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1 Few studies have addressed the mechanisms of coexistence of shade-tolerant and intolerant tree species in the canopy of old-growth, lowland rain forests of southern South America. We explored the hypothesis that their forest dynamics result from frequent, single tree-fall gap episodes. 2 We analysed the disturbance regime and assessed the regeneration modes of shade-tolerant and intolerant canopy trees in a lowland, old growth North Patagonian rain forest in Chiloé Island (42° S) using dendroecological methods. 3 Dominant canopy trees were the shade-intolerant Nothofagus nitida (Fagaceae), Drimys winteri (Winteraceae) and the tolerant Podocarpus nubigena (Podocarpaceae). The oldest individuals, however, were represented by Saxegothaea conspicua, Podocarpaceae (shade tolerant > 498 years) and Weinmannia trichosperma, Cunoniaceae (intolerant > 382 years). Shade-tolerant species have regenerated continuously for the past 400 years, but recruitment of shade-intolerant species has increased only in the past 50 years. These regeneration patterns suggest a lack of catastrophic disturbance, at least since 1650. 4 Analysis of tree radial growth patterns revealed frequent moderate releases of both shade-tolerant and intolerant tree species, consistent with frequent small-scale disturbances, such as individual tree-fall gaps. Increased releases, peaking in 1940 and followed by enhanced recruitment, may be a consequence of individual tree-falls induced by low-intensity windstorms or limited selective logging. Such disturbances have occurred for at least 250 years, but have had little overall effect on stand structure and canopy composition. 5 The replacement and coexistence of shade-tolerant and intolerant tree species in the canopy of this North Patagonian forest can be explained by frequent small-scale disturbances (i.e. gap-phase dynamics) and by the absence of large-scale natural or anthropogenic disturbances over the past four centuries. Journal of Ecology (2004) 92, 598–608 [ABSTRACT FROM AUTHOR]

Periodic natural disturbances shape the mosaic character of many landscapes and influence the distribution and abundance of organisms. In this study, we tested the effect of ice storm-induced treefall gaps on ground-dwelling beetle assemblages in different-aged successional stands of subtropical broad-leaved forest in southeastern China. We evaluated the relative importance of gap-phase microhabitat type (within gap, gap edge, and interior shaded) within different stand ages (regenerating stands and mature stands) as determinants of changes in beetle diversity and community structure. At 18 replicate sites sampled during 2009-2010, no significant differences were found in species richness and the abundances of the most common beetle species captured in pitfall traps among the three gap-phase microhabitat types, but the abundances of total beetles, as well as fungivorous and phytophagous species groups, were significantly lower in gap microhabitats than in interior shaded microhabitats in mature stands. Beetle assemblage composition showed no significant differences among the three microhabitat types, and only the fauna of gap plots slightly diverged from those of edge and shaded plots in mature stands. Cover of shrubs and stand age significantly affected beetle assemblage structure. Our results suggest that beetle responses to gap-phase dynamics in early successional forests are generally weak, and that effects are more discernible in the mature stands, perhaps due to the abundance responses of forest-specialist species. [ABSTRACT FROM AUTHOR]

The recent introduction of chronotaxic systems provides the means to describe nonautonomous systems with stable yet time-varying frequencies which are resistant to continuous external perturbations. This approach facilitates realistic characterization of the oscillations observed in living systems, including the observation of transitions in dynamics which were not considered previously. The novelty of this approach necessitated the development of a new set of methods for the inference of the dynamics and interactions present in chronotaxic systems. These methods, based on Bayesian inference and detrended fluctuation analysis, can identify chronotaxicity in phase dynamics extracted from a single time series. Here, they are applied to numerical examples and real experimental electroencephalogram (EEG) data. We also review the current methods, including their assumptions and limitations, elaborate on their implementation, and discuss future perspectives. [ABSTRACT FROM AUTHOR]

