Pre-disturbance Composition Research Articles

Synthesis of recovery patterns in microbial communities across environments

BackgroundDisturbances alter the diversity and composition of microbial communities. Yet a generalized empirical assessment of microbiome responses to disturbance across different environments is needed to understand the factors driving microbiome recovery, and the role of the environment in driving these patterns.ResultsTo this end, we combined null models with Bayesian generalized linear models to examine 86 time series of disturbed mammalian, aquatic, and soil microbiomes up to 50 days following disturbance. Overall, disturbances had the strongest effect on mammalian microbiomes, which lost taxa and later recovered their richness, but not their composition. In contrast, following disturbance, aquatic microbiomes tended away from their pre-disturbance composition over time. Surprisingly, across all environments, we found no evidence of increased compositional dispersion (i.e., variance) following disturbance, in contrast to the expectations of the Anna Karenina Principle.ConclusionsThis is the first study to systematically compare secondary successional dynamics across disturbed microbiomes, using a consistent temporal scale and modeling approach. Our findings show that the recovery of microbiomes is environment-specific, and helps to reconcile existing, environment-specific research into a unified perspective.FPVwQXB65-N4idcpgwJZ6_Video

Early successional trajectory of benthic community in an uninhabited reef system three years after mass coral bleaching

Severe thermal stress events occurring on the backdrop of globally warming oceans can result in mass coral mortality. Tracking the ability of a reef community to return to pre-disturbance composition is important to inform the likelihood of recovery or the need for active management to conserve these ecosystems. Here, we quantified annual, temporal changes in the benthic communities for the three years following mass coral mortality at Jarvis Island—an uninhabited island in the Pacific Remote Islands Marine National Monument. While Jarvis experienced catastrophic coral mortality in 2015 due to heat stress resulting from the 2015/16 El Niño, significant annual shifts were documented in the benthic community in the three years post-disturbance. Macroalgal and turf dominance of the benthos was temporary—likely reflecting the high biomass of herbivorous reef fishes post-bleaching—giving way to calcifiers such as crustose coralline algae and Halimeda, which may facilitate rather than impede coral recovery. By 2018, indications of recovery were detectable in the coral community itself as juvenile densities increased and stress-tolerant genera, such as Pavona, exceeded their pre-disturbance densities. However, densities of Montipora and Pocillopora remain low, suggesting recovery will be slow for these formerly dominant taxa. Collectively, the assemblage and taxon-specific shifts observed in the benthic and coral community support cautious optimism for the potential recovery of Jarvis Island’s coral reefs to their pre-disturbance state. Continued monitoring will be essential to assess whether reassembly is achieved before further climate-related disturbance events affect this reef system.

Paleoecological evidence for a multi-trophic regime shift in a perialpine lake (Lake Joux, Switzerland)

Freshwater ecosystems are under new and increasing threats from anthropogenic change. Ability to detect and predict consequences of environmental perturbations on ecosystem function and water quality is limited by the lack of empirical data over relevant time scales. Paleoecological records present a unique opportunity to broaden understanding of ecological transitions over decadal to millennial timescales. This study tested the occurrence of regime shifts to track changes throughout the lake food web beyond the typical instrumental era, using both “traditional” paleoecological proxies (e.g., cladoceran zooplankton, zoobenthos, and pigments) and more recently developed molecular genetic methods based on sedimentary DNA. We used sediment cores from the perialpine Lake Joux (Swiss Jura), where the history of human settlement and land-use practices in the catchment has been well documented since the Medieval period. Paleoecological evidence revealed an abrupt and unprecedented biological reorganization in the second half of the 20th century, following several centuries of relatively stable communities despite growing human pressure. Time-varying autoregression computed using dynamic linear modelling identified this transition, triggered by the onset of rapid cultural eutrophication in the 1950s, as a true regime shift. Since this time, despite decades of re-oligotrophication, biotic communities of Lake Joux have not returned to pre-disturbance composition, most likely due to other confounding factors, including climate warming, that may prevent the lake from returning to an earlier equilibrium state. Paleoecological reconstruction further suggested that cladocerans responded earlier to disturbance, which is highly relevant for lake monitoring and management strategies.

