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Impact of the category 5 hurricane Otis on October 25, 2023, was revealed through changes in land use/land cover (Lu/Lc) and vegetation density (NDVI) in an area of ca.640.5 km2, surrounding the Acapulco Bay at southwest Mexico. Waterlogging (ca.110 km2) mostly occurred in the crop land, fallow land and forest located in the swamps as well as on coastal barrier of the Tres Palos Lagoon (SE of the Bay) and included the international airport. Effect on vegetation was more in watershed of the Coyuca Lagoon as well as in the National Park (NW of the Bay) with strong wind of the remnants damaging the forest and crop (NDVI>0.8) in an area of ca.133.5 km2. This scientific communication provided important data through the remote impact assessment for the evaluation of catastrophic events along the coastal Mexico. [Display omitted] • Change in Lu/Lc and NDVI around Acapulco Bay at southwest Mexico from hurricane Otis. • Enhanced waterlogging in swamps and coastal barrier of the Tres Palos Lagoon (SE of the bay). • More damage to forest and crops in watershed of the Coyuca Lagoon and in the National Park (NW of the bay). [ABSTRACT FROM AUTHOR]

Highlights • The agent-based model was created using the basic knowledge of gust, wind, and tree. • The Agent-based model demonstrated wind damage similar to the observed damage in forests. • The model described damage propagation and forest edge effects. • The model showed some phenomena, which were similar to the previous research. • Possibilities of improving the agent-based model were discusses. Abstract Powerful storms, consisting of strong gusts and winds, damage forests. Therefore, foresters need forest management strategies to reduce the damage risk. This paper focused on the damage patterns within the forest as the final results of multiple tree-wind dynamic interactions in time and space during a storm. Recent developments in computer technology allow for the possibility of simulating the complex and dynamic phenomena of damage during a storm but are extremely time consuming. To simplify the simulations without losing the crucial aspects of wind damage in forests, we introduced a computer simulation model using the agent-based modelling (ABM) technique, which capture the phenomena and interactions of individuals called 'agents'. We created an ABM for forest wind damage simulation, coupling together an accepted understanding of wind gusts in forests, tree bending moments, and damage propagation. The model was tested with variations in three conditions: trees acclimated and unacclimated to their wind environment; three levels of gust strength; and three tree planting densities. The ABM was able to replicate damage patterns and demonstrate damage propagation within the forest and the effects of forest edges. The difference in the rate of damage in the forest between acclimated and unacclimated edges became similar with an increase in the gust intensity, and a decrease in tree density through a reduction in the shelter effect of the forest. The ABM could be improved in the future by parametrizing the variation in individual tree resistance, and the variation in gust and wind strength, as well as adding more information on local environmental conditions such as topography and soil variation, and storm characteristics such as duration and intensity. [ABSTRACT FROM AUTHOR]

Windstorms are among the main factors causing damages to forest ecosystems. These meteorological phenomena cannot be predicted, prevented or controlled. They are occurring rapidly and take place in a meteorological context characterized by high velocities of the air currents. This paper analyses the characteristics of the severe meteorological events on 20 July 2011 which have led to windthrows on extended areas within the Apuseni Mountains in the Romanian Carpathians. The study highlights the evolution of the synoptic processes both at regional scale and at mesoscale. The meteorological analysis is carried out based on synoptic maps and by means of the data coming from the doppler WSR-98D radar in Bobohalma. The main results indicate the occurrence of the severe meteorological phenomena against the background of alternating atmospheric circulation types. The main cause is the transition of the zonal circulation into maritime tropical circulation. This contributed to the destabilizing of the warm and moist air masses that have generated strong storms at national level. [ABSTRACT FROM AUTHOR]

Climate change is likely to affect windthrow risks at northern latitudes by potentially changing high wind probabilities and soil frost duration. Here, we evaluated the effect of climate change on windthrow risk in eastern Canada's balsam fir ( Abies balsamea [L.] Mill.) forests using a methodology that accounted for changes in both wind speed and soil frost duration. We used wind speed and soil temperature projections at the regional scale from the CRCM5 regional climate model (RCM) driven by the CanESM2 global climate model (GCM) under two representative concentration pathways (RCP4.5, RCP8.5), for a baseline (1976-2005) and two future periods (2041-2070, 2071-2100). A hybrid mechanistic model (ForestGALES) that considers species resistance to uprooting and wind speed distribution was used to calculate windthrow risk. An increased risk of windthrow (3 to 30%) was predicted for the future mainly due to an increased duration of unfrozen soil conditions (by up to 2 to 3 months by the end of the twenty-first century under RCP8.5). In contrast, wind speed did not vary markedly with a changing climate. Strong regional variations in wind speeds translated into regional differences in windthrow risk, with the easternmost region (Atlantic provinces) having the strongest winds and the highest windthrow risk. Because of the inherent uncertainties associated with climate change projections, especially regarding wind climate, further research is required to assess windthrow risk from the optimum combination of RCM/GCM ensemble simulations. [ABSTRACT FROM AUTHOR]