Jones (1945) was a milestone paper exploring the natural forest concept with examples from the temperate and boreal ecosystems. It has become a classic because of its use of field observation of regeneration, succession and structure to assess theories about disturbance and the dynamic properties of natural forests. His main aim was to review some of the features of the structure and reproduction of the north temperate virgin forests, and this article presents, discusses and evaluates the main features of this legendary paper. Jones had international experience of both the ecological and silvicultural research communities and combined long-term field observations with theory to develop a realistic assessment of natural forest properties that formed the basis for current understanding. He demonstrated that natural disturbance regimes could generate a variety of structures and that a stable, 'climax' forest concept was often not supported by field data. He also showed that even-aged components are common in these forest ecosystems and that the recruitment of tree species proceeds irregularly even in undisturbed stands. His work has influenced subsequent development of related subjects such as disturbance theory, gap-phase dynamics and long-term vegetation changes and has left a legacy with practical relevance for nature conservation and silviculture. [ABSTRACT FROM AUTHOR]

Disturbance may generate population bottlenecks by reducing population size and the number of founders establishing a new colony. We tested the hypothesis that the scale of disturbance affects the levels of genetic diversity and the spatial distribution of genotypes in naturally regenerating stands of Nothofagus dombeyi, an evergreen angiosperm tree, in northwestern Patagonia. At similar spatial scales, we predicted that old-growth stands characterized by fine-scale gap phase dynamics would be genetically diverse due to restricted gene flow among temporal and spatially isolated gaps. In contrast, young massively regenerated postfire cohorts resulting from coarse-scale disturbances would be genetically more homogeneous. At each of three paired old-growth and postfire stands a minimum of 50 trees were mapped and sampled within 1 ha. Fresh tissue was collected for isozyme analysis from a total of 361 trees along with tree cores and diameters. Tree age distributions reflected the dominant modes of regeneration. Six out of nine analysed loci were polymorphic. Mean genetic diversity parameters were greater but not significant in mature stands. Fixation indices suggested significant heterozygous deficit at two-thirds of possible tests indicating a Wahlund effect due to local recruitment of related seeds. FST indicated moderate between-stand divergence. Mature stands concentrated half of positively like joins and yielded significant ( P<0.05) autocorrelation coefficients at small distance classes (<20m). Fine-scale patch dynamics within mature stands favours the maintenance of fine-scale genetic structure as a result of shade intolerance and local seed dispersal. Conversely, postfire stands suffer the effects of genetic drift given that a few reproductive trees produce a somewhat impoverished and genetically uniform progeny. Bottleneck effects will depend upon the density of remnant trees which could also be a function of the severity of fire. [ABSTRACT FROM AUTHOR]

Disturbances of different spatial extent and intensity play an important role in the Western Carpathian Norway spruce forests. These forests are shaped mainly by severe winds, often followed by bark beetle infestations. Their intensity varies substantially, resulting in variability of disturbance regimes. Low- and moderate-severity disturbances create small-scale dynamics associated with small- and medium-sized gaps resulting from the death of individual trees or groups of them. Large stand-replacing disturbances are much less frequent but affect larger areas. In spite of such large variability of disturbance regimes, the structure of old-growth spruce stands varies less, with unimodal diameter distributions being the most common ones. In this review we discuss the possible natural mechanisms behind the relationship between the varied disturbance regimes and the rather uniform tree stand structures. We reviewed a large number of studies done in well preserved spruce stands throughout the Western Carpathians in Poland and Slovakia, which included analyses of the diameter and age distributions of stands and their short-term dynamics, as well as dendroecological reconstructions of disturbances over the last 200 years. The regeneration niches of spruce and accompanying tree species are also analyzed. Two models of the relationship between stand dynamics and stand structure are proposed for Western Carpathian subalpine spruce stands. In the first one, severe stand-replacing disturbances hit forests over a large area, resulting in low variability of the age and size of trees recruited synchronously over extensive areas. In the second model, gap-phase dynamics produce spruce stands composed of distinct age cohorts of trees that originated over extensive areas. In our models, different trajectories of forest dynamics can yield similar stand structures, which will not be good indicators of disturbance regimes. We suggest that the abundance of rowan and European larch is a more reliable indicator of past disturbance regimes, because rowan benefits most from gap dynamics, while European larch is connected with extensive stand-replacing disturbances. [ABSTRACT FROM AUTHOR]

