Successional States Research Articles

Promoting Optimal Habitat Availability by Maintaining Fine-Grained Burn Mosaics: A Modelling Study in an Australian Semi-Arid Temperate Woodland

The pyrodiversity–biodiversity (P–B) hypothesis posits that spatiotemporally variable fire regimes increase wildlife habitat diversity, and that the fine-grained mosaics resulting from small patchy fires enhance biodiversity. This logic underpins the patch mosaic burning (PMB) paradigm and reinforces the benefits of Indigenous fire management, which tends to promote pyrodiversity. However, tests of the P–B hypothesis and PMB paradigm are few. One of the most comprehensive field evaluations—a snapshot study of pre-existing fire mosaics in south-east Australian semi-arid mallee eucalypt woodlands—found little support. To explore the longer-term effects of fire mosaic grain size on habitat availability and biodiversity, we combined published data from the mallee study with a simple fire simulation. We simulated 500 years of landscape burning under different fire sizes. In the resulting mosaics, we assessed the proportional mixture and patch configuration of successional habitat states, then summarised habitat availability through time using a composite index based on the published fire history responses of 22 vertebrate taxa from the mallee study. Small fires formed fine-grained mosaics with a stable habitat mixture and with habitat diversity occurring at fine scales. Large fires formed coarse-grained mosaics with the opposite properties. The fine-grained mosaics maintained optimal habitat availability for vertebrate diversity over 500 years, while the fluctuating habitat mixture in the coarse-grained mosaics was unlikely to maintain maximum vertebrate diversity. Broadly, our results support the P–B hypothesis and justify further field-testing and evaluation of PMB programs to manage both pyrodiversity and biodiversity in the mallee and other flammable landscapes.

Short-interval, high-severity wildfires cause declines in soil seed bank diversity in montane forests of south-eastern Australia

Wildfires in forested ecosystems are increasing in severity and extent. The adaptations many plants have acquired in response to their natural fire regime may not be sufficient to allow some species to persist. This could impact the forest understorey and its seed bank, which are vital reservoirs of biodiversity, and forest resilience in the face of global change. We present a case study of the montane forests of south-eastern Australia, an area subjected to an increase in frequency and severity of fires. We utilise field surveys and a soil seed bank germination study to investigate if short-interval, high-severity wildfires affect the understorey diversity in montane forests, and if the extant vegetation and the soil seed bank exhibit contrasting responses. We consider species diversity and plant functional traits to explore plant diversity in long unburned sites, and sites with one, two or three short-interval, high-severity fires in the past 25 years. With increasing fire frequency, we found a decrease in total species richness, Shannon’s diversity, and the richness of resprouters in the soil seed bank, contrasting a lack of response in the extant vegetation. Increased fire frequency shifted the species composition and the frequency of plant functional groups of both extant vegetation and soil seed bank towards a decrease in clonal resprouters and increase in grasses and other upright herbs. The frequency of wind-dispersed perennials and short-lived seeders and exotics increased sharply following single high severity burn, particularly in the soil seed bank, and remained elevated relative to long unburnt with subsequent fire. The combined species (extant vegetation plus soil seed bank) pool mirrored shifts in the frequency of functional groups in extant vegetation and soil seed bank. These findings highlight the importance of considering the soil seed bank when examining the effects of fire on fire-prone forests. Although a lack of response in the extant vegetation may be a buffering effect of the soil seed bank, the shift in the frequency of plant functional groups in the combined species pool suggests this cannot be maintained indefinitely. The increase in frequency and abundance of species characteristic of early successional states has implications for increased flammability and potential positive feedbacks between past fire and future fire, especially in a warming and drying climate. These shifts were independent of the fire response strategy of eucalypt canopy species raising significant questions of whether artificial re-seeding programs should extend beyond the current focus on obligate seeding forests and an obligate seeding tree.

Wolves alter the trajectory of forests by shaping the central place foraging behaviour of an ecosystem engineer.

