Development Of Forest Structure Research Articles

The effects of intensive eradication efforts for Asian longhorned beetle on understory plant communities, tree regeneration, and forest structure in southern New England hardwood forests

The United States has been experiencing an influx of nonnative pests due to increased globalization, and these pests have the potential to permanently alter the composition, structure, and function of forests. Asian longhorned beetle (ALB) is an invasive pest detected in Worcester, MA in 2008, where it invaded both urban and natural forested areas. As a part of the eradication measures (full host removals, herbicide treatments, and stump grinding), all host tree species, primarily Acer spp. were removed to prevent the spread of ALB. While these eradication measures successfully eliminate ALB, little is known about their effects on forest structural and compositional conditions and recovery over time. To address this, we examined forest compositional and structural development following eradication treatments and in adjacent unimpacted forested areas. Overall, our results indicated forest recovery followed similar pathways documented after natural disturbances in southern New England forests. There was little difference among eradication treatments in terms of the resultant forest composition and structure. Overall, forest types shifted to primarily oak-hickory or pine dominance following the removal of all Acer spp. Notably, maple species were present in high numbers in the regeneration layer regardless of treatment, followed by other early colonizing species. Red maple (Acer rubrum) was the most abundant sapling and seedling species and stump sprouting occurred at 60% of sites but was absent in untreated areas. These results suggest that ALB management does not drastically alter forest compositional dynamics in these mixed species forests in the short term, despite significant reductions in the abundance of mature host species through eradication treatments.

Characterizing Post-Fire Forest Structure Recovery in the Great Xing’an Mountain Using GEDI and Time Series Landsat Data

Understanding post-fire forest recovery is critical to the study of forest carbon dynamics. Many previous studies have used multispectral imagery to estimate post-fire recovery, yet post-fire forest structural development has rarely been evaluated in the Great Xing’an Mountain. In this study, we extracted the historical fire events from 1987 to 2019 based on a classification of Landsat imagery and assessed post-fire forest structure for these burned patches using Global Ecosystem Dynamics Investigation (GEDI)-derived metrics from 2019 to 2021. Two drivers were assessed for the influence on post-fire structure recovery, these being pre-fire canopy cover (i.e., dense forest and open forest) and burn severity levels (i.e., low, moderate, and high). We used these burnt patches to establish a 25-year chronosequence of forest structural succession by a space-for-time substitution method. Our result showed that the structural indices suggested delayed recovery following the fire, indicating a successional process from the decomposition of residual structures to the regeneration of new tree species in the post-fire forest. Across the past 25-years, the dense forest tends toward greater recovery than open forest, and the recovery rate was faster for low severity, followed by moderate severity and high severity. Specifically, in the recovery trajectory, the recovery indices were 21.7% and 17.4% for dense forest and open forest, and were 27.1%, 25.8%, and 25.4% for low, moderate, and high burn severity, respectively. Additionally, a different response to the fire was found in the canopy structure and height structure since total canopy cover (TCC) and plant area index (PAI) recovered faster than relative height (i.e., RH75 and RH95). Our results provide valuable information on forest structural restoration status, that can be used to support the formulation of post-fire forest management strategies in Great Xing’an Mountain.

Old forest structural development drives complexity of nest webs in a naturally disturbed boreal mixedwood forest landscape

