Early Successional Communities Research Articles

Beta diversity subcomponents of plant species turnover and nestedness reveal drivers of community assembly in a regenerating subtropical forest.

Secondary forests represent a significant proportion of global forest cover, with over 70% of forests in East Asia classified as regenerating. While succession has been studied extensively in temperate systems, trajectories of subtropical succession remain poorly characterized in highly disturbed, urban-adjacent forests. Investigating the additive beta diversity components of turnover and nestedness may reveal community assembly mechanisms driving secondary succession. The present study investigates plant community assembly along a successional gradient from 7 to 70 years following the onset of succession in secondary subtropical forests in Hong Kong, China. Plant survey data for 28 plots were analysed, generating additive Simpsons turnover and nestedness beta diversity metrics. Dissimilarity matrices were generated and modelled as a function of environmental matrices including forest plant community age (years following onset of secondary succession), inter-community distance (metres), and soil moisture saturation (%) across three elevational bands using generalized dissimilarity models. Nonmetric multidimensional scaling of plant communities was conducted with Bray-Curtis dissimilarity matrices. Inter-community distance and successional age differentially influenced plant species turnover between lowland and Montane forest types. Models of nestedness found that plot age and soil moisture saturation were significant drivers of nestedness patterns in plant communities across elevational classes. Turnover represented a higher proportion of Sorensen beta diversity than nestedness, while ANOSIM found significant differentiation between plant communities at different successional stages. Turnover patterns suggest a deterministic model of community assembly, with strong patterns of species replacement between communities at fine spatial scales and successional stages, as well as clear compositional shifts between lowland and montane forest types. NMDS analysis and functional compositional assessments suggested a transition from early successional communities with a high proportion of shrub species, to later successional communities with a higher proportion of tree species, with an increase in species turnover with greater age dissimilarity.

The importance of species addition 'versus' replacement varies over succession in plant communities after glacier retreat.

The mechanisms underlying plant succession remain highly debated. Due to the local scope of most studies, we lack a global quantification of the relative importance of species addition 'versus' replacement. We assessed the role of these processes in the variation (β-diversity) of plant communities colonizing the forelands of 46 retreating glaciers worldwide, using both environmental DNA and traditional surveys. Our findings indicate that addition and replacement concur in determining community changes in deglaciated sites, but their relative importance varied over time. Taxa addition dominated immediately after glacier retreat, as expected in harsh environments, while replacement became more important for late-successional communities. These changes were aligned with total β-diversity changes, which were more pronounced between early-successional communities than between late-successional communities (>50 yr since glacier retreat). Despite the complexity of community assembly during plant succession, the observed global pattern suggests a generalized shift from the dominance of facilitation and/or stochastic processes in early-successional communities to a predominance of competition later on.

Interactive effects of ocean acidification and water flow on growth and recruitment of early successional coralline algal communities

ABSTRACTCoralline algae play crucial roles in near-shore ecosystems but are susceptible to ocean acidification (OA). It has been hypothesized that low water velocity, allowing localized photosynthesis-driven pH-increases in the coralline surface boundary layer, could buffer against the negative impacts of OA. To test how water motion affected the sensitivity of coralline algae to OA, coralline communities (from 2 m and 10 m depth) were grown for 220 days at two pH levels (present-day: pH 8.03, OA: pH 7.65) under differing inflow rates (400, 200 and 100 ml min–1) providing water velocities of 2.7, 5.9 and 7.8 cm s–1. Communities from both depths were grown together, photographed to assess growth, and the resulting recruitment was evaluated at the experiment’s conclusion. Low seawater pH reduced growth by c. 11% (highest flow), further decreased by >23% under the lowest flow. This reduction resulted in differential outcomes for the two depths, with skeletal net-dissolution under the combination of low flow and pH 7.65 for 10 m communities. Furthermore, there was a synergistic interaction between the effects of flow and pH, whereby the negative effect of OA strengthened under low flow, with recruitment halved at pH 7.65. This demonstrates that OA impacts can be modulated by the flow environment. Surprisingly, increased flow rates/water velocities reduced negative impacts of low pH, thus further challenging the notion that slow flow habitats offer protection from OA. The observed interactions between water flow and OA on early successional communities and their recruits may hold implications for the future of rocky reef systems dominated by these communities.

