Shawn Fraver

Shawn Fraver
University of Maine | UM · School of Forest Resources

PhD

About

143
Publications
30,978
Reads
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5,230
Citations
Citations since 2016
64 Research Items
3580 Citations
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20162017201820192020202120220100200300400500600
20162017201820192020202120220100200300400500600
Introduction
Shawn Fraver currently works at the School of Forest Resources , University of Maine. Shawn does research in Botany and Ecology.

Publications

Publications (143)
Article
Understanding the forest carbon cycle has become increasingly important as carbon dioxide (CO2) emissions contribute to the changing climate. Decomposition is a major component of the forest carbon cycle; however, aspects of wood decomposition remain poorly understood, especially for stumps. To fill this knowledge gap, we examined the change in CO2...
Article
Black ash (Fraxinus nigra Marsh.) forests of north-central North America are currently threatened by the non-native emerald ash borer (Agrilus planipennis, EAB). Despite the wide distribution of F. nigra ecosystems, and the concern over EAB impact, little is known about their structure and natural stand dynamics. We sampled six old-growth F. nigra...
Article
Deadwood moisture plays a major role in regulating deadwood decomposition rates and may also affect forest microclimate. Despite this, the temporal variability of deadwood moisture at 15‐minute time scales remains relatively unknown because techniques for using high‐frequency sensors for tracking moisture at appropriate spatial and temporal intensi...
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Linking biometric measurements of stand-level biomass growth to tower-based measurements of carbon uptake—gross primary productivity and net ecosystem productivity—has been the focus of numerous ecosystem-level studies aimed to better understand the factors regulating carbon allocation to slow-turnover wood biomass pools. However, few of these stud...
Article
Multi-year drought and climate change can impact tree growth, especially in California’s Mediterranean climate where growing season rainfall is limited or absent. Active forest restoration has the potential to mitigate climate impacts by reducing stand density and conversion towards more resilient species composition. We used dendrochronology metho...
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Citation: Ayrey, E.; Hayes, D.J.; Kilbride, J.B.; Fraver, S.; Kershaw, J.A., Jr.; Cook, B.D.; Weiskittel, A.R. Synthesizing Disparate LiDAR and Satellite Datasets through Deep Learning to Generate Wall-to-Wall Abstract: Light detection and ranging (LiDAR) has become a commonly-used tool for generating remotely-sensed forest inventories. However, Li...
Article
Throughout much of its range, northern white-cedar (Thuja occidentalis L., hereafter cedar) has experienced a bottleneck in recruitment: cedar seedlings are often abundant in these stands, particularly in lowland settings, yet cedar sapling densities are quite low, leading to concerns that cedar canopy trees are not being replaced. Several barriers...
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Due to global change, temperate forests are expected to face growing threats to forest health (e.g. insects/disease) and increasing probabilities of severe disturbances (e.g. wildfires), which may result in amplified tree mortality against a backdrop of a changing climate and associated ecosystem/atmospheric feedbacks (i.e. increased rates of dead...
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A long‐standing goal of ecology has been to understand the cycling of carbon in forests. This has taken on new urgency with the need to address a rapidly changing climate. Forests serve as long‐term stores for atmospheric CO2, but their continued ability to take up new carbon is dependent on future changes in climate and other factors such as age....
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The export of dissolved organic carbon (DOC) from a watershed is a key component of the terrestrial biosphere carbon cycle. There is a need to improve our understanding of how and by how much various environmental factors are driving the temporal patterns of DOC export in order to accurately model and evaluate terrestrial carbon storage and fluxes....
Article
The lateral flux of dissolved organic carbon (DOC) from soils to inland waters and ultimately to the ocean represents a fundamental component of the global carbon cycle. To estimate the DOC flux, we developed an empirical terrestrial-aquatic DOC fluxes model (TAF-DOC). TAF-DOC incorporates various environmental factors (e.g., meteorology, sulfur, a...
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Warming climate and resulting declines in seasonal snowpack have been associated with drought stress and tree mortality in seasonally snow‐covered watersheds worldwide. Meanwhile, increasing forest density has further exacerbated drought stress due to intensified tree‐tree competition. Using a uniquely detailed dataset of population‐level forest gr...
Article
Attributes of dead wood in forests, such as quantity, landscape position, and state of decay influence numerous ecosystem processes such as wildfire behavior, tree regeneration, and nutrient cycling. Attributes of dead wood that vary over sub-diurnal time steps, such as moisture, have not been routinely measured despite the profound effects they ha...
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Eastern white pine (Pinus strobus) is considered a signature species in eastern North America, particularly in New England. In recent years, however, white pine has experienced increased damage due to native pathogens that reduce the species' growth, productivity, and economic value. One disease of concern is Caliciopsis canker, caused by the funga...
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1. Increasing heat and aridity in coming decades is expected to negatively impact tree growth and threaten forest sustainability in dry areas. Maintaining low stand density has the potential to mitigate the negative effects of increasingly severe droughts by minimizing competitive intensity. 2. However, the direct impact of stand density on the gro...
Article
Carbon (C) storage and accumulation in forests is of growing importance as climate change focuses our attention on rising greenhouse gas emissions. In 2012, we measured total ecosystem C pools (including live vegetation, dead wood, and soils) in two unmanaged, mixed-species stands in central Maine, USA. The stands are adjacent to one another and se...
