Search

We tested the effects of phosphorus (P) fertilization and soil water on the growth, physiology, and total nitrogen (N) accumulation in N-fixing Scotch broom in Olympia, WA. We manipulated soil water and P availability via irrigation and fertilization, respectively, in a completely randomized 2 × 2 factorial on potted one-year old Scotch broom seedlings (n = 20) in an N-deficient sand. There was substantial evidence that increased-irrigation and P-fertilization had similar positive effects on N accumulation in Scotch broom approximately equally. High-irrigation rates were more often associated with positive physiological and growth responses in Scotch broom than fertilization, however. Although the irrigation × fertilization interaction was not significant, there were additive effects of high-irrigation and fertilization on biomass and N content as both were 50% greater in the fertilized-and-high-irrigation treatment relative to the respective fertilized and high-irrigation treatments. We noted an accumulation of N and P in the plant tissues. Analyses indicated a pattern of decreasing function and growth with increasing N and P concentrations in Scotch broom biomass, suggesting plant growth and physiology were limited by some other resource. Total plant N content values ranged from 7.0 ± 1.1 g plant−1 in the control and 23.4 g ± 9.0 plant−1 in the fertilized-and-high-irrigation treatment. Extrapolated to typical densities of comparably sized Scotch broom plants on invaded sites in the western Pacific Northwest, these findings suggest that, at least, 12–65 kg N ha−1 would be found in Scotch broom plants in the field.

Emerald ash borer (EAB; Agrilus planipennis Fairmaire, 1888) has been a persistent disturbance for ash forests in the United States since 2002. Of particular concern is the impact that EAB will have on the ecosystem functioning of wetlands dominated by black ash (Fraxinus nigra Marsh.). In preparation, forest managers need reliable and complete maps of black ash dominated stands. Traditionally, forest survey data from the United States Forest Inventory and Analysis (FIA) Program have provided rigorous measures of tree species at large spatial extents but are limited when providing estimates for smaller management units (e.g., stands). Fortunately, geospatial data can extend forest survey information by generating predictions of forest attributes at scales finer than those of the FIA sampling grid. In this study, geospatial data were integrated with FIA data in a randomForest model to estimate and map black ash dominated stands in northern Minnesota in the United States. The model produced low error rates (overall error = 14.5%; area under the curve (AUC) = 0.92) and was strongly informed by predictors from soil saturation and phenology. These results improve upon FIA-based spatial estimates at national extents by providing forest managers with accurate, fine-scale maps (30 m spatial resolution) of black ash stand dominance that could ultimately support landscape-level EAB risk and vulnerability assessments.

The frequency and severity of wind storms, such as hurricanes and tornados, are expected to increase in northeastern North America under climate change. As such, salvage logging is likely to become a more frequently-used post-disturbance management strategy; however, there is concern that the compound disturbance of wind followed by salvage logging could generate negative impacts on species composition, forest structure, and ecological resilience. These impacts are variable and uncertain, posing an opportunity for further research that considers differences in forest recovery following stand-replacing wind alone versus stand-replacing wind and salvage logging. We evaluated the short-term impacts of these singular (tornado) and interactive disturbance events (tornado + salvage logging) on the structure, composition, and function of a mature hemlock-hardwood forest in south-central Massachusetts. Specifically, we were interested in quantifying the impacts of salvage logging practices on forest recovery and resilience. Our analyses consider salvage logging impacts on forest overstory in addition to the regeneration layer (defined here as tree seedlings and saplings that make up the forest understory). We found that (i) delayed overstory mortality was highest on tornado-damaged sites, contributing additional material to dead wood pools, while salvaged sites lacked much of this material and associated structural legacies; (ii) tree regeneration layer diversity, as measured by Shannon’s Index, was higher in the tornado-damaged sites than salvaged sites, but levels of sapling (≥1.4 m in height and

Northern hardwood stands in the Great Lakes region are often managed using single-tree selection, which generally favors regeneration of shade-tolerant species, especially sugar maple (Acer sacchar...

Variable retention harvesting (VRH) systems have gained wide use in many different forest types across the globe, but largely have been implemented in forests characterized by severe, infrequent disturbance regimes. There has been less attention given to developing VRH approaches in forests that are characterized as having a mixed-severity disturbance regime that often results in only partial mortality of canopy trees in spatially heterogeneous patterns. One example of such a forest type is red pine (Pinus resinosa Ait.)-dominated ecosystem of the western Great Lakes region of North America. The purpose of this review is to provide a conceptual foundation for developing VRH approaches in red pine ecosystems that are based on a mixed-severity disturbance regime. Our contention is that red pine forests managed following a natural model are more resilient to disturbances and external threats such as climate change. For the red pine ecosystem, VRH application should reflect the often severe, but partial canopy removal from natural disturbance that is characteristic of this ecosystem and that results in more than trivial numbers of surviving overstory trees across a range of spatial configurations in regenerating stands. Retained live trees should span a range of diameters, but favor the larger end of the diameter distribution, as this reflects the likely pattern of survival after natural disturbance and is often a key structural element lacking from managed areas. VRH should be applied in ways that vary the spatial pattern of legacy trees in and among stands, but largely in ways that reflect the pattern of spatially patchy canopy structure, with large openings surrounded by a less disturbed matrix, as occurs with a natural disturbance regime. Legacy trees and deadwood structures should reflect the composition of the pre-disturbance forest, including species in addition to dominant red pine. Finally, retained structures should be viewed as dynamic entities that grow, die, and decay and that need to be documented and accounted for over time. While more organizations are incorporating some form of VRH into policy and practice for red pine-dominated ecosystems, this application is not always based on a comprehensive understanding of the actual natural model of development, which reflects a mixed-severity disturbance regime. Our goal is to review the ecological evidence for this disturbance regime and interpret the structural and compositional outcomes of the disturbance model, so as to advance VRH approaches that better emulate the actual disturbance and development model for this regionally important ecosystem.

Southern pine beetle (SPB; Dendroctonus frontalis Zimmerman), a native insect that has historically affected pine (Pinus spp.) ecosystems in the southeastern U.S., has recently expanded northward causing extensive tree mortality in pitch pine (P. rigida) and pitch pine-oak (Quercus spp.) forests of eastern Long Island, NY. Given the historic lack of SPB within this region, little is known regarding its potential impacts. This study examined the immediate effects of SPB-induced tree mortality and management (i.e., cut-and leave suppression) on the structure and composition of affected forest communities to inform management recommendations and projections of future forest conditions. Overstory pine basal area declined significantly following SPB infestation and management (67–100% mortality), although management partly mitigated these effects. There was no immediate impact of SPB or management on seedling and sapling density or composition, with hardwood species making up the majority of this layer and pine representing