Rapidly changing conditions alter disturbance patterns, highlighting the need to better understand how the transition from pulse disturbances to more persistent stress will impact ecosystem dynamics. We conducted a global analysis of the impacts of 11 types of disturbances on reef integrity using the rate of change of coral cover as a measure of damage. Then, we evaluated how the magnitude of the damage due to thermal stress, cyclones, and diseases varied among tropical Atlantic and Indo‐Pacific reefs and whether the cumulative impact of thermal stress and cyclones was able to modulate the responses of reefs to future events. We found that reef damage largely depends on the condition of a reef before a disturbance, disturbance intensity, and biogeographic region, regardless of the type of disturbance. Changes in coral cover after thermal stress events were largely influenced by the cumulative stress of past disturbances and did not depend on disturbance intensity or initial coral cover, which suggests that an ecological memory is present within coral communities. In contrast, the effect of cyclones (and likely other physical impacts) was primarily modulated by the initial reef condition and did not appear to be influenced by previous impacts. Our findings also underscore that coral reefs can recover if stressful conditions decrease, yet the lack of action to reduce anthropogenic impacts and greenhouse gas emissions continues to trigger reef degradation. We uphold that evidence‐based strategies can guide managers to make better decisions to prepare for future disturbances. [ABSTRACT FROM AUTHOR]

Abstract: Correct knowledge of disturbance ecology is essential for understanding the characteristic behavior of forest ecosystems and for guiding appropriate management strategies. However, the role of natural disturbances in shaping European mountain forest ecosystems has not been adequately studied, possibly because of the perception that the development of most European forests is primarily shaped by human influences and/or fine-scale gap-phase dynamics. In the present study, we investigate the long-term disturbance history of old protected forest dominated by Norway spruce in the Parangalitsa Reserve, Bulgaria. We used aerial photo interpretation and dendroecological methods to reconstruct the history of wind, insect, and fire disturbances across a topographically complex landscape. Over the past 150years wind has been the most important disturbance agent in this ecosystem and at least 18% of the forested area shows evidence of high-severity blowdowns. Windthrow patches ranged in size from <1ha to >10ha (minimum 0.11ha, mean 0.16ha, maximum 10ha). Although small disturbances were much more frequent, few larger blowdowns accounted for most of the disturbed area. Pure coniferous and single-cohort coniferous forest patches were more affected by blowdowns than mixed coniferous–deciduous and multi-cohort coniferous forest patches. Although bark beetle (Ips typhographus) populations were large enough to cause mortality of some live trees, the populations did not grow to epidemic proportions during recent decades. Fire disturbance was of limited importance in the last 200years and only two patches (4% of the study area) showed evidence of fire. The present research indicates that wind disturbances have been characteristic of these ecosystems at least over the past decades to centuries. Thus, blowdowns appear integral to the normal function and structure of the Picea-dominated mountain forests in the region and such events, in and of themselves, do not represent unhealthy forest conditions or environmental emergencies. Management strategies that aim to maintain these ecosystems within a natural range of variation should incorporate wind disturbances into the management strategy. The frequency and magnitude of future wind disturbances may be considered within the historical framework described in the current study to assess potential effects of climate change on altered disturbance regimes. [Copyright &y& Elsevier]