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In July 2013, an EF1 tornado and straight line winds caused extensive forest damage in the Scientific Forest Management Area of Baxter State Park in northern Maine, USA. Subsequent salvage operations removed damaged trees from some areas, while leaving blowdown in other areas. Undisturbed control, blowdown, and blowdown + salvage (hereafter, salvag...
Article
Individual tree growth and mortality drive forest stand dynamics and are universally important metrics of tree success. Studying factors that affect growth and mortality is particularly challenging in mixed-species, uneven-aged systems due to their defining heterogeneity and strong temporal and spatial variability. The goal of this study was to det...
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Climate change is resulting in shifts in species’ ranges as species inhabit new climatically suitable areas. A key factor affecting range‐shifts is the interaction with predators. Small mammals, being primary seed predators and dispersers in forest ecosystems, may play a major role in determining which plant species will successfully expand and the...
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The authors developed a series of ecological metrics (EM) based on mechanistic principles for quantifying light detection and ranging (LiDAR) to develop forest inventories. These fall into 5 categories: canopy height, canopy complexity, individual tree attributes, crowding, and abiotic. The authors compared the effectiveness of the EMs with more tr...
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The quantity and condition of downed dead wood (DDW) is emerging as a major factor governing forest ecosystem processes such as carbon cycling, fire behavior, and tree regeneration. Despite this, systematic inventories of DDW are sparse if not absent across major forest biomes. The Forest Inventory and Analysis program of the United States (US) For...
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Fires play an important role in the terrestrial biosphere carbon cycle, not only through direct carbon release but also contributing to a potential long‐term storage as pyrogenic carbon (PyC). PyC is formed through fires, and because it may resist further biological and chemical degradation, is more stable in soil and sediment than original biomass...
Chapter
Our understanding of disturbance dynamics of old-growth forest ecosystems in eastern North America has expanded significantly over the past several decades. This expansion has largely stemmed from an active period of discovery of remnant old-growth stands across the region beginning in the late 1980s (Davis 1996; Tyrrell et al. 1998) and parallel d...
Article
Accurate downed woody debris (DWD) volume or mass estimates are needed for numerous applications such as fuel loading, forest carbon, and biodiversity/habitat assessments. The line-intersect sampling (LIS) method of inventorying DWD is widely used in forest inventories and ecological studies because it is time-efficient and unbiased. Despite its wi...
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Downed coarse woody debris, also known as coarse woody detritus or downed dead wood, is challenging to estimate for many reasons, including irregular shapes, multiple stages of decay, and the difficulty of identifying species. In addition, some properties are commonly not measured, such as wood density and carbon concentration. As a result, there h...
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Increasing evidence indicates that forest disturbances are changing in response to global change, yet local variability in disturbance remains high. We quantified this considerable variability and analyzed whether recent disturbance episodes around the globe were consistently driven by climate, and if human influence modulates patterns of forest di...
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The retrospective study of abrupt and sustained increases in the radial growth of trees (hereinafter 'releases') by tree-ring analysis is an approach widely used for reconstructing past forest disturbances. Despite the range of dendrochronological methods used for release-detection, a lack of in-depth comparison between them can lead researchers to...
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The world’s forests sequester and store vast amounts of atmospheric carbon, playing a crucial role in climate change mitigation. Internal stem decay in living trees results in the release of stored carbon back into the atmosphere, constituting an important, but poorly understood, countervailing force to carbon sequestration. The contribution of int...
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Extended rotations have been suggested as a strategy for balancing timber production and ecological objectives. By lengthening the period of stand development, extended rotations may increase tree size inequality and other elements of structural complexity, thus reducing the disparity between managed and old-growth stands. A potential limitation of...
Article
Gradient studies of wetland forests have inferred that competition from upland tree species confines waterlogging-tolerant tree species to hydric environments. Little is known, however, about competition effects on individual-tree growth along stress gradients in wetland forests. We investigated tree growth and competition in mixed-species stands r...
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Forestry practitioners often need to identify old-growth stands because of their high conservation value. To identify the structural and compositional characteristics potentially unique to old-growth northern white-cedar (Thuja occidentalis L.) stands, we compared 16 old-growth stands and 17 partially harvested stands in Maine, USA and New Brunswic...
Article
Wind disturbance generates heterogeneous microsite structures, including downed logs, windthrow mounds, and pits. While these structures can provide opportunities for regeneration of certain tree species, the long-term influence of microsites and microsite heterogeneity on forest development has not been quantified. We used long-term measurements o...
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Wildfires, insect outbreaks, and windstorms are increasingly common forest disturbances. Post-disturbance management often involves salvage logging, i.e. the felling and removal of the affected trees. However, this practice may represent an additional disturbance with effects on ecosystem processes and services. We developed a systematic map to pro...
Article
The conic-paraboloid volume equation is receiving increased use with downed coarse woody material (CWM), but the consequences for taper have not been identified mathematically. Requiring that subdivision of a conic-paraboloid yields two smaller conic-paraboloids leads to an exact taper equation intermediate between those of cones and second-order p...