Balsam fir stands of northeastern North America are resilient to spruce plantation

Globally, there is an increasing demand for wood products. Because of their productivity, forest plantations will increasingly serve to meet this demand. A cumulative anthropogenic disturbance, such as a plantation scenario, could alter resilience of natural forests, thereby triggering alternative successional pathways towards a state that is predominated by planted species. These alternative ecosystems could represent a threat to biodiversity and ecosystem services that are provided by natural forests. Our objective in this study was to evaluate whether a spruce plantation scenario alters the resilience of natural balsam fir stands in the balsam fir ecological region of Quebec (Canada). We studied successional pathways in 897 spruce plantations covering a 40-year period. The spruce plantation scenario does not seem to have altered resilience of natural balsam fir stands. The main tree species naturally regenerating on balsam fir ecological site types had indeed recovered from the plantation scenario to the detriment of planted spruce species. Balsam fir stands are resilient to the spruce plantation scenario, largely because of the effective regeneration processes of balsam fir and birch species, compared to spruce species. Maintaining functional regeneration processes is a way to maintain resilience and insure that biodiversity and ecosystem services will be gradually restored after anthropogenic disturbances. Regeneration processes should enable a resilient forest to follow natural successional pathways back to its pre-disturbance composition, structure and functions. Hence, planting a tree species in a resilient forest that is not in accordance with the successional pathway of the natural forest could put silvicultural investments at risk. With increasing use of plantations to meet wood demand, some sites inevitably will undergo consecutive cycles of the plantation scenario. Cumulative effects of consecutive plantation scenarios may then be detrimental to the resilience of balsam fir stands. We propose initiatives to mitigate these potential threats.

Stand-level windthrow patterns and long-term dynamics of surviving trees in natural secondary stands after a stand-replacing windthrow event

Abstract We examined typhoon windthrow patterns in stand-scale permanent plots within three natural forests and the long-term dynamics of surviving trees in two of these plots. The aim was to verify whether pre-disturbance composition and structure affected windthrow damage and stand recovery. The stands, which were in Hokkaido, the northernmost main island of Japan, differed in pre-disturbance composition (coniferous, mixed and broadleaved stands) and structure, and the basal area losses by the windthrow event were 81–93 per cent. Tree mortality was significantly related to tree size (diameter at breast height) and species. The windthrow patterns differed among the three stands; and, windthrow severity was affected by the pre-disturbance composition and structure. The mortality of trees that survived the windthrow event was ~60 per cent in the two plots. The surviving trees comprised a majority of the canopy layer in the secondary stands. The relative basal area of surviving trees decreased rapidly with increasing tree density in the stand initiation stage but differed between plots. Consequently, the pre-disturbance composition and structure influenced windthrow severity, stand recovery and secondary succession in the recovered stands.

Cross-Shelf Variation in Coral Community Response to Disturbance on the Great Barrier Reef

Changes in coral reef health and status are commonly reported using hard coral cover, however such changes may also lead to substantial shifts in coral community composition. Here we assess the extent to which coral communities departed from their pre-disturbance composition following disturbance (disassembly), and reassembled during recovery (reassembly) along an environmental gradient across the continental shelf on Australia’s Great Barrier Reef. We show that for similar differences in coral cover, both disassembly and reassembly were greater on inshore reefs than mid- or outer-shelf reefs. This pattern was mostly explained by spatial variation in the pre-disturbance community composition, of which 28% was associated with chronic stressors related to water quality (e.g., light attenuation, concentrations of suspended sediments and chlorophyll). Tropical cyclones exacerbated the magnitude of community disassembly, but did not vary significantly among shelf positions. On the outer shelf, the main indicator taxa (tabulate Acropora) were mostly responsible for community dissimilarity, whereas contribution to dissimilarity was distributed across many taxa on the inner shelf. Our results highlight that community dynamics are not well captured by aggregated indices such as coral cover alone, and that the response of ecological communities to disturbance depends on their composition and exposure to chronic stressors.