The aims of the investigation were to (i) quantify the changes in natural regeneration and stand structure, (ii) determine the role of deadwood in the process of regeneration following the disturbance, and (iii) determine the effect of disturbance severity on tree recruitment. The study was conducted in the Szast Protected Forest, which was established after a blowdown in 2002. The results showed that the trees were mainly wind-snapped. The basal area of the slightly disturbed stands increased over time. Herb cover increased, whereas moss cover decreased in 2011. The disturbance severity influenced the density of tree species regeneration, moss and herb ground cover, species diversity, average tree height, tree vitality, and damage caused by herbivores. The density of natural regeneration increased and new species became established after the disturbance. Scots pine (Pinus sylvestris L.) was the dominant tree species during the regeneration process except in the severely disturbed stand from which wood had been removed; in this case, birch was the dominant species. Wind disturbance increased species diversity and created a new forest with a particular species structure and trees that varied in age and height. The results of this study will be useful for foresters and policymakers to change the existing approaches to large-scale disturbances in the Polish forests. [ABSTRACT FROM AUTHOR]

Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (Forest GALES) to an empirical growth model for radiata pine ( Pinus radiata D. Don) and a process-based growth model ( cenw) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The cenw model was used to estimate site productivity for constant CO2 concentration at 1990 values and for assumed increases in CO2 concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1B (mid-range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the Forest GALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO2 concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances. [ABSTRACT FROM AUTHOR]

Islands formed upstream of mega hydroelectric dams are excellent experimental landscapes to assess the impacts of habitat fragmentation on biodiversity. We examined the effects of plot-, patch- and landscape-scale variables on the patterns of floristic diversity across 34 forest islands that had experienced 26 years of isolation since the creation of the 4437 km2 Balbina Hydroelectric Reservoir of central Brazilian Amazonia. In addition, three undisturbed continuous forest sites in neighbouring mainland areas were also sampled across a comparable elevational gradient., We identified all live trees ≥10 cm DBH at species level within a total of 87 quarter-hectare forest plots and conducted a comprehensive compilation of functional attributes of each tree species. We then examined species-area relationships ( SARs) and the additional effects of patch and landscape-scale metrics on patterns of tree assemblage heterogeneity, both in terms of taxonomic and functional diversity., Despite a clearly positive SAR, edge-mediated forest disturbance was the single most important driver of species composition and abundance within islands. Our results suggest that non-random floristic transitions within island plots followed a predictable pattern, with different life-history traits either penalizing or rewarding local persistence of different functional groups. Distance to edges mediated the probability of tree mortality induced by windfalls and episodic surface fires, clearly resulting in faster species turnover and unidirectional changes in guild structure within small islands where light-wooded fast-growing pioneers largely replaced heavy-wooded species of the old-growth flora., Synthesis. Following a simultaneous 26-year post-isolation history, we disentangle the effects of habitat loss and insularization on tree assemblages within a large set of Amazonian 'true' forest islands, of variable sizes, sharing a uniform open-water matrix. Area effects are expressed via a response to edge effects, with trees in smaller islands being more vulnerable to edge-related surface fires and wind-throws. Additionally, forest edge effects can be a powerful driver of non-random floristic transitions across islands within the Balbina archipelago via a process of rapid pioneer proliferation, drastically affecting both the taxonomic and functional composition of insular tree communities. Finally, our results indicate that detrimental effects of forest fragmentation induced by hydroelectric dams are considerably stronger than those of forest patches embedded within a terrestrial vegetation matrix. [ABSTRACT FROM AUTHOR]

Abstract: Land degradation as a result of wind (aeolian processes) is one of the most significant causes of soil loss in northern Iran. In order to gain a broader understanding of the specific effects of aeolian disturbance on soils in this region, research was conducted to evaluate soil microbial respiration and nitrogen mineralization in places where differences in microtopography occur due to the uprooting of trees by windthrow events, thereby causing variations in microtopography hereby referred to as “pit–mound positions”. A twenty-hectare study site situated within the Tarbiat Modares University Experimental Forest Station located in the Mazandaran province of northern Iran was chosen for this research, with thirty-four uprooted trees selected for detailed study. A classification of five microsites was developed to distinguish differences in microtopography in the immediate vicinity of these uprooted trees: mound top, mound wall, pit bottom, pit wall and closed canopy. Soil was sampled in the 0–15, 15–30 and 30–45cm depths at all microsites using a core soil sampler with an 81cm2 cross section. Soil reaction, organic carbon, total nitrogen, carbon-to-nitrogen ratio, moisture, abundance and biomass of earthworms, soil microbial respiration and net N mineralization for all samples were measured in the laboratory. Statistical comparisons revealed that the highest soil microbial respiration and net N-mineralization occurred in pit bottoms. Mound tops showed the lowest levels of soil microbial respiration and net N mineralization. Measurements of soil microbial respiration and net N mineralization were shown to decrease in relation to increased soil depth, with significant differences depending on soil depth. Indications of aeolian processes indicate that windthrow events create different microsites, thereby influencing the specific micro-scale soil characteristics. These micro-scale characteristics should be taken into account when performing forest soils surveys and to inform forest management practices. [Copyright &y& Elsevier]