Ecological forestry is a management approach that uses natural disturbance processes as models for designing silvicultural prescriptions that restore or sustain ecosystem biodiversity and function in actively managed forests. We evaluated how a novel ecologically-based multi-cohort silvicultural treatment affects the soil microbial community (SMC) and tested whether supplemental dead wood in the form of girdled trees alters these effects. We also tested SMC function by measuring soil CO2 flux over multiple growing seasons, and examined if these patterns were related to soil microbial groups. Our experimental harvests were conducted in second-growth northern hardwood forests in northern Wisconsin, USA. Treatments included a modified shelterwood harvest (SH), a shelterwood harvest plus dead wood supplementation (SH + CWD), and an unharvested control; here we report responses three to five years post-treatment. The SMC composition (determined using PLFA) in both harvests was significantly different from the control, a difference driven by greater bacterial abundance in the harvested areas, and particularly by gram negative bacteria in SH. Microbial community composition was not significantly different between the two harvests (SH and SH + CWD). Total soil respiration was significantly lower in SH than in the control and SH + CWD treatments, a difference most likely driven by a reduction of the autotrophic respiration component in SH treatments due to harvesting, while in the SH + CWD treatment roots from living girdled trees contributed to autotrophic soil respiration. The relationship between the SMC and soil respiration varied with treatment and season. In general, soil respiration in the unharvested controls was most significantly correlated with microbes that relate to autotrophic respiration sources, while respiration in SH + CWD was most significantly correlated with heterotrophic microbes. These results indicate that, although the SMC composition was affected by forest harvesting practices incorporating live and dead biological legacies, supplementing the number of standing dead trees through girdling and felling maintained SMC function, as measured through total soil respiration, an indicator of some important aspects of ecosystem function.

Securing desirable forest regeneration outcomes is an essential component of sustainable forest management. When natural reproduction is preferred over planting, achieving desirable outcomes may be the principal challenge for forest managers, as reports of struggles and even failures are common across many regions and forest ecosystems. Informing managers and policymakers of the prospects of regeneration success before practices and policies are implemented promotes long-term sustainability because rehabilitating undesirable regeneration outcomes is often lengthy, expensive, and uncertain. In 2012, the USDA Forest Service, Northern Research Station, Forest Inventory and Analysis program implemented Regeneration Indicator (RI) protocols that added detailed seedling measurements and browse impact assessments to a subsample of inventory plots across 24 states in the northern United States. The goal of this expanded sampling effort is to improve the ability to monitor broad scale regeneration trends and better inform forest management planning and policy. Modeling probable regeneration outcomes is difficult and the rarity of vetted models that can fully utilize RI inventory data highlights an immediate need for flexible methods to evaluate regeneration of different taxa at large scales. This manuscript is premised on estimation of a tree seedling mortality budget for inventoried reproduction. The method offers a transparent structure for leveraging existing literature and expert knowledge to gain provisional insight into plausible regeneration outcomes. The resulting tool provides flexibility for users to examine regeneration for multiple species, site conditions, and user-defined quantitative regeneration objectives. The approach is demonstrated by applying a suite of multispecies regeneration objectives to RI data for two case studies with different forest composition and geographic scales, the Ozark Highland Ecological Section (OHES) and the Monongahela National Forest (MNF). Within the Quercus/Carya dominated OHES, analyses indicate that desirable regeneration outcomes are more likely than not based on current plot conditions. Regeneration events were projected to produce new fully stocked forests on 76% of OHES plots, produce a sizable component of characteristic overstory species on 57%, and produce a sizable component of commercially important species on 59%. Within the Acer/Fagus/Betula and Quercus/Carya forests of the MNF, analyses indicated that difficulties in achieving desirable regeneration outcomes were likely. Only 36% of MNF plots were projected to produce new fully stocked forests following a regeneration event and only 29% were projected to regenerate a sizable component of either characteristic overstory species or commercially important species.

Black ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non-forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site-dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high-resolution (1-cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB-induced ash mortality, compared to wetter sites where open water evaporation and shallow-rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts. Department of Interior Northeast Climate Adaptation Science Center; Minnesota Environmental and Natural Resources Trust Fund; Minnesota Forest Resources Council; USDA Forest Service Northern Research StationUnited States Department of Agriculture (USDA)United States Forest Service Published version Department of Interior Northeast Climate Adaptation Science Center; Minnesota Environmental and Natural Resources Trust Fund; Minnesota Forest Resources Council; USDA Forest Service Northern Research Station Public domain – authored by a U.S. government employee

Scotch broom is an aggressive invasive species of major concern in coast Douglas-fir forests of the Pacific Northwest USA. Control efforts are common, but potential for ecosystem recovery following Scotch broom removal is unclear. We assessed the potential for ecosystem recovery following broom removal at two sites that contrasted strongly in soil quality (i.e., texture and nutrient pool size) in western Washington and Oregon. Comparisons were made among replicated plots where Scotch broom was never present (uninvaded), retained, or removed. Microclimate (photosynthetically active radiation (PAR), soil temperature and moisture), soil properties, and vegetation were monitored during 2013 to 2017. Scotch broom removal increased PAR and soil temperature at both sites but had limited effects on soil moisture. Concentrations of Ca, Mg, K, and P were significantly lower with Scotch broom removal compared to the uninvaded and retained treatments, with the effect being most pronounced at the low-quality site. NMS ordinations indicated that the treatments differed in vegetation composition, with limited evidence for recovery in the removal treatment. Nonnative and native species varied inversely in their abundance responses, where nonnative species abundance was greatest in the removal treatment, intermediate in the retained treatment, and lowest in the uninvaded treatment, indicating occurrence of a secondary invasion following removal. As with the soil response, effects were more pronounced at the low-quality site. Our findings indicate that Scotch broom removal exacerbates negative effects on soil and plant communities, with little evidence of ecosystem recovery over our study period. These findings highlight the importance of controlling Scotch broom invasions immediately after the species establishes, especially at low-quality sites that are more susceptible to Scotch broom invasion and negative legacy effects.

Recovery of ecosystem properties following removal of invasive plants likely varies with characteristics of the plant and the relative soil quality at a given site. These factors may influence the occurrence of soil legacies and secondary invasions, hindering the effectiveness of restoration strategies. We assessed the potential for ecosystem recovery following removal of N-fixing Scotch broom for 4 years at two sites that contrasted strongly in soil quality in western Washington and Oregon, USA. Comparisons were made among plots, where Scotch broom was never present (uninvaded), retained, or removed. Scotch broom removal increased PAR and soil temperature but had limited effects on soil moisture. Concentrations of soil Ca, Mg, K, and P were significantly lower with Scotch broom removal, with the effect being most pronounced at the low-quality site. NMS ordinations indicated that the treatments differed in vegetation composition, with limited recovery following broom removal. Non-native and native species varied inversely in their abundance responses, where non-native species abundance was greatest in the removal treatment, intermediate in the retained treatment, and lowest in the uninvaded treatment, indicating occurrence of a secondary invasion following removal. As with the soil response, effects were more pronounced at the low-quality site. Our findings indicate that Scotch broom removal exacerbates negative effects on soil chemistry and plant communities, with little evidence of recovery over our study period. These findings highlight the importance of controlling Scotch broom invasions immediately after the species establishes, especially on low-quality sites that are more susceptible to Scotch broom invasion.

Mixed-species forests are, or were, a common feature of most forested regions around the globe (Bauhus et al. 2017b). The ecology and silviculture of these systems has been a consistent area of study given the potential benefits of mixed-species forests in relation to minimizing forest health and climate change impacts (Bauhus et al. 2017a) and the occasional higher levels of productivity observed for species mixtures relative to single-species stands (Lu et al. 2016). Nevertheless, the restoration and maintenance of mixed-species forests remains a significant challenge given the complexities of developing silvicultural systems that accommodate a range of silvical traits and resource requirements, particularly where historic land use and current stressors limit recruitment opportunities for constituent species (Pach et al. 2018).