Factors driving bumble bee (Hymenoptera: Apidae: Bombus) and butterfly (Lepidoptera: Rhopalocera) use of sheared shrubland and young forest communities of the western Great Lakes.

In the northern Great Lakes region, the creation and maintenance of early-successional woody communities as wildlife habitat have increasingly become a conservation priority. The extent to which insect pollinators use these systems remains largely anecdotal. In summer (June-August) of 2021, we surveyed 49 early-successional sites in the western Great Lakes region treated with either shrub-shearing or silviculture (young forest) for bumble bees, butterflies, and habitat components (i.e., structural vegetation and floral resources). Hierarchical distance models predicted pollinator densities (λ^) to be, on average, λ^ = 84 bumble bees/ha and λ^ = 102 butterflies/ha. Although sheared shrubland and young forest communities supported comparable densities of bumble bees and butterflies, density was not equal across all sites. At the microhabitat scale, butterfly density and morphospecies richness were negatively associated with tall shrub cover and butterfly morphospecies richness (but not density) was driven by floral richness. Similarly, bumble bee density was positively associated with metrics of floral resources, underscoring the importance of blooming plants within these woody systems. Landscape covariates explained variation in butterfly density/richness but not bumble bee density. Ultimately, our results demonstrate that blooming plant abundance is an important driver of bumble bee and butterfly densities within these managed early-successional communities. Because early-successional woody communities are dynamic and their herbaceous openings are ephemeral, routine management would ensure that a variety of successional conditions exist on the landscape to meet the needs of bumble bees, butterflies, and potentially other insect pollinators.

The effect of surface orientation on early successional fouling communities in the southern gulf of Maine

Artificial environments have hard surfaces positioned at different orientations that attract a wide diversity of sessile invertebrate species, forming fouling communities. Fouling communities play a large role in the spread of a species introduction, as organisms gain purchase in artificial environments and use them as a stepping-stone into neighboring natural systems. These man-made systems harbor a large diversity of species, and there are often vastly different communities present on both vertical and horizontal surfaces. We used a species abundance dataset at three time periods spanning 30 years, collected from fouling panels in a high tidal flow estuary at the mouth of the Piscataqua River (New Castle, New Hampshire) in the southern Gulf of Maine to measure differences in community composition between horizontal and vertical panels. Early successional communities on settlement panels were photographed one year after installment in late summer to capture the highest diversity seasons. Organisms were then identified to the lowest taxonomic level, and communities on the underside of horizontal and vertical panels were compared. Vertical and horizontal communities from 1980 and 2004 were similar, while those from 2009 statistically differed from one another. Vertical and horizontal surfaces in the 1980s were dominated by the blue mussel Mytilus edulis, which declined in later years, and was replaced by invasive ascidians. Species diversity increased between the 1980 and 2004 sampling, but declined by the 2009 sampling. This study captures changes of species composition in early successional communities on vertical and horizontal surfaces at a single locale from three time periods spanning over 30 years.