Understanding natural mortality patterns and processes of forest tree species is increasingly important given projected changes in mortality owing to global change. With this need in mind, the rate and spatial pattern of mortality was assessed over an 89-year period in a natural-origin Pinus resinosa (Aiton)-dominated system to assess these processes through advanced stages of stand development (stand age 120-209 years). Average annual mortality rates fluctuated through time, yet were within the range reported in other studies (0.60%-3.88% depending on species and sampling interval). Tree mortality was attributed to multiple agents, including the senescence of the short-lived Pinus banksiana Lamb., windthrow, root-rot fungi ( Armillaria ostoyae (Romagn.) Herink), and perhaps infrequent droughts. Despite the often contagious nature of many disturbance agents, the overall spatial pattern of mortality events (the arrangement of dead trees within the fixed initial population of live trees) was random at all scales tested. Similarly, the current spatial pattern of dead trees was predominantly random, despite clustering at small scales (2-4 m). These findings underscore the importance of studying mortality rates, agents, and spatial patterns over long time periods to avoid misinterpreting stochastic mortality events, and their influence on longer term stand structure and development. [ABSTRACT FROM AUTHOR]

Downed and standing deadwood (DW) is a key resource for maintaining forest biodiversity. Although extreme events such as windthrow and fires produce large quantities of DW, this substrate is often drastically reduced by logging activities. To elucidate the respecting consequences of salvage-logging, we assessed both quantity and quality of storm-derived DW (storms Vivian 1990 and Lothar 1999) in Swiss forests using a sample of 90 windthrow sites with ≥3 ha complete windthrow and at elevations ranging from 350 to 1,800 m a.s.l. The majority had been salvage-logged (SL) a few years after the windthrow. On each site, we recorded DW amount and quality on six circular sample plots 20 or 50 m in size. DW volume on SL sites was surprisingly high, with 76.4 m ha on average 20 years after Vivian and 73.8 m ha 10 years after Lothar. In comparison, DW volumes on unsalvaged sites, that is, with no post-windthrow intervention (NI), amounted to 270 m ha. A wide variety of wood decay stages and diameter classes (10 to ≥70 cm) was found on both NI and SL sites, suggesting considerable habitat diversity for DW-associated species irrespective of the treatment. The considerable amounts of DW left after salvage-logging distinctly exceed the minimum DW volumes in forest stands proposed by Müller and Bütler (Eur J For Res 129: 981-992, ) in a conservation context, which demonstrates the importance of wind disturbance for biodiversity. Further studies should quantify DW of individual tree species, since habitat requirements are species-specific. [ABSTRACT FROM AUTHOR]

The effect of wind disturbance on ectomycorrhizal fungal (EMF) communities in forests remains largely uninvestigated. We monitored EMF colonizing Pinus strobus L. seedlings in an oak-pine forest in northern Georgia, USA, after catastrophic wind disturbance. Over three years, we sampled naturally regenerating P. strobus seedlings across three growing seasons in the windthrow area and an adjacent undisturbed forest, identifying 53 unique EMF taxa using molecular techniques. The diversity of EMF colonizing seedlings in the undisturbed forest was consistently greater than in the windthrow area. Although the EMF compositional similarity between EMF in the gap and in the undisturbed forest was low throughout the study, many EMF taxa colonized seedlings in both the gap and the undisturbed forest. Seasonal differences in EMF composition and diversity were pronounced in the undisturbed forest, with diversity increasing from spring to fall. In contrast, EMF composition and diversity were relatively constant throughout seasons in the windthrow gap. We hypothesize that the extent of host community mortality and the extent of EMF host community regeneration following disturbance drive both EMF species composition and community dynamics. However, this hypothesis warrants further study. [ABSTRACT FROM AUTHOR]

Abstract: Wind is the dominant agent of damage in forests in Western Europe. Traditional wind-damage models calculate a probability for damage or a critical wind speed at which damage occurs. However, in a dynamic vegetation model actual damage to stands and individual trees is needed to get a dynamical progression of the vegetation. We present a prototype for a new approach to modelling forest wind damage at the regional scale, which we incorporate within a dynamic vegetation model. The approach is based on knowledge from both empirical and mechanical models and calculates the damaged fraction of a cohort based on wind load and a sensitivity that depends on the current physical state and history of the cohort in relation to the ecosystem. The modelling concept has been developed, calibrated and evaluated for Swedish conditions but can be applicable to other similar areas with minor modification. Because of the stochastic nature of local wind load and the difficulty of describing the stand-level exposure, the ability to explain observed damage at stand level was low. Regional level variation in damage, which more depends on the wind load, was however explained reasonably well (R 2 =0.43). We suggest that this is a useful concept for evaluating alternatives of forest management under different climate scenarios in the process of adaptation to future storm-damage risks. [Copyright &y& Elsevier]

