Invaders' control on post-disturbance succession in coastal mangroves

Aims In recent years, coastal mangroves have been frequently affected by large disturbances (cyclones, hurricanes, flooding and tsunamis) and post-disturbance vegetation is often dominated by small stature mangrove, mangrove-associate and non-mangrove species potentially affecting ecosystem functioning. Knowledge on the processes of mangrove vegetation development and recovery (succession) following normal and large disturbances will benefit practitioners in designing robust ecosystem management/restoration plans. Here we propose a conceptual model of disturbance-mediated succession in mangroves.Methods Based on field observations and species' life history traits, we develop conceptual models of mangrove succession under normal disturbance regime and recently experienced increased frequency of large disturbances. We evaluate our conceptual models by conducting a scenario testing experiment.Important findings We suggest two predominant processes affecting mangrove succession after disturbance: propagule limitation due to damage of seed producing mature trees and dispersal barrier resulting from biological invasion associated with large disturbance. We argue that large disturbances affect mature trees more than the small-stature non-tree (shrubs, herbs and climbers) species creating a larger propagule shortage for mangrove tree species than non-tree species. Secondly, large disturbances facilitate invasion of free-floating aquatics, which may interfere with the flow-facilitated propagule dispersal and seedling establishment of mangrove species. In a scenario testing experiment, we have shown that similar levels of disturbance impact vegetation development and recovery differently depending on the presence or absence of invasive species. We conclude that since biological invasion is one of the major drivers of post-disturbance mangrove succession, the dimension of biological invasion should be included in prediction, management and restoration of mangrove forests.     

Biodiversity acts as insurance of productivity of bacterial communities under abiotic perturbations

Anthropogenic disturbances are detrimental to the functioning and stability of natural ecosystems. Critical ecosystem processes driven by microbial communities are subjected to these disturbances. Here, we examine the stabilizing role of bacterial diversity on community biomass in the presence of abiotic perturbations such as addition of heavy metals, NaCl and warming. Bacterial communities with a diversity gradient of 1–12 species were subjected to the different treatments, and community biomass (OD₆₀₀) was measured after 24 h. We found that initial species richness and phylogenetic structure impact the biomass of communities. Under abiotic perturbations, the presence of tolerant species in community largely contributed in community biomass production. Bacterial diversity stabilized the biomass across the treatments, and differential response of bacterial species to different perturbations was the key reason behind these effects. The results suggest that biodiversity is crucial for maintaining the stability of ecosystem functioning and acts as ecological insurance under abiotic perturbations. Biodiversity in natural ecosystems may also uphold the ecosystem functioning under anthropogenic disturbance.     

Repeat disturbances have cumulative impacts on stream communities

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Shift of Conifer Boreal Forest to Lichen–Heath Parkland Caused by Successive Stand Disturbances

In the southern boreal forest (Québec, Canada), tree harvesting is a major disturbance affecting the dominant black spruce (Picea mariana) stands already suffering from naturally recurrent insect and fire disturbances. Although recovery of the spruce forest after an insect infestation or a fire is possible under current site conditions, it is less likely when both types of disturbance occur during a short period of time. The addition of yet another disturbance, such as tree harvesting, can thus have catastrophic consequences. We analyzed the impact of three successive disturbances—tree harvesting, insect infestation, and fire—on the regeneration of boreal spruce–moss forests within a period of approximately 50 years. The spruce forests were harvested in the 1940s and the 1950s. Recovery from the logging consisted of advance regeneration (spruce layers less than 1 m high that were left intact during clear-cuts), which was burned in 1991. The vegetation cover (mostly heath and lichen species) and soil conditions (acidic, nutrient-poor podzolic soils developed from coarse materials) of the postfire sites that we studied were similar. Stand structure and tree regeneration were documented from large quadrats (0.25 ha) using age, size, and tree ring data from postlogged and postfire spruce. At an early stage of development, the growing advance regeneration was damaged by insect defoliators in the late 1970s and the mid-1980s, and several trees died a few years before the 1991 fire. The successive disturbances considerably reduced the number of seed-bearers, leading to the collapse of postfire regeneration and a shift to parkland. Through a successional trajectory far from the expected trend for boreal forests influenced by single disturbance, the shift resulted in the formation of divergent plant communities. The development of divergent communities at the landscape scale is generally overlooked due to their small size. They indicate, however, the weak resilience of boreal forests faced with cascading perturbations, which are likely to increase in intensively logged areas.     

