Explore the vast range of titles available.

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 annual growth of entire tree populations responds to drought and competition in eight, long‐term (multi‐decadal), experiments with replicated levels of density (e.g., competitive intensity) arrayed across a broad climatic and compositional gradient. Forest growth (cumulative individual tree growth within a stand) declined during drought, especially during more severe drought in drier climates. Forest growth declines were exacerbated by high density at all sites but one, particularly during periods of more severe drought. Surprisingly, the influence of forest density was persistent overall, but these density impacts were greater in the humid sites than in more arid sites. Significant density impacts occurred during periods of more extreme drought, and during warmer temperatures in the semi‐arid sites but during periods of cooler temperatures in the humid sites. Because competition has a consistent influence over growth response to drought, maintaining forests at lower density may enhance resilience to drought in all climates.

What are typical values and dynamic status of live‐tree biomass pools in old‐growth, mesic, cool temperate forests? A handful of biomass density estimates in eastern North American temperate forests show large biomass/carbon reserves on a per‐area basis. However, it is less clear whether these ecosystems are, over multi‐decade scales, typically steady‐state or non‐equilibrial carbon pools. Previous studies have suggested both possibilities, but claims are based on inferences from short‐term studies or proxy data sets. An unusually long‐term and extensive data set from repeatedly sampled permanent plots (84 yr, ca. 10 ha sample area, 6–8 measurements), from old‐growth conifer‐hardwood forest in northern Michigan, USA, allows direct estimation of multi‐decade trends in aboveground live‐tree biomass. Results confirm prior suggestions of high‐biomass density for old‐growth temperate forests (averaging >300 Mg/ha), but, despite significant decade‐scale variation, show no overall, long‐term directional change. Study plots typically show multi‐decade trends of gradually increasing biomass density, interrupted by sharp declines attributed to intermediate‐severity disturbances, with recovery of pre‐disturbance biomass density requiring upwards of a half‐century. At the stand scale, biomass dynamics are strongly historically contingent, and short‐term studies may yield biased or misleading results. Disturbance legacies, through demographic and structural effects, can have multi‐decade effects on vulnerability to further disturbance. While this study shows no general trend in aboveground biomass pools, it suggests that changes in disturbance regime may drive important feedbacks in biomass pool dynamics.

Sustainable management of forest ecosystems requires the use of reliable and easy to implement biodiversity and naturalness indicators. Tree-related microhabitats (TreMs) can fulfill these roles as they harbor specialized species that directly or indirectly depend on them, and are generally more abundant and diverse in natural forests or forests unmanaged for several decades. The TreM concept is however still recent, implying the existence of many knowledge gaps that can challenge its robustness and applicability. To evaluate the current state of knowledge on TreMs, we conducted a systematic review followed by a bibliometric analysis of the literature identified. A total of 101 articles constituted the final corpus. Most of the articles (60.3%) were published in 2017 or after. TreM research presented a marked lack of geographical representativity, as the vast majority (68.3%) of the articles studied French, German or Italian forests. The main themes addressed by the literature were the value of TreMs as biodiversity indicators, the impact of forest management on TreMs and the factors at the tree- and stand-scales favoring TreMs occurrence. Old-growth and unmanaged forests played a key role as a “natural” forest reference for these previous themes, as TreMs were often much more abundant and diverse compared to managed forests. Arthropods were the main phylum studied for the theme of TreMs as biodiversity indicators. Other more diverse themes were identified, such as restoration, remote sensing, climate change and economy and there was a lack of research related to the social sciences. Overall, current research on TreMs has focused on assessing its robustness as an indicator of biodiversity and naturalness at the stand scale. The important geographical gap identified underscores the importance of expanding the use of the TreMs in other forest ecosystems of the world. The notable efforts made in recent years to standardize TreM studies are an important step in this direction. The novelty of the TreM concept can partially explain the thematic knowledge gaps. Our results nevertheless stress the high potential of TreMs for multidisciplinary research, and we discuss the benefits of expanding the use of TreMs on a larger spatial scale.