Predators can directly and indirectly alter the foraging behaviour of prey through direct predation and the risk of predation, and in doing so, initiate indirect effects that influence myriad species and ecological processes. We describe how wolves indirectly alter the trajectory of forests by constraining the distance that beavers, a central place forager and prolific ecosystem engineer, forage from water. Specifically, we demonstrate that wolves wait in ambush and kill beavers on longer feeding trails than would be expected based on the spatio-temporal availability of beavers. This pattern is driven by temporal dynamics of beaver foraging: beavers make more foraging trips and spend more time on land per trip on longer feeding trails that extend farther from water. As a result, beavers are more vulnerable on longer feeding trails than shorter ones. Wolf predation appears to be a selective evolutionary pressure propelled by consumptive and non-consumptive mechanisms that constrain the distance from water beavers forage, which in turn limits the area of forest around wetlands, lakes and rivers beavers alter through foraging. Thus, wolves appear intricately linked to boreal forest dynamics by shaping beaver foraging behaviour, a form of natural disturbance that alters the successional and ecological states of forests.

The REBURN model: simulating system-level forest succession and wildfire dynamics

BackgroundHistorically, reburn dynamics from cultural and lightning ignitions were central to the ecology of fire in the western United States (wUS), whereby past fire effects limited future fire growth and severity. Over millennia, reburns created heterogenous patchworks of vegetation and fuels that provided avenues and impediments to the flow of future fires, and feedbacks to future fire event sizes and their severity patterns. These dynamics have been significantly altered after more than a century of settler colonization, fire exclusion, and past forest management, now compounded by rapid climatic warming. Under climate change, the area impacted by large and severe wildfires will likely increase — with further implications for self-regulating properties of affected systems. An in-depth understanding of the ecology of reburns and their influence on system-level dynamics provides a baseline for understanding current and future landscape fire-vegetation interactions.ResultsHere, we present a detailed characterization of REBURN — a geospatial modeling framework designed to simulate reburn dynamics over large areas and long time frames. We interpret fire-vegetation dynamics for a large testbed landscape in eastern Washington State, USA. The landscape is comprised of common temperate forest and nonforest vegetation types distributed along broad topo-edaphic gradients. Each pixel in a vegetation type is represented by a pathway group (PWG), which assigns a specific state-transition model (STM) based on that pixel’s biophysical setting. STMs represent daily simulated and annually summarized vegetation and fuel succession, and wildfire effects on forest and nonforest succession. Wildfire dynamics are driven by annual ignitions, fire weather and topographic conditions, and annual vegetation and fuel successional states of burned and unburned pixels.ConclusionsOur simulation study is the first to evaluate how fire exclusion and forest management altered the active fire regime of this landscape, its surface and canopy fuel patterns, forest and nonforest structural conditions, and the dynamics of forest reburning. The REBURN framework is now being used in related studies to evaluate future climate change scenarios and compare the efficacy of fire and fuel management strategies that either enable the return of active fire regimes or depend on fire suppression and wildfire effects on forest burning.

Restoration priorities: Integrating successional states and landscape resilience in tropical dry forest compensation projects in Colombia

Ecological conservation and restoration are global strategies for halting biodiversity loss and ecosystem degradation. However, Infrastructure projects in Colombia have not yet fully incorporated successional dynamics and the identification of priority areas to improve restoration efficiency. We evaluated the dynamics of change in successional trajectories and restoration performance of the Tropical Dry Forest at the El Quimbo Hydroelectric Power Plant during the period from 2008 to 2019. We identified areas with three different levels of resilience based on their connectivity and habitat percentage and used a synthetic Zonal Prioritization Index for focal landscapes with intermediate resilience (ZPI) to identify priority areas for restoration processes. The results showed a predominance of advanced and early intermediate successional trajectories, a 12.5% net change in the overall successional trajectories, and slow ecosystem recovery. Habitat availability was a stronger determinant of resilience types than connectivity. Water availability and proximity to areas with advanced succession trajectories were the determining factors for ZPI. We conclude that the landscape resilience approaches are a first step in the identification of suitable areas for ecological restoration. We also consider that intermediate resilience areas may be more suitable for restoration actions in infrastructure projects, where it crucial to optimize on investment.