Species richness and resilience of forest communities: combined effects of short-term disturbance and long-term pollution

Recovery of the species richness of plant communities after experimental disturbances of various severities were studied in spruce forests polluted by atmospheric entry of SO₂ and heavy metals from a copper smelter. In the three toxic load zones (impact, buffer, and background), 60 experimental “pit-and-mound” complexes (sized 1 m × 2 m, 20 complexes in each zone) were created. Colonization of disturbed areas by vascular plants was observed during a 6-year period after the disturbance. The results showed that the recovery processes were affected by disturbance severity and that the recovery differed significantly among the communities. In all of the zones, species richness increased rapidly after mild disturbance. In degraded communities, levelling of differences in the rate of colonization after mild and severe disturbances was observed. The highest colonization rate was found in the communities of background zone, while the lowest was found in the heavily degraded communities of impact zone. The disturbances significantly increased the species diversity of communities in all zones and caused a certain reversion of degraded communities to previous stage of anthropogenic succession. Mild disturbance promoted the greatest increase in the diversity indices. The study results indicate that recovery rate of species richness of plant communities is determined by the duration of negative effect of disturbances. Recovery also depends significantly on the magnitude and endurance of positive effect of disturbances. The studied communities differed significantly in these parameters. The study results also suggest that short-term disturbances can significantly modify the process of transformation of plant communities by atmospheric pollution. On the other hand, long-term pollution can considerably modify the response of forest communities to disturbances. The results also conclude that the resilience of communities does not exclusively depend on their species richness.     

Temporal variability within disturbance events regulates their effects on natural communities

Disturbances are processes inherently variable in time and space. This variability comprises a key determinant of ecosystem responses to disturbance. Temporal patterns can, however, vary significantly both among and within individual disturbance events. While recent research has demonstrated an importance of the former, studies on the effects of variability within perturbations have consistently confounded temporal variability with other disturbance attributes (e.g. overall intensity or duration). We established a field experiment to test explicitly the hypothesis that the temporal pattern within perturbations can drive ecosystem responses independently of other disturbance traits. We examined the effects of two disturbance regimes comprising sediment pulses of contrasting temporal pattern (constant and temporally variable intensities) on the benthic invertebrate assemblage of a headwater stream. The overall intensity, duration, timing and frequency of the perturbations were, however, identical. Invertebrates drifting during the temporally variable pulses were more abundant and differed in taxonomic and trophic structure than those exposed to constant perturbations. Moreover, whereas temporal patterns of disturbance events had no immediate effect on benthic invertebrate assemblages in situ, assemblages exposed to the constant perturbations took longer to recover from sediment disturbances than those exposed to temporally variable perturbations. Our results demonstrate that variability in the temporal pattern of intensity within individual perturbations can regulate, independently of other disturbance attributes, the extent and type of ecosystem responses to, and recovery from, disturbances. Effective environmental management and policy therefore necessitate the explicit quantification of temporal patterns of intensity both within and among perturbations.     

Response of two oligohaline marsh communities to lethal and nonlethal disturbance