A number of factors influence the amount of mercury (Hg) in forest floors and soils, including deposition, volatile emission, leaching, and disturbances such as fire. Currently the impact on soil Hg pools from other widespread forest disturbances such as blowdown and management practices like salvage logging are unknown. Moreover, ecological and biogeochemical responses to disturbances are generally investigated within a single-disturbance context, with little currently known about the impact of multiple disturbances occurring in rapid succession. In this study we capitalize on a combination of blowdown, salvage logging and fire events in the sub-boreal region of northern Minnesota to assess both the singular and combined effects of these disturbances on forest floor and soil total Hg concentrations and pools. Although none of the disturbance combinations affected Hg in mineral soil, we did observe significant effects on both Hg concentrations and pools in the forest floor. Blowdown increased the mean Hg pool in the forest floor by 0.76 mg Hg m-2 (223%). Salvage logging following blowdown created conditions leading to a significantly more severe forest floor burn during wildfire, which significantly enhanced Hg emission. This sequence of combined events resulted in a mean loss of approximately 0.42 mg Hg m-2 (68% of pool) from the forest floor, after conservatively accounting for potential losses via enhanced soil leaching and volatile emissions between the disturbance and sampling dates. Fire alone or blowdown followed by fire did not significantly affect the total Hg concentrations or pools in the forest floor. Overall, unexpected consequences for soil Hg accumulation and by extension, atmospheric Hg emission and risk to aquatic biota, may result when combined impacts are considered in addition to singular forest floor and soil disturbances. [ABSTRACT FROM AUTHOR]

Abstract: We present a retrospective method for studying forest disturbance regimes, and especially the role of windthrows, based on circular statistical models of directions of fallen logs. This approach was applied to fallen log data from three areas of pristine Picea abies-dominated boreal forests in northern Europe. The data consisted of 5 plots from each of the three areas, totaling 15 plots and covering an area of 24ha. The disturbance history of the plots, which varied from area to area, was known from previous detailed studies. We selected and fitted the most suitable circular model for each plot, based on goodness-of-fit and the Akaike information criterion. For uneven-aged forests, the symmetric von Mises distribution, was best fitted, while for the even-aged forest the sine-skewed wrapped Cauchy distribution was selected. The degree of concentration around the mean direction of fallen trees was strongest for the late-successional even-aged forest most exposed to windthrow, while an uneven-aged forest with drought-driven mortality had the lowest concentration and the greatest variance over the mean directions. For the third area, characterized by an uneven age structure and tree mortality driven by heart-rot fungi in old trees in interaction with wind, an intermediate between these two were derived. Our results suggested the utility of circular distributions of fallen logs and their statistical models for retrospective assessments of forest disturbance regimes. [Copyright &y& Elsevier]

The geomorphic process domain concept predicts consistent associations between stream channel geomorphology and large woody debris (LWD) input mechanisms. We used synoptic surveys at 51 stream reaches adjacent to undisturbed mature or old-growth forests in central and southern British Columbia to test associations between stream geomorphology and the input processes, source distances, physical characteristics, and geomorphic functions of LWD within the bankfull channel. Standing dead tree fall was the dominant input mechanism, but bank erosion was important in low- and medium-gradient channels >3 m bankfull width. Wind-induced inputs (stem breakage and windthrow) were relatively more important in small or steep channels. LWD piece size and source distance varied among delivery processes. LWD originated at ground distances up to 65 m from the streams, but 90% of the LWD at a site originated within 18 m of the channel at 90% of the sites. Statistical models incorporating tree size and stream characteristics (bankfull width, channel type) explained 40%-64% of the variation among sites in the distances from which LWD entered streams. In general, LWD source distances increased with increasing tree height and decreased with increasing stream width; however, the strengths of these relationships were modified by channel type. [ABSTRACT FROM AUTHOR]

Effects of a catastrophic blowdown event in northern Minnesota, USA were assessed using field inventory data, aerial sketch maps and satellite image data processed through the North American Forest Dynamics programme. Estimates were produced for forest area and net volume per unit area of live trees pre- and post-disturbance, and for changes in volume per unit area and total volume resulting from disturbance. Satellite image-based estimates of blowdown area were similar to estimates derived from inventory plots and aerial sketch maps. Overall accuracy of the image-based damage classification was over 90%. Compared to field inventory estimates, image-based estimates of post-blowdown mean volume per unit area were similar, but estimates of total volume loss were substantially larger, although inaccessibility of the most severely damaged inventory plots may have depressed the inventory-based estimate. This represents the first application of state model differencing to storm damage assessment. The image-based procedure can be applied to historical archives of satellite imagery and does not require pre-disturbance field inventory data. [ABSTRACT FROM AUTHOR]