Structural complexity generated by forest development processes and tree species compositional changes provide key habitat features for vertebrate communities that rely upon tree size and decay processes for foraging, denning or nesting. Complexity of forest structure in old stands could not only be key for harboring increased taxonomic species diversity but also greater functional diversity through more complexity in networks of tree cavity dependent species. Using a nest web approach that hierarchically links cavity-bearing trees with cavity formation agents (natural decay processes and avian excavators) and cavity users (non-excavator species), we compared network characteristics of nest webs along a time since fire gradient in a naturally disturbed boreal mixedwood forest landscape in eastern North America. Since 2003, twelve 24 to 40 ha plots ranging from 61 to more than 245 years after fire were surveyed at the Lake Duparquet Research and Teaching Forest in Abitibi, Quebec, Canada to detect active nesting, and denning cavities. We found that network complexity both in terms of number of vertebrate species and number of interactions among species, increased along the age gradient and was significantly higher in the older stands than predicted by chance. Whereas cavity-nesting communities in old forests used a higher diversity of tree species over a wide range of decay stages, trembling aspen remained a key cavity-bearing tree throughout the age gradient. Woodpeckers were the main cavity formation agents whereas less than 1% of cavities originated from natural decay. The structural development of older forests is thus a driver for functional diversity in cavity-using vertebrate communities through higher interaction richness in nest webs, among cavity-bearing trees, excavators and non-excavating users. The pivotal contribution of the entire gradient of old forest cover types to the overall complexity of nest webs in the boreal mixedwood zone is also a key for the resilience of the cavity-using vertebrate community to natural disturbances. We discuss how such resilience may be compromised by even-aged industrial timber harvesting with short rotations that shifts the age structure of boreal landscapes toward regenerating and young pole forests whereas old forest cover types become below their historical range of variability.

Enhancing structural complexity: An experiment conducted in the Black Forest National Park, Germany.

We report on a structural complexity enhancement (SCE) experiment that was designed to test ecological restoration measures in the Black Forest National Park, Germany. The main goal was to understand as to whether the creation of standing and downed deadwood within previously managed, single-layered Norway spruce (Picea abies L.) forests accelerates the development of forest structure, richness, and diversity of a range of taxonomic groups. Here we introduce the experimental design and describe the development of stand structure including abundance and richness of tree-related microhabitats (TreMs) within 5 years after initiation of the experiment in October 2016. To enhance structural complexity in treatment plots, 10 trees per plot were toppled using a skidder winch, and another 10 trees were ring barked at a height of around 60 cm above ground level with a chainsaw. To monitor stand structure, we collected data on common forest attributes such as diameter at breast height (DBH), tree height, and TreMs of all trees in the six experimental and six control plots measuring 0.25 ha in size before the treatments were carried out in 2016 and again in 2020/21. We analyzed the abundance and richness of TreMs using generalized linear mixed models with DBH and treatment vs. control as predictors. The SCE treatment resulted in a significant increase in deadwood volumes (4.2 vs. 439.5 m3) as well as in TreM abundance and richness (increase of 0.74 TreMs per tree). This indicates that the SCE treatment was effective to increase biodiversity-relevant structures such as deadwood and TreMs, in previously managed Norway spruce-dominated stands. The ongoing monitoring of a range of taxonomic groups (birds, bats, small mammals, coleoptera, fungi, mosses, and vascular plants) in this experiment will demonstrate to what extent the enhancement in structural complexity will lead to an enrichment in species richness and diversity.

Enhancing monitoring of mangrove spatiotemporal tree diversity and distribution patterns

AbstractSpatiotemporal information on mangrove species assemblage of natural, disturbed, and rehabilitated is an essential prerequisite for effective strategies for biodiversity conservation and management. However, appropriate field‐based sampling strategies of spatial heterogeneity still hamper the detection of the species distribution and its temporal development. An increasing amount of remote sensing data seems the perfect way to tackle these challenges. With this article, we fill this gap by presenting a review of the challenges and limitations to assess the current status of species diversity. We conclude that species discrimination based on remote sensing techniques is still limited by atmospheric contamination and tidal fluctuations. The lack of accurate information on the spatiotemporal development of species diversity and forest structure further curtails an understanding of functional indicators and the predictive power of modeling approaches. Nevertheless, multi‐source remote‐sensing techniques could seemingly capture the landscape heterogeneity and support systematic sampling designs. Spatially balanced (systematic) training and validation data are necessary to compile robust spatiotemporal information, supporting reliable predictions for optimizing restoration efforts. A systematic sampling of spatiotemporal ecological information is vital to derive the historical state of mangroves, detecting their degradation, and predicting future patterns of species distribution that are generally crucial for restoration, and particularly to rehabilitate species diversity.

