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Contributed Talk

Session: : Effects Of Multiple Global Changes On Communities And Ecosystems 4

COS 127-4 - Big Trouble, Little Forest: Differential Responses of Sugar Pine (Pinus lambertiana) and Douglas-Fir (Pseudotsuga menziesii) to Ecological Restoration in SW Oregon.

Tuesday, August 8, 2023

4:15 PM – 4:30 PM PDT

Location: D137

Presenting Author(s)

AB

Alexander B. Bentley

Reed College, United States

Coauthor(s)

IB

Isaac Ball

Portland State University, United States
JC

Juliette Carton

L’Institut Argo Dijon, France
AH

Andres Holz

Associate Professor
Portland State University
Portland, Oregon, United States
WK

William Kuhn

Ecologist, Southwest Oregon
USDA Forest Service, United States
LL

Laura Lowrey

Entomologist, Southwest Oregon Service Center
USDA Forest Service, United States
KM

Kerry Metlen

The Nature Conservancy, United States
AR

Aaron Ramirez

Assistant Professor
Department of Biology & Department of Environmental Studies, Reed College, United States

Abstract: Twentieth-century fire suppression and prevention of traditional Native American burning practices in the American West has caused changes in forest structure and function, resulting in more severe and frequent fires due to the accumulation of woody understory fuels. These changes in fire conditions have been further amplified by anthropogenic climate change through more extreme fire weather conditions. A recent effort to restore the dry, mixed conifer forest surrounding the watershed of the City of Ashland Forest (the Ashland Forest Resiliency Project) is an important case study for examining the responses of different tree species to ecological restoration. Furthermore, few studies have focused on metrics that allow for assessing changes in forest resilience, such as improved responses to climate change-exacerbated drought conditions. We assessed the annual radial growth rates and drought resistance/resilience (i.e. drought period growth response, drought-induced stomatal regulation via 13C isotope discrimination analysis, and xylem embolism responses to prescribed fire) of legacy sugar pine (Pinus lambertiana) and douglas-fir (Pseudotsuga menziesii) trees in the Ashland watershed over ten years pre and post-treatment, as well as between trees in treated and control (untreated) conditions.

Dendrochronological analysis found an overall increase in P. lambertiana radial growth rates post-treatment. However, P. menziesii individuals showed no statistically significant response to treatment. Furthermore, these growth responses occurred despite climate change-exacerbated drought years, suggesting improved drought resistance and resilience of P. lambertiana trees in managed stands. Additional assessment of ecophysiological traits in trees experiencing prescribed fire also suggests these treatments do not increase tree drought stress, as is suggested by recent studies of angiosperm-dominated forests. The Ashland Watershed is at the northern end of the geographic distribution of P. lambertiana and the dryer end of P. menziesii distribution. The divergent growth trends observed between surveyed P. lambertiana and P. menziesii individuals indicate that management practices may have differential effects on species and that geographic distributions with respect to moisture availability may be predictive of species-level responses in the Ashland Watershed and similar ecoregions.