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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]

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]

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]

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]

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]

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]

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]