Severity is recognized as an important attribute of disturbance in many plant communities. However, the effects of disturbances of different severity on patterns of regeneration in oligohaline marsh vegetation have not been experimentally examined. In these communities, a critical difference in the effects of disturbance severity may be whether the vegetation dies as a result of the disturbance or is merely damaged and hence capable of resprouting. We described the regeneration of vegetation in two Louisiana marsh community types, one dominated by Sagittaria lancifolia L. and the other by Spartina patens (Ait.) Muhl., following three levels of disturbance: no disturbance, a nonlethal disturbance, and a lethal disturbance. In the nonlethal disturbance, aboveground vegetation was clipped to simulate common disturbances such as fire and herbivory that remove aboveground vegetation but leave rhizomes intact. In the lethal disturbance vegetation was killed using herbicide to simulate disturbances causing plant mortality such as wrack deposition, sedimentation, scouring, and flooding following fire or herbivory. Regeneration was assessed over a 2-year period by measuring plant species richness, relative abundance, relative dominance, cover, and final biomass. To elucidate mechanisms for observed responses of vegetation, the species composition of the seed bank, light penetration, water level, salinity, and soil redox potential were evaluated. Despite differences in the structure of undisturbed vegetation in the two community types, they exhibited the same overall pattern of regeneration. Following nonlethal disturbance, the dominant species resprouted and quickly reestablished the structure of the vegetation. In contrast, recolonization following lethal disturbance occurred primarily via seedling recruitment, which resulted in marked shifts in community structure that persisted throughout the study. While the two communities responded similarly overall to disturbance, the response of individual species was not uniform; abundance, dominance, biomass, or cover increased for some species but decreased for others in response to disturbance. Seed bank species occurred in the vegetation following lethal disturbance in the Spartina community and in both disturbed and undisturbed plots in the Sagittaria community, indicating that the seed bank is a source of propagules for regeneration and maintenance of oligohaline marshes. Of the environmental variables measured, light level was most closely related to the effect of disturbance severity on community structure. Our results suggest that lethal and nonlethal disturbances have differential effects on regeneration of vegetation that can create pattern in oligohaline marshes communities. Received: 29 September 1997 / Accepted: 12 May 1998     

Grassland responses to multiple disturbances on the New England Tablelands in NSW,Australia

Disturbances have played a significant role in shaping vegetation patterns following European settlement and agricultural development in Australia, particularly over the last 100 years. However, little is known about the temporal dynamics of plant communities in relation to disturbances and their interactions. In this study we examined the response and recovery of temperate grassland communities to disturbance, using a multi-factorial experiment involving grazing exclusion (absent and present), fire (absent and present), soil cultivation (none, 5 and 20 cm) and soil amendment (none, fertiliser and fertiliser plus clover seeds) on the New England Tablelands in NSW, Australia. Temporal patterns of plant communities were analysed using detrended correspondence analysis for eight surveys over 24 months. Vegetation patterns at each survey were analysed using principal components analysis. The effects of treatments on malleability (Bray–Curtis dissimilarity) of plant communities were analysed using a linear mixed model, and the relationships between malleability and plant species groups were depicted using a generalised additive model and further analysed using a linear model. Perennial native grasses and a non-native forb (Hypochaeris radicata) initially dominated the vegetation, but after the disturbances H. radicata and other non-native species dominated. Compositional changes from the initial states were greatest in the first spring (7 months after treatment application), and then the vegetation tended to recover towards its original state. Soil cultivation resulted in the greatest deviation in community composition, followed by soil amendment, fire, with grazing exclusion the least. The recovery process and rate of recovery varied with treatment reflecting the dominance of soil cultivation and its interactions with other forms of disturbances. Soil amendment and grazing exclusion tended to reduce the effects of soil cultivation. Malleability was negatively related to perennial native grasses; positively to other non-native species, annual native grasses and perennial native sedges/rushes; and negatively to H. radicata when its cover was below 18%, but positively when above 18%. The degree of malleability reflected the high resilience of the vegetation to disturbance, and was mainly due to the recovery of perennial native grasses and H. radicata. This resilience demonstrated that the small-scale disturbances did not cause vegetation to cross an ecological threshold and that the present vegetation is resilient to common disturbances occurring at small scales. The results also suggest (1) that the present vegetation has developed mechanisms to adapt to these disturbances, (2) the importance of disturbance scale or (3) that the ecological threshold had already been crossed and the present vegetation is in a degraded state compared with its original state before the end of the 19th century.     

Are Large, Infrequent Disturbances Qualitatively Different from Small, Frequent Disturbances?

