Intermediate Levels Of Disturbance Research Articles

Predicting plant trait similarity along environmental gradients

Plant traits affect the success or failure of plants to establish, grow, and reproduce. Although we have an increased understanding of certain individual plant traits and their relative effects on performance and fitness, it is a challenge to predict relative similarity of traits between neighbouring plants. Assembly rules suggest that abiotic filters will restrict the range of viable strategies, thus creating a community of plants that share a similar suite of traits. In contrast, limiting similarity predicts that segregation of species’ resource use will lead to character displacement. What is the relative strength of these two processes and do they differ depending on site condition? We know that trait similarity of plants can vary with site productivity and disturbance. In this study, we investigate the interaction of these two ecological factors and how they affect plant trait similarity. We find support for the hypothesis that trait convergence occurs at low productivity/high disturbance and high productivity/low disturbance, and trait dispersion is most likely at intermediate levels of disturbance and productivity. The relationships among evolution, plant traits, and ecology are multivariate, hierarchical, and complex making plant traits at the ecosystem level an exciting and challenging agenda for the future.

Habitat Dynamics of the Virginia Opossum in a Highly Urban Landscape

Abstract As urban habitats vary in composition and structure along the urban to rural gradient, different degrees of urbanization likely result in a diversity of landscape responses from wildlife. We investigated this relationship with the Virginia opossum (Didelphis virginiana), an urban adapted species that is both common and understudied in highly metropolitan landscapes. We investigated which landscape factors affect opossum occupancy, colonization, extinction, and detection by using a large system of motion-triggered camera traps in the Chicago metropolitan area over 10 seasons from spring 2010 to summer 2012. Opossum patch occupancy rates were highest near natural water sources regardless of urbanization, whereas occupancy rates in patches ≥1000 m from natural water sources decreased with increasing urbanization. Our results suggest opossums have relaxed habitat needs at intermediate levels of disturbance, as the ability to locate anthropogenic water sources may allow them to occupy previously uninh...

Efficiency of numerical and parametrical indices to determine biodiversity in mountain rangelands

Among various numeric and parametrical indices of plant species diversity, numerical ones may not provide a comprehensive description about abundance and richness of species, so application of parametric indices in addition to numerical ones would be a better approach to investigate on plant communities. For this purpose, indices of species richness, evenness and diversity were calculated for each of four plant communities of mountain rangelands in northwest of Iran. Then abundance–diversity and species ranking curves were plotted for each plant community and the best models for abundance distribution of diversity were fitted by chi-square goodness of fit test and the best representative one was selected. The results showed that there are significant differences in terms of numerical diversity among the communities and each of the indices showed higher value of diversity in every community so it was so difficult to decide on the community with the highest species diversity. Also the difficulty to explain the plotted curves species diversity and abundance ranking was obvious so the curves were not efficient to identify the distribution of species richness. So determination of species diversity by models of abundance distribution and adjustment of species distribution with expected values of distribution for plant species was implemented. The results showed the log-normal model as the best one for all locations with moderate intensity of grazing. Also the intermediate disturbance hypothesis (IDH) was supported by this model. As overall result species richness, evenness and diversity increases in intermediate levels of disturbance (moderate grazing).

Local and continental determinants of giant anteater (Myrmecophaga tridactyla) abundance: Biome, human and jaguar roles in population regulation