Most Central African rainforests are characterized by a remarkable abundance of light‐demanding canopy species: long‐lived pioneers (LLP) and non‐pioneer light demanders (NPLD). A popular explanation is that these forests are still recovering from intense slash‐and‐burn farming activities, which abruptly ended in the 19th century. This "human disturbance" hypothesis has never been tested against spatial distribution patterns of these light demanders. Here, we focus on the 28 most abundant LLP and NPLD from 250 one‐ha plots distributed along eight parallel transects (~50 km) in the Yangambi forest. Four species of short‐lived pioneers (SLP) and a single abundant shade‐tolerant species (Gilbertiodendron dewevrei) were used as reference because they are known to be strongly aggregated in recently disturbed patches (SLP) or along watercourses (G. dewevrei). Results show that SLP species are strongly aggregated with clear spatial autocorrelation of their diameter. This confirms that they colonized the patch following a one‐time disturbance event. In contrast, LLP and NPLD species have random or weakly aggregated distribution, mostly without spatial autocorrelation of their diameter. This does not unambiguously confirm the "human disturbance" hypothesis. Alternatively, their abundance might be explained by their deciduousness, which gave them a competitive advantage during long‐term drying of the late Holocene. Additionally, a canonical correspondence analysis showed that the observed LLP and NPLD distributions are not explained by environmental variables, strongly contrasting with the results for the reference species G. dewevrei, which is clearly aggregated along watercourses. We conclude that the abundance of LLP and NPLD species in Yangambi cannot be unambiguously attributed to past human disturbances or environmental variables. An alternative explanation is that present‐day forest composition is a result of adaptation to late‐Holocene drying. However, results are inconclusive and additional data are needed to confirm this alternative hypothesis. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) can work as excellent saturable absorber (SA) due to its advantages of fast recovery, low saturation intensity, polarization insensitivity, deep modulation depth, broad operation bandwidth, outstanding environmental stability, and affordable fabrication. Its successful application as SA has promoted the development of scientific research and practical application of mode-locked fiber lasers. Besides, mode-locked fiber laser constitutes an ideal platform for investigating soliton dynamics which exhibit profound nonlinear optical dynamics and excitation ubiquitous in many fields. Up to now, a variety of soliton dynamics have been observed. Among these researches, CNT-SA is a key component that suppresses the environmental perturbation and optimizes the laser system to reveal the true highly stochastic and non-repetitive unstable phenomena of the initial self-starting lasing process. This review is intended to provide an up-to-date introduction to the development of CNT-SA based ultrafast fiber lasers, with emphasis on recent progress in real-time buildup dynamics of solitons in CNT-SA mode-locked fiber lasers. It is anticipated that study of dynamics of solitons can not only further reveal the physical nature of solitons, but also optimize the performance of ultrafast fiber lasers and eventually expand their applications in different fields. [ABSTRACT FROM AUTHOR]

When deforestation results in small forest fragments surrounded by a non‐forest matrix, forest stands within these fragments experience changes in structure and community composition. They also continue to experience natural disturbances like hurricanes and ice storms. It remains unclear whether the landscape context of forest stands influences plant community response to natural disturbances.Using data from surveys of forested plots in the years immediately following and 19 years after a severe ice storm, we measured changes in woody stem density, species richness and beta diversity.Plots with greater storm damage had greater gains in stems and species, and greater shifts in community composition. In addition, there were interactions between the degree of storm damage and landscape context. The short‐term effects of storm damage were magnified in plots with less forest on the surrounding landscape and farther from the forest edge. In plots with high damage, a return towards pre‐storm conditions over the long‐term occurred more often in plots farther from the forest edge compared to those close to the edge.Synthesis. Future climate scenarios predict increases in severe weather and accompanying ecosystem disturbance. Our results show that it is important to consider landscape context when assessing the response of forest communities to such disturbances. [ABSTRACT FROM AUTHOR]

Forest managers are often required to restore forest stands following natural disturbances, a situation that may become more common and more challenging under global change. In parts of Central Europe, particularly in mountain regions dominated by mixed temperate forests, the use of relatively low intensity, uneven-aged silviculture is a common management approach. Because this type of management is based on mimicking less intense disturbances, the restoration of more severe disturbance patches within forested landscapes has received little attention. The goal of this paper is to synthesize research on the restoration of forests damaged by disturbances in temperate forests of Slovenia and neighbouring regions of Central Europe, where uneven-aged silviculture is practiced. Research indicates that active management aimed at favouring mixed uneven-aged forest reduces the risk of disturbance and improves the resilience of stands. Salvage logging may have positive or negative effects on regeneration, much of which is due to the method applied and the quality of work. The most prominent factors that negatively affect restoration are: lack of advanced regeneration and decomposed woody debris, high altitude, steep slopes, dense ground vegetation, and overbrowsing. Planting or sowing should be applied in post-disturbance forests where many negative factors interact and where a high demand for sustainability of forest ecosystem services is present. [ABSTRACT FROM AUTHOR]