In this article, we develop a heuristic model of ecosystem-disturbance dynamics that illustrates a range of responses of disturbance impact to gradients of increasing disturbance extent, intensity, or duration. Three general kinds of response are identified and illustrated: (a) threshold response, (b) scale-independent response, and (c) continuous response. Threshold responses are those in which the response curve shows a discontinuity or a sudden change in slope along the axis of increasing disturbance extent, intensity, or duration. The response threshold occurs at a point where the force of the disturbance exceeds the capacity of internal mechanisms to resist disturbance, or where new mechanisms of recovery become involved. Within this conceptual framework, we find that some unusually large or intense disturbances, but not all, produce qualitatively different responses compared with similar disturbances of lesser magnitude. If disturbance impact does not increase with increasing disturbance extent, intensity, or duration, or if the response curve changes monotonically, then large disturbances are not qualitatively different from small ones. For example, jack pine tends to become reestablished after stand-replacing fire in boreal forests, regardless of fire size, because its serotinous cones provide an adequate seed source throughout the burned area. Thus, large fires are not qualitatively different from small fires in terms of jack pine reproduction. However, if disturbance impact does increase abruptly at some point with increasing disturbance extent, intensity, or duration, often because of thresholds in the capacity of internal mechanisms to resist or respond to disturbance impact, then large disturbances are qualitatively different from small ones, at least for some parameters of ecological response. For example, balsam fir and white cedar can recolonize a small burned patch of boreal forest in close proximity to surviving individuals of these species, but they will be eliminated from a large burn because of their susceptibility to fire-caused mortality and their inability to disperse their seeds over long distances. The conceptual framework presented here permits some new insights into the dynamics of natural systems and may provide a useful tool with which managers can assess the potential for catastrophic damages resulting from large, infrequent disturbances. Received 14 July 1998; accepted 29 September 1998     

Trophic compensation reinforces resistance: herbivory absorbs the increasing effects of multiple disturbances

Disturbance often results in small changes in community structure, but the probability of transitioning to contrasting states increases when multiple disturbances combine. Nevertheless, we have limited insights into the mechanisms that stabilise communities, particularly how perturbations can be absorbed without restructuring (i.e. resistance). Here, we expand the concept of compensatory dynamics to include countervailing mechanisms that absorb disturbances through trophic interactions. By definition, ‘compensation’ occurs if a specific disturbance stimulates a proportional countervailing response that eliminates its otherwise unchecked effect. We show that the compounding effects of disturbances from local to global scales (i.e. local canopy‐loss, eutrophication, ocean acidification) increasingly promote the expansion of weedy species, but that this response is countered by a proportional increase in grazing. Finally, we explore the relatively unrecognised role of compensatory effects, which are likely to maintain the resistance of communities to disturbance more deeply than current thinking allows.     

Forecasting intensifying disturbance effects on coral reefs

Anticipating future changes of an ecosystem's dynamics requires knowledge of how its key communities respond to current environmental regimes. The Great Barrier Reef (GBR) is under threat, with rapid changes of its reef‐building hard coral (HC) community structure already evident across broad spatial scales. While several underlying relationships between HC and multiple disturbances have been documented, responses of other benthic communities to disturbances are not well understood. Here we used statistical modelling to explore the effects of broad‐scale climate‐related disturbances on benthic communities to predict their structure under scenarios of increasing disturbance frequency. We parameterized a multivariate model using the composition of benthic communities estimated by 145,000 observations from the northern GBR between 2012 and 2017. During this time, surveyed reefs were variously impacted by two tropical cyclones and two heat stress events that resulted in extensive HC mortality. This unprecedented sequence of disturbances was used to estimate the effects of discrete versus interacting disturbances on the compositional structure of HC, soft corals (SC) and algae. Discrete disturbances increased the prevalence of algae relative to HC while the interaction between cyclones and heat stress was the main driver of the increase in SC relative to algae and HC. Predictions from disturbance scenarios included relative increases in algae versus SC that varied by the frequency and types of disturbance interactions. However, high uncertainty of compositional changes in the presence of several disturbances shows that responses of algae and SC to the decline in HC needs further research. Better understanding of the effects of multiple disturbances on benthic communities as a whole is essential for predicting the future status of coral reefs and managing them in the light of new environmental regimes. The approach we develop here opens new opportunities for reaching this goal.     