Disrupted montane forest recovery hinders biodiversity conservation in the tropical Andes

AbstractAimAndean montane forests are biodiversity hotspots and large carbon stores and they provide numerous ecosystem services. Following land abandonment after centuries of forest clearing for agriculture in the Andes, there is an opportunity for forest recovery. Field‐based studies show that forests do not always recover. However, large‐scale and long‐term knowledge of recovery dynamics of Andean forests remains scarce. This paper analyses tropical montane forest recovery trajectories over a 15‐year time frame at the landscape and tropical Andean scale to inform restoration planning.MethodsWe first detect “potential recovery” as areas that have experienced a forest transition between 2000 and 2005. Then, we use Landsat time series analysis of the normalized difference water index (NDWI) to classify four “realized recovery” trajectories (“ongoing”, “arrested”, “disrupted” and “no recovery”) based on a sequential pattern of 5‐yearly Z‐score anomalies for 2005–2020. We compare these results against an analysis of change in tree cover to validate against other datasets.ResultsAcross the tropical Andes, we detected a potential recovery area of 274 km2 over the period. Despite increases in tree cover, most areas of the Andes remained in early successional states (10–25% tree cover), and NDWI levelled out after 5–10 years. Of all potential forest recovery areas, 22% showed “ongoing recovery”, 61% showed either “disrupted” or “arrested recovery”, and 17% showed “no recovery”. Our method captured forest recovery dynamics in a Peruvian arrested succession context and in landscape‐scale tree‐planting efforts in Ecuador.Main conclusionsForest recovery across the Andes is mostly disrupted, arrested or unsuccessful, with consequences for biodiversity recovery and provision of ecosystem services. Low‐recovery areas identified in this study might be good candidates for active restoration interventions in this UN Decade on Restoration. Future studies could determine restoration strategies and priorities and suggest management strategies at a local planning scale across key regions in the biodiversity hotspot.

Territoriality drives patterns of fixed space use in Caribbean parrotfishes.

Animals often occupy home ranges where they conduct daily activities. In many parrotfishes, large terminal phase (TP) males defend their diurnal (i.e., daytime) home ranges as intraspecific territories occupied by harems of initial phase (IP) females. However, we know relatively little about the exclusivity and spatial stability of these territories. We investigated diurnal home range behavior in several TPs and IPs of five common Caribbean parrotfish species on the fringing coral reefs of Bonaire, Caribbean Netherlands. We computed parrotfish home ranges to investigate differences in space use and then quantified spatial overlap of home ranges between spatially co-occurring TPs to investigate exclusivity. We also quantified the spatial overlap of home ranges estimated from repeat tracks of a few TPs to investigate their spatial stability. We then discussed these results in the context of parrotfish social behavior. Home range sizes differed significantly among species. Spatial overlap between home ranges was lower for intraspecific than interspecific pairs of TPs. Focal TPs frequently engaged in agonistic interactions with intraspecific parrotfish and interacted longest with intraspecific TP parrotfish. This behavior suggests that exclusionary agonistic interactions may contribute to the observed patterns of low spatial overlap between home ranges. The spatial overlap of home ranges estimated from repeated tracks of several TPs of three study species was high, suggesting that home ranges were spatially stable for at least 1 month. Taken together, our results provide strong evidence that daytime parrotfish space use is constrained within fixed intraspecific territories in which territory holders have nearly exclusive access to resources. Grazing by parrotfishes maintains benthic reef substrates in early successional states that are conducive to coral larval settlement and recruitment. Behavioral constraints on parrotfish space use may drive spatial heterogeneity in grazing pressure and affect local patterns of benthic community assembly. A thorough understanding of the spatial ecology of parrotfishes is, therefore, necessary to elucidate their functional roles on coral reefs.