Many studies have been conducted to quantify the possible ecosystem/landscape response to the anticipated global warming. However, there is a large amount of uncertainty in the future climate predictions used for these studies. Specifically, the climate predictions can be very different based on a variety of global climate models and alternative greenhouse emission scenarios. In this study, we coupled a forest landscape model, LANDIS-II, and a forest process model, PnET-II, to examine the uncertainty (that results from the uncertainty in the future climate predictions) in the forest-type composition prediction for a transitional forest landscape [the Boundary Water Canoe Area]. Using an improved global-sensitivity analysis technique [Fourier amplitude sensitivity test], we also quantified the amount of uncertainty in the forest-type composition prediction contributed by different climate variables including temperature, CO2, precipitation and photosynthetic active radiation (PAR). The forest landscape response was simulated for the period 2000–2400ad based on the differential responses of 13 tree species under an ensemble of 27 possible climate prediction profiles (monthly time series of climate variables). Our simulations indicate that the uncertainty in the forest-type composition becomes very high after 2200ad, which is close to the time when the current forests are largely removed by windthrow disturbances and natural mortality. The most important source of uncertainty in the forest-type composition prediction is from the uncertainty in temperature predictions. The second most important source is PAR, the third is CO2 and the least important is precipitation. Our results also show that if the optimum photosynthetic temperature rises due to CO2 enrichment, the forest landscape response to climatic change measured by forest-type composition may be substantially reduced. [ABSTRACT FROM AUTHOR]

Abstract: Biomechanical effects of trees on soils and surface processes may be extensive in forest environments. Two blowdown sites caused by a November 2005 tornado in the Ouachita National Forest, Arkansas allowed a case study examination of bioturbation associated with a specific forest blowdown event, as well as detailed examination of relationships between tree root systems, soils, and underlying bedrock. The sites occur within mixed shortleaf pine and hardwood forests. More than 95% of trees in the severe blowdown areas were either uprooted or suffered trunk break, with uprooting more common than breakage. Within the most heavily damaged areas all uprooted trees were pines, while all trees left standing were hardwoods. Root wads of uprooted trees had a mean surface area of about 3 m2 and volume of about 2 m3, though individual sizes were quite variable. Nearly 4% of the ground surface area was affected by uprootings, with a soil volume equivalent to a disturbance of the entire surface area to a depth of 2.4 cm. Tree size (as measured by diameter at breast height) was significantly related to the area and volume of root wads (R 2 =0.55, 0.71, respectively), with volume of uprooted soil varying as diameter to the ~3 power, suggesting that the timing of blowdown events relative to tree age or growth stage significantly influences the area of disturbance and the mass and volume of material involved. In 93% of cases the roots of the uprooted trees contacted or penetrated the underlying bedrock, and in all those cases bedrock was quarried by uprooting. Only 11% of the tree throws showed evidence of general lateral root turning at the soil–bedrock interface; in most cases roots penetrated bedrock along joints. The propensity for tree roots to penetrate bedrock joints, facilitate weathering, and excavate bedrock during uprooting supports the idea that tree roots play a predominant role in locally deepening soils. [Copyright &y& Elsevier]

In natural forest, disturbance changes tree species composition which in turn affects soil properties. Two areas in the Central Forest State Biosphere Reserve, in the Russian Southern Taiga Zone, differed in the intensity of disturbance: Norway spruce was the dominant species at one site, while at the other spruce was mixed with broadleaves. The presence of broadleaves was due to large gaps in the canopy having been formed, which have triggered vegetation succession. At both sites, five plots were selected to evaluate how the presence of broadleaves influences the properties of the soils under spruce. Soil samples were taken close to spruce trees and the O, A and E horizons were analysed. A difference in the distribution of organic matter in the soil horizons was evident, with a higher concentration in the O and A horizons at the spruce dominated site, while a more homogeneous distribution was found under spruce at the site where broadleaves were abundant. The organic matter did not only differ in quantity, but also in quality as estimated by the C/N ratio, and therefore affected the CEC and element relative availability. No differences at the two sites were found for water-extractable and exchangeable elements, but the ratio between the exchangeable and the acid-extractable forms were different, suggesting a higher relative availability of the elements at the spruce dominated site, and thus potentially higher leaching. Both theoretical and empirical studies have suggested that podzolisation and accumulation of organic matter in the O horizon are related to stagnation of ecosystem processes and ecosystem decline. Our data suggest that the presence to windthrow sites and the inclusion of broadleaf species acts to slow or even reverse podzolisation even in spruce dominated sites. [ABSTRACT FROM AUTHOR]