Effects of natural and artificial disturbance on landscape and forest structure in Tiantong National Forest Park,East China

This paper aims to understand the ecological effects of disturbance on broadleaved evergreen forest in East China. We used a manipulative field experiment approximating the common natural and artificial disturbance types in this area to investigate the community physiognomy, floristic composition, and 5-year recovery dynamics of the post-disturbance forest community. The results indicated that the landscape and forest structure have degraded into shrub communities, structure-damaged evergreen broadleaved communities, and so on. The post-disturbance communities presented different means of plant recruitment and vegetation recovery patterns at an early successional stage. The recovery of disturbed forests primarily depended on external seed sources and re-sprouting from stumps, rather than on soil seed banks, as few buried seeds were found. Re-sprouting thus appears to be key in allowing rapid vegetation recovery in evergreen broadleaved forest. Disturbances seem to be one of the most important factors that can contribute to regional species coexistence across temporal and spatial scales in evergreen broadleaved forests.     

Resilience of native ant community against invasion of exotic ants after anthropogenic disturbances of forest habitats

The positive association between disturbances and biological invasions is a widely observed ecological pattern in the Anthropocene. Such patterns have been hypothesized to be driven by the superior competitive ability of invaders or by modified environments, as well as by the interaction of these factors. An experimental study that tests these hypotheses is usually less feasible, especially in protected nature areas. An alternative approach is to focus on community resilience over time after the anthropogenic disturbance of habitats. Here, we focused on ant communities within a forest to examine their responses after disturbance over time. We selected the Yanbaru region of northern Okinawa Island, which is a biodiversity hotspot in East Asia. We compared ant communities among roadside environments in forests where the road age differed from 5 to 25 years. We also monitored the ant communities before and after disturbance from forest thinning. We found that the species richness and abundance of exotic ants were higher in recently disturbed environments (roadsides of 5–15 years old roads), where the physical environment was warmer and drier. In contrast, the roadsides of 25‐year‐old roads indicated the potential recovery of the physical environment with cooler and moister conditions, likely owing to regrowth of roadside vegetation. At these sites, there were few exotic ants, except for those immediately adjacent to the road. The population density of the invasive species Technoymex brunneus substantially increased 1–2 years after forest thinning. There was no evidence of the exclusion of native ants by exotic ants that were recorded after disturbance. Our results suggest that local ant communities in the Yanbaru forests have some resilience to disturbance. We suggest that restoration of environmental components is a better strategy for maintaining native ant communities, rather than removing exotic ants after anthropogenic disturbance.     

Impacts and negative feedbacks in community recovery over eight years following removal of habitat-forming macroalgae

The decline or loss of habitat-forming species has affected rocky shore marine communities worldwide. Many short-term studies have documented the initiation of cascading effects due to canopy losses of macroalgae, but relatively few studies have followed recovery dynamics over many years. Here, we show that the experimental removal of a dominant intertidal fucoid in southern New Zealand had numerous community effects up to 8 years later. Even though the dominant fucoid returned to a nearly closed canopy, there remained many differences between disturbed and control communities. The disturbed treatments had lower plant density and biomass of the dominant fucoid, fewer species and more turfing coralline algae than controls. Plots with press disturbances were more affected than those with pulse disturbances. The negative feedback of turfing algae on the recovery of fucoid recruitment resulted in effects on cover and diversity in the wider community being evident after 8 years. We discuss the feedbacks between fucoids, benthic turfing algae and community recovery and argue that if biodiversity impacts on marine rocky reefs are to be understood, the role of non-trophic interactions in structure, function and dynamics must be better delineated.     

