

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

Dr. Jeffrey M. Kane

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. David F. Greene

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Erik S. Jules

Third Committee Member Affiliation

HSU Faculty or Staff

Keywords

Seed dispersal, Seedling establishment, Serotiny, Baker cypress, Fuel succession, Foliar moisture, Fire behavior

Subject Categories

Forestry

Abstract

Climate change is predicted to cause widespread redistribution of suitable tree habitats, as well as increase the size and frequency of wildfires in the western United States during the forthcoming century. Rare serotinous conifers may have heightened sensitivity to the impacts of both fire regime and climate shifts for multiple reasons. First, the rapid spatial rearrangement of suitable habitat will disproportionately affect trees with constrained seed dispersal capabilities, and limited dispersal is a trait associated with some genera of serotinous trees. Second, a number of serotinous conifers depend on fire disturbances for regeneration, though with the expected increase in annual area burned, immature forests may risk re-burning prior to producing sufficient seed banks. In such a case, high post-fire tree mortality without regeneration would result in population loss or substantial reductions in population size. Baker cypress (Hesperocyparis bakeri) is a rare, serotinous conifer with 11 extant populations, and could be adversely impacted by changes in climate and fire regimes. Some remaining populations recently burned in wildfires, which caused extensive overstory mortality and dense post-fire seedling establishment. However, these young cohorts could re-burn before producing viable seed. Further, dispersal capacity has not been quantified in this species. In two separate chapters, the present study examined both 1) the regeneration patterns and dispersal capacity and 2) the fuel succession patterns and associated potential surface fire behavior across a time-since-fire chronosequence in Baker cypress forests.

Specifically, the first chapter investigated the dispersal capabilities of Baker cypress using both empirical observation of post-fire seedling establishment and mechanistic seed dispersal modeling. Post-fire recruitment was dense, averaging 11 recruits/m², and occurred primarily in the first two years after fire. However, recruitment was markedly constrained spatially. Most seedlings (~81 percent) established within 5 m of the parent tree, and maximum distance of established seedlings from stand edges averaged 19.2 m. A two-sample Kolmogorov-Smirnov test indicated that the distributions of modeled seeds and observed seedlings were not significantly different, suggesting secondary and long distance dispersal (that would increase dispersal capacity and blur the distinction between a model of primary anemochory and subsequent recruitment) was not a common event. These results aid in explaining why appreciable range expansions in Baker cypress are unlikely and have not been observed. Poor dispersal capacity of this species may hinder its response to rapid climate change.

Chapter 2 examined the fuel succession patterns across a time-since-fire chronosequence of Baker cypress forests, including surface fuel loading by type and tree foliar moisture content. Stand characteristics such as density, composition, and tree-level metrics were also quantified, and stands examined were 3, 10, 40, 107, and 147 years post-fire. A 26 y old planted stand was included for foliar moisture measurements. Fine fuel loading was highest in the 10 y and 147 y stands, while coarse woody fuels peaked in the 10 y stand and thereafter generally decreased with time since fire. Duff loading generally increased with time since fire, though litter loading followed a pattern more similar to the fine woody fuels. Baker cypress foliar moisture content was significantly lower in older foliage, and inversely correlated with stand age. Modeled fire behavior peaked in the 10 y and 147 y stands in accordance with the fine fuel accumulations, and cones were not yet present on the 3 y or 10 y old trees. This indicates that early successional stages of Baker cypress forests contain a narrow temporal window wherein stands could burn prior to seed production. Replicating this research in other Hesperocyparis species will provide a better understanding of the ecological processes in rare serotinous conifers, and inform management actions that reduce the chance of population losses.

Citation Style

APA

Recommended Citation

McNamara, Bret Anthony, "Post-fire regeneration and fuel succession patterns in Hesperocyparis bakeri forests" (2018). Cal Poly Humboldt theses and projects. 130.
https://digitalcommons.humboldt.edu/etd/130