Acceleration of Forest Structural Development for Large Trees and Mammals: Restoration in Decades or Centuries?

There is a demand for more progressive restoration directives to regenerate forest ecosystems impacted by harvesting, wildfire, insect outbreaks, and mineral resource extraction. Forest restoration may take many decades and even centuries without active silvicultural intervention to grow large trees that provide suitable habitat for various wildlife species. We tested the hypotheses (H) that, compared with unmanaged (unthinned and old-growth) stands, large-scale precommercial thinning (heavy thinning to <500 stems/ha) of young lodgepole pine (Pinus contorta var. latifolia), at 20–25 years post-treatment, would enhance: (H1) the architecture of large overstory trees (e.g., diameter, height, and crown dimensions); (H2) mean (i) total abundance and species diversity of forest-floor small mammals, (ii) abundance of tree squirrels; and (H3) relative habitat use by mule deer (Odocoileus hemionus). There were three levels of thinning with mean densities of crop trees/ha: 353 (low), 712 (medium) and 1288 (high), an unthinned, and old-growth stand replicated at three areas in south-central British Columbia, Canada. Mammal abundance and habitat use were measured during the period 2013 to 2015. Mean diameter of crop trees was significantly different among stands with the low-density, medium-density, and old-growth stands having diameters larger than the high-density and unthinned stands. Mean height of crop trees was highest in the old-growth stands. Mean crown volume of crop trees was significantly different among stands with the low-density stands 2.1 to 5.8 times higher than the high-density, unthinned, and old-growth stands, and hence partial support for H1. Mean total abundance of forest-floor small mammals was significantly different among stands with the low-density and old-growth stands 1.9 to 2.4 times higher than the other three treatment stands. Mean abundances per stand of the red squirrel (Tamiasciurus hudsonicus) (range of 4.8 to 12.0) and the northern flying squirrel (Glaucomys sabrinus) (range of 3.2 to 4.3) were similar among stands. Mean relative habitat use by mule deer was similar among stands, but variable with counts of pellet-groups/ha in the thinned stands were 3.8 to 4.2 and 2.1 to 2.3 times higher than the unthinned and old-growth stands, respectively. Thus, mean total abundance of forest-floor small mammals of H2 was supported, but species diversity and abundance of tree squirrels was not. Enhanced relative habitat use by mule deer (H3) was not supported. To our knowledge, this is the first concurrent measurement of several mammal species in heavily thinned, unthinned, and old-growth forest across three replicate study areas at 20–25 years post-treatment. Although not all mammal responses were significant, there was a strong indication that restored forests via heavy thinning (<500 trees/ha) produced large overstory trees (at least for diameter and crown dimensions) in stands 33 to 42 years old. Comparable old-growth stands, albeit with crop trees of greater height and merchantable volume, ranged from 120 to 167 years of age. Restored forests with large trees capable of supporting at least these mammal species may be achieved in decades rather than centuries.

Structural diversity and development in active fire regime mixed-conifer forests

Nearly a century of fire suppression in most forested land of the United States has limited researchers’ ability to construct and rigorously test conceptual models of forest structural development in mixed-conifer ecosystems. As a result, land managers must rely on conceptual models of forest development that may overemphasize idealized stand structures and developmental pathways, which ultimately hampers management of many forest systems for resilience to future climate change impacts. We sought to determine the relative importance of fire history (frequency, severity, and time since fire) and biophysical variables on forest structural diversity and development. Importantly, we conducted our study in an ecosystem with a contemporary active fire regime where wildland fire has been managed as an ecosystem process for four decades. Using data from unburned (≥80 years since fire), once-burned and twice-burned mixed-conifer forests in the Bob Marshall Wilderness of Northwest Montana, we conducted a hierarchical clustering analysis to identify forest stand structure classes. We then used a Classification and Regression Tree analysis, combined with other post-hoc analyses, to elucidate the biophysical and disturbance history drivers that lead to each structure class. The cluster analysis revealed six forest structure classes. The CART analysis indicated that time since fire plays a large role in determining forest structure, but at intermediate time scales structure is further shaped by repeat fires and interactions with biophysical variables. The CART and post-hoc analyses did not, however, indicate a singular fire history or biophysical pathway to any one structure class. We synthesize our results in a conceptual model of forest structural development under an active fire regime. This model supports existing theory that succession following severe fire plays a large role in shaping forest structure. It also recognizes the role of fire at variable severities and frequencies, the physical environment, and tree community composition in influencing forest structural development. The complexity of forest structure and development generated by an active fire regime points to the need to incorporate a process-based view of wildfire if the goal is to manage for improved resiliency and adaptive capacity to future climate change impacts.

