Tropical cyclones are increasing in intensity and size and, thus, are poised to increase in importance as disturbance agents. Our understanding of cyclone ecology is biased towards the North Atlantic ...Basin, because cyclone effects do differ across oceanic basins. Cyclones have both short and long-term effects across the levels of biological organization, but we lack a scale‐perspective of cyclone ecology. Effects on individual trees, such as defoliation or branch stripping and uprooting, are mechanistically linked to effects at the community and ecosystem levels, including forest productivity and stand regeneration time. Forest dwarfing via the gradual removal of taller trees by cyclones over many generations illustrates that cyclones shape forest structure through the accumulation of short-term effects over longer timescales.
Our understanding of cyclone ecology is biased toward the Atlantic Basin, but cyclone effects on forests differ among oceanic basins because of differences in storm frequency and strength.Projected increases in cyclone frequency, intensity, and geographic distribution will threaten the tall old trees of the world, especially those in old-growth forests, which historically have few cyclones, such as those in the southeastern USA and southern Japan.Cyclone effects on ecosystem processes, such as primary productivity and nutrient cycling, are mediated through the range of direct disturbance effects on individuals and species, such as defoliation and tree mortality.Forest dwarfing, because of the gradual removal of tall trees by individual cyclones, illustrates the accumulative short-term effects of individual cyclones on shaping long-term forest structure.
•Accurate simulations of forest regeneration under climate change remain aspirations.•Tree regeneration models often rely on strong assumptions.•More dynamic representations of forest regeneration ...are needed.•Increasing the ecological data basis is required to close knowledge gaps.
Climate change impacts on Europe’s forests are becoming visible much sooner than previously anticipated. The increase in natural disturbances leads to tree mortality and raises concerns about the forest’s adaptive potential to sustain vital ecosystem services. In this context, the regeneration phase is crucial and comprises the largest potential to adapt to new environmental conditions with long lasting implications. Yet, forest regeneration is particularly susceptible to climatic changes due to the many directly climate-dependent processes, such as seed production and germination but also seedling and sapling development. Models of forest dynamics (MFDs) are essential to describe, understand and predict the effects of changing environmental and management factors on forest dynamics and subsequently on associated ecosystem services. We review a large variety of MFDs with regard to their representation and climate sensitivity of regeneration processes. Starting with a description of the underlying biological processes, we evaluate the various approaches taking into account specific model purposes, and provide recommendations for future developments. We distinguish between models based on ecological principles and models based on empirical relationships. We found an ample mix of regeneration modelling approaches tailored to different model purposes. We conclude that current approaches should be refined to adequately capture altered regeneration trends. Specifically, refinement is needed for MFDs that rely on ecological principals, as they suffer from knowledge gaps and underrepresented processes, thereby limiting their ability to accurately simulate forest regeneration under climate change. Global vegetation models are strongly constrained by their weak representation of vegetation structure and composition, and need to include more detail regarding structural complexity and functional diversity. Models focused on timber yield often rely on strong assumptions regarding the abundance and composition of the next tree generation, which may no longer hold true with changes in climate and forest management. With the increased utilization of natural regeneration as a source of forest renewal, more dynamic representations of tree regeneration are needed. Our review highlights the necessity to increase the data basis to close knowledge gaps and to enable the adequate incorporation and parameterization of the involved processes. This would allow to capture altered regeneration patterns and subsequent effects on forest structure, composition and, ultimately, forest functioning under climate change.