Importance of the forest state in estimating biomass losses from tropical forests: combining dynamic forest models and remote sensing

Abstract. Disturbances, such as extreme weather events, fires, floods, and biotic agents, can have strong impacts on the dynamics and structures of tropical forests. In the future, the intensity of disturbances will likely further increase, which may have more serious consequences for tropical forests than those we have already observed. Thus, quantifying aboveground biomass loss of forest stands due to stem mortality (hereafter biomass loss rate) is important for the estimation of the role of tropical forests in the global carbon cycle. So far, the long-term impacts of altered stem mortality on rates of biomass loss have not been adequately described. This study aims to analyse the consequences of long-term elevated stem mortality rates on forest dynamics and biomass loss rate. We applied an individual-based forest model and investigated the impacts of permanently increased stem mortality rates on the growth dynamics of humid, terra firme forests in French Guiana. Here, we focused on biomass, leaf area index (LAI), forest height, productivity, forest age, quadratic mean stem diameter, and biomass loss rate. Based on the simulation data, we developed a multiple linear regression model to estimate biomass loss rates of forests in different successional states from the various forest attributes. The findings of our simulation study indicated that increased stem mortality altered the succession patterns of forests in favour of fast-growing species, which increased the old-growth forests' gross primary production, though net primary production remained stable. The stem mortality rate had a strong influence on the functional species composition and tree size distribution, which led to lower values in LAI, biomass, and forest height at the ecosystem level. We observed a strong influence of a change in stem mortality on biomass loss rate. Assuming a doubling of stem mortality rate, the biomass loss rate increased from 3.2 % yr−1 to 4.5 % yr−1 at equilibrium. We also obtained a multidimensional relationship that allowed for the estimation of biomass loss rates from forest height and LAI. Via an example, we applied this relationship to remote sensing data on LAI and forest height to map biomass loss rates for French Guiana. We estimated a countrywide mean biomass loss rate of 3.0 % yr−1. The approach described here provides a novel methodology for quantifying biomass loss rates, taking the successional state of tropical forests into account. Quantifying biomass loss rates may help to reduce uncertainties in the analysis of the global carbon cycle.

Informal road networks and sustainability of Siberian boreal forest landscapes: case study of the Vershina Khandy taiga

Boreal forest landscapes are experiencing various anthropogenic pressures from industrial activity, transportation, urbanization, and recreation compounding already significant changes in regional climate. However, the impact of the transportation infrastructure on boreal forests is rarely considered, and information about road extent is often incomplete, especially in the case of informal roads. Using a combination of landscape observations and interviews with local residents this case study examines the role of informal roads, i.e. vehicular roadways existing outside of the current publicly governed road networks, in transforming Siberian boreal forest landscapes in the Vershina Khandy taiga, Russia. Informal roads constitute 88% of the total road length in the study area and exert significant and multifaceted effects on social-ecological systems and landscape sustainability. Native dark coniferous forests have been disturbed by cutting, logging and human-caused fires proliferated from the roads. In their immediate vicinity, the informal road networks also exacerbate the replacement of primary forests with different successional states. Landscape vulnerability was assessed using three main factors of road-related disturbance: erosion, permafrost degradation and wildfires. Valley landscapes, where roads are prevalent, found to be the most vulnerable to environmental degradation. They are more often located within the wetlands with permafrost occurrences. The impact of informal roads is not limited to environmental changes. Among consequences there are also increased mobilities of local and Indigenous communities, as well an improved access to the area by outsiders: recreational anglers and poachers. The effects on subsistence activities and mobility vary across different landscapes. Further research on natural and social components of landscape sustainability in boreal forests affected by informal road networks is needed to better understand the local, regional and global role of this phenomena.