Contrasting rates of coral recovery and reassembly in coral communities on the Great Barrier Reef

Changes in the relative abundances of coral taxa during recovery from disturbance may cause shifts in essential ecological processes on coral reefs. Coral cover can return to pre-disturbance levels (coral recovery) without the assemblage returning to its previous composition (i.e., without reassembly). The processes underlying such changes are not well understood due to a scarcity of long-term studies with sufficient taxonomic resolution. We assessed the trajectories and time frames for coral recovery and reassembly of coral communities following disturbances, using modeled trajectories based on data from a broad spatial and temporal monitoring program. We studied coral communities at six reefs that suffered substantial coral loss and subsequently regained at least 50 % of their pre-disturbance coral cover. Five of the six communities regained their coral cover and the rates were remarkably consistent, taking 7–10 years. Four of the six communities reassembled to their pre-disturbance composition in 8–13 years. The coral communities at three of the reefs both regained coral cover and reassembled ten years. The trajectories of two communities suggested that they were unlikely to reassemble and the remaining community did not regain pre-disturbance coral cover. The communities that regained coral cover and reassembled had high relative abundance of tabulate Acropora spp. Coral communities of this composition appear likely to persist in a regime of pulse disturbances at intervals of ten years or more. Communities that failed to either regain coral cover or reassemble were in near-shore locations and had high relative abundance of Porites spp. and soft corals. Under current disturbance regimes, these communities are unlikely to re-establish their pre-disturbance community composition.     

Comparison of regeneration following burning,clearing or mineral sand mining at Tomago,NSW: I. Structure and growth of the vegetation

Abstract We have begun a long-term ecological research project to address questions about the impact of multiple disturbances on the species richness of communities and whether multiple disturbances are additive or interactive. A protected water catchment area was chosen, which is subjected to fires, sand mining and clearing, and for which detailed records are available. The study area, at Tomago (32°52′S, 151°45′E), has forest, woodland, shrubland and swamp on a sand substrate, with the vegetated dunes forming part of a coastal embayment. Forty-four sites were located in forested areas that had undergone disturbance by either fire, sand mining or clearing. Sites of each disturbance type were grouped into four age classes: less than 1 year since disturbance, nominally 1991; 5 years, nominally 1986; 11 years, nominally 1980; and 17 years, nominally 1974. A set of burned sites, with the time of the last fire matched to the times of the other disturbances, was used as the control response. In this paper we describe the study area and sites, then examine the effects of each single disturbance on vegetation structure. Canopy cover increased with time and type of disturbance, with 17 year old cleared or mined sites similar to the cover of 11 year old burned sites. In the first two years after disturbance, burned sites had significantly more understorey vegetation than cleared or mined sites, but by 5 years all three were similar. The data presented here show that regeneration of mined sites at Tomago is substantially slower than regeneration following disturbance by fire, with the regeneration of cleared sites intermediate but closer to mining than fire. After 17 years regeneration, cleared and sand mined sites had not returned to the vegetation structure of the pre-disturbance state. Understorey height and the amount of vegetation on cleared or mined sites have not achieved the levels in the original forest, although canopy cover did seem to have reached pre-disturbance levels. Current rehabilitation techniques are more sophisticated than those used 17 years ago and continued monitoring of sites currently being rehabilitated may show a faster return to pre-disturbance states. Having established the hierarchy and nature of the response to each single disturbance here, we are now in a position to investigate the impact of multiple disturbances.     

Habitat dynamics,marine reserve status,and the decline and recovery of coral reef fish communities

Severe climatic disturbance events often have major impacts on coral reef communities, generating cycles of decline and recovery, and in some extreme cases, community‐level phase shifts from coral‐ to algal‐dominated states. Benthic habitat changes directly affect reef fish communities, with low coral cover usually associated with low fish diversity and abundance. No‐take marine reserves (NTRs) are widely advocated for conserving biodiversity and enhancing the sustainability of exploited fish populations. Numerous studies have documented positive ecological and socio‐economic benefits of NTRs; however, the ability of NTRs to ameliorate the effects of acute disturbances on coral reefs has seldom been investigated. Here, we test these factors by tracking the dynamics of benthic and fish communities, including the important fishery species, coral trout (Plectropomus spp.), over 8 years in both NTRs and fished areas in the Keppel Island group, Great Barrier Reef, Australia. Two major disturbances impacted the reefs during the monitoring period, a coral bleaching event in 2006 and a freshwater flood plume in 2011. Both disturbances generated significant declines in coral cover and habitat complexity, with subsequent declines in fish abundance and diversity, and pronounced shifts in fish assemblage structure. Coral trout density also declined in response to the loss of live coral, however, the approximately 2:1 density ratio between NTRs and fished zones was maintained over time. The only post‐disturbance refuges for coral trout spawning stocks were within the NTRs that escaped the worst effects of the disturbances. Although NTRs had little discernible effect on the temporal dynamics of benthic or fish communities, it was evident that the post‐disturbance refuges for coral trout spawning stocks within some NTRs may be critically important to regional‐scale population persistence and recovery.     

