Conservation of Dry Forest Old Growth in Eastern Oregon

Abstract

Conservation of old-growth forests has become an increasingly important objective of Forest Service managers over the last three decades. The US Forest Service recently made changes to policies that prohibit cutting of live trees >53 cm (the “21-inch rule”). We review the disturbance ecology of dry and mesic old-growth forests of Oregon and contrast conservation policies for these two forest types. We describe the development of age-based alternatives to the 21-inch rule on the Klamath Reservation and in the Malheur National Forest in eastern Oregon. We conclude by outlining an adaptive management strategy to conserve dry forest old growth that seeks to restore the ecological processes that perpetuate old tree populations over time. We argue that what is good for dry forest ecosystems is good for dry forest old growth, especially in the face of changing climate and disturbance regimes. Study Implications: Age-based limits are a viable alternative to the size-based limits that the U.S. Forest Service has been using to conserve old growth in dry, fire-prone forests of eastern Oregon. Another alternative is a process-based approach that emphasizes restoring processes, including frequent fire that make old-growth trees resistant to a warmer and more fiery future. Multiscale inventories that track the abundance and distribution of trees of different species, sizes, and ages can inform tree conservation priorities and assess progress towards desired outcomes. Robust monitoring programs can facilitate collaborative data-driven adaptation at the local level and improve dry forest old-growth conservation outcomes.

Using a trait-based approach to asses fire resistance in forest landscapes of the Inland Northwest, USA

“…Land use changes in the nineteenth and twentieth centuries, including fire exclusion, livestock grazing and timber harvesting, favored the expansion of grand fir in the study area (Hessburg and Agee 2003;Merschel et al 2014;Johnston et al 2018). In many ponderosa pine forests maintained historically by a high frequency, low-severity fire regime, the transition towards denser forests dominated by Douglasfir and grand fir would explain why ponderosa pine and Douglas-fir still compose a significant proportion of basal area in the grand fir forest type, and many maintain large, old, fire-resistant ponderosa pine trees (Johnston et al 2021;Merschel et al 2021). Therefore, the particular structure and composition of these "recent" grand fir forests (e.g., Merschel et al 2014), with an important presence of large-diameter trees of fire-resistant species, may provide latent fire resistance (Larson et al 2013).…”

“…In fact, Flint (1925) highlighted that grand fir can have a degree of fire resistance nearly equal to Douglas-fir. Similarly, open and heterogeneous forest structures of fire-resistant species are likely to experience lower fire severity (Johnston et al 2021;Merschel et al 2021;North et al 2021). Applying forest structure spatial data (e.g., based on basal area and tree size classes) across broad scales could complement the FRS concept (Reilly et al 2018).…”

Too hot, too cold, or just right: Can wildfire restore dry forests of the interior Pacific Northwest?

“…Less fire-tolerant white fir ( Abies concolor) , grand fir ( Abies grandis ), and Douglas-fir ( Pseudotsuga menziesii ) occurred as components of mixed stands at higher elevations and in more mesic topographic settings [ 67 ]. Before Euro-American colonization, frequent, low severity fire (8–31-year return intervals) maintained forests conditions that were relatively resistant to fire, drought, and native pathogens [ 21 , 68 ]. Fire exclusion due to decreased cultural burning, land use changes, and fire suppression policies has increased the abundance of less fire-tolerant species and overall forest density across these landscapes [ 21 , 65 ].…”

“…To simulate stand-level residual tree density, basal area, and species composition following fire across a range of RdNBR severity values, we applied mortality probabilities from the species-level, unstandardized GLMM equations to individual trees in contemporary dry forest stands in eastern Oregon. We modeled stand structure and composition in inventoried, unburned stands on four National Forests across eastern Oregon classified as dry mixed-conifer or ponderosa pine forest types [ 68 ]. Stand-level data came from existing studies of contemporary, minimally managed stands representative of current forest conditions from the Malheur, Deschutes, Ochoco, and Fremont-Winema National Forests.…”

Classifying, inventorying, and mapping mature and old-growth forests in the United States

“…Second, as a forest recovers following major disturbance, it typically changes from an open stand of young saplings, to a closed-canopied, relatively uniform forest, eventually transitioning into a dynamic system of horizontally and vertically diverse structure as trees die, fall over and are replaced 10.3389/ffgc.2022.1070372 by younger trees (Bormann and Likens, 1979;Oliver and Larson, 1996). Forests subject to frequent, non-catastrophic disturbances (e.g., surface fire) maintain old forest structure through different mechanisms, but both types of forest exhibit relatively large trees, decadence and decay, large snags, and spatial heterogeneity in the old-growth stage (Morgan, 1994;Kaufmann et al, 2007;Johnston et al, 2021). These structural characteristics can be used to classify late-successional forest, and in fact, structural definitions are by far the most common approach to classifying old growth (Hilbert and Wiensczyk, 2007).…”