The giant anteater (Myrmecophaga tridactyla) is currently found in a wide variety of habitats from Honduras to Argentina. Across this wide range, researchers have postulated that anteater populations are negatively affected by several factors, including hunting, habitat loss and fragmentation, fire, vehicle collisions, and predation by jaguars. But no studies to date have evaluated the relative importance of these factors across sites, either at a regional or continental scale. We used camera traps to analyze variation in giant anteater abundance at two spatial scales. At a regional scale, we conducted camera trap surveys in the dry Chaco of Argentina and used occupancy models to explore the effect of protection status and human accessibility on giant anteaters’ relative abundance. At a continental scale, we used data from 40 camera trap studies (representing 42 different locations) and Generalized Linear Models (GLM) to assess the potential relation of biome, human disturbance and the presence of jaguars on giant anteater camera trap records. In the Argentine Chaco, protection and human disturbance do not significantly affect the proportion of area used by the species. The average anteater records/100 camera days and the proportion of sites used are very high across the study area. At a continental scale, anteaters are more frequently recorded in dry forests than in moist forests. Locations with very high human disturbance have camera trap rates that are 5–10 times lower compared to intermediate or low disturbance locations. Finally, giant anteater capture frequency increases up to 70% where jaguars are absent. Dry biomes and intermediate levels of human disturbance may favor anteaters by providing greater habitat heterogeneity coupled with a lower jaguar abundance. This may explain the relatively high abundance of giant anteaters in the Argentine Chaco. However, growing human populations, the advancing agriculture-livestock frontier, and an expanding road network may in time eliminate giant anteaters from most of this region.

Response of tree species diversity to disturbance in humid tropical forests of Borneo

AbstractQuestionsThe intermediate disturbance hypothesis (IDH) predicts that the highest species diversity occurs at an intermediate level of disturbance. The validity of the IDH remains contentious in tropical forests because the IDH has been supported in tropical dry forests but often not in humid tropical forests. We addressed the following questions: (1) is the IDH valid in humid tropical forests of Borneo; (2) how does the disturbance index (DI) influence conformity to the IDH; and (3) does the rainfall regime influence conformity to the IDH within the tropical biome?LocationHumid tropical forests of northern Borneo.MethodsWe established approximately 50 20‐m radius circular plots across primary to highly degraded forests in each of three logging concessions. Species richness was regressed against the following four DIs: above‐ground biomass (AGB), relative number (RNO) of pioneer trees, average wood density, and the principal component analysis (PCA) axis 1 score for the three DIs. For studies that examined the IDH in tropical forests, the relationship between total and dry season precipitation and the percentage reduction in species diversity from a unimodal maximum to the lowest disturbance level was examined.ResultsSpecies richness peaked at intermediate disturbance levels when average wood density and PCA 1 score, but not AGB and pioneer RNO, were used as DIs. The peaks were relatively flat, with 8–11% reduction in species richness from a unimodal maximum to the lowest disturbance level. The percentage reduction in species richness from a unimodal maximum to the lowest disturbance level increased with decreasing total and dry season precipitation within the tropical biome.ConclusionSpecies richness showed a unimodal response to disturbance, but conformity to the IDH varied with DI because different DIs may have different biological meanings. Species richness changed little from a moderately disturbed to the least disturbed stand in humid tropical forests compared with tropical dry forests, indicating that IDH is dependent on rainfall regime.

Anthropogenic disturbances are key to maintaining the biodiversity of grasslands.

Although anthropogenic disturbances are often perceived as detrimental to plant biodiversity, the relationship between biodiversity and disturbance remains unclear. Opinions diverge on how natural diversity is generated and maintained. We conducted a large-scale investigation of a temperate grassland system in Inner Mongolia and assessed the richness-disturbance relationship using grazing intensity, the primary anthropogenic disturbance in the region. Vascular plant-species richness peaked at an intermediate level of anthropogenic disturbance. Our results support the Intermediate Disturbance Hypothesis, which provides a valid and useful measure of biodiversity at a metacommunity scale, indicating that anthropogenic disturbances are necessary to conserve the biodiversity of grassland systems.