Northern temperate coniferous forests serve as crucial connectors between boreal and temperate forests, yet they are vulnerable to various stressors such as climate change and human activities. ...Severe drought poses a significant threat to plant species within these forests, prompting recent research into its impacts. However, many studies lack explicit definitions of post-disturbance vegetation processes and fail to identify potential interactions with disturbance factors, necessitating comprehensive discussions. This study examines the effects of drought on tree growth patterns of the main dominant species in northern temperate regions: Abies nephrolepis and Picea jezoensis, along with two commonly associated Betula ermanii, and Quercus mongolica. Additionally, new disturbance factors in forests inhabited by these species (A. nephrolepis and P. jezoensis) were evaluated based on community classification. The study sites were located in the Mt. Baekdu (Changbai) and South Korea regions, which are positioned at the southern limit of the phytogeographical patterns of target species. Results indicate that A. nephrolepis and P. jezoensis exhibit high levels of recovery and resilience, while B. ermanii and Q. mongolica demonstrate high resistance. Species-specific responses align with drought intensity, with resistance, recovery, and resilience decreasing notably with increasing pre-drought radial growth. South Korean forests, the invasion of the vine species Tripterygium regelii after the death of A. nephrolepis in the overstory vegetation threatens the regeneration of new trees. However, certain environmental factors, such as high rock exposure and dense overstory canopy, limit vine invasion. Based on the results, pre-drought radial growth emerges as a key determinant in how trees respond to drought. Additionally, the results suggest the potential for new disturbances to emerge in forest gaps due to overstory vegetation mortality induced by global warming. These findings contribute to a deeper understanding of increasing drought stress, aid in identifying climate refugia, and inform conservation priorities based on habitat characteristics.
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•Gymnosperms and angiosperms reacted differently to extreme drought.•Higher levels of pre-drought radial growth increased vulnerability to drought stress.•Vine invasion into forest gaps by dead upper vegetation hinders forest regeneration.•High rock exposure and dense overstory canopy, limit vine invasion.
Slash walls are an effective forest management practice to prevent deer herbivory and promote forest regeneration following a timber harvest. However, the material cost, i.e. amount of wood material, ...needed for quality slash walls is unknown or at best based on highly uncertain empirical estimation. Quantifying how total and merchantable timber wood volume varies with width and height across slash walls will facilitate future planning and application of slash walls. In this study, we estimated wood volume per unit length (∼30.48 m) from total stem cross-sectional area in 40 randomly selected cut-through passages cut into 14 slash walls located at Cornell University’s Arnot Teaching and Research Forest (ATRF) in south-central New York. Within each passage we used Terrestrial Laser Scanning (TLS) to identify individual stems and obtain cross-sectional surface area. We found that TLS derived stem diameters were highly consistent with manual stem diameter measurements for 10 selected wall passages (N = 308, R2 = 0.933, RMSE = 1.881 cm). However, TLS tends to underestimate total cross-sectional area due to omission of small stem cross-sections (diameter < 5.08 cm). Cross-sections of small stems often have a low number of total points even when point density is high, especially when they are not facing the scanner. They are also more vulnerable to occlusion (i.e., lack of points due to blocking by other stems). TLS-based wood volume estimates were similar across both short and tall slash walls in the study with an average volume of 21.34 m3/30 m for short slash walls and 21.50 m3/30 m for tall slash walls, corresponding to 16.9 t dry biomass /30 m and 17.0 t dry biomass /30 m respectively. The small difference in woody volume was due to tall slash walls achieving additional height mainly through non-compacted small diameter crown and brush tops that have little woody volume. Average merchantable (diameter > 15.24 cm) and non-merchantable (diameter < 15.24 cm) timber fraction was 68.75 % and 31.35 % for short slash walls and 65.04 % and 34.96 % for tall slash walls. We further assessed slash wall height and width using Airborne Laser Scanning (ALS) for eight other tall slash walls. We found TLS measurements are representative of whole slash wall height and width variability based on ALS measurements. Our results provide novel data and methodology to estimate the construction cost of slash walls which are critical for optimizing slash wall applications.
•Terrestrial Laser Scanning can estimate slash wall cross-sectional area and volume.•Similar volume estimates for short & tall slash walls: 21.3 m³/30 m & 21.5 m³/30 m.•Average merchantable wood for slash walls was 66.53 % and 33.47 % for non-merchantable.•Airborne Laser Scanning can estimate slash wall height and width variability.•Provides novel data to estimate the construction cost of slash walls.