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A range of environmental factors regulate tree growth; however, climate is generally thought to most strongly influence year-to-year variability in growth. Numerous dendrochronological (tree-ring) studies have identified climate factors that influence year-to-year variability in growth for given tree species and location. However, traditional dendr...
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Determining the drivers of shifting forest disturbance rates remains a pressing global change issue. Large-scale forest dynamics are commonly assumed to be climate driven, but appropriately scaled disturbance histories are rarely available to assess how disturbance legacies alter subsequent disturbance rates and the climate sensitivity of disturban...
Chapter
Coarse woody debris plays a crucial role in forest ecosystems. The current amount of woody debris on a given site represents a balance between additions (tree mortality) and depletions (wood decomposition, combustion, transport). Understanding woody debris dynamics has recently gained much attention, primarily because of the need to improve forest...
Article
Dead woody material (DWM) plays numerous important roles in forest ecosystems; however, through the process of decomposition, it undergoes structural and chemical changes that progressively alter its function in these roles. Much remains unknown about how DWM mechanical strength and structural integrity change through decomposition in natural fores...
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As Light Detection and Ranging (LiDAR) technology advances, it has become common for datasets to be acquired at a point density high enough to capture structural information from individual trees. To process these data, an automatic method of isolating individual trees from a LiDAR point cloud is required. Traditional methods for segmenting trees a...
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Black ash ( Fraxinus nigra Marsh.) plays a central role in several Native American teachings (including a Wabanaki creation story) and has long been used for basketry, yet relatively little is known about the species' ecology. The recent and ongoing invasion of emerald ash borer ( Agrilus planipennis Fairmaire), an invasive beetle killing millions...
Article
This study investigated the growth response of mature, isolated reserve trees (n = 528) in two multiaged silvicultural systems in the Acadian Forest Ecosystem Research Project (AFERP). Absolute and percent increases in basal area increment (BAI; cm²·year⁻¹) were assessed for the five predominant reserve tree species in AFERP: Acer rubrum L., Picea...
Article
Eddy covariance methodologies have greatly improved our understanding of the forest carbon cycle, including controls over year-to-year variability in productivity (measured as net ecosystem productivity, NEP, where NEP is the difference between the mass of carbon fixed by photosynthesis and that lost by ecosystem respiration). However, establishing...
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Forests around the world are experiencing increasingly severe droughts and elevated competitive intensity due to increased tree density. However, the influence of interactions between drought and competition on forest growth remains poorly understood. Using a unique dataset of stand-scale dendrochronology sampled from 6405 trees, we quantified how...
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Understanding forest structural changes resulting from postdisturbance management practices such as salvage logging is critical for predicting forest recovery and developing appropriate management strategies. In 2013, a tornado and subsequent salvage operations in northern Maine, USA, created three conditions (i.e., treatments) with contrasting for...
Article
Forest fires cause large emissions of C (carbon), N (nitrogen) and Hg (mercury) to the atmosphere and thus have important implications for global warming (e.g. via CO2 and N2O emissions), anthropogenic fertilisation of natural ecosystems (e.g. via N deposition), and bioaccumulation of harmful metals in aquatic and terrestrial systems (e.g. via Hg d...
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Climate models predict increasing drought intensity and frequency for many regions, which may have negative consequences for tree recruitment, growth, and mortality, as well as forest ecosystem services. Furthermore, practical strategies for minimizing vulnerability to drought are limited. Tree population density, a metric of tree abundance in a gi...
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Quesions: What were the long-term disturbance rates (including variability) and agents in pristine Norway spruce-dominated (Picea abies (L.) Karst.) forests? Have soil moisture conditions influenced disturbance rates across this boreal spruce-dominated forest? Were the temporal recruitment patterns of canopy dominants associated with past disturban...
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Developing strategies for reducing atmospheric CO2 is one of the foremost challenges facing natural resource professionals today. The goal of this study was to evaluate total ecosystem and harvested wood product carbon (C) stocks among alternative forest management treatments (selection cutting, shelterwood cutting, commercial clearcutting, and no...
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Resource availability and its influence on tree-to-tree interactions are expected to change over the course of forest stand development, but the rarity of long-term datasets has limited examinations of neighborhood crowding over extended time periods. How do a history of neighborhood interactions and population-level dynamics, including demographic...
Article
Dead wood pools are strongly influenced by natural disturbance events, stand development processes, and forest management activities. However, the relative importance of these influences can vary over time. In this study, we evaluate the role of these factors on dead wood biomass pools across several forest management alternatives after 60 years of...
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Empirical knowledge of forest structure and development in early successional and range-margin populations is often lacking, limiting our ability to effectively model and manage these forests. Such is the case for jack pine (Pinus banksiana Lamb.) in central Minnesota, USA, where it reaches its southwestern range limit. Our objective was to quantif...