Andrew Merschel - Academia.edu (original) (raw)

Papers by Andrew Merschel

Managing forest ecosystems, 2021

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activi... more The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, sexual orientation, marital status, family status, status as a parent (in education and training programs and activities), because all or part of an individual's income is derived from any public assistance program, or retaliation. (Not all prohibited bases apply to all programs or activities.) If you require this information in alternative format (Braille, large print, audiotape, etc.), contact the USDA's TARGET Center at (202) 720-2600 (Voice or TDD). If you require information about this program, activity, or facility in a language other than English, contact the agency office responsible for the program or activity, or any USDA office.

Journal for Nature Conservation, Jun 1, 2020

Local and regional species extirpations may become more common as changing climate and disturbanc... more Local and regional species extirpations may become more common as changing climate and disturbance regimes accelerate species' in situ range contractions. Identifying locations that function as both climate and disturbance refugia is critical for biodiversity conservation. Here, we investigate the persistence of a disjunct, fire-sensitive conifer population, yellow-cedar (Callitropsis nootkatensis), in the historically frequent-fire landscape of the Blue Mountains in eastern Oregon, USA. We used tree rings to reconstruct multi-century fire histories, which were then used to compare historical mean fire return intervals (MFRIs) inside of the cedar grove to the surrounding dry forest matrix, as well as to examine relationships between historical fire occurrence and reconstructed climate. We also examined trends in post-fire yellow-cedar mortality and regeneration between 2006, when the grove burned in a wildfire, through 2017. Results indicated that fire was less frequent in the cedar grove (MFRI = 35.8 years) than in the surrounding dry mixed-conifer forest (MFRI = 14.4 years). Historical fire occurrence was associated with hotter and drier conditions. Following the 2006 fire, cedar mortality was high (>90 %), but by 2017 post-fire regeneration was abundant (median = 8125 seedlings ha −1). The eastern Oregon cedar grove appears to occupy a fire refugium historically decoupled from the frequent-fire regime of the broader landscape. The topographic position of the grove suggests it is also a climate refugium. Managing for climate and disturbance refugia has been identified as an important option for conservation in the context of rapid global change, and this study provides evidence that locations where climate and disturbance refugia overlap may be disproportionately important for the maintenance of regional biodiversity. However, active management may be required for populations to persist in some of these locations as anthropogenic change is capable of overwhelming the underlying buffering capacity of refugia.

Landscape Ecology, Mar 14, 2019

Context Lack of quantitative observations of extent, frequency, and severity of large historical ... more Context Lack of quantitative observations of extent, frequency, and severity of large historical fires constrains awareness of departure of contemporary conditions from those that demonstrated resistance and resilience to frequent fire and recurring drought. Objectives Compare historical and contemporary fire and forest conditions for a dry forest landscape with few barriers to fire spread. Methods Quantify differences in (1) historical (1700-1918) and contemporary (1985-2015) fire extent, fire rotation, and stand-replacing fire and (2) historical (1914-1924) and contemporary (2012) forest structure and composition. Data include 85,750-ha tree-ring reconstruction of fire frequency and extent; [ 375,000-ha timber inventory following [ 78,900-ha fires in 1918; and remotely-sensed maps of contemporary fire effects and forest conditions. Results Historically, fires [ 20,000 ha occurred every 9.5 years; fire rotation was 14.9 years; seven fires [ 40,469 ha occurred during extreme drought (PDSI \-4.0); and stand-replacing fire occurred primarily in lodgepole (Pinus contorta var. murrayana). In contemporary fires, only 5% of the ecoregion burned in 30 years, and stand-replacing fire occurred primarily in ponderosa (Pinus ponderosa) and mixed-conifer. Historically, density of conifers [ 15 cm dbh exceeded 120 trees/ha on \ 5% of the area compared to 95% currently. Conclusions Frequent, large, low-severity fires historically maintained open-canopy ponderosa and mixed-conifer forests in which large fire-and drought-tolerant trees were prevalent. Stand-replacing patches in ponderosa and mixed-conifer were rare, even in fires [ 40,469 ha (minimum size of contemporary ''megafires'') during extreme drought. In this frequent-fire landscape, mixed-severity fire historically influenced lodgepole and adjacent forests. Lack of large, frequent, low-severity fires degrades contemporary forest ecosystems.

Journal of Forestry, May 28, 2021

Conservation of old-growth forests has become an increasingly important objective of Forest Servi... more 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.