A hypothesis was verified that forest floor chemistry varies according to position within the windthrow (mound, pit, or control). A parallel assessment was made of differences in the chemistry of horizons and their forms. A total number of 1720 windthrows were studied in the fir–beech primeval forest in the flysch zone of the Western Carpathians. A total of 100 samples were taken on three positions from the following horizons and their forms (in brackets): litter, fermented (amphigenous, zoogenous, or mycogenous), humification (unresolved, zoogenous, residues, or humic), and mineral. A random sampling eliminated the effect of correlation between the horizons and positions. Parameters assessed were Q4/6, HA/FA, C-forms, total N, P, K, and Mg contents, soil reaction, and cation-exchange capacity. The positions exhibited a significant difference in the forest floor chemistry even at a level of horizon forms. The position’s significance decreased with the horizon depth. Organic horizons in the pit, in particular, exhibited the lowest content of total humic substances, fulvic acids, and the lowest colour coefficient values. However, the mineral horizon showed no significant differences between the positions within the windthrow. Compared with other humus types, the decomposing wood mass did not exhibit a different ratio of humic and fulvic acids. [ABSTRACT FROM AUTHOR]

Prediction of windthrow risk to individual or groups of retained trees in harvested stands requires an improved understanding of canopy airflow dynamics. Large-eddy simulations were used to simulate wind-tunnel experiments in two and three dimensions to compare with observations for model validation and to address parameter space considerations for the design of subsequent retention pattern experiments. The three-dimensional simulations were similar to the observed wind-tunnel data for the statistical profiles for $$u/u_\ast, \overline {u^{{\prime}}w^{{\prime}}}/u_\ast^2, \sigma_u/\overline u, \sigma_u/u_\ast, \sigma_v/u_\ast$$ but there were greater differences in skewness and kurtosis. These results were obtained using a common leaf-area drag formulation without either skin friction or speed dependent drag that enables scaling with U 0 (ambient wind speed) and h (height of the canopy). This scaling results in a single non-dimensional parameter h/ h c where h c ( x, y, z) is the momentum range resulting from the canopy drag. The validity of the model scaling was tested using two-dimensional simulations. The irrotational component of the flow (potential flow) was found to be important when defining vertical domain limitations and has significant implications for time dependent flow (i.e. turbulent conditions) when considering retention pattern design. The sudden onset of drag associated with the isolated stand presents some unexpected challenges. The horizontal scales of the shearing instabilities were simulated in two dimensions and found to range between 2 h for early times to 7 h for later times. The early-time horizontal scales are in the range of logical retention pattern scales and as such need to be taken into account as part of the parameter space, i.e. a range of retention pattern lengths need consideration. [ABSTRACT FROM AUTHOR]

Wind throw is an important risk factor in forest management in North-western Europe. In recent years, mechanistic models have been developed to estimate critical wind speeds needed to break or uproot the average tree of a forest stand. Based on these models, we developed a wind damage module for the individual tree model ForGEM (Forest Genetics, Ecology and Management). For a given wind speed this module assesses the forces on each individual tree, based on the tree dimensions, and support and sheltering provided by other trees. Due to this individual approach, irregular stands can also be assessed. The module is demonstrated on Douglas fir stands (Pseudotsuga menziesii (Mirb.) Franco) of different densities in the Netherlands. Patterns of damage are explained, both in freshly exposed stands as well as in sheltered stands. Wind speeds needed to cause damage approximated those of known wind throw events. The wind damage module proved to be very sensitive to simulated tree heights and diameters. Furthermore, the newly introduced support mechanism played an important role in the stability of trees and stands. Lower individual tree stability in dense stands was clearly compensated for by the support of other trees. [Copyright &y& Elsevier]

Management of planted forests in Britain is changing to incorporate biodiversity and other nontimber values by lengthening rotations, seeking alternatives to clear-felling, and identifying stands for nonintervention. However, there are particular uncertainties over stand development of exotic species on areas of high windthrow hazard. This study considered the effect of strong winds between 1987 and 2000 on stand development of Sitka spruce (Picea sitchensis (Bong.) Carrière) planted in 1923. Windthrown gap area increased eightfold through at least 38 separate events. Windthrow of trees assessed as stable occurred during periods of higher wind speed than those with windthrow of trees assessed as vulnerable, and there was a nonlinear relationship between wind speed and increase in gap area. Gap expansion contributed more to the increase in gap area than new gap formation, and the centre of the largest gap migrated downwind. Nevertheless, a substantial proportion of the stand remains undisturbed to an extent not predicted. Therefore, a complex stand structure may develop, including a partial wave of natural regeneration of Sitka spruce in the expanding gaps, but species diversification will be slow due to the absence of local seed sources. The results provide insights for stand dynamics in windy, maritime environments. [ABSTRACT FROM AUTHOR]