The constraint caused by wild ungulates on forest regeneration is increasing worldwide. Hypotheses for plant association effects predict that species susceptible to herbivory can gain protection from ...other neighbouring plant species. In theory, such interactions could help limit the impact of browsing on the regeneration of specific tree species. However, the presence of neighbouring species can also result in increasing competition for resources between species. The resultant effects on forest regeneration of these interactions, both positive (protection against herbivores) and negative (inter-specific competition) are still unclear.
To gain insight, we coupled models of browsing by roe deer (Capreolus capreolus) and of forest dynamics to simulate trajectories of oak (Quercus petraea (Matt.) Liebl.) regeneration admixed with species of contrasted palatability and growth rate under different scenarios of browsing pressure and initial sapling density. We also investigated how releasing oak saplings from all or specific neighbours during the simulation affect regeneration.
We found that admixed species composition had a relatively weak effect on the density of oak recruits, but a strong effect on the duration of the regeneration phase. Oak regenerated faster when admixed with species of intermediate growth and low palatability (Fagus sylvatica) than with species of fast growth and high palatability (Carpinus betulus L.), except at intermediate sapling density and high browsing pressure where we found the opposite. Releasing oak from all competitors was most effective in promoting oak regeneration when admixed with both species together, although the benefit of competition release was much weaker at high browsing pressure. Lastly, we found that at low initial sapling density (i.e., 10 saplings/m2), oak regeneration was driven only by browsing and the effect of admixing species became negligible.
Our study showed that admixing oak with palatable neighbours impedes rather than improves oak regeneration due to increased competition for resources. As such, we suggest that the benefits of herbivore diversion can be off-set by increased inter-specific competition.
•In forests, saplings compete for resources and protect each other from herbivory.•We studied the balance between facilitation and competition by neighbour species.•We coupled models of oak regeneration dynamics (RReShar) and of roe deer browsing.•Our simulations suggest that herbivory diversion is generally offset by competition.
•Thinned and shearbladed treatments can promote tree recruitment.•Shearblading has greater long-term impacts on understory composition and thaw depth.•Fire behavior modeling did not capture temporal ...shifts in shearbladed understory.•Treatments did not consistently reduce fire behavior relative to an untreated stand.
Wildfire activity is increasing in boreal forests as climate warms and dries, increasing risks to rural and urban communities. In black spruce forests of Interior Alaska, fuel reduction treatments are used to create a defensible space for fire suppression and slow fire spread. These treatments introduce novel disturbance characteristics, making longer-term outcomes on ecosystem structure and wildfire risk reduction uncertain. We remeasured a network of sites where fuels were reduced through hand thinning or mechanical shearblading in Interior Alaska to assess how successional trajectories of tree dominance, understory composition, and permafrost change over ∼ 20 years after treatment. We also assessed if these fuel reduction treatments reduce modeled surface rate of fire spread (ROS), flame length, and fireline intensity relative to an untreated black spruce stand, and if surface fire behavior changes over time. In thinned areas, soil organic layer (SOL) disturbance promoted tree seedling recruitment but did not change over time. In shearbladed sites, by contrast, both conifer and broad-leaved deciduous seedling density increased over time and deciduous seedlings were 20 times more abundant than spruce. Thaw depth increased over time in both treatments and was greatest in shearbladed sites with a thin SOL. Understory composition was not altered by thinning but in shearbladed treatments shifted from forbs and horsetail to tall deciduous shrubs and grasses over time. Modeled surface fire behavior was constant in shearbladed sites. This finding is inconsistent with expert opinion, highlighting the need for additional fuels-specific data to capture the changing vegetation structure. Treatment effectiveness at reducing modeled surface ROS, flame length, and fireline intensity depended on the fuel model used for an untreated black spruce stand, pointing to uncertainties about the efficacy of these treatments at mitigating surface fire behavior. Overall, we show that fuel reduction treatments can promote low flammability, deciduous tree dominated successional trajectories, and that shearblading has strong effects on understory composition and permafrost degradation that persist for nearly two decades after disturbance. Such factors need to be considered to enhance the design, management, and predictions of fire behavior in these treatments.