Higher plant colonisation and lower resident diversity in grasslands more recently abandoned from agriculture

Abstract Rates of species colonisation and extirpation are increasing in plant communities world‐wide. Colonisation could potentially help compensate for, or compound, resident diversity loss that results from global environmental change. We use a multifactorial seed addition grassland experiment to examine relationships between plant colonisation, resident species diversity and key community assembly factors over 3 years. By manipulating colonist seed rate, imposing disturbance and examining abundance and diversity impacts of 14 formerly absent sown colonists in communities that varied in successional stage and time since agricultural abandonment, we were able to disentangle effects of global change factors (species introduction, novel disturbance and land use change) that are usually confounded. Evidence suggested that cover abundance of sown colonists was most strongly influenced by successional stage of recipient communities, though number of growing seasons was also important for the group of seven colonists with resource conservative ‘slow’ life history traits. Colonist type, seed rate and disturbance had weaker relationships with colonist cover. Factors affecting sown colonist cover were highly conditional. A negative relationship between plot‐level disturbance and colonist cover in early successional communities meant that, despite a positive relationship in late succession, colonisation was negatively related to disturbance overall, defying theoretical expectations. Non‐sown resident diversity was negatively related to colonist cover and positively related to successional stage. Resource acquisitive colonists with ‘fast’ life history traits appeared to limit cover of ‘slow colonists’ when the two groups were sown together, likely reflecting niche pre‐emption. Communities at earlier stages of succession had lower resident diversity and experienced higher levels of colonisation than communities at later stages of succession. Elevated colonisation and lower resident diversity both appeared to be symptoms of human‐induced land use change. However, results suggested that resource competition from plant colonists may also limit resident diversity in grasslands abandoned from agriculture more recently. Synthesis. Our findings point to the importance of resource availability and competition on plant colonisation and colonist impacts on residents. Although colonisation is potentially a source of biodiversity in the short term, our results suggest that plant colonists that reach high abundance may be a further threat to resident plant diversity in secondary grasslands recovering from a recent history of agriculture.

Wood anatomical spectrum of co-occurring species in early and late-successional tropical dry forest communities

Key messageAnalysis of wood anatomical traits revealed that drought tolerance predominates in early-successional communities, and vessel variability is relevant for species’ ecological success in seasonally dry tropical environments.Successional tropical dry forests harbor a diverse array of species subjected to a strong seasonal precipitation regime. Considering that wood encompasses diverse functional properties related to stem hydraulics and mechanical support, in this study, we asked which quantitative anatomical traits are exhibited by co-occurring species in early (EC)- and late (LC)-successional communities. We used generalized linear mixed-effects models to estimate and compare means and standard deviations of wood traits (vessel area, vessel density, vessel grouping, and fiber dimensions) between eight EC and between 13 LC co-occurring species. Wood traits were highly heterogeneous. High vessel redundancy, a property associated with water safety involved in the prevention of hydraulic failure, prevails among species coexisting in EC but is maintained through succession by the same species in LC. Highly variable fiber dimensions indicate that species coexisting in LC possess different characteristics associated with mechanical resistance. Low wood density species typical of LC, which are absent from EC, displayed wood anatomical features associated with drought-evasion mechanisms. This result implies that deforestation not only reduces taxonomic but also functional diversity. Future research should adopt a standard deviation analysis approach, as this will allow confirming the high variability in vessel diameter, even in diffuse porous species, as a key feature for the ecological success of plants facing succession-driven changes in seasonally dry environments.

Assessing American woodcock use of habitat managed through programs targeting a declining songbird

AbstractThe implementation of habitat management guidelines for golden‐winged warblers (Vermivora chrysoptera) is believed to benefit additional species. To address widespread population declines of the golden‐winged warbler, species‐specific best management practices were developed and are guiding habitat‐based conservation programs across the species' breeding range. To date, thousands of hectares of golden‐winged warbler nesting habitat have been created across portions of the Appalachian Mountains and Great Lakes regions in the United States. The American woodcock (Scolopax minor) is expected to benefit from this habitat management. The woodcock has been declining for decades (0.84%/year in the eastern United States) largely because of loss of early successional communities like those required by the golden‐winged warbler. We examined the extent to which habitat management targeting golden‐winged warblers contributes to American woodcock conservation goals across a broad geographic extent. Additionally, we assessed various site‐ and landscape‐level factors to elucidate the context dependencies associated with successful conservation outcomes for this non‐target species. From 2015 to 2017, we conducted 1,554 American woodcock surveys at 774 unique locations treated with golden‐winged warbler best management practices across the Great Lakes and Appalachian Mountains. Woodcock density was 0.84–1.24 males/ha in the Great Lakes region and 0.30 males/ha in the Appalachian Mountains. Density was also dependent upon within‐stand conditions (e.g., basal area, woody regeneration) and landscape features (e.g., wetland cover, mixed forest cover), the latter of which yielded strong geographic heterogeneity in woodcock densities. American woodcock can benefit from habitat management targeting the golden‐winged warbler, but the extent of these benefits is influenced by regional, landscape, and within‐stand contexts.