The author discusses a report by J. Q. Chambers and colleagues concerning the steady-state succession and disturbance mosaic across the forest landscape in Central Amazon. The author says that the work provides a fresh perspective on the strategies in addressing challenge to quantify and understand forest disturbance regimes. He adds that the drivers of subsequent biotic responses and disturbance show a geographic variation.

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Much of our understanding of natural forest dynamics in the temperate region of Europe is based on observational studies in old-growth remnants that have emphasized small-scale gap dynamics and equilibrium stand structure and composition. Relatively little attention has been given to the role of infrequent disturbance events in forest dynamics. In this study, we analyzed dendroecological data from four stands and three windthrow patches in an old-growth landscape in the Dinaric Mountains of Bosnia and Herzegovina to examine disturbance history, tree hfe history traits, and compositional dynamics. Over all stands, most decades during the past 340 years experienced less than 10% canopy loss, yet each stand showed evidence of periodic intermediate-severity disturbances that removed >40% of the canopy, some of which were synchronized over the study area landscape. Analysis of radial growth patterns indicated several life history differences among the dominant canopy trees; beech was markedly older than fir, while growth patterns of dead and dying trees suggested that fir was able to tolerate longer periods of suppressed growth in shade. Maple had the fastest radial growth and accessed the canopy primarily through rapid early growth in canopy gaps, whereas most beech and fir experienced a period of suppressed growth prior to canopy accession. Peaks in disturbance were roughly linked to increased recruitment, but mainly of shade-tolerant beech and fir; less tolerant species (i.e., maple, ash, and elm) recruited successfully on some of the windthown sites where advance regeneration of beech and fir was less abundant. The results challenge the traditional notions of stability in temperate oldgrowth forests of Europe and highlight the nonequilibrial nature of canopy composition due to unique histories of disturbance and tree life history differences. These findings provide valuable information for developing natural disturbance-based silvicultural systems, as well as insight into maintaining less shade-tolerant, but valuable broadleaved trees in temperate forests of Europe. [ABSTRACT FROM AUTHOR]

ABSTRACT For tropical lowland rain forests, Denslow (1987) hypothesized that in areas with large-scale disturbances tree species with a high demand for light make up a larger proportion of the flora; results of tests have been inconsistent. There has been no test for warm temperate rain forests ( WTRFs), but they offer a promising testing ground because they differ widely in the extent of disturbance. WTRF is dominated by microphylls sensu Raunkiaer and has a simpler structure and range of physiognomy than tropical or subtropical rain forests. It occurs in six parts of the world: eastern Asia, New Zealand, Chile, South Africa, SE Australia and the Azores. On the Azores it has been mostly destroyed, so we studied instead the subtropical montane rain forest ( STMRF) on the Canary Islands which also represents a relict of the kind of WTRF that once stretched across southern Eurasia. We sought to find whether in these six regions the proportion of tree species needing canopy gaps for establishment reflects the frequency and/or extent of canopy disturbance by wind, landslide, volcanic eruptions (lava flow and ash fall), flood or fire. We used standard floras and ecological accounts to draw up lists of core tree species commonly reaching 5 m height. We excluded species which are very rare, very localized in distribution, or confined to special habitats, e.g. coastal forests or rocky sites. We used published accounts and our own experience to classify species into three groups: (1) needing canopy gaps for establishment; (2) needing either light shade throughout or a canopy gap relatively soon (a few months or years) after establishment; and (3) variously more shade-tolerant. Group 1 species were divided according the kind of canopy opening needed: tree-fall gap, landslide, lava flow, flood or fire. Only some of the significant differences in proportion of Group 1 species were consistent with differences in the extent of disturbance; even in some of those cases other factors seem likely to have had a major determining influence during evolution. We also sought to determine whether the species that are at least 'short-term persistent' in the soil seed bank (lasting 2-4 years) are all species needing canopy gaps for establishment. The answer was negative; large numbers of seeds of some shade-tolerants accumulate in the soil, and these species are able to benefit from soil disturbance in deep shade. We found a significant and strong positive relationship in Japan between mean seed mass and mature tree height, a weak positive relationship in New Zealand and no relationship in any of the other four regions. When comparing the seed mass values of Group 1 and Group 3 species we obtained different answers depending on whether or not we confined ourselves to taxonomically controlled contrasts. In only two of the four regions with an appreciable number of species in Group 1 is the mean seed mass of such species significantly lower than that of Group 3 species when taxonomic relatedness is ignored. [ABSTRACT FROM AUTHOR]