Relationships between woody vegetation and geomorphological patterns in three gravel-bed rivers with different intensities of anthropogenic disturbance

We compared three gravel-bed rivers in north-eastern Italy (Brenta, Piave, Tagliamento) having similar bioclimate, geology and fluvial morphology, but affected by different intensities of anthropogenic disturbance related particularly to hydropower dams, training works and instream gravel mining. Our aim was to test whether a corresponding difference in the interactions between vegetation and geomorphological patterns existed among the three rivers. In equally spaced and sized plots (n = 710) we collected descriptors of geomorphic conditions, and presence–absence of woody species. In the less disturbed river (Tagliamento), spatial succession of woody communities from the floodplain to the channel followed a profile where higher elevation floodplains featured more developed tree communities, and lower elevation islands and bars were covered by pioneer communities. In the intermediate-disturbed river (Piave), islands and floodplains lay at similar elevation and both showed species indicators of mature developed communities. In the most disturbed river (Brenta), all these patterns were simplified, all geomorphic units lay at similar elevations, were not well characterized by species composition, and presented similar persistence age. This indicates that in human-disturbed rivers, channel and vegetation adjustments are closely linked in the long term, and suggests that intermediate levels of anthropogenic disturbance, such as those encountered in the Piave River, could counteract the natural, more dynamic conditions that may periodically fragment vegetated landscapes in natural rivers.

Applying indicators of disturbance from plant ecology to vertebrates: The hemeroby of bird species

In plant ecology, hemeroby is a widely used indicator reflecting the anthropogenic disturbance level of a habitat. It is scaled on a range of point scores, higher scores of hemeroby meaning higher level of disturbance. In this study two indicators of sensitivity to disturbance based on the habitat preferences of bird species were used: HS (mean hemeroby score), calculated on the habitat types where each species occurs, and HH (mean hemerobiotic habitat diversity), indicating the level of a species generalism with respect to the range of disturbance levels characterizing the habitat where it occurs. Although already known in plant ecology, HS, so far, has never been applied to a group of vertebrates, while HH is a newly proposed index based on Shannon diversity. Both indexes are based on species position and range, along a gradient of disturbance, from pristine to completely man-made habitats. Drawing from a recently published atlas of bird species, it was possible to calculate the ecological preferences for a large number of habitat types in 75 common breeding bird species found in Latium (Central Italy). For each habitat, the average level of disturbance (based on hemeroby) within a 5-point scale was assessed. From the occurrences of birds in each habitat, HS (averaged disturbance calculated on the habitat types where each species occurs) and HH (the level of a species generalism with respect to the range of disturbance levels characterizing the habitats where it occurs) were calculated. The distribution of bird species number along the gradient showed a pattern of intermediate disturbance. Two different trends were found when analyzing the relationship between HS and HH: (i) a hump-shaped curve peaking at intermediate levels of HS, suggesting that generalism (HH) is maximum at intermediate levels of disturbance, and (ii) a second linear relationship pointing to a decrease of HH with increasing HS for a sub-set of synanthropic species (i.e., species linked to man-made habitats). The latter developed a further arm on the right of the hump-shaped curve: synanthropic species occurred only at higher levels of disturbance, and showed an increasing specialization with increasing levels of disturbance. Such a distribution was confirmed by analysing other data sets obtained from a real case study: the fraction of species with low values of HS sharply decreased from forest to urban habitats, while the fraction with high values increased; species with mid values of HS showed a maximum in crop-lands. HS and HH indexes are promising tools both in theoretical study and in practice, e.g. in management and monitoring of vertebrate communities.

Multiple successional pathways in human-modified tropical landscapes: new insights from forest succession, forest fragmentation and landscape ecology research.