Linkages between Plant Community Composition and Soil Microbial Diversity in Masson Pine Forests.

Plant species identity influences soil microbial communities directly by host specificity and root exudates, and indirectly by changing soil properties. As a native pioneer species common in early successional communities, Masson pine (Pinus massoniana) forests are widely distributed in subtropical China, and play a key role in improving ecosystem productivity. However, how pine forest composition, especially the dominance of plant functional groups, affects soil microbial diversity remains unclear. Here, we investigated linkages among woody plant composition, soil physicochemical properties, and microbial diversity in forests along a dominance gradient of Masson pine. Soil bacterial and fungal communities were mainly explained by woody plant community composition rather than by woody species alpha diversity, with the dominance of tree (without including shrub) species and ectomycorrhizal woody plant species accounting for more of the variation among microbial communities than pine dominance alone. Structural equation modeling revealed that bacterial diversity was associated with woody plant compositional variation via altered soil physicochemical properties, whereas fungal diversity was directly driven by woody plant composition. Bacterial functional groups involved in carbohydrate and amino acid metabolism were negatively correlated with the availability of soil nitrogen and phosphorus, whereas saprotrophic and pathogenic fungal groups showed negative correlations with the dominance of tree species. These findings indicate strong linkages between woody plant composition than soil microbial diversity; meanwhile, the high proportion of unexplained variability indicates great necessity of further definitive demonstration for better understanding of forest-microbe interactions and associated ecosystem processes.

Herbivory selects for tolerance and constitutive defence across stages of community succession.

Plants defend themselves from herbivory by either reducing damage (resistance) or minimizing its negative fitness effects with compensatory growth (tolerance). Herbivore pressure can fluctuate from year to year in an early secondary successional community, which can create temporal variation in selection for defence traits. We manipulated insect herbivory and successional age of the community as agents of natural selection in replicated common gardens with the perennial herb Solidago altissima. In these genotypic selection experiments, herbivory consistently selected for better defended plants in both successional communities. Herbivore suppression increased plant survival and the probability of flowering only in mid-succession. Despite these substantial differences in the effects of herbivory between early and mid-succession, the selection on defence traits did not change. Succession affected selection only on aboveground biomass, with positive selection in early but not mid-succession, suggesting an important role of competition in the selective environment. These results demonstrate that changes in the community that affect key life-history traits in an individual species can occur over very short timescales in a dynamic secondary successional environment. The resulting community context-driven variation in natural selection may be an important, yet overlooked, contributor to adaptive mosaics across populations.

Drivers of community assembly change during succession in wood-decomposing beetle communities.