Ecological Applications, Oct 1, 2014

Twentieth-century land management has altered the structure and composition of mixed-conifer fore... more Twentieth-century land management has altered the structure and composition of mixed-conifer forests and decreased their resilience to fire, drought, and insects in many parts of the Interior West. These forests occur across a wide range of environmental settings and historical disturbance regimes, so their response to land management is likely to vary across landscapes and among ecoregions. However, this variation has not been well characterized and hampers the development of appropriate management and restoration plans. We identified mixed-conifer types in central Oregon based on historical structure and composition, and successional trajectories following recent changes in land use, and evaluated how these types were distributed across environmental gradients. We used field data from 171 sites sampled across a range of environmental settings in two subregions: the eastern Cascades and the Ochoco Mountains. We identified four forest types in the eastern Cascades and four analogous types with lower densities in the Ochoco Mountains. All types historically contained ponderosa pine, but differed in the historical and modern proportions of shade-tolerant vs. shade-intolerant tree species. The Persistent Ponderosa Pine and Recent Douglas-fir types occupied relatively hotdry environments compared to Recent Grand Fir and Persistent Shade Tolerant sites, which occupied warm-moist and cold-wet environments, respectively. Twentieth-century selective harvesting halved the density of large trees, with some variation among forest types. In contrast, the density of small trees doubled or tripled early in the 20th century, probably due to land-use change and a relatively cool, wet climate. Contrary to the common perception that dry ponderosa pine forests are the most highly departed from historical conditions, we found a greater departure in the modern composition of small trees in warm-moist environments than in either hot-dry or cold-wet environments. Furthermore, shade-tolerant trees began infilling earlier in cold-wet than in hot-dry environments and also in topographically shaded sites in the Ochoco Mountains. Our new classification could be used to prioritize management that seeks to restore structure and composition or create resilience in mixed-conifer forests of the region.

Ecosphere

Fire regimes in North American forests are diverse and modern fire records are often too short to... more Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree‐ring fire‐scar network (NAFSN), which contains 2562 sites, >37,000 fire‐scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000‐m elevation and across a range of topographic settings that vary by ecoregion. Mul...

Forest Ecology and Management, 2022

Journal of Forestry, 2021

Journal of Forestry, 2019

Logging and fire suppression have reduced the number of large old trees, increased the density of... more Logging and fire suppression have reduced the number of large old trees, increased the density of small shade-tolerant trees, and decreased forest resistance to fire, drought, insects, and disease in the interior Pacific Northwest. In Central Oregon, interim Old-growth definitions, the Deschutes Large Tree Layer, and the Gradient Nearest Neighbor (GNN) mapping tool are used to identify dry old-growth forests and guide forest planning. We used a recent characterization of dry old forests to evaluate interim old-growth definitions and GNN mapping. Historical old tree species composition should be used in old-growth definitions. The 21-in.-diameter harvest limitation maintains large trees but fails to protect smaller old individuals; it does not allow for removal of younger large shade-tolerant species more prevalent since fire suppression. GNN mapping accurately identified old forest based on abundance of large trees at a coarse landscape scale but was less accurate at a finer stand scale.

Ecological Applications, 2014

Twentieth‐century land management has altered the structure and composition of mixed‐conifer fore... more Twentieth‐century land management has altered the structure and composition of mixed‐conifer forests and decreased their resilience to fire, drought, and insects in many parts of the Interior West. These forests occur across a wide range of environmental settings and historical disturbance regimes, so their response to land management is likely to vary across landscapes and among ecoregions. However, this variation has not been well characterized and hampers the development of appropriate management and restoration plans. We identified mixed‐conifer types in central Oregon based on historical structure and composition, and successional trajectories following recent changes in land use, and evaluated how these types were distributed across environmental gradients. We used field data from 171 sites sampled across a range of environmental settings in two subregions: the eastern Cascades and the Ochoco Mountains.We identified four forest types in the eastern Cascades and four analogous ...

Trees, Forests and People, 2021

Wildland fires (WLF) have become more frequent, larger, and severe with greater impacts to societ... more Wildland fires (WLF) have become more frequent, larger, and severe with greater impacts to society and ecosystems and dramatic increases in firefighting costs. Forests throughout the range of ponderosa pine in Oregon and Washington are jeopardized by the interaction of anomalously dense forest structure, a warming and drying climate, and an expanding human population. These forests evolved with frequent interacting disturbances including low-severity surface fires, droughts, and biological disturbance agents (BDAs). Chronic low-severity disturbances were, and still are, critical to maintaining disturbance resistance, the property of an ecosystem to withstand disturbance while maintaining its structure and ecological function. Restoration of that historical resistance offers multiple social and ecological benefits. Moving forward, we need a shared understanding of the ecology of ponderosa pine forests to appreciate how restoring resistance can reduce the impacts of disturbances. Given contemporary forest conditions, a warming climate, and growing human populations, we predict continued elevation of tree mortality from drought, BDAs, and the large high-severity WLFs that threaten lives and property as well as ecosystem functions and services. We recommend more comprehensive planning to promote greater use of prescribed fire and management of reported fires for ecological benefits, plus increased responsibility and preparedness of local agencies, communities and individual homeowners for WLF and smoke events. Ultimately, by more effectively preparing for fire in the wildland urban interface, and by increasing the resistance of ponderosa pine forests, we can greatly enhance our ability to live with fire and other disturbances.