Background:Tropical forest biomass is not at steady state, being determined by a balance between deterministic growth and stochastic disturbances. Understanding tropical carbon sources and sinks therefore requires better characterisation of the incidence and intensity of disturbance at critical scales. Aims:We determine if information from remotely sensed biomass maps (ALOS-PALSAR) can constrain estimates of miombo woodland biomass dynamics and disturbance. Methods:We analyse biomass maps created over Mozambican woodlands undergoing varied disturbances. We use a simple ensemble model of biomass dynamics to test the hypothesis that biomass distributions can diagnose disturbance processes in specified areas, and use the model to explore the sensitivity of biomass to disturbance parameters. Results:Ensemble runs can reproduce qualitatively similar biomass patterns to those observed in miombo, through varying two parameters that determine frequency and intensity of biomass loss. Using sensitivity analyses, we show for a synthetic case that these two disturbance parameters can be retrieved from satellite observations. Conclusions:Biomass distributions provide enough information to constrain the two critical parameters of the disturbance model, the local probability of disturbance, and its intensity (fraction of biomass lost). These results provide a proof of concept for assimilating biomass maps into models of carbon cycling. [ABSTRACT FROM PUBLISHER]

Floods are frequently associated with disturbance in structuring riverine forests and they lead to environmental heterogeneity over space and time. We evaluated the distribution of tree species, ecological groups, species richness and diversity from the point bar to the slope of a riverside forest in southern Brazil (Lat. 30°01′S, Long. 52°47′W) to analyze the effects of flooding on soil properties and forest structure. A plot of 50 × 200 m divided in five contiguous transects of 10 × 200 m parallel to the river was installed, where we measured all the individual trees with pbh ≥ 15 cm. A detailed topographical and soil survey was carried out across the plot and indicated significant differences in organic matter and most mineral nutrients through the topographical gradient. The 1,229 surveyed individuals belonged to 72 species and 35 families. We used Partial CCA and Species Indicator Analysis to observe the spatial distribution of species. Both analyses showed that species distribution was strongly related to the flooding gradient, soil properties and also by space and pure spatial structuring of species and environmental variables (spatial autocorrelation), although a large part of variation remains unexplained. The ecological groups of forest stratification, plant dispersal and requirements for germination indicated slight differences among frequently, occasional and non-flooded transects. Species richness and diversity were higher at intermediate elevations and were associated to the increased spatial–temporal environmental heterogeneity. Across the plot, the direct influence of flooding on tree species distribution created a vegetation zonation that is determined by predicted ecological traits. [ABSTRACT FROM AUTHOR]

Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However, canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron tulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees... [ABSTRACT FROM AUTHOR]