In recent decades, a paradigm shift in forest management and associated policies has led to greater emphasis on harvest practices that retain mature, overstory trees in forest stands that would otherwise be clear-cut. While it is often assumed that the maintenance of compositional and structural complexity, such as that achieved through retention forestry approaches, will also mitigate negative impacts to functional diversity, empirical evidence of this relationship is sparse. We examined the effects of an aggregated retention system on taxonomic and functional diversity in a regenerating aspen-dominated forest. Sampling was conducted along transects arranged to capture the transition from harvested (regenerating) forest to mature, unharvested forest (both intact forest stands and 0.1 ha retention aggregates). We then assessed the magnitude and distance of edge effects on multiple indices of taxonomic and functional diversity as well as functional identity. Twelve years after harvest, the distance and magnitude of edge effects on functional and taxonomic diversity did not differ between the two unharvested patch sizes (intact vs. aggregate); however, intact forest exhibited greater resistance to edge effects and greater depth of edge influence into harvested areas for some traits compared to aggregates. Analyses relying on functional traits were generally applicable across sites within a highly variable forest type, and our results demonstrate the promise of using functional traits to assess management impacts on plant diversity across a landscape. Aggregates maintained some functional attributes associated with interior forest and influenced adjacent regeneration. However, trends in some traits (i.e., shade tolerance and seed mass), particularly in the seedling layer, suggest aggregates of this size provide primarily edge habitat.

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 data set of population-level forest growth (n = 2,495 sampled trees), we examined how inter-annual variability in growth relates to snow volume across a range of forest densities (e.g., competitive environments) in sites spanning a broad aridity gradient across the United States. Forest growth was positively related to snowpack in water-limited forests located at low latitude, and this relationship was intensified by forest density. However, forest growth was negatively related to snowpack in a higher latitude more energy-limited forest, and this relationship did not interact with forest density. Future reductions in snowpack may have contrasting consequences, as growth may respond positively in energy-limited forests and negatively in water-limited forests; however, these declines may be mitigated by reducing stand density through forest thinning.

The monitoring of tree range dynamics has emerged as an important component of adaptive responses of forest management to global change scenarios such as extreme precipitation events and/or invasive species. Comparisons between the locations of adults versus seedlings of individual tree species using contemporary forest inventories is one tool widely used to assess the status of tree ranges in light of these changing conditions. With the consistent remeasurement of standard forest inventory plots across the entire eastern US occurring since the 2000s, the opportunity exists to evaluate the stability of tree ranges of focal species across a decade. Using said inventory, the northern range margins of tree distributions were examined by comparing differences (Holm-Sidak adjusted p-value = 0.2) in the 95th percentile locations of seedlings to adults (i.e., trees) by 0.5 degree longitudinal bands over nearly 10 years and by categories of canopy disturbance (i.e., canopy gap formation) for 20 study species. Our results suggest that range margins are stable for 85% of study species at both time one and at remeasurement regardless of canopy disturbance. For the very few species that had a significant difference in seedlings and adults at their range margins, there was nearly a 0.4 degree difference in latitude with seedlings being farther south irrespective of disturbance. Our findings of tree range stability across forests of the eastern US indicate a general propensity towards range contraction, especially for study species forecasted to lose range and located on disturbed sites, which may present substantial hurdles for adaptive management strategies focused on maintaining and enhancing forest ecosystem resilience in the context of global change and associated rapid climate change.

Background 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 widespread use, the appropriate transect length needed to achieve a desired precision at a particular location has received relatively little attention. Methods We conducted intensive LIS sampling at 33 locations representing eight mature or old-growth forest types in northeastern USA, providing a range of forest conditions and DWD volumes (from 17 to 323 m3∙ha− 1). We used these empirical field data to test, through simulations, the effect of increasing transect length (up to 340 m at each location) on precision of associated LIS volume estimates. Importantly, we used a novel application of copula models to account for within-transect spatial autocorrelation of DWD volumes during our simulations, thereby properly addressing variance estimates. Results As expected, precision consistently improved with increasing cumulative transect length, and locations with lower DWD volumes required longer transects to achieve a given level of precision. We developed models relating precision, transect length, and DWD volume that allows us to gauge a suitable LIS transect length for desired precision levels. Conclusions LIS provides an attractive method for estimating DWD volume for a given localized area of interest. For the forest types sampled here, and for the particular copula model framework employed, transect lengths of ca. 120 m provide a reasonable level of precision, ranging from 18% to 60% coefficients of variation.

Scotch broom [Cytisus scoparius (L.) Link] is a globally important nitrogen (N)-fixing invasive plant species that has potential to alter soil water dynamics, soil chemistry, and plant communities. We evaluated the effects of Scotch broom on soil moisture, soil chemistry, soil temperature, photosynthetically active radiation (PAR), and vegetation communities over 4years at a site recently harvested for timber. Treatments of Scotch broom (either present via planting or absent) and background vegetation (either present or absent via herbicide treatments) were applied to 4m(2) plots. Background vegetation was associated with the greatest decrease of soil water content (SWC) among treatments. During the driest year, Scotch broom showed some evidence of increased early-and late-season soil water usage, and, briefly, a high usage relative to background vegetation plots. On a percent cover basis, Scotch broom had a substantially greater negative influence on SWC than did background vegetation. Surprisingly, Scotch broom was not consistently associated with increases in total soil N, but there was evidence of increasing soil water N when Scotch broom was present. Scotch broom-only plots had greater concentrations of soil water magnesium (Mg2+) and calcium (Ca2+) than other treatments. On a percent cover basis, Scotch broom had a uniquely high demand for potassium (K+) relative to the background vegetation. Average soil temperature was slightly greater, and soil surface PAR lower, with Scotch broom present. Scotch broom-absent plots increased in species diversity and richness over time, while Scotch broom-present plots remained unchanged. Scotch broom presence was associated with an increase in cover of nonnative sweet vernalgrass (Anthoxanthum odoratum L.). Scotch broom generated positive feedbacks with resource conditions that favored its dominance and the establishment of nonnative grass. USDA National Institute for Food and Agriculture [GRANT 11325729] Financial support for this research was provided by the USDA National Institute for Food and Agriculture (Grants.gov number: GRANT 11325729). We wish to thank Green Diamond Resource Company for use of their land and logistical support. We would like to thank James Dollins for all of his efforts on this project. Public domain – authored by a U.S. government employee

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 representing a waterlogging stress gradient in Fraxinus nigra Marsh. (black ash) forests in Minnesota, USA. Using competition indices, we examined how F. nigra basal area increment (BAI) responded to competition along the gradient and whether competition was size-asymmetric (as for light) or size-symmetric (as for soil resources). We modeled spatial distributions of F. nigra and associated tree species to assess how variation in species mixtures influenced competition. We found that although F. nigra BAI did not significantly differ with variations in site moisture, the importance of competition decreased as waterlogging stress increased. Competition across the gradient was primarily size-asymmetric (for light). Variation in species mixtures along the gradient was an important influence on competition. Some segregation of tree species occurred at all but the most upland site, where waterlogging stress was lowest and evidence of competition was greatest, confirming that competition from upland tree species confines F. nigra and potentially other waterlogging-tolerant species to hydric environments.