Lined Snake (Tropidoclonion lineatum) Prescribed Fire Mortality

Functioning prairie ecosystems are characterized by periodic and cyclical disturbances (e.g., grazing, drought, fire, etc.). Grazing and fire were historically widespread drivers of habitat structure. Many native species are adapted to fire and rely on the diverse habitats it maintains in a range of successional states. Wildlife mortality is an inevitable result of many prescribed fires and various species of small terrestrial vertebrates with limited dispersal abilities are most commonly affected. Herein, we report on the detected mortality of an individual Lined Snake (Tropidoclonion lineatum) after a prescribed burn along a lowland tallgrass prairie - wet meadow ecotone in South Central Nebraska. Little information exists on this topic as our record is only the second published observation of T. lineatum mortality resulting from a prescribed burn to our knowledge. Land managers can limit the negative impacts of prescribed fire on native species of conservation concern by considering their natural histories during the planning process.

Comparing the stability of successional transient models in kelp forests and barrens (south‐east Pacific): Implications for conservation monitoring

Abstract Ecological stability based on statistical variability was contrasted with the asymptotical local stability of transient states during successional changes in community structure in kelp forests and barren grounds. Simplified semi‐quantitative ecological models with different levels of complexity were constructed to represent transient successional states in kelp and barrens, and Routh–Hurwitz's criteria and Levins' criterion of local stability were also estimated. The results suggest that ecological stability based on statistical variation does not match local (mathematical) stability, since although successional changes in kelp exhibited less variability (measured as percentage coefficient of variation), barren beds were more locally stable. The local stability criteria used in the current work could be a suitable technique for evaluating the likelihood of transient ecological states to resist or change, since it considers states at equilibrium to maintain their properties only against small disturbances. These outcomes are relevant because the natural alternation between kelp and barrens could be disrupted by the intensive harvest of kelp species carried out over the last 10 years on the central‐north Chilean coast and in other temperate ecosystems. Additionally, the negative effects of harvesting kelp species could have a synergetic relationship with other drivers such as climate change and coastal pollution. Thus, strict policy managements to limit the kelp harvest are deeply encouraged. A monitoring programme for assessing the current conditions of benthic–pelagic ecosystems along the Chilean coast is also required.

Effects of repeated thinning at different intensities on the recovery of hardwood species diversity in a Cryptomeria japonica plantation

ABSTRACT To explore how and to what extent repeated thinning at different intensities affects the recovery of species diversity, we investigated the recruitment patterns of hardwoods (height ≥1.5 m) from 2003 to 2017 after first (2003) and second (2008) thinnings in 67% (Intensive), 33% (Weak), and 0% (Control) thinning treatments in a Cryptomeria japonica plantation in northern Japan. With intensive thinning, the numbers of individuals and species both increased rapidly after the first thinning, but slowly after the second thinning, irrespective of successional status (i.e., early, mid, and late succession). With weak thinning, both numbers increased monotonically but slowly in most years. With time after the second weak thinning, the numbers of early and mid-successional species both decreased, while the numbers of late-successional species increased monotonically, suggesting a replacement of shade-intolerant early and mid-successional species by shade-tolerant late-successional species. As a result, little differences were observed in both the numbers between the two thinning intensities. These traits suggest that thinning intensity has a minimal effect on species richness, but affects the future species composition (i.e., the dominance of late-successional species with weak thinning and co-dominance of all successional states with intensive thinning). For large individuals (diameter at breast height ≥5 cm), the numbers of both individuals and species were greater with intensive thinning. Therefore, although recovery of the species diversity in the forest understory can be realised with weak thinning, a mixed conifer–hardwood forest at the canopy level is more likely to be achieved with repeated intensive thinning.