Old-growth tropical forests are being extensively deforested and fragmented worldwide. Yet forest recovery through succession has led to an expansion of secondary forests in human-modified tropical landscapes (HMTLs). Secondary forests thus emerge as a potential repository for tropical biodiversity, and also as a source of essential ecosystem functions and services in HMTLs. Such critical roles are controversial, however, as they depend on successional, landscape and socio-economic dynamics, which can vary widely within and across landscapes and regions. Understanding the main drivers of successional pathways of disturbed tropical forests is critically needed for improving management, conservation, and restoration strategies. Here, we combine emerging knowledge from tropical forest succession, forest fragmentation and landscape ecology research to identify the main driving forces shaping successional pathways at different spatial scales. We also explore causal connections between land-use dynamics and the level of predictability of successional pathways, and examine potential implications of such connections to determine the importance of secondary forests for biodiversity conservation in HMTLs. We show that secondary succession (SS) in tropical landscapes is a multifactorial phenomenon affected by a myriad of forces operating at multiple spatio-temporal scales. SS is relatively fast and more predictable in recently modified landscapes and where well-preserved biodiversity-rich native forests are still present in the landscape. Yet the increasing variation in landscape spatial configuration and matrix heterogeneity in landscapes with intermediate levels of disturbance increases the uncertainty of successional pathways. In landscapes that have suffered extensive and intensive human disturbances, however, succession can be slow or arrested, with impoverished assemblages and reduced potential to deliver ecosystem functions and services. We conclude that: (i) succession must be examined using more comprehensive explanatory models, providing information about the forces affecting not only the presence but also the persistence of species and ecological groups, particularly of those taxa expected to be extirpated from HMTLs; (ii) SS research should integrate new aspects from forest fragmentation and landscape ecology research to address accurately the potential of secondary forests to serve as biodiversity repositories; and (iii) secondary forest stands, as a dynamic component of HMTLs, must be incorporated as key elements of conservation planning; i.e. secondary forest stands must be actively managed (e.g. using assisted forest restoration) according to conservation goals at broad spatial scales.

Functional diversity from network response dynamics

We consider competing functional groups of tree species and develop a model of network response dynamics in order to measure the impacts of perturbations on the population distribution and diversity. The analysis of the equilibrium states relies on the connection between mean field game dynamics and replicator dynamics. We simulate our theoretical results from the data inventoried in French Guiana. Our results show that different types of disturbances modify the competitive interactions by affecting the evolutions of group densities. At the high regimes of disturbance, the canopy shade-intolerant species supplant the canopy shade-tolerant species. Tropical forest managers can thus take advantage of the competitive interactions between the functional groups to stimulate the abundance of marketable timber species. We also validate the hypothesis of maximum diversity at the intermediate disturbance levels.

Sensitivity of breeding birds to the “human footprint” in western Great Lakes forest landscapes

Breeding birds in forest ecosystems are generally diverse, habitat selective, and easily sampled. Because they must integrate environmental variables over space and time, local populations of forest birds (like other animal and plant taxa) may provide meaningful signals of local forest health or degradation. We evaluated 949 breeding bird surveys in areas ranging from degraded urban/suburban forest remnants to relatively pristine old growth forests in the western Laurentian Great Lakes region of North America. The “human footprint” across this landscape was represented by a one‐dimensional numeric gradient derived from land cover variables, forest fragmentation metrics, and publicly available data on housing density and transportation corridors. We used an iterative, maximum likelihood approach to quantify species‐specific responses to this human disturbance gradient. Many species showed significant directional responses, consistent with known life history attributes. Other species were most commonly detected at intermediate levels of anthropogenic disturbance, yielding unimodal responses. Relationships between the “human footprint” and occurrences of 38 bird species were illustrated by general Gaussian functions that represented both unidirectional and unimodal patterns. These biotic response (BR) functions were combined into a bird‐based index of ecological condition (IEC) ranging from 0 (maximally degraded) to 10 (minimally degraded). We described a successful application of the IEC method at the Wild Rivers Legacy Forest (WRLF), a >260 km2 conservation landscape in northeastern Wisconsin, USA, managed primarily under a working forest conservation easement established in 2006. In general, areas within the WRLF yielded high IEC values (7.0–9.0), but nearby forest areas not under the conservation easement were characterized by significantly lower IEC values based on breeding bird assemblages.