Estimating the current status and future trends of carbon (C) stocks and stock changes in forests of the northeastern United States is desired by policy makers and managers as these forests can mitigate climate change through sequestration of atmospheric carbon dioxide (CO2). We developed C flux matrix models using tree and stand variables by tree diameter class and stand age class to compare size-structured models with age-structured models in their capacity to predict forest C dynamics that are central to policy decisions. The primary control variables for the C flux matrix models (diameter at breast height, stand basal area, stem density, and stand age) were all statistically significant at the α ≤ 0.05 level. Through comparing the simulation results and root mean square error of C flux matrix models by tree diameter class and stand age class, we found that tree diameter class more accurately predicted C stock change status across the broad compositional and structural conditions in the spatial and temporal domain. An uncertainty analysis revealed that predictions of aboveground C and soil C would be distinctively different whether using tree diameter class or stand age class with high certainty. Overall, this work may enable better integration of forest inventory data and remotely sensed data for the purpose of strategic-scale forest C dynamic simulations.

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 disturbance. We combined remote sensing data on recent (2001–2014) disturbances with in-depth local information for 50 protected landscapes and their surroundings across the temperate biome. Disturbance patterns are highly variable, and shaped by variation in disturbance agents and traits of prevailing tree species. However, high disturbance activity is consistently linked to warmer and drier than average conditions across the globe. Disturbances in protected areas are smaller and more complex in shape compared to their surroundings affected by human land use. This signal disappears in areas with high recent natural disturbance activity, underlining the potential of climate-mediated disturbance to transform forest landscapes., Climate change may impact forest disturbances, though local variability is high. Here, Sommerfeld et al. show that disturbance patterns across the temperate biome vary with agents and tree traits, yet large disturbances are consistently linked to warmer and drier than average conditions.

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 extended rotations is the tradeoff between reduced stand-level productivity and greater large-tree growth that typically occurs with stand age. The mechanisms driving this tradeoff have not been fully explored. To fill this knowledge gap, we investigated the size-growth relationship (SGR), tree spatial patterns, and tree-tree competition along an established 160-yr chronosequence of 19 single-cohort, unthinned red pine (Pinus resinosa) stands in northern Minnesota, USA. We analyzed SGR, a stand-level metric used to estimate the relative efficiency with which different sized trees utilize available resources, to assess how the relationship between tree size and growth changed over an extended period of stand development. We performed spatial analysis to examine whether tree spatial clustering, a criterion of structural complexity, increased with stand age. We modeled individual-tree biomass increment to test whether competition along the chronosequence was size-symmetric (access of individual trees to resources is directly proportional to size) or size-asymmetric (larger trees suppress the growth of smaller individuals by preempting resources), and how SGR, tree spatial patterns, and competition together influenced individual-tree growth. We found low SGR (i.e., disproportionately slow growth of larger trees compared to smaller trees) across the chronosequence, a finding that contrasts with hypothesized models of SGR during stand development but is consistent with previous research on pine-dominated systems. Tree spatial patterns trended towards clustering with stand age, indicating higher structural complexity over time. In agreement with our SGR findings, competition across the chronosequence was size-symmetric, suggesting that competition reduced individual-tree growth while maintaining relative size equality. Individual-tree biomass increment was strongly dependent on tree size, with the growth of small trees appearing relatively less affected by competition. Differences in SGR did not translate into individual-tree growth, and tree spatial clustering was associated with reduced growth, especially in larger trees. Our results indicate that disproportionately slow large-tree growth and size-symmetric competition throughout stand development may delay the emergence of stand structural complexity in extended rotation red pine stands. Silvicultural treatments may be required to promote stand structural complexity and increase large crop-tree growth.

In the past several decades, a trend in forestry and silviculture has been toward promoting complexity in forest ecosystems, but how complexity is conceived and described has shifted over time as new ideas and terminology have been introduced. Historically, ecologically-focused silviculture has focused largely on manipulation of structural complexity, but often with the functional role of features in mind. Recently there has been a shift toward viewing complexity in an “adaptive” or “resilience” context, with a focus on understanding forests as complex adaptive systems. As new concepts and terminology are introduced it will be essential that silviculture researchers understand their dissemination into silviculture research, experimental design, and treatment implementation. With this goal in mind we set out to better understand: (1) how complexity terminology and ideas have shifted over time in silviculture, (2) how different conceptions of complexity have been incorporated into silviculture experiments and treatments, and (3) how various complexity concepts are being reconciled with each other in practice. We conducted a multi-stage review of the silvicultural literature for the time period 1992–2017 that included: (1) a broad keyword analysis, (2) a detailed review of a narrower subset of publications, and (3) a thorough review of a set of silvicultural experiments that included a focus on complexity in their design. We also developed a set of case studies that illustrate shifts in complexity conceptions in silvicultural experiment design and analysis. Our analysis indicates considerable lags in incorporation of complexity-focused terminology and ideas into silvicultural research and experimental treatment design. Very few silviculture-focused studies have incorporated adaptive complexity concepts explicitly into design or analysis, even though these concepts were introduced nearly a decade ago and are widely discussed in the literature. However, in our case studies we document how silviculture experiments and research programs that were not designed explicitly around complexity concepts have begun to incorporate these ideas into analysis of treatment outcomes. Silviculture researchers should focus on reconciling conceptions of complexity through analysis of existing experiments and with modeling studies, as well as attempting to better understand mechanistic relationships among structural, functional, and adaptive conceptions of complexity.

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 of a formerly old-growth Tsuga canadensis – Pinus strobus forest severely damaged by a category 3 hurricane in 1938 to quantify the impact of microsite conditions on overstory composition and structure. We asked (i) “What are the patterns in live-tree size, growth, and mortality five and seven decades after disturbance?” and (ii) “What roles do microsite heterogeneity and the presence of disturbance-generated microsites play in long-term forest development following disturbance?” We compared live-tree (>2 cm DBH) development and survival to microsite heterogeneity at the 100 m2 scale. Microsite diversity was positively related to overstory species diversity and stem density and negatively related to average tree size. We propose that plots with higher microsite diversity may have experienced more severe local disturbance, which allowed more species and individuals to establish and created varied niches that allowed these individuals to coexist and generate greater stand-level diversity. These persistent relationships highlight how microsite conditions affect forest development after severe disturbances.