The patterns of successional change of decomposer communities is unique in that resource availability predictably decreases as decomposition proceeds. Saproxylic (i.e. deadwood-dependent) beetles are a highly diverse and functionally important decomposer group, and their community composition is affected by both deadwood characteristics and other environmental factors. Understanding how communities change with faunal succession through the decomposition process is important as this process influences terrestrial carbon dynamics. Here, we evaluate how beta-diversity of saproxylic beetle communities change with succession, as well as the effects of different major drivers of beta-diversity, such as deadwood tree species, spatial distance between locations, climate and forest structure. We studied spatial beta-diversity (i.e. dissimilarity of species composition between deadwood logs in the same year) of saproxylic beetle communities over 8 years of wood decomposition. Our study included 379 experimental deadwood logs comprising 13 different tree species in 30 forest stands in Germany. We hypothesized that the effects of tree species dissimilarity, measured by phylogenetic distance, and climate on beta-diversity decrease over time, while the effects of spatial distance between logs and forest structure increase. Observed beta-diversity of saproxylic beetle communities increased over time, whereas standardized effects sizes (SES; based on null models) of beta-diversity decreased indicating higher beta-diversity than expected during early years. Beta-diversity increased with increasing phylogenetic distance between tree species and spatial distance among regions, and to a lesser extent with spatial distance within regions and differences in climate and forest structure. Whereas effects of space, climate and forest structure were constant over time, the effect of phylogenetic distance decreased. Our results show that the strength of the different drivers of saproxylic beetle community beta-diversity changes along deadwood succession. Beta-diversity of early decay communities was strongly associated with differences among tree species. Although this effect decreased over time, beta-diversity remained high throughout succession. Possible explanations for this pattern include differences in decomposition rates and fungal communities between logs or the priority effect of early successional communities. Our results suggest that saproxylic beetle diversity can be enhanced by promoting forests with diverse tree communities and structures.

Vegetation structure and food availability following disturbance in recently restored early successional plant communities

AbstractFields dominated by nonnative grasses, such as tall fescue (Schedonorus arundinaceus), are being restored to native plant communities across the eastern U.S. Upon restoration, disturbance is necessary to maintain native communities in an early seral stage, and plant response to different management practices is of interest to managers to guide habitat enhancement for various wildlife species. We evaluated effects of burning and mowing following restoration of native plant communities via 2 methods (planting native grasses and forbs and seedbank response without planting), across 11 replicated sites in Tennessee and Alabama, 2019–2020. We compared vegetation composition and structure, openness at ground level, forage availability, and nutritional carrying capacity (NCC) following 4 treatments (Seedbank Burned, Seedbank Mowed, Planted Burned, Planted Mowed, and tall fescue Control), and we related these measurements to the food and cover requirements for 3 popular game species: white‐tailed deer (Odocoileus virginianus), wild turkey (Meleagris gallopavo), and northern bobwhite (Colinus virginianus). The combination of planting and mowing increased grass coverage, whereas units that were established via seedbank response and managed by burning had greater forb coverage. Visual obstruction above 25 cm was greater in all treatments than Control, which provided cover that has been described as selected nesting cover by wild turkey and bedding cover for deer. Openness at ground level, which is especially important for bobwhite and wild turkey broods, was 30% greater in Seedbank Burned than Planted Mowed where we recorded the least openness among treatments by the second year of treatment. Similarly, coverage of bobwhite food and deer forage plant species was greatest in Seedbank Burned. Biomass (kg/ha) of plant species known to be selected as forage by deer was greater in all treatments than in Control, and NCC (deer days/ha) was greatest in Seedbank Burned by year 2. Our results highlight differences in plant composition and structure following management of early successional communities. Where possible, we encourage managers to use fire instead of mowing to maintain plant communities, especially if food plants and enhanced structure at multiple levels for bobwhite, wild turkey, and deer are management objectives. Furthermore, our results illustrate planting native grasses and forbs is not necessary to restore native early successional plant communities on most sites.

Calcification accretion units (CAUs): A standardized approach for quantifying recruitment and calcium carbonate accretion in marine habitats