Stand recovery of a temperate hardwood forest 60 years after a stand-replacing windthrow based on a permanent plot study

ABSTRACTWe examined the dynamics of stand structure and composition over a 60-year period in two permanent plots in a deciduous hardwood forest in Hokkaido, Japan, which were severely disturbed by a stand-replacing windthrow, to reveal trends that could be valuable to the development of a model of forest recovery after a severe windthrow. We analyzed temporal trends in tree density, species richness and diversity, successional composition, and stand development stage in the plots. Both plots recovered as hardwood stands. Tree density and species richness increased, peaking 35‒40 years after the windthrow, and then decreased in both plots. Based on these results, we concluded that both plots were in the stand-initiation stage for 35‒40 years after the windthrow and then transitioned into the stem-exclusion stage. Species diversity increased with an increase in species richness during the stand-initiation stage and then decreased slightly in both plots. In both plots, successional composition did not fluctuate greatly in the 60 years after the windthrow, and both returned to pre-disturbance composition during the stem-exclusion stage. The temporal trends observed in this study were remarkably similar to those in a previous study of permanent plots located near the plots used in this study. Therefore, this study provides valuable information that can be useful in the development of a stand recovery model in temperate forests after stand-replacing windthrows.

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.

Influence of skidder traffic and canopy removal intensities on the ground flora in a clearcut-with-reserves northern hardwood stand in Minnesota, USA

We investigated the effects of skidder traffic intensity, soil disturbance intensity, and canopy removal intensity on the richness, diversity, composition, and cover of the entire ground flora (woody and herbaceous vegetation ≤2 m tall), various individual life forms, invasive/noxious species, and species with different requirements with respect to moisture, nutrients, heat, and light (synecological coordinates) in a mesic northern hardwood stand 6 years after a clearcut-with-reserves regeneration harvest removed 50–100% of the canopy. Skidder traffic was restricted to a network of trails and a global positioning system (GPS) tracked skidder movement to quantify the number of passes at pre-established sampling points along the anticipated soil disturbance gradient on and off skid trails. Soil disturbance intensity within the top 15 cm of soil was quantified by relativized resistance to penetration (RRP) compared to untrafficked plots; post-harvest increases in RRP ranged from 81 to 272%. Regression analysis and ordination revealed a pattern of increasing difference from pre-disturbance composition with increasing skidder traffic (i.e., forest floor disturbance), with increased RRP (i.e., soil compaction) and (less so) canopy removal intensity. The ground flora shifted from interior forest species such as Anemone quiquefolia, Aralia nudicaulis, Clintonia borealis, Maianthemum canadense, and Oryzopsis asperifolia to more ruderal, invasive/noxious, and disturbed-forest species such as Aster lateriflorus, Cirsium spp., Phleum pretense, Rubus idaeus, and Trifolium spp. The relative resistance of the initial ground flora to change (inverse of the distances between pre- and post-harvest samples in ordination space) was nonlinearly related to skidder traffic intensity and linearly related to RRP, indicating that the largest compositional changes occurred with the first few passes of the skidder. Mean plot scores for the synecological coordinates revealed that the post-harvest species were on average less demanding of water and nutrients; the opposite was true for light. Plots exposed to less skidder traffic and RRP had higher herb cover and higher nutrient scores; those with more skidder traffic and higher RRP levels had higher shrub cover and higher light scores. We conclude that protection of the ground flora from forest floor and soil disturbance requires careful planning of skid trail networks. Concentrating skidder traffic to a designated skid trail system can result in less area disturbed and spatially connected networks of larger, untrafficked remnant forest patches that may maintain species that are sensitive to forest floor and soil disturbance.