•Implications and promise of effective usefulness of Lidar metrics for monitoring forest landscape restoration.•Canopy structural attributes were useful to characterize and distinguish different ...forest types.•Canopy structure showed relation with the tree community Shannon Index but not with richness.•A novel Lidar metric (LAHV) showed promising results for qualifying tree cover and assess its functions.•We expect our results can help address realistic restoration goals and actions under a global change context.
Ambitious pledges to restore over 400 million hectares of degraded lands by 2030 have been made by several countries within the Global Partnership for Forest Landscape Restoration (FLR). Monitoring restoration outcomes at this scale requires cost-effective methods to quantify not only forest cover, but also forest structure and the diversity of useful species. Here we obtain and analyze structural attributes of forest canopies undergoing restoration in the Atlantic Forest of Brazil using a portable ground lidar remote sensing device as a proxy for airborne laser scanners. We assess the ability of these attributes to distinguish forest cover types, to estimate aboveground dry woody biomass (AGB) and to estimate tree species diversity (Shannon index and richness). A set of six canopy structure attributes were able to classify five cover types with an overall accuracy of 75%, increasing to 87% when combining two secondary forest classes. Canopy height and the unprecedented “leaf area height volume” (a cumulative product of canopy height and vegetation density) were good predictors of AGB. An index based on the height and evenness of the leaf area density profile was weakly related to the Shannon Index of tree species diversity and showed no relationship to species richness or to change in species composition. These findings illustrate the potential and limitations of lidar remote sensing for monitoring compliance of FLR goals of landscape multifunctionality, beyond a simple assessment of forest cover gain and loss.
Ensuring the recruitment of desired tree species is a primary goal when considering successful regeneration of timber harvests. Deer populations that are overabundant relative to forage availability ...within their local landscapes pose a considerable challenge to successful forest regeneration. We evaluated the short-term (<10 years) impact of white-tailed deer browsing on woody structure and composition in northcentral Pennsylvania. Specifically, we compared woody plant species density, height, and cover within 10 pairs of fenced and unfenced regenerating timber harvests. Percent of browsed stems was higher in unfenced harvests for red maple (Acer rubrum), oaks (Quercus spp.), Rubus spp., sassafras (Sassafras albidum), and witch hazel (Hamamelis virginiana). Stem density did not differ between fenced and unfenced harvests for any species except Rubus spp., which was greater in the former. However, height of serviceberry (Amalanchier spp.), sassafras, northern red oak (Quercus rubra), Rubus spp., and red maple was taller in fenced harvests. Both vertical and horizontal vegetation density were greater in fenced harvests, suggesting a more structurally complex understory in fenced harvests. Rubus spp. and tall (>1.5 m) sapling cover were greater in fenced harvests, while unfenced harvests had greater forb, fern, and blueberry/huckleberry (Vaccinium spp./Gaylussacia spp.) cover. Our results suggest that browsing by deer in the years initially (<10 years) following timber harvest may not immediately impact woody species density, but can considerably reduce seedling height, overall horizontal and vertical structure, and composition of vegetation strata. Reduced sapling height and greater prevalence of blueberry/huckleberry, forbs, and ferns in unfenced harvests threaten the successful recruitment of desired species into the future overstory. Our results from large, operational-scale timber harvests combined with those from previous small-scale studies stress the potential value of deer exclusion fencing to achieve successful forest regeneration. Future research should examine the timing of fence removal to achieve forest regeneration success, while also providing deer access to available foraging opportunities during the later portion of stand initiation.
•Propose new index (Forest Recovery Index – FRI) to detect post-fire larch forest regeneration.•Synergistic use of different remote sensing based indices (FVC and FRI) to monitor different stages of ...post-fire larch forest succession.•First assessment and trajectory of larch forest regeneration after fire in the taiga-steppe transition zone in northern Mongolia/south central Siberia using remote sensing.