1. Habitat fragmentation, degradation and abiotic disturbances may strongly affect population dynamics and genetic diversity of plant populations. 2. In this study, a Life Table Response Experiment (LTRE) and stochastic simulations were used to investigate how different types of disturbance affected the fitness and population dynamics of small, fragmented populations of the long-lived perennial Primula vulgaris and how this was related to genetic diversity. Nested factors were included in the LTRE analysis in order to assess population-specific contributions to changes in population growth rate and to contrast these with contributions derived for year and type of disturbance. 3. Stochastic growth rates (λs) varied considerably among disturbance types: sites continuously disturbed throughout the year had a mean stochastic growth rate smaller than one, whereas sites receiving low or cyclic disturbance had stochastic growth rates larger than one. 4. LTRE analysis revealed that disturbance had a major impact on variation in growth rate, whereas year effects were less pronounced. However, contributions of individual populations equalled or exceeded those of the disturbance regime and mainly originated from negative or positive contributions of seedling recruitment and growth. 5. Linear regression analysis showed that these deviations of population demography from the disturbance type contribution were positively related to genetic diversity and effective population size, whereas inbreeding and isolation had no effect. Similar analyses revealed a positive effect of effective population size on λs. 6. Our data indicate that disturbance has an important impact on population dynamics of this plant species, but that populations containing a higher number of reproductive adults are buffered against large fluctuations due to environmental stochasticity so that stochastic growth rates are higher. However, because population specific contributions to changes in population growth rate were as large as the contributions of disturbance itself, and because they were significantly related to population genetic diversity, our study suggests that, along with local and regional environmental variables, genetic diversity may also play a key role in determining population viability of perennial plant species. [ABSTRACT FROM AUTHOR]

Physiological processes and local-scale structural dynamics of mangroves are relatively well studied. Regional-scale processes, however, are not as well understood. Here we provide long-term data on trends in structure and forest turnover at a large scale, following hurricane damage in mangrove ecosystems of South Florida, U.S.A. Twelve mangrove vegetation plots were monitored at periodic intervals, between October 1992 and March 2005. Mangrove forests of this region are defined by a −1.5 scaling relationship between mean stem diameter and stem density, mirroring self-thinning theory for mono-specific stands. This relationship is reflected in tree size frequency scaling exponents which, through time, have exhibited trends toward a community average that is indicative of full spatial resource utilization. These trends, together with an asymptotic standing biomass accumulation, indicate that coastal mangrove ecosystems do adhere to size-structured organizing principles as described for upland tree communities. Regenerative dynamics are different between areas inside and outside of the primary wind-path of Hurricane Andrew which occurred in 1992. Forest dynamic turnover rates, however, are steady through time. This suggests that ecological, more-so than structural factors, control forest productivity. In agreement, the relative mean rate of biomass growth exhibits an inverse relationship with the seasonal range of porewater salinities. The ecosystem average in forest scaling relationships may provide a useful investigative tool of mangrove community biomass relationships, as well as offer a robust indicator of general ecosystem health for use in mangrove forest ecosystem management and restoration. [ABSTRACT FROM AUTHOR]

Question: We were interested if and how variation in frequency and/or size of disturbances affect the dynamics of a montane old-growth forest in Central Europe. Location: The forest, co-dominated by Fagus sylvatica, Picea abies and Abies alba, is located in Lower Austria and represents one of the few sizable virgin forests in Central Europe. Methods: We extracted cores from 100 trees using systematic grid sampling (grid cell size 10 m × 10 m) on each of four 1-ha plots distributed across the old-growth remnant of 300 ha. We inferred disturbance events from rapid early growth and release events. For defining release criteria, we applied the boundary line method. We investigated the spatial structure of current age and gap distributions and past disturbance events in grid cells, using a pair density statistic. Results: The disturbance histories indicate decades with peaks and also extended periods without disturbance. Some peaks occurred synchronously at three of the four plots (1910s, 1930s, 1960s and 1980s). Peaks and gaps in the disturbance chronologies widely agreed with peaks and gaps in the age distributions. Most disturbance events during single decades showed a random spatial distribution. Conclusions: There is considerable variation in disturbance frequency and/or severity over time. Most disturbance events will rather thin the stand than clear larger areas at once. Following scattered disturbance two pathways occur: (1) gap expansion leading to creation of larger gaps, and (2) gap closure by lateral encroachment or by subcanopy trees growing into the canopy. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The montane rain forest in Chiapas, Mexico has been subject to continuous human disturbance, mainly by wood extraction, cattle grazing and fire. To address the effect of this kind of disturbance regime on regeneration, survival and growth of naturally established tree seedlings were evaluated during a 3-yr period in three forest stands which varied in frequency and intensity of human disturbance. Frequency of cattle browsing on transplanted seedlings of Cornus disciflora, Liquidambar styraciflua and Oreopanax xalapensis planted on different facing slopes was evaluated over an 18-mo period, their survival and growth was also determined. The density of seedlings, number of species and survival of naturally recruited tree seedlings decreased with increased intensity of disturbance. Only seedlings of Pinus and Quercus species were recorded in heavily disturbed conditions. Seedlings grew more vigorously under moderately disturbed than in undisturbed or heavily disturbed conditions. More extreme microclimatic variation (air temperature, relative humidity and solar radiation) was recorded in heavily vs moderately disturbed forest. Survival and growth of transplanted tree seedlings differed with species. Grazing damage varied among seedlings located on different facing slopes. Plants located on NE facing slopes survived better than those on other slope positions. The mean proportion of surviving individuals of L. styraciflua (80%) and C. disciflora (78%) was higher than those for O. xalapensis (60%). A higher number of C. disciflora and O. xalapensis seedlings were grazed than L. styraciflua in any slope orientation treatment. The results suggest that human disturbance negatively affects natural recruitment, reduces richness of tree seedlings and favours a small number of tree species. [ABSTRACT FROM AUTHOR]

