This first account of Oregon ash somatic embryogenesis identifies unique auxin and abscisic acid responses distinct from green and white ash, advancing clonal propagation techniques for reforestation. Oregon ash (Fraxinus latifolia), the only ash species native to the Pacific Northwest, is vulnerable to the invasive beetle, emerald ash borer (EAB; Agrilus planipennis). EAB was first detected in North America in 2002, and subsequently spread primarily east of the Rocky Mountains, with greatest concern centered on more abundant and economically valuable ash species, such as green ash (Fraxinus pennsylvanica) and white ash (Fraxinus americana). Given the devastating effects of EAB on ash populations and limited natural regeneration capacity of Oregon ash, developing reliable propagation methods is essential for restoration efforts. Thus, our objective was to develop somatic embryogenesis (SE) protocols for Oregon ash by evaluating effects of auxin concentration, explant manipulation, and abscisic acid supplementation on embryogenesis induction, proliferation, and maturation. Embryogenesis induction was influenced by the interaction between picloram concentration and explant cutting (p = 0.03), with optimal rates achieved using 0.2 mg/L picloram with intact embryos (16
Forests can affect stream structure and function, but evaluations linking freshwater biodiversity to watershed-scale forest-stand conditions are limited. We evaluated competing hypotheses about spatial patterns of freshwater biodiversity by combining species inventories of vertebrates and invertebrates from traditional and environmental DNA (eDNA) methods across 24 temperate watersheds of young to old forests (37 to 124 y old). Freshwater taxonomic and functional richness of invertebrates were, on average, 1.2-fold and 1.5-fold higher, respectively, in older forests (>75 y) than in younger forests, consistent with the late-seral hypothesis. Vertebrate taxonomic and functional richness were 1.6-fold and 2.4-fold higher, respectively, in older forests, marginally supporting the late-seral hypothesis. Collectively, these findings suggest that heterogeneous habitat conditions of older forests support more rare, specialized, or intolerant freshwater species with diverse community roles. Evenness generally did not vary with mean watershed stand age, thus the diversity of habitats within a watershed may be shaped by other factors, such as disturbance history, watershed characteristics, and landscape heterogeneity. However, as measured by traditional sampling, invertebrate taxonomic evenness declined with increasing mean watershed stand age, slightly supporting the early-seral hypothesis, as younger forests may promote more evenly distributed assemblages. Ultimately, although greater freshwater richness is supported by older forests, evenness may depend more heavily on other factors in forested watersheds. Our findings provide empirical support for long-held ideas about the tight relationship between forests and freshwater biodiversity, emphasizing the interconnectedness between terrestrial and aquatic ecosystems and the importance of considering forests in watershed-scale conservation.
Tree growth and yield are important parameters for management of forests. Forest disturbance is included in many landscape studies but not in stand growth and yield models because badly damaged or destroyed stands are not part of model calibration data. To help account for this, a risk discounting method is developed based on hazard functions. Because stands that are destroyed are replanted, the entire yield from that stand is not lost but is only delayed by the age of the stand when destroyed. This means that the discount coefficient for age-independent disturbances is roughly half the empirical landscape disturbance rate, as verified by simulation of even-aged managed forest. Disturbances such as planting failure that only destroy the youngest stands have a very small discount rate compared to landscape disturbance data because few years of growth are lost in these cases. If only the oldest stands are subject to destruction, the discounting function underestimates yield reduction for high levels of disturbance. Including risk allows a more realistic assessment of expected yield under uncertainty. Discounted yields can be used to assess adequacy of wood supply for a mill or as input for an economic analysis. Cite this article as: Loehle, C. (2026). A risk discounting model for forest growth and yield. Forestist, 76, 0128, doi: 10.5152/forestist.2026.25128.
Climate change is intensifying wildfire activity across western North America, altering disturbance regimes with far-reaching consequences for aquatic ecosystems that support high biodiversity. However, the effects of wildfire on host-parasite interactions, as key components of food webs and ecosystem functioning, remain poorly understood. We investigated whether wildfire influences trematode infection prevalence and cercarial emergence by sampling Juga plicifera snails in 16 headwater streams in Oregon’s Cascade Range, 1 year after the 2020 Labor Day Fires. We also evaluated the influence of abiotic and biotic factors on parasite dynamics using concurrent field data. Trematode infections were widespread, with prevalence ranging from 2 to 40
Abstract Ecological forestry rooted in natural disturbance‐based silviculture (NDBS) aims to help maintain or facilitate recovery of ecosystem structure and function toward conditions found in unharvested stands. In the short term, leaving a portion of a stand's merchantable trees intact at harvest should increase similarity in composition and function relative to stands following non‐stand‐replacing natural disturbances such as low‐intensity fires, windthrow, or insect outbreaks and thus maintain biodiversity and other ecosystem services. Testing NDBS requires long‐term data, while assessing the generality of responses to NDBS requires such data from multiple experiments across diverse stand and site conditions. To date, our understanding of forest responses to NDBS has been limited by a lack of opportunities to explore responses across time. In this study, we utilized data from three long‐term experiments encompassing 21 combinations of harvest treatments by stand type plus unharvested reference stands. These experiments provide data to assess responses for 12 to 20 years post‐treatment. We quantified the direction (increasing or decreasing), duration (persisting or transient), magnitude, and temporal dynamics of responses in stand‐level tree growth, mortality, and regeneration abundances. High‐intensity treatments (≥40%) produced strong initial impacts, particularly increased tree mortality (although not statistically significant across all treatments), which in turn had prolonged effects on stand‐level growth through reduced tree density. These treatments also promoted increased broadleaf regeneration, likely due to greater canopy opening and enhanced light availability. We observed an inconsistent stand‐level growth response to treatments, with some treatments showing initial decline while others eventually resulted in higher growth in harvested stands. In mixed stands, coniferous species showed growth benefits when coexisting with broadleaf species, possibly due to reduced intraspecific competition or improved access to resources mediated by broadleaf neighbours. This growth advantage was not observed for broadleaf species, indicating asymmetric benefits in mixed stands. Response patterns and magnitude vary over time and are influenced by local factors such as stand type, overstory retention, species, and initial treatment impact. This variability highlights the potential for tailoring NDBS approaches locally to achieve desired outcomes and underscores the need to incorporate stand‐specific conditions into ecological forestry practices.