Abstract Standardized metrics that quantify a component of ecosystem functioning are essential for evaluating the current status of coastal marine habitats and for monitoring how ecologically important ecosystems are changing in response to global and local environmental change. Calcification accretion units (CAUs) are a standardized tool for quantifying net calcium carbonate accretion, early successional community structure, recruitment of algae and sessile invertebrates and other response metrics that can be determined from image analyses in coastal marine habitats. CAUs are comprised of paired‐settlement tiles that are separated by a spacer. This design mimics the presence of different representative habitats that are common in most marine systems such as exposed benthic surfaces, cryptic spaces inaccessible to grazers and shaded overhangings. The protected space between the tiles facilitates recruitment and inclusion of cryptic taxa in community assemblage estimates. After a period of deployment, CAUs are photographed for image analysis and then decalcified to quantify calcium carbonate accretion rates. The CAU methodology provides a cost‐effective, standardized protocol for evaluating structure and function in marine benthic habitats. We illustrate how CAU data can be used to compare accretion rates and the relative proportion of carbonate polymorphs in ecosystems across the globe. Here we provide a comprehensive standard operating procedure for building, deploying and processing CAUs, to ensure that a consistent protocol is used for accurate data collection and cross‐system comparative studies.

Disturbance has lasting effects on functional traits and diversity of grassland plant communities.

BackgroundLocalized disturbances within grasslands alter biological properties and may shift species composition. For example, rare species in established communities may become dominant in successional communities if they exhibit traits well-suited to disturbance conditions. Although the idea that plant species exhibit different trait ‘strategies’ is well established, it is unclear how ecological selection for specific traits may change as a function of disturbance. Further, there is little data available testing whether disturbances select for single trait-characters within communities (homogenization), or allow multiple trait-types to persist (diversification). We investigated how (a) traits and (b) functional diversity of post-disturbance gap communities compared to those in adjacent undisturbed grasslands, and (c) if altered functional diversity resulted in the homogenization or diversification of functional traits.MethodsHere we emulate the impacts of an extreme disturbance in a native grassland site. We measured plant community composition of twelve paired 50 × 50 cm plots (24 total) in Alberta, Canada. Each pair consisted of one undisturbed plot and one which had all plants terminated 2 years prior. We used species abundances and a local trait database to calculate community weighted means for maximum height, specific leaf area, specific root length, leaf nitrogen percent, and root nitrogen percent. To test the impacts of disturbance on community functional traits, we calculated functional diversity measures and compared them between disturbed and undisturbed communities.ResultsWithin 2 years, species richness and evenness in disturbed communities had recovered and was equivalent to undisturbed communities. However, disturbed and undisturbed communities had distinct community compositions, resulting in lower functional divergence in disturbed plots. Further, disturbance was linked to increases in community-weighted mean trait values for resource-acquisitive traits, such as specific leaf area, and leaf and root nitrogen.DiscussionDisturbance had lasting effects on the functional traits and diversity of communities, despite traditional biodiversity measures such as richness and evenness recovering within 2 years. The trait space of gap communities shifted compared to undisturbed communities such that gap communities were dominated by traits enhancing resource uptake and growth rates. Overall, these results show that short-term disturbance fundamentally changes the functional character of early-successional communities, even if they superficially appear recovered.

Vertical root distribution and biomass allocation along proglacial chronosequences in Central Switzerland

ABSTRACT Investigating changes in belowground functional plant traits is an important step toward a better understanding of vegetation dynamics during primary succession. However, in alpine glacier forelands, we still lack an accurate assessment of plant rooting patterns. In this study, we established two proglacial chronosequences with contrasting bedrocks to investigate changes in rooting patterns and biomass allocation with terrain age. We extracted soil cores up to 1 m depth and measured root traits every 10 cm of each drilled core. Furthermore, we sampled aboveground biomass determining the contributions of functional groups to total aboveground biomass. We found that root traits associated with the root economics spectrum varied significantly along the chronosequences. Vertical root distribution coefficients revealed that early successional communities had more evenly distributed root systems compared to late successional communities. Biomass allocation showed diverging patterns. We found evidence for both the isometric allocation and optimal partitioning hypotheses. In addition, we observed a significant correlation between rooting parameters and plant community composition, suggesting that the dominance of distinct plant functional groups was one important factor explaining the observed rooting patterns. Our results shed light on the often neglected belowground compartments during plant succession and contribute to a better understanding of hillslope functioning.