Dead wood (dead standing tree (snag), woody debris (WD), buried wood, and stump) abundance was estimated in Newfoundland balsam fir (Abies balsamea (L.) Mill.) and black spruce (Picea mariana (Mill.) BSP) forests regrown following natural and anthropogenic disturbances. Although harvesting left few snags standing, natural disturbances generated many snags. Most were still standing 2 years after natural disturbance, but almost all had fallen after 33–34 years. Snag abundance then increased in stands aged 86–109 years. Natural disturbances generated little WD 0–2 years following disturbance. Harvesting, however, immediately generated large amounts of WD. Thirty-two to forty-one years following disturbance, most harvesting slash had decomposed, but naturally disturbed sites had large amounts of WD from collapsed snags. Harvested sites contained less WD 32–72 years following disturbance than naturally disturbed sites. Amounts of WD in black spruce regrown following harvesting and fire converged 63–72 years following disturbance, despite significant initial differences in WD quantities, diameter distribution, and decay classes. Abundance of WD increased from sites regrown 32–72 years following disturbance to older sites. Precommercial thinning had a minor impact on dead wood stocks. Stumps contained minor biomass. Buried wood and WD biomass were equivalent at some sites. [ABSTRACT FROM AUTHOR]

The influence of wind damage from Hurricane Hugo on bottomland forest community structure and composition over a 12 year period was evaluated using data generated from repeated measurements in permanent plots. The resistance and responsiveness of the forests to hurricane disturbance at the community level are dependent on the prehurricane species composition and structure. However, there is no evidence to support the hypothesis that forests with higher species diversity are more resistant to hurricane disturbances. The hurricane disturbance does restructure species composition and may enrich species diversity, but the evidence of diversity enrichment is not strong. The effects of the hurricane on the succession of the bottomland forests are complex at the tree population level: both promoting colonization of some shade-intolerant pioneer species and removing other established pioneers. Changes in community composition and structure suggest that hurricane disturbance can accelerate succession of the bottomland hardwood forests. [ABSTRACT FROM AUTHOR]

Catastrophic windthrow and postdisturbance salvage logging each have the potential to profoundly influence understory vegetation communities. This study compared understory vegetation cover, composition, and diversity in Routt National Forest, a subalpine forest in northwestern Colorado that sustained a 10 000 ha blowdown in 1997 and was partially salvage logged in 1999. Understory and edaphic variables were measured in five heavily wind-disturbed Picea–Abies stands, five stands salvage logged 20 months after the blowdown, and five intact stands. Understory species cover and diversity were greater in blown down areas than in salvage-logged or control areas. Community composition of each treatment area was distinct and related to a gradient in organic soil depth, which reflected the severity of understory disturbance. Composition and diversity in blowdown areas relative to control areas stabilized in the 5 years following the blowdown, but vegetation cover continued to increase. Blowdown areas contained early and late successional species. Salvage-logged areas exhibited a shift towards graminoid dominance. This structural change could delay future conifer seedling establishment. The interaction among disturbance severity, understory vegetation composition, and regeneration dynamics should be considered in future decisions to salvage log similar areas because the long-term effects of salvage logging are unknown. [ABSTRACT FROM AUTHOR]

In the coming century, forecast climate changes caused by increasing greenhouse gases may produce dramatic shifts in tree species distributions and the rates at which individual tree species sequester carbon or release carbon back to the atmosphere. The species composition and carbon storage capacity of northern Wisconsin (USA) forests are expected to change significantly as a result. Projected temperature changes are relatively large (up to a 5.8°C increase in mean annual temperature) and these forests encompass a broad ecotone that may be particularly sensitive to climate change. Our objective was to estimate the combined effects of climate change, common disturbances, and species migrations on regional forests using spatially interactive simulations. Multiple scenarios were simulated for 200 years to estimate aboveground live biomass and tree species composition. We used a spatially interactive forest landscape model (LANDIS-II) that includes individual tree species, biomass accumulation and decomposition, windthrow, harvesting, and seed dispersal. We used data from two global circulation models, the Hadley Climate Centre (version 2) and the Canadian Climate Center (version 1) to generate transient growth and decomposition parameters for 23 species. The two climate change scenarios were compared with a control scenario of continuing current climate conditions. The results demonstrate how important spatially interactive processes will affect the aboveground live biomass and species composition of northern Wisconsin forests. Forest composition, including species richness, is strongly affected by harvesting, windthrow, and climate change, although five northern species (Abies balsamea,Betula papyrifera,Picea glauca,Pinus banksiana,P. resinosa) are lost in both climate scenarios regardless of disturbance scenario. Changes in aboveground live biomass over time are nonlinear and vary among ecoregions. Aboveground live biomass will be significantly reduced because of species dispersal and migration limitations. The expected shift towards southern oaks and hickory is delayed because of seed dispersal limitations. [ABSTRACT FROM AUTHOR]