A simple grid-based framework for simulating forest structural trajectories linked to transient forest management scenarios in Fennoscandia

Forest structural properties largely govern surface fluxes of moisture, energy, and momentum that strongly affect regional climate and hydrology. Forest structural properties are greatly shaped by forest management activities, especially in the Fennoscandia (Norway, Sweden, and Finland). Insight into transient developments in forest structure in response to management intervention is therefore essential to understanding the role of forest management in mitigating regional climate change. The aim of this study is to present a simple grid-based framework – the Fennoscandic Forest State Simulator (F2S2) -- for predicting time-dependent forest structural trajectories in a manner compatible with land models employed in offline or asynchronously coupled climate and hydrological research. F2S2 enables the prescription of future regional forest structure as a function of: i) exogenously defined scenarios of forest harvest intensity; ii) forest management intensity; iii) climate forcing. We demonstrate its application when applied as a stand-alone tool for forecasting three alternative future forest states in Norway that differ with respect to background climate forcing, forest harvest intensity (linked to two Shared Socio-economic Pathways (SSPs)), and forest management intensity. F2S2 captures impacts of climate forcing and forest management on general trends in forest structural development over time, and while climate is the main driver of longer-term forest structural dynamics, the role of harvests and other management-driven effects cannot be overlooked. To our knowledge this is the first paper presenting a method to map forest structure in space and time in a way that is compatible with land surface or hydrological models employing sub-grid tiling.

Using lidar to assess the development of structural diversity in forests undergoing passive rewilding in temperate Northern Europe.

Forested areas are increasing across Europe, driven by both reforestation programs and farmland abandonment. While tree planting remains the standard reforestation strategy, there is increased interest in spontaneous regeneration as a cost-effective method with equal or potentially greater benefits. Furthermore, expanding areas of already established forests are left for passive rewilding to promote biodiversity conservation. Effective and objective methods are needed for monitoring and analyzing the development of forest structure under these management scenarios, with airborne laser scanning (lidar: light detection and ranging) being a promising methodology. Here, we assess the structural characteristics and development of unmanaged forests and 28- to 78-year old spontaneously regenerated forests on former agricultural land, relative to managed forests of similar age in Denmark, using 25 lidar-derived metrics in 10- and 30-m grid cells. We analyzed the lidar-derived cell values in a principal component analysis (PCA) and interpreted the axes ecologically, in conjunction with pairwise tests of median and variance of PCA-values for each forest. Spontaneously regenerated forest in general had increased structural heterogeneity compared to planted and managed forests. Furthermore, structural heterogeneity kept increasing in spontaneously regenerated forest across the maximal 78-year timespan investigated. Natural disturbances showed strong impacts on vegetation structure, leading to both structural homogeneity and heterogeneity. The results illustrate the utility of passive rewilding for generating structurally heterogeneous forested nature areas, and the utility of lidar surveys for monitoring and interpreting structural development of such forests.

Long-term influence of disturbance-generated microsites on forest structural and compositional development

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.