Hydrological conditions explain variation in wood density in riparian plants of south‐eastern Australia

Summary Wood density is a key plant functional trait which integrates the trade‐offs characteristic to riparian plant ecological strategies. Although high‐density wood is costly to construct, it confers mechanical stiffness to stems, increasing a plant's capacity to withstand flooding, and also enables increased tolerance to water stress. For riparian plants, fluctuations in soil moisture driven by surface hydrology should therefore be an important driver of variation in wood density. We asked the following questions in the study: (1) Does wood density increase with increasing frequency and magnitude of flood disturbance? (2) Does wood density increase with increasing unpredictability of water availability in the riparian zone? (3) Does dispersion of wood density peak at intermediate levels of hydrological disturbance? We surveyed wood density of dominant species at 15 riparian sites along flow‐gauged rivers across south‐eastern Australia. Due to the broad range of hydrological variability associated with Australian river systems, this set of sites functions as a useful model for assessing the response of riparian plants to changing hydrological conditions. We found wood density varied strongly along a single axis of hydrological variability. This axis integrates flood intensity and frequency with metrics of hydrological unpredictability and can be conceptualized as a gradient of environmental harshness, with higher wood density associated with harsher conditions. Synthesis. Our study highlights the importance of hydrological conditions, particularly disturbance and environmental unpredictability, as determinants of ecological strategy in riparian plants. Large, rare flood events in particular appear to favour higher wood density strategies. This is likely to have significant ecological consequences for riparian plant communities in a south‐east Australian context, as well as in other regions where increasing climatic variability and frequency of extreme events are hallmarks of climate change predictions.

The response of phytoplankton community to anthropogenic pressure gradient in the coastal waters of the eastern Adriatic Sea

In order to test the response of phytoplankton to anthropogenic pressure, data of chlorophyll a concentration, phytoplankton abundance, and composition are analyzed in relation to anthropogenic pressure gradient and environmental variables such as temperature, salinity and nutrients. Investigated sites encompassed wide tropic range according to a preliminary determination of anthropogenic pressure, quantified through the LUSI index. Statistical analyses indicated nitrates and silicates as proxies of freshwater influence, and phytoplankton single metrics such as concentrations of chlorophyll a and abundances as indicators of anthropogenic pressure. Boundary values for different water quality classes for coastal waters under indirect freshwater influence (Type II) are obtained according to gradient between concentration of chlorophyll a and pressure index (LUSI), which empirically fit to exponential equation. The response of phytoplankton diversity was not linear, as the highest diversity was observed in the area with intermediate disturbance level. CCA analysis identified Skeletonema marinoii, Scrippsiella trochoidea, Guinardia flaccida, Leptocylindrus spp., Prorocentrum spp., Proboscia alata, Eutreptiella spp., and Pseudonitzschia spp. as local eutrophication indicators, whose abundances increased with nutrients loads.

Ecological assessment of a southeastern Brazil reservoir

Reservoirs are artificial ecosystems with multiple functions having direct and indirect benefits to humans; however, they also cause ecological changes and influence the composition and structure of aquatic biota. Our objectives were to: (1) assess the environmental condition of Nova Ponte Reservoir, Minas Gerais state, southeastern Brazil; and (2) determine how the aquatic biota respond to disturbances. A total of 40 sites in the littoral zone of the reservoir were sampled to characterize physical and chemical habitat, land use, and benthic macroinvertebrate and fish assemblages. The predominant type of land cover near the reservoir was natural vegetation. A total of 29 fish species and 39 macroinvertebrate taxa were collected, including eight alien species. Most sites had intermediate levels of human disturbance, however, high levels of degradation were associated with high proportions of alien species. Disturbances at multiple scales may alter natural patterns and processes, leading to environmental changes and damaging biological communities. Our results reinforce the importance of assessing reservoir ecological conditions at several scales. The study of land use, littoral zone physical habitat characteristics, water quality, and assemblage structure set the ground for proposing actions to rehabilitate and conserve aquatic ecosystems.

Snowpack, fire, and forest disturbance: interactions affect montane invasions by non-native shrubs.