First Community in Abandoned Pasture Lands or Crops in Eastern Cuba’s Rainforest over Metamorfics Rocks

Miconio prasinae–Cyatheion arboreae alliance is described. Although it has five associations, we address three in this work, corresponding to immediate, secondary and early successional communities in abandoned pasture lands or crops in submountains rainforest over metamorphic rocks. The objective of this work is to study the first communities in used and abandoned fields, because they are of a great importance in the understanding of the vegetation’s evolution and for management purposes. In the submontane forest on the metamorphic complex, the destruction of mature vegetation produces important losses in climatic biodiversity and transcendental changes in ecosystem composition. The change in soil use, especially the transformation to pastureland, has favored the development of herbaceous and shrubby plant communities. This study is not only of practical relevance in describing the associations of the pine forests the plant associations and the study of the ecological conditions in which they develop, but its results can be used as a working tool in the environmental management and silviculture for the restoration of degraded areas. The study of diverse Cuban vegetation types suggests that the methodology of Zurich Montpellier’s school is more effective as compared to other authors because its syntaxa is good to recognize and is able to transform in a forest typology. The main species are pioneers heliophilous with a type of r selection.

Successional dynamics shape tree diversity in evergreen forests of Côte d’Ivoire, West Africa

AbstractDisturbances and successional dynamics shape the composition of tree communities, but data remain scarce for tropical forests of West Africa. We assessed the imprint of past disturbances on the composition of evergreen forests in an Ivorian National Park. We hypothesized that (i) Pioneer indices (PI) based on the relative proportion of pioneer and non-pioneer trees relate to changing floristic composition due to successional dynamics, (ii) local community richness peaks at an intermediate value of PI under the Intermediate Disturbance Hypothesis (IDH) and (iii) early successional communities have higher beta diversity due to erratic founder effects. We performed a Correspondence Analysis of tree composition of 38 plots and examined how the main components of floristic variation related to environmental factors and PI. In addition, we tested the relationship between PI, local richness and beta diversity. The variation of PI better explained the main components of floristic variation than abiotic environmental variation, supporting a primary role of successional dynamics in shaping tree communities. We found a peak of richness at intermediate values of PI, supporting the IDH, with a mixture and earlier and later-successional species and more even abundances. The communities were very diverse and included many endemics and rare species. The results underline that the composition of early successional forests greatly varies depending on chance colonization events, while more similar old-growth communities are eventually observed after several decades. The findings should guide management practices for forest restoration, and for conservation of endangered species depending on their successional status.

Examining Land Use Changes to Evaluate the Effects of Land Management in a Complex, Dynamic Landscape

Anthropogenic alterations to landscapes have increased as the human population continues to rise, leading to detrimental changes in natural habitats. Ecological restoration assists in recovery by altering habitats to improve conditions and foster biodiversity. We examined land cover changes over time within a complex, dynamic region in the Midwest to assess the long-term effects of conservation. We used Landsat 8 bands for a 15-class land cover map of Oak Openings Region using supervised classification. We validated our map and achieved an overall accuracy of 71.2% from correctly classified points out of total visited points. Change over 10 years, from 2006 to 2016, was explored by comparing class statistics from FRAGSTATS between our map and original land cover map. We found that natural land, i.e., forest and early successional, covered 33%, with 10% permanently protected, while human-modified land, i.e., agricultural and developed, covered 67% of the region. Over 10 years, natural classes increased, and cultural classes decreased by 5.8%. There were decreases for the three forest communities and increases for the two early successional communities. These changes are likely the result of natural recovery and disturbance, and conservation efforts by the Green Ribbon Initiative. Changes in habitat also came with distribution changes, e.g., increased fragmentation for some classes, which was readily visible. Our useful method measured functionality by emphasizing changes in composition and configuration. Our approach provides a tool for assessing cumulative regional-scale effects from site-level management and conservation. This large-scale view for conservation is needed to effectively mitigate future changes.