Silviculture to Restore Oak Savannas and Woodlands

Variability in historic fire regimes in eastern North America resulted in an array of oak natural communities that were dominant across the region. In the past century, savannas and woodlands have become scarce because of conversion to agriculture or development of forest structure in the absence of fire. Their restoration is a primary goal for public agencies and conservation organizations. Although they can be restored with a long-term regimen of prescribed burning, a combination of fire, timber harvesting, and forest thinning produces the desired structure and composition more efficiently. Prescribed fire is useful for sustaining oak savannas and woodlands, but it must be used judiciously to minimize timber damage and decreases in value. Integrating fire within a modified shelterwood approach promotes competitive oak reproduction and is flexible enough to produce savannas or woodlands. Sustaining these communities requires the replacement of the overstory during periods of no fire.

Seven decades of change in forest structure and composition in Pinus resinosa forests in northern Minnesota, USA: Comparing managed and unmanaged conditions

An understanding of long-term patterns of forest structural and compositional development is critical for anticipating management outcomes and developing appropriate silvicultural strategies for restoring complex forest conditions. In most cases, this information comes from stand-level assessments; however, the impacts and outcomes of management and other disturbances on forest development occur over multiple spatial scales across a landscape. We compared historical (1941) and contemporary (2012–2014) forest structure and composition on 301 plots distributed across managed and unmanaged, late seral red pine (Pinus resinosa)-dominated forests in a 1230ha landscape in north-central Minnesota, USA. Discriminate factor analysis was used to determine which compositional and structural attributes best described the forest conditions between two sampling periods (1941, 2012–2014) and management histories (managed and unmanaged). Plot basal area, average diameter of live trees, richness of tree size classes, and the basal area of standing deadwood were the four most important variables in discriminating between the managed and unmanaged plots in 1941 and 2013. In some cases, structural conditions between managed and unmanaged plots converged, including contemporary BA, trees per hectare, size inequality, and structural complexity indices. In contrast, several attributes, including standing deadwood basal area and percent hardwood basal area, were significantly greater in unmanaged plots after 72years and highlight the lasting influence of land use on these structural and compositional conditions. The broad ranges of structural and compositional conditions observed across the landscape highlight the importance of having spatially varying desired future conditions across managed stands to approximate this range in live and dead-tree attributes in unmanaged forests. In addition, the lower basal area of standing dead trees documented in this and other comparisons of unmanaged and managed P. resinosa systems argues for an increased emphasis on deliberate deadwood and live-tree retention to recruit these features if the restoration of late-successional forest conditions is included as a management objective.

Regeneration Responses to Management for Old-Growth Characteristics in Northern Hardwood-Conifer Forests

Successful tree regeneration is essential for sustainable forest management, yet it can be limited by the interaction of harvesting effects and multiple ecological drivers. In northern hardwood forests, for example, there is uncertainty whether low-intensity selection harvesting techniques will result in adequate and desirable regeneration. Our research is part of a long-term study that tests the hypothesis that a silvicultural approach called “structural complexity enhancement” (SCE) can accelerate the development of late-successional forest structure and functions. Our objective is to understand the regeneration dynamics following three uneven-aged forestry treatments with high levels of retention: single-tree selection, group selection, and SCE. Regeneration density and diversity can be limited by differing treatment effects on or interactions among light availability, competitive environment, substrate, and herbivory. To explore these relationships, manipulations and controls were replicated across 2 ha treatment units at two Vermont sites. Forest inventory data were collected pre-harvest and periodically over 13 years post-harvest. We used mixed effects models with repeated measures to evaluate the effect of treatment on seedling and sapling density and diversity (Shannon–Weiner H’). The treatments were all successful in recruiting a sapling class with significantly greater sapling densities compared to the controls. However, undesirable and prolific beech (Fagus americana) sprouting dominates some patches in the understory of all the treatments, creating a high degree of spatial variability in the competitive environment for regeneration. Multivariate analyses suggest that while treatment had a dominant effect, other factors were influential in driving regeneration responses. These results indicate variants of uneven-aged systems that retain or enhance elements of stand structural complexity—including old-growth characteristics—can generally foster abundant regeneration of important late successional tree species depending on site conditions, but they may require beech control where beech sprouting inhibits desired regeneration.