Introduction: Global climate change and associated stressors threaten forest ecosystems due to the rapid pace of climate change, which could exceed the natural migration rate of some tree species. In response, there is growing interest to research and implement forest assisted migration (FAM). Here, we used a species-independent indicator based on climate analogy, according to the sigma (dis)similarity (σd) index, to match planting sites across the eastern US with (future) climatically-compatible seedlots (CCS).Methods: We developed CCS for a grid composed of 1 × 1° of latitude and longitude. CCS were based on future climate analogs with ≤2σd analogy to ensure CCS were representative of future climate change. CCS were located for three time periods, 2030's, 2050's, and 2090's and three emissions scenarios (SSP2-4.5, SSP3-7.0, and SSP5-8.5) from the Coupled Model Intercomparison Project phase 6 database, using 12 climate variables.Results: CCS were identified for the majority of 1 × 1° grids based on the SSP3-7.0 scenario. Approximately 28% of 1 × 1° grid's 2090's projections included future climate novelty. The 2030's, 2050's, and 2090's CCS were located on average 222, 358, and 662 km or 1, 2, and 3 eastern seed zones away from the 1 × 1° grids, respectively. CCS were also located further south-southwest (188–197°). In addition, the average forest cover of CCS was approximately 2%, 5%, and 10% less than that of the 1 × 1° grids.Discussion: Our development and synthesis of CCS emphasized four key results: (i) average distances to 2030's and 2050's CCS were similar to seed-transfer guidelines for some tree species, but 2090's CCS exceeded current recommendations; (ii) south-southwesterly locations of CCS aligned with tree species habitat distribution dynamics; (iii) future climate novelty potentially challenges the conceptual basis of FAM if tree species are not adapted to climate change; and (iv) variation in forest cover among CCS presents potential opportunities and challenges due the presence or absence of forestland to source seed. Ultimately, our goal was to locate and synthesize CCS that could enable FAM decision support.

Ecological communities are being impacted by global change worldwide. Experiments are a powerful tool to understand how global change will impact communities by comparing control and treatment replicates. Communities consist of multiple species, and their associated abundances make multivariate methods an effective approach to study community compositional differences between control and treated replicates. Dissimilarity metrics are a commonly employed multivariate measure of compositional differences; however, while highly informative, dissimilarity metrics do not elucidate the specific ways in which communities differ. Integrating two multivariate methods, dissimilarity metrics and rank abundance curves (RACs), have the potential to detect complex differences based on dissimilarity metrics and detail the how these differences came about through differences in richness, evenness, species ranks, or species identity. Here we use a database of 106 global change experiments located in herbaceous ecosystems and explore how patterns of ordinations based on dissimilarity metrics relate to RAC‐based differences. We find that combining dissimilarity metrics alongside RAC‐based measures clarifies how global change treatments are altering communities. We find that when there is no difference in community composition (no distance between centroids of control and treated replicates), there are rarely differences in species ranks or species identities and more often differences in richness or evenness alone. In contrast, when there are differences between centroids of control and treated replicates, this is most often associated with differences in ranks either alone or co‐occurring with differences in richness, evenness, or species identities. We suggest that integrating these two multivariate measures of community composition results in a deeper understanding of how global change impacts communities.

The impact of fuelwood harvesting on forest structure and composition is not clear, especially on the understudied and scarce Arasbaran forests in Iran. This research compared woody species density, species diversity, forest composition, and regeneration status in areas of continuous and ceased fuelwood harvesting in Arasbaran forests. We expected fuelwood harvesting to decrease stem density, species diversity, tree size (diameter at the breast height (DBH) and height), and shift composition away from preferred fuelwood species. We measured woody species size and frequency and identified species in three fuelwood harvest and three no harvest sites, with six sample plots (100 m × 50 m) per site. Results tended to show differences in composition, diversity, woody species height, and density. Carpinus orientalis, a preferred fuelwood species, tended to be more dominant in no harvest (importance values index (IVI) = 173.4) than harvest areas (IVI = 4.4). The diversity or richness of woody species tended to be higher in harvest (20 ± 1 species per ha) than in no harvest (14 ± 2 species per ha) areas, and other measures of diversity supported this trend as well. Harvest areas tended to also be characterized by shorter tree height and lower density of trees, a higher density of regeneration, and fewer small pole-sized trees than no harvest areas. Ongoing fuelwood harvests may further shift composition and structure away from no harvest area, compromising future fuelwood availability, but further detailed research is needed. Close to nature practices may be useful in sustaining fuelwood harvest areas and diversifying areas where fuelwood harvesting has ceased.