Disturbance events affect forest composition and structure across a range of spatial and temporal scales, and subsequent forest development may differ after natural, anthropogenic, or compound disturbances. Following large, natural disturbances, salvage logging is a common and often controversial management practice in many regions of the globe. Yet, while the short-term impacts of salvage logging have been studied in many systems, the long-term effects remain unclear. We capitalized on over eighty years of data following an old-growth Tsuga canadensis-Pinus strobus forest in southwestern New Hampshire, USA after the 1938 hurricane, which severely damaged forests across much of New England. To our knowledge, this study provides the longest evaluation of salvage logging impacts, and it highlights developmental trajectories for Tsuga canadensis-Pinus strobus forests under a variety of disturbance histories. Specifically, we examined development from an old-growth condition in 1930 through 2016 across three different disturbance histories: (1) clearcut logging prior to the 1938 hurricane with some subsequent damage by the hurricane (“logged”), (2) severe damage from the 1938 hurricane (“hurricane”), and (3) severe damage from the hurricane followed by salvage logging (“salvaged”). There were no differences in current overstory composition between the different disturbance histories, as most areas shifted strongly away from pre-hurricane composition through nearly complete elimination of P. strobus and corresponding increases in hardwoods (Betula and Acer spp.), while T. canadensis remained dominant. In contrast, eight decades later, structural characteristics remain distinct between logged, hurricane, and salvaged sites. Specifically, trees were larger in the logged and salvaged sites, and pit and mound structures were largest and most abundant in the hurricane site. Tree densities and coarse woody debris biomass was greater in the hurricane site than the logged sites, but not significantly different from salvaged sites. These findings underscore the long-term influence of salvage logging on forest development, indicating convergence in overstory composition over time between logged, salvaged, and non-salvaged areas, but persistent structural differences, especially in microtopographic structures and live tree development. Future salvage logging efforts should consider these impacts and provide a greater range of unsalvaged areas across the landscape to maintain important structural legacies over the long term.

Maximum stand density index (SDImax) is an important factor controlling stand dynamics that varies by species and region, but less is understood how it differs within a region for a given species. In this analysis, linear quantile mixed modeling (LQMM) and an extensive network of permanent plots were utilized to examine regional variation in the SDImax of 15 species (7 softwoods and 8 hardwoods) across the complex forests of the Acadian Region in North America. Observed plot-level SDImax was then linked to various stand, plant trait, site, and climatic factors and the spatial patterns throughout the region examined. Results indicated high variability of SDImax for a given species with northern hardwood species like yellow birch (Betula alleghaniensis Britt.), sugar maple (Acer saccharum Marsh.), and American beech (Fagus grandifolia Ehrh.) having the lowest values (555 – 627), while softwood species such as northern white cedar (Thuja occidentalis L.; 1014), eastern hemlock (Tsuga canadensis (L.) Carr.; 1026), and white pine (Pinus strobus L.; 967) had the highest values. Compared to the other stand and site factors examined, climate showed the strongest relationship with SDImax with R2 ranging from 82 to 98%. Of the climatic variables examined, those representing growing season length and the timing of precipitation were most influential. For the majority of the species examined, reductions in SDImax were forecasted due to changing climatic conditions. Across species, mean SDImax was found to linearly decline with wood specific gravity and increase with leaf longevity, but showed limited relationships with other species-level functional traits. Overall, the analysis highlights the strong variability of SDImax within and between species as well as the important role that climate has on this attribute within a region.

Prescribed fire is increasingly viewed as a valuable tool for reversing ecological consequences of fire suppression within fire-adapted forests. While the use of burning treatments in northern temperate conifer forests has received considerable attention, the long-term (>10 year) effects on understory composition and dynamics have not been quantified. We describe the persistence of prescribed fire effects on the woody and herbaceous understory in a mature red pine (Pinus resinosa Ait.) forest in northern Minnesota, USA, over a ∼50-year period, as well as the relative roles of fire season and frequency in affecting vegetation responses. Burning treatments were applied from 1960 to 1970 on 0.4 ha experimental units and crossed fire season and frequency in a randomized block design. Burning altered shrub layer dynamics and composition in both the short and long terms and was influenced by both fire season and frequency, with frequent summer season burns having the largest impact, including greatest control of hazel (Corylus spp.). The application of fire facilitated regeneration of pine; however, recruitment into the overstory was limited. Additionally, community composition of the herbaceous understory diverged 40+ years following burning. This study highlights the importance of continued burning in affecting vegetation responses and the potential of fire as a long-lasting vegetation management tool in these forests.

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 forest settings. We assessed changes in wood strength (bending strength, compressive strength, and surface hardness) using standard wood stakes of known initial mass from three species. The stakes were placed in forested settings for two and four years before collection for laboratory analyses. All three strength metrics decreased as stakes lost mass due to decay; however, bending strength had the strongest relationship with mass loss, a result that was consistent for all species, as well as species-pooled data. Results for all strength-loss metrics indicate that stakes had experienced ca. 10% strength loss before any detectable mass loss had occurred. Further, our results suggest that the decay class system typically used during field inventories — based in large part on tactile assessments of wood structural integrity — may provide a reasonable characterization of DWM mass loss, which is a critical assumption for carbon accounting and modelling based on inventory data.

Uncertainty about global environmental change has led to increased emphasis on the climate adaptation and mitigation potential of forests. Given the linkages between adaptive capacity and ecosystem complexity, this increased emphasis has motivated evaluations of the compositional, functional, and structural conditions characterizing a given forest ecosystem in the context of future stressors; however, less is known about how these conditions develop over time or vary between secondary forests shaped by a history of land use. To address this need, we capitalize on a 69-year field experiment to examine the long-term structural and compositional dynamics of transition ecotone hardwood (forests containing species from both southern and northern communities) and Pinus strobus-Quercus mixedwood (stands characterized by hardwood and softwood species mixtures) forests, communities which are commonly found in the Northeastern US. As expected, we observed a general increase in biomass over time and increasing density and structural complexity, with live aboveground biomass greatest in structurally complex mixedwood systems dominated by large diameter P. strobus. While all forests trended toward greater shade tolerance with increasing stand age, the functional identities of hardwood stands were stable over time compared to mixedwoods, which were more transient and ultimately generated trait profiles resembling hardwood-dominated stands. Ingrowth on all sites favored shade-tolerant Fagus grandifolia and Tsuga canadensis, which have lower future climate compatibility and adaptability compared to overstory trees, with a noticeable absence of P. strobus and Quercus spp. regeneration. Although all forest types exhibited some conditions that foster adaptation potential, the compositional stability of hardwood-dominated systems highlight the capacity of these stands to maintain comparable levels of adaptive capacity into the future. Conversely, given that P. strobus-Quercus mixedwoods examined are largely an artifact of land use, the natural successional patterns of these forests may lead to a reduction in these mixed species communities and a depreciation of associated climate benefits without silvicultural intervention to favor recruitment of these constituent species.

Understanding how stand structure responds to stresses such as drought and pollution could aid forest managers in evaluating silvicultural treatment success, predicting treatment durability, and designing adaptive management approaches. The size-growth relationship (SGR), a measure of growth partitioning among different size trees in a stand, may provide a means of linking stresses impacting individual trees to forest stand development and growth. No study to date has tested SGR’s response to drought and pollution, specifically N deposition, across landscapes. We combined Forest Inventory and Analysis (FIA) stand development and plot-level lichen bioindicator data on N deposition with climate data denoting moisture availability. Using linear regression, we examined SGR, stand structural complexity, individual tree growth and mortality in largely multi-aged, mixed species stands in California, Oregon, and Washington, USA, coniferous and pine-oak forests. Our goals were to determine a) the influence of moisture availability and/or N deposition on SGR, b) whether SGR translates to differences in stand structural complexity over time, and c) the extent to which SGR mediates the impacts of abiotic stress on tree growth and mortality. Consistent with previous research, our results indicated that SGR increased with stand density, indicative of larger trees possessing a disproportionate advantage in aboveground competition for light. SGR declined linearly with stand age, trending over time towards disproportionately slow large-tree growth. SGR strongly increased with low-moderate bioindicated N deposition, which is consistent with past findings that SGR increases with site quality and suggests that N deposition disproportionately increases growth in larger trees. We did not find evidence that drought stress (as indicated by the Palmer Drought Severity Index) influenced SGR. Stands that were already more structurally complex showed further gains in complexity under high SGR (disproportionately rapid large-tree growth), whereas stands that were initially structurally simpler increased in complexity under low SGR (disproportionately slow large tree growth). As such, individual-tree growth and mortality may drive changes in complexity. Our results support the utility of SGR as a predictor of how stress impacts stand structure, but only when accounting for initial structural complexity. Our findings also have implications for the design and durability of silvicultural treatments, given that silvicultural prescriptions often involve the manipulation of tree size distributions. Moreover, these findings underscore the importance of accounting for the historical influence of N deposition on stand development during treatment planning, as well as the likelihood of socioeconomic changes altering N deposition in the future.