Post‐fire development of faunal habitat depends on plant regeneration traits

AbstractThe concept that vegetation structure (and faunal habitat) develops predictably with time since fire has been central to understanding the relationship between fire and fauna. However, because plants regenerate after fire in different ways (e.g. resprouting from above‐ground stems vs. underground lignotubers), use of simple categories based on time since fire might not adequately represent post‐fire habitat development in all ecosystems. We tested the hypothesis that the post‐fire development of faunal habitat structure differs between ecosystems, depending on fire regeneration traits of the dominant canopy trees. We measured 12 habitat components at sites in foothill forests (n = 38), heathy woodlands (n = 38) and mallee woodlands (n = 98) in Victoria, Australia, and used generalised additive models to predict changes in each variable with time since fire. A greater percentage of faunal habitat variables responded significantly to time since fire in mallee woodlands, where fires typically are stand‐replacing, than in foothill forests and heathy woodlands, where canopy tree stems generally persist through fire. In the ecosystem with the highest proportion of epicormic resprouters (foothill forests), only ground cover and understorey vegetation responded significantly to time since fire, compared with all but one variable in the ecosystem dominated by basal resprouters (mallee woodlands). These differences between ecosystems in the post‐fire development of key habitat components suggest there may also be fundamental differences in the role of fire in shaping the distribution of fauna. If so, this challenges the way in which many fire‐prone ecosystems currently are categorised and managed, especially the level of dependence on time since fire and other temporal surrogates such as age‐classes and successional states. Where time since fire is a poor surrogate for habitat structural development, additional complexity (e.g. fire severity, topography and prior land‐use history) could better capture processes that determine faunal occurrence in fire‐prone ecosystems.

Wild bee distribution near forested landscapes is dependent on successional state

BackgroundForested landscapes are valuable sources of ecosystem services especially in areas dedicated to intense agricultural activities. Distance from forest margin is known to influence the wild bee community in the landscape surrounding forested patches. Yet little is known regarding how bee communities distribute themselves in landscapes that exhibit different forest successional states.MethodsWe examined how land use type and distance from the forest edge affect the abundance and richness of the wild bee community across four forest successional states. Bees were collected in sites representing four stages of forest succession and analyzed using generalized linear mixed models with negative binomial distributions.ResultsWild bee diversity is reduced in forested environments that maintain dense stands of trees and high canopy cover. Additionally, distance from the forest edge was an important factor determining wild bee distribution in successional stages adjacent to forest edges. Furthermore, we found that bees maintain high specificity for distinct successional states and distances.ConclusionsOur results demonstrate how different successional stages can harbor different bee species and highlight the ability of microhabitats to act as reservoirs of bee diversity in and around forest margins. Furthermore, we found that maximizing successional patchiness across forested landscapes increases the amount of available habitat that can support a diverse suite of bees with different nesting biologies and behaviors.

Habitat mosaic of gravel pit as a potential refuge for carabids: a case study from Central Europe

In gravel pits, a mosaic of habitats with various environmental conditions created during mining has a great potential for persistence of many species. We focused on such a mosaic in a gravel pit surrounded by agricultural landscape. We investigated which habitats within sludge deposits in different successional stages (from bare sands to secondary forest) and agriculturally reclaimed area enhanced diversity, species richness and abundance of carabids and supported occurrence of threatened species. Since some of these habitats were extensively managed while others were invaded by the alien plant Solidago gigantea, we also tested the effect of management and the cover of S. gigantea on carabid assemblages. We found a gradient in carabid assemblages from psammophilous ones in bare sandy soils towards similar assemblages in plots with well-developed vegetation cover. Here, carabid assemblages were represented predominantly by common species of agricultural and forest lands without higher habitat requirements. Contrarily, plots with bare sand could serve as a refuge for rare psammophilous carabid species, which cannot occur in surrounding landscape due to vanished suitable habitats. Therefore, keeping some of habitats in early plant successional states is important for maintaining habitat mosaic and for persistence of such species as well. Management of grasslands and cover of S. gigantea had no effect on carabid assemblage. We presume that carabids were likely more affected by vegetation structure and density than species composition.