Disturbance and diversity at two spatial scales

The spatial scale of disturbance is a factor potentially influencing the relationship between disturbance and diversity. There has been discussion on whether disturbances that affect local communities and create a mosaic of patches in different successional stages have the same effect on diversity as regional disturbances that affect the whole landscape. In a microcosm experiment with metacommunities of aquatic protists, we compared the effect of local and regional disturbances on the disturbance–diversity relationship. Local disturbances destroyed entire local communities of the metacommunity and required reimmigration from neighboring communities, while regional disturbances affected the whole metacommunity but left part of each local community intact. Both disturbance types led to a negative relationship between disturbance intensity and Shannon diversity. With strong local disturbance, this decrease in diversity was due to species loss, while strong regional disturbance had no effect on species richness but reduced the evenness of the community. Growth rate appeared to be the most important trait for survival after strong local disturbance and dominance after strong regional disturbance. The pattern of the disturbance–diversity relationship was similar for both local and regional diversity. Although local disturbances at least temporally increased beta diversity by creating a mosaic of differently disturbed patches, this high dissimilarity did not result in regional diversity being increased relative to local diversity. The disturbance–diversity relationship was negative for both scales of diversity. The flat competitive hierarchy and absence of a trade-off between competition and colonization ability are a likely explanation for this pattern.     

Assessing the hydrologic impact of historical railroad embankments on wetland vegetation response in Canaan Valley,West Virginia: the value of high‐resolution data

The recovery of natural ecological processes after disturbance is poorly understood. Some disturbances may be so severe as to set ecosystems onto a new trajectory. The Canaan Valley National Wildlife Refuge in West Virginia protects a unique high‐altitude wetland that was heavily disturbed by logging 100 years before present (BP) and has since transitioned to a new ecological state (shrub wetland). Refuge managers interested in preserving and restoring ecosystem states expressed concern about lingering impacts of previous disturbances (logging, railroads, beaver, deer, fire). Available data suggested hydrologic impacts from a remnant railroad grade, but managers had insufficient quantitative data to assess these impacts. We initiated a fine‐scale assessment of topography, vegetation distribution, and hydrology to assess impacts from the remnant rail grade using lidar data, vegetation surveys, and piezometers. We developed topographic models, hydrological models, and mapped vegetation distribution. We developed statistical models to assess relationships between vegetation communities, hydrology, and distance to the rail grade. Surprisingly, we found that hydrologic flow paths did not conform to expectation and were not restricted by remnant land use features. For the most part, vegetation communities are responding to topographic and environmental gradients that existed prior to disturbance. Use of highly detailed topographic data (lidar), field hydrology, and vegetation studies allowed us to more accurately assess hydrologic and vegetation regimes, eliminating the need for mitigation, thus saving significant resources.     

Recovery of a northern New England salt marsh plant community from winter icing

High latitude salt marsh plant communities are frequently exposed to conspicuous winter ice disturbances, which trigger secondary succession. In this paper, we document the recovery of a northern New England salt marsh from a severe winter icing event in 1998. Ice disturbances that killed plants but that left the underlying peat intact recovered rapidly. However, ice damage that killed plants and removed the underlying peat, led to areas of physiologically harsh edaphic conditions, specifically waterlogged and anoxic soils that limited plant recolonization. A transplant experiment revealed that only the most stress-tolerant plants were capable of invading the most stressful portions of ice disturbances. A second experiment that artificially dried disturbance patches accelerated patch recovery. These data suggest that recovery from intense ice disturbance is dependent on stress-tolerant plants invading edaphically harsh disturbances, eventually facilitating the recolonization of the community. This process likely takes longer than a decade for full recovery to occur in the areas where both plants and the peat base are removed.