Recent Trends in Large Hardwoods in the Pacific Northwest, USA

Abstract

Forest densification, wildfires, and disease can reduce the growth and survival of hardwood trees that are important for biological and cultural diversity within the Pacific Northwest of USA. Large, full-crowned hardwoods that produce fruit and that form large cavities used by wildlife were sustained by frequent, low-severity fires prior to Euro-American colonization. Shifts in fire regimes and other threats could be causing declines in, large hardwood trees. To better understand whether and where such declines might be occurring, we evaluated recent trends in Forest Inventory and Analysis (FIA) data from 1991–2016 in California and southern Oregon. We included plots that lay within areas of frequent fire regimes during pre-colonial times and potential forest habitats for fisher, a rare mammal that depends on large live hardwoods. We analyzed changes in basal area for eight hardwood species, both overall and within size classes, over three time periods within ecoregions, and in public and private land ownerships. We found the basal area to generally be stable or increasing for these species. However, data for California black oak suggested a slight decline in basal area overall, and among both very large trees and understory trees; that decline was associated with fire mortality on national forest lands. In addition, mature trees with full crowns appeared to sharply decline across all species. Many trends were not statistically significant due to high variation, especially since more precise data from remeasured trees were only available for the two most recent time periods. Continued analysis of these indicators using remeasured trees will help to evaluate whether conservation efforts are sustaining large, full-crowned trees and their associated benefits.

Shifting Perspectives in Assessing Socio-Environmental Vulnerability

“…While emphasizing values that are important to community stakeholders, these facets can be built on recommended principles of scientific reliability [59]. Work with tribes in the US has similarly emphasized biophysical metrics to quantify the usability and availability of key forest product species, including the abundance of mature hardwood trees that produce culturally important foods [84,85]. Assessments will be more likely to result in social change where indicators have been developed in collaboration with local communities [86].…”

Evaluating Model Predictions of Fire Induced Tree Mortality Using Wildfire-Affected Forest Inventory Measurements

“…Fewer than 1% of the surviving burned trees of the other species discussed here had recovered from 100% crown scorch. Canyon live oak is increasing in basal area despite increased fire activity in California, possibly due to exploiting niches in unburned stands where fuels are sparse and to its shade-tolerance [59].…”

“…Nevertheless, basal sprouting can greatly affect post-fire stand dynamics, with up to 70% of the top-killed black oak resprouting in one study [13]. California black oak has been experiencing a decline in basal area in California [59], in part due to conifer encroachment into black oak canopies resulting in greater crown-fire caused mortality [61].…”

Applying optimal control theory to a spatial simulation model of sudden oak death: ongoing surveillance protects tanoak while conserving biodiversity

“…Tanoak trees are highly valued by Native American tribes in Northern California for their acorns, which were used historically for trade and are still used for traditional cooking [15]. Tanoak is also believed to be highly important to coast redwood forest ecosystems [16,17]. The spread of P. ramorum is a significant threat to tanoak.…”