Remote sensing with time series data offers considerable potential in the trajectory of post forest fire dynamics beyond the current monitoring of structural attributes that are displayed in the post-fire area. Many studies have addressed this topic by using time series remote sensing indices; however, this approach has sometimes been demonstrated as an unrealistic and biased representation of the post-fire forest patterns due to the saturation issues of vegetation indices. These saturation issues then lead to an underestimation of the forest successional stages and an overestimation of the forest recovery rate. This paper aims to develop a framework for trajectory of the post-fire forest patterns in the Siberian boreal larch forest (Larix sibirica) with the synergistic use of different remote sensing based vegetation-cover indicators derived from the Landsat time series and the WorldView-2 images. A time-series of the forest recovery index (FRI) and fractional vegetation cover (FVC) has been analyzed to estimate the rates of forest regeneration and vegetation recovery across different burn severity levels in the Siberian larch forest. The results showed that the FRI method can be used to observe the regrowth of the larch forest from the tenth year after the fire overlapping with the period of significant increase in the sapling stem volume. The post-fire larch forest canopy can fully recover to the pre-fire condition with respect to the magnitude of the FRI values after 30–47 years where the highest regeneration rate was observed in the moderate burn severity areas followed by the low and high burn severity. On the other hand, the FVC method was positively correlated with burn severity and more sensitive for evaluating the early stages of the forest succession in which the FVC dramatically increases after 5–6 years after the fire. The significant growth of FVC was accentuated by the maximum emergence of the sapling density as well as the rapid growth of herbaceous plants, grasses, shrubs, and shade-intolerant trees immediately after the fire, which could not be evaluated using the FRI. Both time series of the FRI and the FVC are valuable tools for determining the dominant stages of the post-fire larch forest succession in order to understand the relationships between fire disturbance and natural cycles of the boreal larch forest.
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•Oak forests are of great economic and conservation importance.•We identify integrative management options for forestry and nature conservation.•Light availability is a strong link ...between forestry and conservation demands.•There is an urgent need for integrative oak forest planning approaches.•Ecological continuity should be secured in structural “sustainability units”.
Central European temperate oak woodlands are highly valued for their rich biodiversity. They are also of great economic importance and forest management aims to produce high quality timber, which demands high investments. The aim of this literature review is to identify management options for forestry and nature conservation that sustain both the ecological value of oak forests and the economic viability of oak silviculture.
We addressed three main questions: (a) Oaks and close-to-nature forestry – what are the key silvicultural challenges and options?, (b) What is the particular significance of ecological continuity and which structural features are of importance for biodiversity conservation in oak forests?, (c) What are the key elements and possible strategies of forest management that sustain the ecological values in oak forests in combination with viable forestry?
Light availability appeared to be a conspicuous link connecting the conservation and the silvicultural aspects of multifunctional oak forest management: Both young oak trees and multiple oak woodland specialist species are characterized by their need for increased sunlight exposure. This common denominator provides a sound basis for integrative management practices for forestry and nature conservation. The concept of retention forestry offers purposeful approaches. So the harvest of valuable timber oaks or the creation of canopy gaps for oak regeneration can be used to release the crowns and trunks of habitat oaks from shading and competition. When looking at the management of oak woodland biodiversity hotspots, the re-establishment of (modified) historical forest management techniques, which increase stand openness and create transitional habitats that provide suitable oak regeneration niches, seems to be necessary.
Not only the continuity of oak woodland cover and natural site conditions, but also the uninterrupted temporal continuity and availability of wood-related structural features turned out to be of particular importance for oak woodland specialist species. We identified an urgent need for systematic forest planning approaches that secure the long-term availability of these structural features within areas or “sustainability units” that are large enough to maintain viable populations of oak woodland specialist species. In particular, conservation-oriented forestry measures should mainly be implemented in those areas, where the greatest effectiveness is to be expected. In the sustainability units, oak regeneration measures ought to take place either in close vicinity to old oak stands or directly in these stands. The choice of one of these options should be based on a careful consideration of the needs and possibilities of both silvicultural and nature conservation management.
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