Diversity Patterns of Bornean Butterfly Assemblages

Borneo contains a diverse rainforest butterfly community, but its forests are under threat from logging and ENSO- (El Nino Southern Oscillation) induced fires. Contrasts in butterfly assemblage structure were examined in nine 450 ha landscapes in logged forest, primary unburned continuous and isolated forest, and forest affected by surface fires during the 1997/98 ENSO event. Temporally the effect of the 1997/98 ENSO event was followed in a single burned landscape from 1997 to 2004. In total, 517 species were present in 190 sampling sites. There was a five-fold difference in species richness among landscapes, with highest richness in continuous landscapes and lowest richness in burned landscapes. Richness was also higher in logged forest than proximate unlogged forest. Temporally, species richness dropped dramatically from 1997 to 1998, but after-wards increased remaining, however, substantially lower than pre-ENSO (1997) sampling. Sites in burned landscapes were distinct from other sites in terms of vegetation structure with the slash-and-burn area the most dissimilar to other landscapes. There was much less structure among unburned landscapes. The pattern of butterfly community composition was similar to that of vegetation structure with the community from the slash-and-burn area the most distinct. However, there was much less overlap among sites from different landscapes. Temporally, 1998 possessed the most distinct assemblage when compared to assemblages from other years. The community composition was, however, slowly returning to a pre-disturbance composition. Variance in community composition explained by environmental and spatial factors differed substantially among landscapes. The spatial fraction was the only explanatory component in recently burned landscapes and a proximate small unburned isolate, but explained no variation in logged landscapes. The environmental fraction explained substantial amounts of variation in logged landscapes and the slash-and-burn area. When all landscapes were pooled high proportions of variation in butterfly community composition were explained by both geographic distance between sites and environmental variables. In contrast when only unburned landscapes were considered, most variation was explained by the geographic distance among them. Despite differences among landscapes there was a general pattern of relatively sharp decline in similarity at short distances that levels out over greater distances, a result that agrees with previous studies on other tropical species assemblages.

Changes in forest floor bryophyte (moss and liverwort) communities 4 years after forest harvest

Forest harvest presents a potential threat to forest floor bryophyte communities primarily through alteration of the microclimate and disturbance of substrates on the forest floor. Management, including harvest, applied at the landscape scale creates patches of disturbance of differing severities at the spatial scale experienced by bryophytes. Presumably, bryophyte diversity in managed landscapes is best conserved by forest harvest techniques that minimize community change, thereby allowing disturbed communities to reassemble to approach predisturbance composition. We monitored bryophyte community reassembly by sampling quadrats established in a 54-ha management block of Acadian forest in New Brunswick, before and after harvest. Quadrats were either in unharvested areas, or experienced a range of disturbance severities from removal of some or all canopy, to forest floor disturbance with complete canopy removal. Bryophyte communities showed compositional change over 4 years, even in areas that were not harvested. Although species richness was maintained or recovered 4 years after harvest, changes in species composition were significant in all disturbance classes with greatest change related to forest floor disturbance. In particular, liverworts were lost in areas with forest floor disturbance. We suggest that the simplest method to reduce immediate species loss, and presumably promote conservation of bryophyte communities within managed forest landscapes, is to utilize techniques that reduce the area of forest floor and associated substrates that are physically disrupted.Key words: bryophyte, community change, disturbance, forest harvest, monitoring.

Early Successional Pathways and the Resistance and Resilience of Forest Communities

Vegetation changes were studied for 21 yr in two clearcut logged and slash—burned Pseudotsuga forests in the western Cascade Range of Oregon. Detrended correspondence analysis (DCA) was used to examine the successional relationships among six understory communities exposed to a gradient of disturbance intensity. Euclidean disturbances between pre— and postdisturbance samples in ordination space were used to compare community resistance to disturbance and long—term recovery, or resilience. Ordination through time for plant communities revealed a common pattern of rapid floristic change away from predisturbance composition, followed by gradual, unidirectional return. Early, but transient, convergence of successional pathways was common among mesic— and dry—site communities, reflecting the broad distribution of colonizers and the floristic similarity of predisturbance understories. Distinct sequences were observed on moist sites, reflecting more unique residual and colonizing floras. Ordinations also revealed increasing compositional change with disturbance intensity. Successional sequences were dominated by residual species on relatively undisturbed sites and by alternate suites of invading species on moderately disturbed and burned sites. Variation in the response gradient between watersheds reflected the modifying influence of local environment, stand history, and change in succession. Resistance and resilience varied little among plant communities but were generally lowest for the depauperate Coptis community and greatest for the compositionally and structurally diverse Polystichum and Rhododendrom—Gaultheria types. Both measures were strongly influenced by disturbance intensity. The stability of Pseudotsuga understories derives from the moderate tolerance of initial understory dominants to burning and in their ability to subsequently perennate from subterranean structures. Variation in the long—term response of communities reflects complex interactions between species life history, disturbance intensity, and chance, suggesting that both deterministic and stochastic factors must be considered in evaluating community stability and response to disturbance.