We compiled data from several independent, long-term silvicultural studies on USDA Forest Service experimental forests across a latitudinal gradient in the northeastern and north-central U.S.A. to evaluate factors influencing aboveground live-tree carbon sequestration and mortality. Data represent five sites with more than 70,000 repeated tree records spanning eight decades, five ecoregions, and a range of stand conditions. We used these data to test the relative influence of factors such as climate, treatment history (uneven-aged or no management), species composition, and stand structural conditions on aboveground live-tree carbon sequestration and mortality in repeatedly measured trees. Relative to no management, we found that uneven-aged management tended to have a positive effect on carbon sequestration at low stocking levels and in areas of favorable climate (expressed as a combination of growing season precipitation and annual growing degree days > 5 °C). In addition, losses of carbon from the aboveground live-tree pool due to tree mortality were lower in managed than unmanaged stands. These findings suggest that there may be conditions at which rate of sequestration in living trees is higher in stands managed with uneven-aged silviculture than in unmanaged stands, and that this benefit is greatest where climate is favorable.

Forest management planning requires the specification of measurable objectives as desired future conditions at spatial extents ranging from stands to landscapes and temporal extents ranging from a single growing season to several centuries. Effective implementation of forest management requires understanding current conditions and constraints well enough to apply the appropriate silvicultural strategies to produce desired future conditions, often for multiple objectives, at varying spatial and temporal extents. We administered an online survey to forest managers in the eastern US to better understand how wildlife scientists could best provide information to help meet wildlife-related habitat objectives. We then examined more than 1000 review papers on bird–vegetation relationships in the eastern US compiled during a systematic review of the primary literature to see how well this evidence-base meets the information needs of forest managers. We identified two main areas where wildlife scientists could increase the relevance and applicability of their research. First, forest managers want descriptions of wildlife species–vegetation relationships using the operational metrics of forest management (forest type, tree species composition, basal area, tree density, stocking rates, etc.) summarized at the operational spatial units of forest management (stands, compartments, and forests). Second, forest managers want information about how to provide wildlife habitats for many different species with varied habitat needs across temporal extents related to the ecological processes of succession after harvest or natural disturbance (1–2 decades) or even longer periods of stand development. We provide examples of review papers that meet these information needs of forest managers and topic-specific bibliographies of additional review papers that may contain actionable information for foresters who wish to meet wildlife management objectives. We suggest that wildlife scientists become more familiar with the extensive grey literature on forest bird–vegetation relationships and forest management that is available in natural resource management agency reports. We also suggest that wildlife scientists could reconsider everything from the questions they ask, the metrics they report on, and the way they allocate samples in time and space, to provide more relevant and actionable information to forest managers.

Concern over global environmental change and associated uncertainty has given rise to greater emphasis on fostering resilience through forest management. We examined the impact of standard silvicultural systems (including clearcutting, shelterwood, and selection) compared with unharvested controls on tree functional identity and functional diversity in three forest types distributed across the northeastern United States. Sites included the Argonne, Bartlett, and Penobscot Experimental Forests located in Wisconsin, New Hampshire, and Maine, respectively. We quantified functional trait means for leaf mass per area, specific gravity, maximum height, height achieved at 20 years, seed mass, drought tolerance, shade tolerance, and flood tolerance as well as standard functional diversity measures from standing biomass reconstructed at the beginning and end of a 20-year study period using increment cores and historic inventory data. As expected, functional identity differed between harvest methods with means for plant traits associated with later stages of succession (e.g. shade tolerance) increasing in stands managed with selection systems. Opposite trends occurred with greater canopy disturbance, and functional diversity indices remained stable over time in the absence of disturbance. Estimates of functional diversity and functional identity hold promise as important approaches for evaluating outcomes of forest management, particularly as the connections among functional diversity, delivery of ecosystem services, and ecosystem resilience are further developed.

A rare, stand-replacing fire in northern Minnesota, USA provided the opportunity to compare the effects of wildfire and timber harvesting in two peatland forest communities, nutrient-poor black spruce (Picea mariana) bogs (BSB) and nutrient-rich tamarack (Larix laricina) swamps (RTS). We found the response between the two communities and their corresponding vegetation to be highly sensitive to different types and severity of disturbance, ranging from modest shifts in ground layer vascular plants and bryophyte species abundance, to wholesale plant community transformation resulting from the removal of the upper peat surface. Fire had a positive influence on black spruce regeneration within BSB sites, particularly areas experiencing lower levels of fire severity, with seedling densities significantly higher than harvest and control areas. Our results also suggest that ecosystem recovery will be rapid after low-severity fire in these areas, given that localized areas of peat combustion created suitable microsites for black spruce seedling establishment ensuring this species will remain a component of the post-fire communities. In contrast, tamarack regeneration was only documented in harvested RTS sites. For BSB, there was spatial heterogeneity in peat consumption as a result of fire behavior interacting with varying moisture conditions throughout peat hummocks and hollows. Light to moderate burning created suitable black spruce seedbeds by reducing cover of Sphagnum moss and the dominant ericaceous shrub Rhododendron groenlandicum, and increasing the cover of pioneering mosses, such as Polytrichum strictum. In RTS sites, fire typically consumed the entire upper peat surface, resulting in homogenization of community composition and retrogression towards marsh-like conditions dominated by cattails (Typha spp.). These findings underscore the importance of accounting for post-fire microsite heterogeneity when developing silvicultural systems for emulating natural disturbance processes in conifer forests with a naturally accumulated surface peat layer. In addition, the state shifts observed in areas experiencing high severity fire suggest that increases in fire frequency and severity may create significant challenges to maintaining forested conditions in these areas, particularly in RTS.

Forest managers in the United States must respond to the need for climate-adaptive strategies in the face of observed and projected climatic changes. However, there is a lack of on-the-ground forest adaptation research to indicate what adaptation measures or tactics might be effective in preparing forest ecosystems to deal with climate change. Natural resource managers in many areas are also challenged by scant locally or regionally relevant information on climate projections and potential impacts. The Adaptive Silviculture for Climate Change (ASCC) project was designed to respond to these barriers to operationalizing climate adaptation strategies by providing a multiregion network of replicated operational-scale research sites testing ecosystem-specific climate change adaptation treatments across a gradient of adaptive approaches, and introducing conceptual tools and processes to integrate climate change considerations into management and silvicultural decisionmaking. Here we present the framework of the ASCC project, highlight the implementation process at two of the study sites, and discuss the contributions of this collaborative science-management partnership.