Montane regions worldwide have experienced relatively low plant invasion rates, a trend attributed to increased climatic severity, low rates of disturbance, and reduced propagule pressure relative to lowlands. Manipulative experiments at elevations above the invasive range of non-native species can clarify the relative contributions of these mechanisms to montane invasion resistance, yet such experiments are rare. Furthermore, global climate change and land use changes are expected to cause decreases in snowpack and increases in disturbance by fire and forest thinning in montane forests. We examined the importance of these factors in limiting montane invasions using a field transplant experiment above the invasive range of two non-native lowland shrubs, Scotch broom (Cytisus scoparius) and Spanish broom (Spartium junceum), in the rain-snow transition zone of the Sierra Nevada of California. We tested the effects of canopy closure, prescribed fire, and winter snow depth on demographic transitions of each species. Establishment of both species was most likely at intermediate levels of canopy disturbance, but at this intermediate canopy level, snow depth had negative effects on winter survival of seedlings. We used matrix population models to show that an 86% reduction in winter snowfall would cause a 2.8-fold increase in population growth rates in Scotch broom and a 3.5-fold increase in Spanish broom. Fall prescribed fire increased germination rates, but decreased overall population growth rates by reducing plant survival. However, at longer fire return intervals, population recovery between fires is likely to keep growth rates high, especially under low snowpack conditions. Many treatment combinations had positive growth rates despite being above the current invasive range, indicating that propagule pressure, disturbance, and climate can all strongly affect plant invasions in montane regions. We conclude that projected reductions in winter snowpack and increases in forest disturbance are likely to increase the risk of invasion from lower elevations.

Building relevant ecological indicators with basic data: Species and community specialization indices derived from atlas data

Species and community specialization have become popular indicators to track the spatial and temporal changes of species and community dynamics during current global changes. However, measuring specialization requires detailed and quantitative descriptions of habitat requirements or resource use, which are difficult to obtain for many species. Here, we propose and test a new method to quantify and map the relative composition of specialist and generalist species in local plots compatible with very basic ecological data, typically used for atlases. We used co-occurrence patterns of 1090 plant species recorded in the French Mediterranean region of Languedoc-Roussillon in a systematic grid of 1225 5×5km atlas cells to estimate species specialization. We then calculated the averaged specialization of each cell and tested several expected relationships of these indices. In particular, we tested the relationship between species richness and average specialization and the relationship between community specialization and landscape disturbance induced by land use. As expected from studies conducted on fine-scale data, we found that specialist species were those with more restricted distributions and occurring in richer species assemblages. We also found that community specialization was maximized at an intermediate level of landscape disturbance. These results suggest that aggregating specialization at large spatial scales provides useful species and community level indicators. Estimating specialization level with co-occurrence data is a good complementary approach to traditional estimations of diversity indices for conservation and landscape planning.

Large-scale wind disturbances promote tree diversity in a Central Amazon forest.

Canopy gaps created by wind-throw events, or blowdowns, create a complex mosaic of forest patches varying in disturbance intensity and recovery in the Central Amazon. Using field and remote sensing data, we investigated the short-term (four-year) effects of large (>2000 m2) blowdown gaps created during a single storm event in January 2005 near Manaus, Brazil, to study (i) how forest structure and composition vary with disturbance gradients and (ii) whether tree diversity is promoted by niche differentiation related to wind-throw events at the landscape scale. In the forest area affected by the blowdown, tree mortality ranged from 0 to 70%, and was highest on plateaus and slopes. Less impacted areas in the region affected by the blowdown had overlapping characteristics with a nearby unaffected forest in tree density (583±46 trees ha−1) (mean±99% Confidence Interval) and basal area (26.7±2.4 m2 ha−1). Highly impacted areas had tree density and basal area as low as 120 trees ha−1 and 14.9 m2 ha−1, respectively. In general, these structural measures correlated negatively with an index of tree mortality intensity derived from satellite imagery. Four years after the blowdown event, differences in size-distribution, fraction of resprouters, floristic composition and species diversity still correlated with disturbance measures such as tree mortality and gap size. Our results suggest that the gradients of wind disturbance intensity encompassed in large blowdown gaps (>2000 m2) promote tree diversity. Specialists for particular disturbance intensities existed along the entire gradient. The existence of species or genera taking an intermediate position between undisturbed and gap specialists led to a peak of rarefied richness and diversity at intermediate disturbance levels. A diverse set of species differing widely in requirements and recruitment strategies forms the initial post-disturbance cohort, thus lending a high resilience towards wind disturbances at the community level.