Depth gradients drive changes in early successional community composition and associated coral larvae settlement interactions

Depth gradients are known to drive patterns of adult and juvenile coral distribution, but the influence on early successional communities and subsequent interactions with coral larvae settlement are poorly understood. We studied how early successional communities changed across a 40 m depth gradient to test whether patterns of coral larvae settlement could be explained by changes in preferred settlement substrates. Light decreased 83-fold from 3 to 40 m, and coral settlement orientation switched from tile undersides at 3 and 8 m to tile topsides at 25 and 40 m as expected. Regardless of the reduction in light, community composition on the topsides of settlement tiles did not change across depths, being dominated by turf algae (49%), crustose coralline algae (CCA; 29%), and biofilmed tile (12%). In contrast, settlement tile undersides were dominated by coralline and fleshy algae at 3 m, transitioning to ascidians and bryozoans at 8 m and 25 m, and biofilmed tile (80%) at 40 m. Following multiple regression analysis from an initial 21 bio-physical variables (R2 = 0.34), the optimal reduced model for predicting coral settlement included just five variables and explained most of the variability (R2 = 0.29). CCA contributed an R2 of 0.14 to the model and was positively correlated with Acroporidae settlement, biofilmed tile contributed an R2 of 0.09 to the model and was negatively correlated with Acroporidae settlement, while the other predictors explained nominal model variance. As assessed using electivity indices, Acroporidae switched settlement preference from CCA at shallower depths to biofilmed tile in deeper environments. In addition to the influence of light on larval settlement behaviour as described in previous research, our results show that CCA also provide an important facilitator of coral settlement behaviour across depth gradients. However, as in shallow reefs environments, further work is required to elucidate whether changes occurring at a finer taxonomic resolution within the CCA community can help to further explain switches in coral larval settlement behaviour in light-limited environments.

Impact of pathogenic fungi, herbivores and predators on secondary succession of tropical rainforest vegetation

Abstract There is growing evidence that top–down biotic factors play an important role in plant community dynamics and are able to maintain the high plant diversity of primary tropical forests. However, the top–down impact by herbivores on the accumulation of plant biomass, richness and the community assembly process remains poorly known for the initial stages of secondary ecological succession. Here we test the top–down effects of natural enemies on the biomass, richness, diversity, community composition, trait dynamics and randomness during the assembly process on an early successional community in a lowland tropical forest in Papua New Guinea. We initiated secondary succession on 36 vegetation plots (5 × 5 m) organized in six blocks. After 1 year we evaluated successional community characteristics in each block containing a control plot and five treatment plots: experimentally excluding (a) insects by insecticides, (b) fungal pathogens by fungicides, (c) vertebrate predators and ants with exclosures and traps and experimentally adding (d) low and (e) high levels of a generalist herbivore species. Insects were responsible for increased plant diversity, shifts in plant community composition and a decrease in community weighted mean of leaf dry matter content. The lack of herbivores resulted in a diversifying effect but did not affect plant biomass and stem density. No other treatment had a significant effect on plant diversity during succession. The highest level of artificially increased herbivore density reduced plant biomass, while the fungicide treatment decreased stem density of woody plants. Using a null model approach, we showed that the removal of insects and their vertebrate predators increased randomness during the community assembly processes for woody plants, whilst the same effect was not found for the removal of fungi or elevated herbivore abundances. Synthesis. Early rainforest succession was not entirely plant driven. During the early succession of lowland tropical forest, insect herbivores enhanced plant diversity and caused shifts in community structure by promoting species with acquisitive leaf traits. As expected, the early successional communities were highly variable, but insects and vertebrate predators reduced randomness during the assembly process. Insect and vertebrate communities can thus impact the regeneration dynamics of tropical forests. In contrast, fungal pathogens were less important in maintaining high diversity of successional communities in our system.