Identifying Opportunities to Conserve Farm Ponds on Private Lands: Integration of Social, Ecological, and Historical Data

In some landscapes, effective conservation of wildlife habitat requires extending beyond the boundaries of reserves and addressing stewardship of private lands. This approach could be especially valuable for the conservation of farm ponds, which are abundant and serve key agricultural functions on private lands. Though farm ponds also provide wildlife habitat, little is known about how they are managed or how values and beliefs of their owners relate to their quality. To address this knowledge gap, we collected data on pond habitat quality and management using historical aerial imagery and high-resolution Google Earth satellite imagery of the Grand River Grasslands of southern Iowa and Northern Missouri. We also collected spatially congruent social data using a mail back survey sent to 456 landowners in the region (32.7% response rate). We used mixed-effects linear regression to link indicators of habitat quality to the survey results. We found that many ponds were permanent, accessible to cattle, in early successional states, and had little wetland vegetation, indicating a scarcity of suitable habitat for wildlife. At the same time, 35–57% of survey respondents said they would be willing to change their management to benefit aquatic organisms. Our analyses indicated that higher cover of cattails correlated with ownership by respondents who regarded row crops or income from agriculture as less important and ponds tended to be temporary if owned by respondents who had many ponds. Moving forward, large landowners and those willing to manage their land to benefit wildlife may constitute a core set of future partners for conservation efforts focused on improving pond habitat in the region.

A spatial model of streaked horned lark breeding habitat in the Columbia River, USA

The streaked horned lark (hereafter “lark”; Eremophila alpestris strigata) is a federally listed bird subspecies of the Pacific Northwest that occupies open landscapes with short vegetation and abundant bare ground. Across its breeding range, which has contracted dramatically, the lark relies primarily on human-modified habitats maintained in early successional states (e.g., agricultural fields, airfields, deposition islands). The focus of our study is the lower Columbia River where larks primarily occupy deposition islands created as a byproduct of shipping channel deepening (dredging) projects. The U.S. Army Corps of Engineers has proactively adopted a shifting-habitat-mosaic management approach when placing dredge (sand) materials to maintain lark habitat throughout the project area. To help achieve their goal, we created a geospatial tool capable of quantifying and tracking habitat suitability for larks throughout the project area with satellite imagery. We created spatial models of lark breeding habitat by incorporating lark survey data, Sentinel-2 satellite imagery, dredge-deposition maps, and surface-elevation models. We built candidate predictive models of lark breeding habitat after combining survey data (years 2016 and 2017), predictor variables, and logistic regression. In addition, we created a novel seral-stage predictor variable to identify young, mature, old, and unsuitable locations; critical information for lark conservation planning and dredge-disposal operational planning. We challenged probability models the year they were constructed (2016) and the following year (2017) with set-aside survey data. The best model contained terrain ruggedness, deposition age, vegetation greenness (e.g., lushness and density of vegetation) inside a 10-m cell, and heterogeneity in greenness within a 100-m radius. Verification accuracy ranged from 75 to 83% depending on the model tested and year. Importantly, the seral-stage variable allowed us to quantify and locate early, optimal, and late habitats. Model results will facilitate conservation planning decisions by informing real-time management decisions. Furthermore, they provide a foundation for application in other human-modified habitats across the species’ range.

Managing farm ponds as breeding sites for amphibians: key trade-offs in agricultural function and habitat conservation.