Abstract Aim There is increasing research attention being given to the role of interactions among natural disturbances in ecosystem processes. We studied the interactions between fire and spruce beetle (Dendroctonus rufipennis Kirkby) disturbances in a Colorado subalpine forest. The central questions of this research were: (1) How does fire history influence stand susceptibility to beetle outbreak? And conversely, (2) How does prior occurrence of a beetle outbreak influence stand susceptibility to subsequent fire? Methods We reconstructed the spatial disturbance history in a c. 4600 ha area by first identifying distinct patches in the landscape on aerial photographs. Then, in the field we determined the disturbance history of each patch by dating stand origin, fire scars, dates of mortality of dead trees, and releases on remnant trees. A geographical information system (GIS) was used to overlay disturbance by fire and spruce beetle. Results and main conclusions The majority of stands in the study area arose following large, infrequent, severe fires occurring in c . 1700, 1796 and 1880. The study area was also affected by a severe spruce beetle outbreak in the 1940s and a subsequent low-severity fire. Stands that originated following stand-replacing fire in the late nineteenth century were less affected by the beetle outbreak than older stands. Following the beetle outbreak, stands less affected by the outbreak were more affected by low-severity fire than stands more severely affected by the outbreak. The reduced susceptibility to low-severity fire possibly resulted from increased moisture on the forest floor following beetle outbreak. The landscape mosaic of this subalpine forest was strongly influenced by the interactions between fire and insect disturbances. [ABSTRACT FROM AUTHOR]

Recent developments in UK forestry policy require the adoption of management practices that maintain and improve the biodiversity of managed forests. One approach is to use natural disturbance in unmanaged forests as a template for setting the scale, frequency and pattern of forest operations in managed forests. This review considers the relevance of this approach for conifer plantations in upland Britain. [ABSTRACT FROM PUBLISHER]

In forest ecosystems, natural and anthropogenic disturbances alter canopy structure, understory vegetation, amount of woody debris, and the properties of litter and soil layers. The magnitude of these environmental changes is context-dependent and determined by the properties of the disturbance, such as the frequency, intensity, duration, and extent. Therefore, disturbances can dynamically impact forest communities over time, including populations of ground-dwelling invertebrates that regulate key ecosystem processes. We propose conceptual models that describe the dynamic temporal effects of canopy gap formation and coarse woody debris accumulation following disturbances caused by invasive insects, wind, and salvage logging, and their impacts on ground-dwelling invertebrate communities. Within this framework, predictions are generated, literature on ground-dwelling invertebrate communities is synthesized, and pertinent knowledge gaps identified. [ABSTRACT FROM AUTHOR]