Conservation or Co-evolution? Intermediate Levels of Aboriginal Burning and Hunting Have Positive Effects on Kangaroo Populations in Western Australia

Studies of conservation in small scale societies typically portray indigenous peoples as either sustainably managing resources, or forsaking long-term sustainability for short-term gains. To explain this variability, we propose an alternative framework derived from a co-evolutionary perspective. In environments with long histories of consistent interaction, we suggest that local species will frequently be well adapted to human disturbance; but where novel interactions are introduced, human disturbance may have negative environmental consequences. To test this co-evolutionary hypothesis, we examine the effect of Aboriginal burning and hunting on hill kangaroo (Macropus robustus) abundance. We find that hill kangaroo populations peak at intermediate levels of human disturbance, showing that in ecosystems characterized by long-term human-environmental interactions, humans can act as trophic mediators, resulting in patterns consistent with epiphenomenal conservation. Framing the question within this co-evolutionary perspective provides an explanation for the underlying mechanisms that drive environmental outcomes of subsistence practices.

Fish Assemblages, Connectivity, and Habitat Rehabilitation in a Diked Great Lakes Coastal Wetland Complex

AbstractFish and plant assemblages in the highly modified Crane Creek coastal wetland complex of Lake Erie were sampled to characterize their spatial and seasonal patterns and to examine the implications of the hydrologic connection of diked wetland units to Lake Erie. Fyke netting captured 52 species and an abundance of fish in the Lake Erie–connected wetlands, but fewer than half of those species and much lower numbers and total masses of fish were captured in diked wetland units. Although all wetland units were immediately adjacent to Lake Erie, there were also pronounced differences in water quality and wetland vegetation between the hydrologically isolated and lake‐connected wetlands. Large seasonal variations in fish assemblage composition and biomass were observed in connected wetland units but not in disconnected units. Reestablishment of hydrologic connectivity in diked wetland units would allow coastal Lake Erie fish to use these vegetated habitats seasonally, although connectivity does appear to pose some risks, such as the expansion of invasive plants and localized reductions in water quality. Periodic isolation and drawdown of the diked units could still be used to mimic intermediate levels of disturbance and manage invasive wetland vegetation.Received October 1, 2013; accepted March 5, 2014

A plant‐functional‐type approach tailored for stakeholders involved in field studies to predict forage services and plant biodiversity provided by grasslands

AbstractThe plant‐trait‐based method is powerful for assessing ecosystem services provided by species‐rich grasslands, but its use presents difficulties for stakeholders involved in field studies. Therefore, we examined whether a simplified plant‐functional‐type method could overcome such difficulties. A total of 1287 grasslands, spread over eight regions, were characterized according to their environmental and management factors, eight indicator (including Ellenberg) values and abundance of five previously defined grass functional types (GFTs) differing in growth strategies (fast–slow, early–late). Four related plant‐community‐composition descriptors indicating forage services (forage production, digestibility, distribution of herbage biomass throughout the growing season and management flexibility) responded to environmental and management factors that are correlated to indicator values. Based on GFTs, cluster analysis defined vegetation types (VTs). Their relationships to environmental and management factors (or proxies of them), forage services and species richness were subsequently analysed. Of the thirteen VTs, four consisted mainly of GFTs with a dominant fast‐growth strategy and three with a slow‐growth strategy. These clusters were clearly related to two stress axes (temperature and nutrients). The other six VTs consisted of a mixture of both strategies and corresponded to intermediate levels of stress and disturbance. Although simplified, the method distinguished VTs that responded consistently to environmental and management factors and provides accurate indicators of forage services.