Millions of farm ponds have been constructed in agricultural landscapes around the globe. These ponds are built to support a variety of functions, including erosion control, cattle grazing, and recreational fishing, but their role as breeding habitat for amphibians remains poorly understood. We addressed this knowledge gap by studying farm ponds in the eastern Great Plains of the United States, a pond-dense region dominated by agriculture. We used field surveys and occupancy modeling to identify the important biophysical components of amphibian habitat and to assess the species-specific effects of cattle and fish presence on breeding occupancy. We next used a chronosequence to determine whether pond renovation, which often occurs when ponds are about 40yr old, threatens the development of amphibian habitat. Nine amphibian species bred in the farm ponds that we surveyed, and the relationship between breeding occupancy and habitat variables varied by species. We found that the pH conditions associated with amphibian breeding occupancy were significantly more likely to occur in older ponds (>50yr old). Emergent vegetation cover was also associated with increased breeding probability and rarely reached high levels in newer ponds. Since the older ponds with suitable habitat are at an age where renovation is likely needed to restore their agricultural function, this habitat may be at risk. We suggest that conservation of amphibians in farm ponds in the United States will require adopting renovation and management practices that balance the multiple uses of these sites and maintain a mosaic of pond successional states.

Variation in different measures of diversity during primary succession on a tropical coastal dune

ABSTRACTBackground: The understanding of the processes that govern community assembly during ecological succession helps determine the ecological attributes in restoration and monitoring programmes.Aims: The aim of this long-term study of primary succession was to analyse changes in species richness, diversity, taxonomic distinctness and functional types to understand community assembly processes.Methods: For 25 years, species turnover was monitored in 150 permanent plots in a dune system on the coast of the Gulf of Mexico.Results: Earliest successional states had low species diversity and richness, a high unevenness in the taxonomic tree structure, and a lower number of functional groups, with psammophytes being dominant. Richness and diversity increased in a humped-back shape with intermediate states reaching the highest values. Succession generated taxonomic trees that became less uneven and more diverse, and the diversity of functional groups increased.Conclusions: The processes underlying community assembly are complex during succession: sand movement acts as an environmental filter affecting the dominant functional groups, and species interactions probably change from facilitation to competition. The understanding of the combined processes affecting the different measures of diversity over time can improve the effectiveness of restoration and conservation practice in dune systems.

Using Functional Trait Diversity Patterns to Disentangle the Processes Influencing the Recovery of Subalpine Grasslands Following Abandonment of Agricultural Use

Grasslands in the Qinghai-Tibetan Plateau, as in much of the world, are increasingly degrading due to agriculture exploitation. Restoring such grasslands or facilitating recolonization to create late-successional communities requires an understanding of how communities within grasslands are structured within a secondary succession series. Here we studied community assembly using species abundance, soil nutrient levels, three functional traits (photosynthesis rate, seed mass and seed germination rate) in two comparable chronosequences of sub-alpine grasslands in the Qinghai-Tibetan Plateau. These grasslands range from ‘natural grassland’ (without human managements), to those that have been excluded from agricultural exploitation for 4 to 13 years. We were interested in shifts in functional trait diversity (FD; the value and range of functional traits in a community) and trait dispersion represented by the differences between observed FD and the expectation under neutral assembly. We found that a series of abiotic and/or biotic filters significantly influenced the success of species in different successional states, leading to systematic shifts in plant life history strategies from traits that indicated high relative growth rate to traits that signified highly competitive ability. We also found comparable community assembly processes between 13-year and natural grasslands, where hierarchical competition led to the exclusion of forb species by graminoid species and facilitation induced by legume species. Our results have three implications for degraded subalpine grasslands caused by agriculture exploitation in Qinghai Tibetan plateau. First, in the course of the abandonment of agricultural use and the return from degraded to natural grasslands, deterministic processes induced a shift in plant strategies from rapid relative growth rate under low N competition to slow relative growth rate under high N competition. Second, active seeding of graminoid and legume species may reduce the hierarchical competition, which in turn speedup recovery from agriculture exploitation. Finally, monitoring FD and trait dispersion patterns may be a good way to evaluate the restoration efforts in degraded grasslands caused by agriculture exploitation in Qinghai Tibetan plateau, due to the close connection of functional attributes (e.g., growth, colonization, recruitment and resource competition) and natural state of this ecosystem.