Climate adaptation planning and implementation are likely to increase rapidly within the forest sector not only as climate continues to change but also as we intentionally learn from real-world examples. We sought to better understand how adaptation is being incorporated in land management decision-making across diverse land ownership types in the Midwest by evaluating project-level adaptation plans from a suite of forest management projects developed through the Climate Change Response Framework. We used quantitative content analysis to evaluate 44 adaptation-planning documents developed through the Framework’s Adaptation Workbook within two ecoregional provinces of the Midwest. This approach was used to assess the components of adaptation planning, including the resources that adaptation actions targeted within planning documents, the climate changes and impacts of concern, and the adaptation strategies managers identified. Analyses of adaptation plans show that the most frequent climate changes and impacts of concern included alterations in the amount and timing of precipitation, increased vegetation moisture stress, and forest pest and pathogen impacts. Individual projects identified a diversity of adaptation options, rather than focusing singly on actions that aimed to resist climate impacts, enhance resilience, or transition systems. Multivariate analyses indicate that ecoregion and land ownership influenced adaptation planning, while the type of resources and the climate change impacts managers were concerned with were significantly correlated with the adaptation strategies selected during planning. This finding reinforces the idea that one-size-fits-all guidance on adaptation will be insufficient for land managers. Perceptions of relevant climate impacts differ based on regional and ownership contexts, which naturally leads to differences in preferred adaptation actions.

The emerald ash borer (EAB; Agrilus planipennis) is an invasive beetle that causes almost complete mortality of ash trees (Fraxinus spp.) in North America and Europe. Northern temperate wetlands, where black ash (F. nigra) is a dominant and foundation species, will likely undergo dramatic shifts after EAB invasion. Utilizing published knowledge on amphibian and aquatic invertebrate responses to environmental gradients and the effects of ash loss on forest structure and function, we provide a mechanistic framework to discuss how changes in hydrology, canopy structure, and litter inputs could affect wetland communities. Changes in leaf litter could affect primary production and food web structure in the aquatic environment; overall changes in habitat structure might shift the community to species with longer aquatic stages that prefer open-canopy habitats. Amphibians and aquatic invertebrates serve as linkages between aquatic and terrestrial ecosystems. Therefore, understanding how the abundance and functional diversity of these taxa change in response to EAB is necessary to understand whole ecosystem responses. Using a mechanistic framework to formulate hypotheses and predictions is vital for our ability to manage target systems, retain biodiversity, and sustain ecosystem function.

Recent emphasis on increasing structural complexity and species diversity reflective of natural ecosystems through the use of retention harvesting approaches is coinciding with increased demand for forest-derived bioenergy feedstocks, largely sourced through the removal of harvest residues associated with whole-tree harvest. Uncertainties about the consequences of such approaches prompted us to examine the combined impacts of aggregated overstory retention and harvest residue retention on the composition and density of regeneration following biomass harvests on four operational-scale (40 ha) study areas dominated by Populus tremuloides Michx. in northern Minnesota. Whole-tree harvest had no statistically significant effects on initial (2-year) regeneration densities, including root suckers, sprouts, and seedlings relative to conventional, stem-only harvest. The density of shrub stems was also unaffected by harvest residue retention. Despite having a lower mean leaf area index than intact forest controls, aggregates maintained comparable densities of the four most common tree species, individually, as well as all tree species combined. The composition of regeneration within aggregates differed from surrounding harvested areas as expected, but this increase in complexity at the stand scale was achieved without diminishing P. tremuloides densities in the edge area (0–5 m) surrounding aggregates 2 years after harvest. These initial findings suggest even small aggregates of overstory reserves may achieve basic objectives related to structural complexity and sustaining shade-tolerant tree species in harvested units without compromising regeneration objectives for less tolerant species.

Soil functions that control plant resource availability can be altered by management activities such as increased organic matter (OM) removal and soil compaction during forest harvesting. The Long Term Soil Productivity study was established to evaluate how these practices influence soil and site productivity using experimental treatments that span a range of forest types and soil conditions at sites across North America. Here we report on the effects of these treatments on soil properties after 20 years at three of the oldest sites in the study. The sites all are located in aspen (Populous tremuloides) forests of the Lake States region USA, and span a soil texture (silt loam, sand, and clay) and productivity gradient. Treatments were applied in a 3 × 3 factorial design that included three levels of OM removal (stem only harvest, SOH; whole tree harvest, WTH; and WTH plus forest floor removal, FFR) and three levels of soil compaction (no additional, intermediate, and high). After 20 years, effects of OM removal were primarily associated with the extreme FFR treatment, and generally limited to the lower productivity sand and clay texture sites. At the sand texture site with low initial pools of C and nutrients, FFR resulted in soil C and Ca reductions over the 20-year period, which may have caused large reductions in aspen growth that were previously observed at that site. Although treatment effects of SOH and WTH were limited, soil P tended to decrease at all sites during the study period, which may affect future productivity at these sites. Effects of soil compaction treatments were generally linear and only apparent at the silt loam and sand texture sites. At all sites, bulk density in the upper 10 cm had fully recovered from harvest- and treatment-induced increases after 20 years, but remained elevated and increased with increasing compaction at depths below 10 cm. Previous work indicates that soil compaction had neutral to positive effects on growth at the sand texture site, but strongly negative effects on growth at the silt loam texture site. These 20-year results demonstrate that the effect of OM removal and soil compaction on soil properties is site-specific, which generally aligns with concepts of soil quality and its influence on vegetation growth. Although the LTSP study has proved invaluable in clarifying these linkages across North America, there are some limitations with measurement protocols that limit the overall utility of the soil assessment. These limitations inhibit the development of soil-based indices to identify high risk sites and practices at odds with sustainable forest management.

Interactions between tree roots and sidewalks can result in damage to sidewalks and when sidewalk damage is repaired adjacent tree roots are often severed. The objective of this study was to quantify the growth response of urban trees in restricted planting spaces pre- and post-sidewalk construction. The research included four trees species commonly planted along streets in Minneapolis and Saint Paul, Minnesota, USA. Species included were: Acer platanoides, Celtis occidentalis, Gleditsia triacanthos, and Tilia spp. Two street tree populations were sampled: trees adjacent to replaced sidewalk panels (

Changes in the frequency, duration, and severity of climate extremes are forecast to occur under global climate change. The impacts of climate extremes on forest productivity and health remain difficult to predict due to potential interactions with disturbance events and forest dynamics-changes in forest stand composition, density, size and age structure over time. Such interactions may lead to non-linear forest growth responses to climate involving thresholds and lag effects. Understanding how forest dynamics influence growth responses to climate is particularly important given stand structure and composition can be modified through management to increase forest resistance and resilience to climate change. To inform such adaptive management, we develop a hierarchical Bayesian state space model in which climate effects on tree growth are allowed to vary over time and in relation to past climate extremes, disturbance events, and forest dynamics. The model is an important step toward integrating disturbance and forest dynamics into predictions of forest growth responses to climate extremes. We apply the model to a dendrochronology data set from forest stands of varying composition, structure, and development stage in northeastern Minnesota that have experienced extreme climate years and forest tent caterpillar defoliation events. Mean forest growth was most sensitive to water balance variables representing climatic water deficit. Forest growth responses to water deficit were partitioned into responses driven by climatic threshold exceedances and interactions with insect defoliation. Forest growth was both resistant and resilient to climate extremes with the majority of forest growth responses occurring after multiple climatic threshold exceedances across seasons and years. Interactions between climate and disturbance were observed in a subset of years with insect defoliation increasing forest growth sensitivity to water availability. Forest growth was particularly sensitive to climate extremes during periods of high stem density following major regeneration events when average inter-tree competition was high. Results suggest the resistance and resilience of forest growth to climate extremes can be increased through management steps such as thinning to reduce competition during early stages of stand development and small-group selection harvests to maintain forest structures characteristic of older, mature stands.