Past research has established that diverse scientific communities foster innovation and problem solving more effectively than communities with a narrow range of knowledge, skills, and experience. However, gender diversity among scientists is limited, particularly in natural-resource fields. We compared data on scientist gender and rank from the US Department of Agriculture Forest Service Research and Development (FSR&D, a hierarchical organization) with data on faculty gender and tenure status from universities (loosely coupled systems) with comparable areas of study. We found that the representation of women was greater among FSR&D scientists than among university faculty but declined with seniority in both institutions. Within FSR&D, data showed demographic inertia, suggesting that the representation of women in senior scientist positions will increase. Although many mechanisms affect gender representation, our findings suggest that organizational structure affects the diversity of the scientific workforce.

Understanding the complexity of forest community dynamics is essential in forest management planning and stewardship, yet lowland northern white-cedar (Thuja occidentalis L.) are often managed as homogenous communities. Through this study, we defined lowland white-cedar forest community types in unharvested and harvested forest stands within the State of Michigan and examined community type associations with ecological variables. Data collected in unharvested stands revealed three white-cedar community subtypes: (1) cedar-deciduous, (2) cedar-conifer, and (3) cedar-shrub. These unharvested subtypes were dominated by white-cedar, yet characterized by different soils, hydrology, geochemical gradients, and associated tree species. In harvested stands, six community types were identified: (1) aspen-fir, (2) winterberry-willow, (3) balsam fir, (4) cedar-red maple, (5) cedar-black spruce, and (6) alder-tamarack. These harvested community types were located along ecological gradients, including soil type (organic or mineral) and soil water pH. Using community types in unharvested and harvested stands, and associated ecological gradients, potential pathways of compositional transition were theorized. Findings suggest that cedar community subtype affects the likelihood of cedar regeneration and dictates the alternative species replacing cedar after harvest. These findings and potential pathways are useful to forestry practitioners, as they highlight potential changes in tree species dominance following harvest across a range of lowland white-cedar community types, allowing refinement of silvicultural prescriptions to ensure desired outcomes.

1. Concerns about loss of biodiversity and structural complexity in managed forests have recently increased and led to the development of new management strategies focused on restoring or maintaining ecosystem functions while also providing wood outputs. Variable retention harvest (VRH) systems, in which mature overstorey trees are retained in various spatial arrangements across harvested areas, represent one potential approach to this problem. However, long-term evaluations of the effectiveness of this strategy at sustaining plant community composition are needed as this strategy is increasingly applied in managed forest landscapes throughout the world. 2. The forest ground layer plays a central role in forest ecosystem functioning, and we evaluated the long-term (11+ year) dynamics in ground-layer plant communities in response to VRH study in Pinus resinosa Aiton, forests. This large-scale, manipulative study included four overstorey (control, small gap-aggregated, large gap-aggregated and dispersed) and two understorey (ambient and reduced shrubs) treatments replicated four times in 16-ha stands. 3. Changes in ground-layer community composition were apparent 11 years following harvest, regardless of live-tree retention pattern. Richness and diversity increased and were driven by introduction and colonization of ruderal species, while forest interior species continued to persist across treatments. All life-forms responded positively to harvest with the exception of moss and clubmoss species. 4. The lack of effect of spatial pattern of retention on ground-layer plant communities was likely related to the presence of a dense and persistent shrub layer, a result of decades of fire suppression. In particular, the greatest responses to overstorey retention pattern occurred in areas receiving shrub reduction treatments, indicating this recalcitrant layer likely filtered response to retention pattern. 5. Synthesis and applications. Overall, this work highlights flexibility in choosing a variable retention harvest approach when sustaining ground-layer plant community diversity and composition are goals, but altered disturbance regimes (e.g. fire suppression, timber harvesting) that have facilitated the presence or formation of recalcitrant understories, need to be considered. The legacy effects of historical land use and alterations to natural disturbance regimes on the understorey in northern temperate forests are of equal, if not greater, importance to overstorey retention patterns in eliciting desired responses to variable retention harvest and need to be more carefully considered in future applications of this method.

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.