Changing forests—changing streams: riparian forest stand development and ecosystem function in temperate headwaters

AbstractLight availability influences temperature, primary production, nutrient dynamics, and secondary production in aquatic ecosystems. In forested freshwater ecosystems, shading by streamside (riparian) vegetation is a dominant control on light flux and represents an important interaction at the aquatic–terrestrial interface. Changes in forest structure over time, particularly tree mortality processes that gradually increase light penetration through maturing forest canopies, are likely to influence stream light fluxes and associated ecosystem functions. We provide a set of conceptual models describing how stream light dynamics change with the development of complex canopy structure and how changes in light availability are likely to affect stream ecosystem processes. Shortly after a stand‐replacing event, light flux to the stream is high, but light fluxes decline as canopies reestablish and close. Tree density, the degree of understory growth, patterns of tree mortality, and small‐scale disturbances interact as drivers of multiple pathways of forest structural development. Changes in canopy structure will, in turn, influence stream light, which is expected to impact primary production and stream nutrient dynamics as well as the amount of autochthonous carbon supporting aquatic food webs. Ultimately, these conceptual models stress the importance of recovery from historic forest disturbances as well as future forest change as important factors influencing the long‐term trajectories of ecosystem processes in headwaters.

Salt marsh‐mangrove ecotones: using structural gradients to investigate the effects of woody plant encroachment on plant–soil interactions and ecosystem carbon pools

Summary Changing winter climate extremes are expected to result in the poleward migration of mangrove forests at the expense of salt marshes. Although mangroves and marshes are both highly valued ecosystems, the ecological implications of mangrove expansion have not been fully investigated. Here, we examined the effects of mangrove expansion on below‐ground properties related to peat development and carbon storage. We investigated plant–soil interactions in marshes and across mangrove forest structural gradients in three locations in the northern Gulf of Mexico (USA). We compared our results to those from terrestrial grasslands where the effects of woody plant encroachment are often influenced by rainfall and plant traits. Abiotic conditions at our study locations differed, particularly in terms of physicochemical properties related to precipitation. Marsh species composition, marsh above‐ground biomass, and mangrove forest structural complexity also varied across these locations. Marshes in the driest location (Central Texas) had higher salinities and were dominated by low biomass succulent plants and lower soil carbon pools. Marshes in the wetter, less saline locations (Louisiana and North Florida) contained high biomass grasses and higher soil carbon pools. At all locations, above‐ground biomass and above‐ground carbon pools were higher in mangroves than marshes; however, below‐ground soil carbon pools were only higher in mangroves than marshes in the driest location. In the wetter locations, the linkages between mangrove forest structure and soil properties were minimal or not significant. However, in the driest location, there was a significant increase in soil properties related to peat development and carbon storage with increased mangrove forest structural development. Synthesis: Our results indicate that the ecological implications of woody plant encroachment in tidal saline wetlands are dependent upon precipitation controls of plant–soil interactions. Although the above‐ground effects of mangrove expansion are consistently large, below‐ground influences of mangrove expansion appear to be greatest along low‐rainfall coasts where salinities are high and marshes being replaced are carbon poor and dominated by succulent plants. Collectively, these findings complement those from terrestrial ecosystems and reinforce the importance of considering rainfall and plant–soil interactions within predictions of the ecological effects of woody plant encroachment.