When an invasive organism targets a dominant tree species, it can trigger unprecedented shifts in forest plant communities. Emerald ash borer (EAB; Agrilus planipennis Fairmaire), an invasive insect that kills by girdling trees, represents a significant threat to North American Fraxinus (ash) species. EAB has already decimated many Fraxinus populations and threatens loss of overstory cover in Great Lakes region wetland forests dominated by Fraxinus nigra (black ash). Canopy treatments, such as clearcutting and group selection, are being evaluated to promote regeneration of non-EAB-host tree species. Studies suggest clearcutting may raise water tables, lower tree regeneration, and shift the composition of woody and herbaceous ground-layer plant communities. However, no empirical research to date has examined the effects of canopy treatments on ground-layer plant communities in F. nigra wetlands. We used a large-scale field experiment in northern Minnesota F. nigra wetlands to examine the response of the woody and herbaceous ground-layer to four overstory treatments: clearcutting, group selection, F. nigra girdling, and unharvested forest. Our objectives were to determine: (1) to what extent established regeneration of associated tree species could be expected to contribute to overstory maintenance under EAB- and management-induced canopy changes; (2) the impact of canopy changes on the composition of the overall woody ground-layer; and (3) the effect of canopy treatments on the herbaceous layer. We found density of established tree regeneration was significantly higher in the clearcut treatment than in the group selection, girdle, and control. Fraxinus nigra had the highest seedling density in all treatments, while Ulmus americana (American elm) was the most abundant non-EAB-host tree species across treatments. Regeneration density of associated tree species varied by treatment and fell short of seedling stocking guidelines. Background variation in experimental blocks exerted a greater influence than treatment on overall woody community composition. Treatment influenced herbaceous layer height, but did not significantly impact total cover. Herbaceous species richness and diversity increased in all treatments, with the clearcut and group selection moving toward greater graminoid cover, while the control and girdling treatment increased in wetland indicator species. Our findings suggest artificial regeneration, combined with herbaceous and shrub competition control treatments, will be necessary to restock F. nigra forests following EAB invasion. Sites with lower abundance of shrub species and higher established tree regeneration should be prioritized for management activities.

Prescribed fire is widely used for ecological restoration and fuel reduction in fire-dependent ecosystems, most of which are also prone to drought. Despite the importance of drought in fire-adapted forests, little is known about the cumulative effects of repeated prescribed burning on tree growth and related response to drought. Using dendrochronological data in red pine (Pinus resinosa Ait.)-dominated forests in northern Minnesota, USA, we examined growth responses before and after understory prescribed fires between 1960 and 1970 to assess whether repeated burning influences growth responses of overstory trees and vulnerability of overstory tree growth to drought. We found no difference in tree-level growth vulnerability to drought, expressed as growth resistance, resilience, and recovery, between areas receiving prescribed fire treatments and untreated forests. Annual mortality rates during the period of active burning were also low (less than 2%) in all treatments. These findings indicate that prescribed fire can be effectively integrated into management plans and climate change adaptation strategies for red pine forest ecosystems without significant short- or long-term negative consequences for growth or mortality rates of overstory trees.

The development of old-growth forests in northeastern North America has largely been within the context of gap-scale disturbances given the rarity of stand-replacing disturbances. Using the 10-ha old-growth Harvard Tract and its associated 90-year history of measurements, including detailed surveys in 1989 and 2009, we document the long-term structural and biomass development of an old-growth Tsuga canadensis-Pinus strobus forest in southern New Hampshire, USA following a stand-replacing hurricane in 1938. Measurements of aboveground biomass pools were integrated with data from second- and old-growth T. canadensis forests to evaluate long-term patterns in biomass development following this disturbance. Ecosystem structure across the Tract prior to the hurricane exhibited a high degree of spatial heterogeneity with the greatest levels of live tree basal area (70-129 m2 /ha) on upper west-facing slopes where P. strobus was dominant and intermixed with T. canadensis. Live-tree biomass estimates for these stratified mixtures ranged from 159 to 503 Mg/ha at the localized, plot scale (100 m2 ) and averaged 367 Mg/ha across these portions of the landscape approaching the upper bounds for eastern forests. Live-tree biomass 71 years after the hurricane is more uniform and lower in magnitude, with T. canadensis currently the dominant overstory tree species throughout much of the landscape. Despite only one living P. strobus stem in the 2009 plots (and fewer than five stems known across the entire 10-ha area), the detrital legacy of this species is pronounced with localized accumulations of coarse woody debris exceeding 237.7-404.2 m3 /ha where this species once dominated the canopy. These patterns underscore the great sizes P. strobus attained in pre-European landscapes and its great decay resistance relative to its forest associates. Total aboveground biomass pools in this 71-year-old forest (255 Mg/ha) are comparable to those in modern old-growth ecosystems in the region that also lack abundant white pine. Results highlight the importance of disturbance legacies in affecting forest structural conditions over extended periods following stand-replacing events and underscore that post-disturbance salvage logging can alter ecosystem development for decades. Moreover, the dominant role of old-growth P. strobus in live and detrital biomass pools before and after the hurricane, respectively, demonstrate the disproportionate influence this species likely had on carbon storage at localized scales prior to the widespread, selective harvesting of large P. strobus across the region in the 18th and 19th centuries.

Concerns over loss of ecosystem function and biodiversity in managed forests have led to the development of silvicultural approaches that meet ecological goals as well as sustain timber production. Variable Retention Harvest (VRH) practices, which maintain mature overstory trees across harvested areas, have been suggested as an approach to balance these objectives; however, long-term evaluations of outcomes of VRH strategies do not exist for most forest types. The objective of this study was to determine the 11-year effects of overstory tree retention pattern and shrub removal on regeneration in P. resinosa forests in Minnesota, USA using a large-scale manipulative study in which four overstory (control, small gap-aggregated, large gap-aggregated, and dispersed) and two shrub (ambient and reduced shrubs) treatments were applied. Hardwood regeneration greatly outnumbered conifer regeneration and several mechanisms (disease, browse, and seedbed conditions) likely interacted to limit P. resinosa regeneration across treatments. The presence of recalcitrant shrub layers filtered response to retention with regeneration of P. strobus L. being greater under an intact Corylus layer irrespective of overstory conditions. This work reinforced the importance of accounting for shrub competition when designing VRH to secure natural regeneration.