Wind damage to forests is determined by numerous factors that interact to produce complex, seemingly random damage patterns. However, the complexity may lie mostly among stands and be less within stands: in this study, I attempted to discern how predictable tree fall risk is within five southern boreal forest stands in northeastern Minnesota. I sampled five stands in the Boundary Waters Canoe Area Wilderness, following a July 1999 catastrophic windstorm. Levels of damage varied from 29.5% to 86.8% of basal area fallen and 23.3% to 63.4% of stems fallen. In all sites, the disturbance reduced mean trunk diameter of standing trees. In general, Abies balsamea (L.) Mill. was the most vulnerable species. I split the data set from each site into predictor and test portions and used the predictor data sets to derive logistic regression parameters for the relationship of tree size (trunk diameter) to probability of tree fall. Models based on these parameters allowed quite accurate predictions of the levels of damage in the test portion of each stand. For the five sites, the proportion of test trees predicted to fall differed from the proportion observed to fall by 5.7%, 3.9%, 8.3%, 1.4%, and 3.7% of the total test sample size. This suggests that while numerous factors indeed influence tree fall risk, the sizes and identities of trees may account for most of the within-stand variation in damage. [ABSTRACT FROM AUTHOR]

The northeastern boreal forest of Quebec is characterized by a humid climate. Consequently, fires are less frequent and small-scale disturbances play an important role in forest dynamics. Natural mortality and nonfire disturbances such as insect outbreaks and windthrow lead to gap-driven processes. Changes in structure and species composition can result from gap dynamics. The objectives of this study were to characterize gaps and examine patterns of species replacement in gaps in old conifer stands. Line intersect sampling was used to sample stands dominated by balsam fir (Abies balsamea (L.) Mill.) and (or) black spruce (Picea mariana (Mill.) BSP). Results show that 54% of the forest was in expanded gaps and that canopy gaps are relatively small, since 87% of them were smaller than 100 m2. The majority (94%) of the openings were caused by the mortality of less than 10 gap makers. Replacement probabilities show self-replacement of A. balsamea in Abies stands and of P. mariana in Picea stands. However, in Abies-Picea stands, there seems to be a reciprocal replacement of the two species. These results provide knowledge of the disturbance dynamics of the region as a basis for development of silvicultural practices that preserve the structural components of older forest stands. [ABSTRACT FROM AUTHOR]

Three major disturbances affect subalpine forests in the Rocky Mountains: blowdown, insect outbreaks, and fire. These disturbances may influence one another temporally and spatially, creating a mosaic of disturbance patches. In 1997, a severe windstorm blew down trees on over 10,000 ha of subalpine forest in northern Colorado. Did previous disturbances influence the spatial pattern of blowdown in a representative part of the blowdown in the Middle Fork Elk River watershed? Dendrochronological evidence and a geographic information system were used to reconstruct the disturbance history, and the relationship between disturbance history (i.e., patch age) and the 1997 blowdown was examined. The fire regime varies temporally and spatially, with an area-weighted mean fire interval/fire rotation of 108 to 195 years. Stand-replacing fires appear to have had the most impact on the fire regime, but evidence of nonstand-replacing fires was also found. South-facing, lower-elevation slopes were the settings most likely to burn. Lowseverity spruce-beetle disturbance was found in the mid-1700s and mid- to late 1800s, possibly related to regional outbreaks. Sheep-grazing and fire suppression may have influenced tree-regeneration and fire-frequency patterns. Each disturbance event occurred with varying severity across the landscape, influenced, in part, by the patterns of severity of previous disturbances. Patch age contributed to the pattern of the 1997 blowdown, but the relationship is complicated. The vegetation mosaic influenced spatial patterns of blowdown, resulting in new complexity and maintaining landscape heterogeneity. Key Words: blowdown; disturbance interactions; fire ecology; subalpine forest. [ABSTRACT FROM AUTHOR]

Storm events are capable of causing windthrow to large forest areas. A rapid detection of the spatial distribution of the windthrown areas is crucial for forest managers to help them direct their limited resources. Since synthetic aperture radar (SAR) data is acquired largely independent of daylight or weather conditions, SAR sensors can produce temporally consistent and reliable data with a high revisit rate. In the present study, a straightforward approach was developed that uses Sentinel-1 (S-1) C-band VV and VH polarisation data for a rapid windthrow detection in mixed temperate forests for two study areas in Switzerland and northern Germany. First, several S-1 acquisitions of approximately 10 before and 30 days after the storm event were radiometrically terrain corrected. Second, based on these S-1 acquisitions, a SAR composite image of before and after the storm was generated. Subsequently, after analysing the differences in backscatter between before and after the storm within windthrown and intact forest areas, a change detection method was developed to suggest potential locations of windthrown areas of a minimum extent of 0.5 ha—as is required by the forest management. The detection is based on two user-defined parameters. While the results from the independent study area in Germany indicated that the method is very promising for detecting areal windthrow with a producer's accuracy of 0.88, its performance was less satisfactory at detecting scattered windthrown trees. Moreover, the rate of false positives was low, with a user's accuracy of 0.85 for (combined) areal and scattered windthrown areas. These results underscore that C-band backscatter data have great potential to rapidly detect the locations of windthrow in mixed temperate forests within a short time (approx. two weeks) after a storm event. Furthermore, the two adjustable parameters allow a flexible application of the method tailored to the user's needs. [ABSTRACT FROM AUTHOR]