Long-term impacts of prescribed fire on stand structure, growth, mortality, and individual tree vigor in Pinus resinosa forests

Prescribed fire is increasingly being viewed as a valuable tool for mitigating the ecological consequences of long-term fire suppression within fire-adapted forest ecosystems. While the use of burning treatments in northern temperate conifer forests has at times received considerable attention, the long-term (>10years) effects on forest structure and development have not been quantified. We describe the persistence of prescribed fire effects in a mature red pine (Pinus resinosa Ait.)-dominated forest in northern Minnesota, USA over a ∼50year period, as well as the relative roles of fire season and frequency in affecting individual tree and stand-level structural responses. Burning treatments were applied on 0.4ha compartments arranged in a randomized block design with four blocks. Burning treatments crossed fire season (dormant, summer) and frequency (annual, biennial, and periodic), and include an unburned control for comparison. Treatments were applied from 1960 to 1970, with no further management interventions occurring since. Data were collected periodically from 1960 to 2014.Forest structural development trajectories were significantly altered by the application of fire treatments. Burning treatments led to lower overstory densities, lower stand basal area, and larger tree diameters when compared to the unburned control over the study period. Differences between burning treatments were less apparent suggesting that the application of burning itself rather than a particular season and/or frequency of burning drives this long-term response. Overstory tree mortality and stand growth showed little or no response to burning treatments. In addition, we detected no impact of burning on long-term overstory tree growth efficiency (based on assessments >40years post burning) suggesting these treatments had little cumulative effect on tree vigor. Our results indicate that the effects of burning treatments on structural dynamics are not ephemeral, but rather alter stand development trajectories in the long-term. The persistent nature of these effects highlights their potential as a tool for long-lasting structural alterations in treated stands without compromising overstory tree growth and vigor. The lack of red pine recruitment throughout the duration of the study suggests that prescribed fire alone cannot regenerate this species, and that further alteration to overstory and seedbed conditions would be needed to secure new cohorts of this species.

Spatial aspects of tree mortality strongly differ between young and old-growth forests.

Rates and spatial patterns of tree mortality are predicted to change during forest structural development. In young forests, mortality should be primarily density dependent due to competition for light, leading to an increasingly spatially uniform pattern of surviving trees. In contrast, mortality in old-growth forests should be primarily caused by contagious and spatially autocorrelated agents (e.g., insects, wind), causing spatial aggregation of surviving trees to increase through time. We tested these predictions by contrasting a three-decade record of tree mortality from replicated mapped permanent plots located in young (< 60-year-old) and old-growth (> 300-year-old) Abies amabilis forests. Trees in young forests died at a rate of 4.42% per year, whereas trees in old-growth forests died at 0.60% per year. Tree mortality in young forests was significantly aggregated, strongly density dependent, and caused live tree patterns to become more uniform through time. Mortality in old-growth forests was spatially aggregated, but was density independent and did not change the spatial pattern of surviving trees. These results extend current theory by demonstrating that density-dependent competitive mortality leading to increasingly uniform tree spacing in young forests ultimately transitions late in succession to a more diverse tree mortality regime that maintains spatial heterogeneity through time.

Spatial distribution of trees on light taiga plots before selective thinning

Since 2009 the School of Agroecology and Business, Institute of Plant and Agricultural Sciences of the Mongolian University of Life Sciences in Darkhan has established research plots in two research areas in the Selenge aimag. The establishment was conducted in close cooperation with development organisations (FAO, GIZ) and the University of Goettingen. The purpose of the research initiative is to combine capacity development and monitoring of forest structure in the mountain forest steppe zone and taiga zone. Here we report results on the horizontal spatial structure of forest stands. We analysed the spatial distribution of trees on birch and larch plots of the research area «Altansumber» before a selective thinning took place on some plots in 2009. The research area is situated in the mountain forest steppe zone. The forests belong to the light taiga. The selected stands approach a chronosequence. The results showed that the tree distributions were mainly irregular («clumped»).Random spatial tree distribution occurred especially in the medium-aged birch stand. We found no indication of regular tree distributions in any of the plots. We assume that the disturbance regime and successional processes are the driving factors leading to the specific tree distribution pattern on the plots. Due to different regeneration strategies and life span of the dominating species the birch stands and the larch stands seem to differ slightly concerning the chronological occurrence of clumped and random spatial tree distribution. We finally conclude that a better control of the disturbance regime would not only support an undisturbed forest succession to riper forest stands but also result in less forest stands with irregular spatial distribution. This may also have implications on forest productivity.Mongolian Journal of Agricultural Sciences Vol.15(2) 2015; 91-99

Ecological restoration and fine-scale forest structure regulation in southwestern ponderosa pine forests

Fine-scale forest patterns are an important component of forest ecosystem complexity and spatial pattern objectives are an increasingly common component of contemporary silviculture prescriptions in dry fire-adapted forests of North America. Despite their importance, questions remain regarding the assessment of silvicultural treatments designed to meet spatial objectives. We initiated a replicated silvicultural assessment of two forest management approaches commonly applied in dense ponderosa pine forests of the Southwest United States: historical evidence-based ecological restoration guidelines (ERG) and northern goshawk (Accipiter gentilis) foraging area management recommendations (GMR). We compared stand-level characteristics, global tree location point patterns and tree group-level attributes resulting from the marking of these approaches to current forest conditions and patterns of historical forest remnants in six, 2.02ha stem mapped plots. We also assessed group-level Vegetative Structural Stage (VSS; a classification of fine-scale forest structural development used to regulate fine-scale spatial patterns in these forests). ERG and GMR-based treatments significantly reduced densities and basal area from the current condition, but did not significantly differ in density from historical forest remnant estimates. GMR-based treatments retained greater stand level basal area than ERG-based treatments, primarily in large, 28–48cm tree diameter classes. GMR-based treatments approximated global tree location point patterns of forest remnants better than ERG-based treatments, primarily due to a 5–6m minimum spacing of residual trees, but also likely due to specific aspects of ERG-based marking techniques. Despite this difference, both treatments resulted in group-level characteristics similar to those exhibited by historical forest remnants. Both treatments significantly altered group-level VSS area and reduced variation of tree diameters within classified VSS groups.Our study provides insight how tree marking techniques using historical forest remnants may have important effects on resulting fine-scale forest structure patterns. We also demonstrate how the use of global point or group-level pattern assessment methods can affect the evaluation of fine-scale spatial pattern objectives. Our analysis of VSS group characteristics highlights implementation and assessment issues associated with group-level spatial pattern identification, classification and regulation. We conclude that group-level classification and regulation is not necessary for maintaining fine-scale spatial patterns in complex ponderosa pine ecosystems subject to frequent fire disturbances and changing future climate conditions and societal demands. Both ERG and GMR-based approaches applied in this study may have utility in maintaining fine-scale spatial heterogeneity and promoting resiliency in Southwest ponderosa pine forests.

Harvest residue removal and soil compaction impact forest productivity and recovery: Potential implications for bioenergy harvests

Understanding the effects of management on forest structure and function is increasingly important in light of projected increases in both natural and anthropogenic disturbance severity and frequency with global environmental change. We examined potential impacts of the procurement of forest-derived bioenergy, a change in land use that has been suggested as a climate change mitigation strategy, on the productivity and structural development of aspen-dominated ecosystems. Specifically, we tested the effects of two factors: organic matter removal (stem-only harvest, whole-tree harvest, whole-tree harvest plus forest floor removal) and soil compaction (light, moderate, and heavy) over time. This range of treatments, applied across three sites dominated by aspen (Populus tremuloides Michx.) but with different soil textures, allowed us to characterize how disturbance severity influences ecosystem recovery.Disturbance severity significantly affected above-ground biomass production and forest structural development with responses varying among sites. At the Huron National Forest (sandy soils), the removal of harvest residues reduced above-ground biomass production, but no negative effect was observed following whole-tree harvest at the Ottawa and Chippewa National Forests (clayey and loamy soils, respectively) relative to stem-only harvest. Maximum diameter and the density of stems greater than 5cm DBH exhibited negative responses to increased disturbance severity at two sites, indicating that structural development may be slowed. Overall, results suggest that disturbance severity related to procuring harvest residues for bioenergy production may impact future productivity and development, depending on site conditions and quality.