Perennial Plant Communities Research Articles

Mechanical soil disturbance in a pine savanna has multiyear effects on plant species composition

AbstractSoil disturbance threatens native perennial grasslands and savannas worldwide, including pine savannas of the North American Coastal Plain. Disk harrows are used in the region to plow linear features for firebreaks to contain prescribed fires, to manage game and other wildlife, and to reduce wildfire hazard to protect forest resources. However, the long‐term response of vegetation to these disturbances has not been well investigated. Our aim was to compare vegetation changes over time (0–9 years) following repeated disturbance by disking and a single disturbance by disking for firebreaks with undisturbed vegetation within a native pine savanna. We hypothesized that (1) a single disking event has multiyear effects on plant species composition and abundance because of the loss of perennial, dispersal‐limited species, but that partial survival of propagules allows the recovery to be more complete than following repeated disturbance, and (2) post‐disturbance changes are determined by species' life‐history characteristics resulting in a successional trajectory toward the undisturbed community. We established 10 plots within a repeated‐disturbance firebreak and a single‐disturbance firebreak, and in undisturbed vegetation (n = 30). We identified plant species within the plots six times over nine years, categorized plant species by life span, seed bank persistence, and dispersal mechanism, and assessed changes in the plant community using ordination. Changes in species composition in both repeated and single disturbance treatments showed a pattern consistent with succession toward the undisturbed plant community, but vegetation in neither disturbance treatment matched undisturbed treatment conditions within the nine years of study. Repeated‐disturbance plots progressed from a high occurrence of annuals to species with persistent seed banks and wind‐dispersed species. Single‐disturbance plots were more strongly associated with perennials, species lacking a persistent seed bank, and species dispersed by vertebrate consumption, but not to the same degree as undisturbed plots, although differences decreased slightly over time. Our results relating to narrow mechanical soil disturbances in pine savanna vegetation are consistent with studies concluding that similar but larger scale disturbances have long‐term degradational effects on the plant community. Therefore, conservation management plans should consider the possible negative long‐term effects of soil disturbance on native perennial herbaceous plant communities.

The diversity of plant communities in different habitats can lead to distinct methanotrophic communities

Methanotrophic communities are susceptible to environmental interference in natural ecosystems. However, little is known about methanotrophs and their drivers in the riparian zone ecosystem. Therefore, the soil methanotrophic community structure, assembly process, and their driving factors were examined in five habitats in the riparian zone ecosystem of Three Gorges Reservoir in China. Soil samples were collected from the woody plant community, perennial plant community, annual plant community, perennial mixed annual plant community, and bare land in the riparian zone areas. We assessed plant community diversity, analyzed soil physiochemical properties, and measured enzyme activities to find the driving factors for the methanotrophic community. The findings revealed that Methylosarcina, Methylocystis, and rice paddy clusters dominated habitats. They preferred different pH levels and plant diversity. The diversity of the soil methanotrophic community was greater in vegetation-covered areas than on bare land. Likewise, the co-occurrence network of soil methanotrophs was more complex in vegetation-covered areas than in bare land, indicating a more stable community structure. Soil nitrogen, catalase, and plant diversity influence stability and diversity. During the transformation from bare land to plant community, the assembly process of the soil methanotrophic community converted from stochastic to deterministic processes, in which dispersal limitation and homogenous selection played prominent roles and were primarily influenced by soil pH and plant diversity. This research helps us understand the evolution of methanotrophs during vegetation restoration. It can also help us find plant communities that can effectively sequester carbon pools and plant them in riparian zones around reservoir systems to maintain soil and water quality.

Effects of biotic interactions on plant fecundity depend on spatial and functional structure of communities and time since disturbance

Abstract Biotic interactions in plant communities affect individual fitness and community dynamics. Interactions between plants vary in space, over time and with organisational complexity. Yet it is challenging to quantify temporal, spatial and functional determinants of different types of interactions between long‐lived perennial plant species and their effect on lifetime fecundity. We studied how plant–plant, pollinator‐ and seed predator‐mediated interactions affect year‐to‐year variation in three fecundity components (cone production, seed set and seed survival) during post‐fire recovery. Age‐stratified data on the three fecundity components were collected in 19 even‐aged communities comprising 20 serotinous Protea shrub species in the South African Fynbos. We analyse data on these fecundity components with neighbourhood models to infer the sign and strength of interactions throughout post‐disturbance recovery, the neighbour plant traits that shape them and the spatial scale at which interactions take place. For each fecundity component, these models describe how neighbourhood effects change over time and with spatial distance between plants. We then predicted neighbourhood effects on individual fecundity components and cumulative reproductive output at different post‐fire stand ages for each focal plant. Competitive effects on cone production and seed set increased with post‐fire stand age as biomass and floral resources for pollinators build up. In contrast, neighbourhood effects on seed survival were weak throughout post‐disturbance recovery. Plant–plant interactions were shaped by neighbour traits related to resource acquisition, whereas animal‐mediated interactions depended on neighbour traits related to resource availability for pollinators and seed predators. The spatial scale of the interactions increased from plant–plant over predator‐mediated to pollinator‐mediated interactions. The joint effect of these interactions on cumulative reproductive output caused the proportion of focal plants experiencing competition to increase with time since fire. Synthesis. We show that temporal changes in biotic interactions throughout post‐disturbance recovery of perennial plant communities depend on functional traits and can be integrated into neighbourhood effects on lifetime fecundity. Studying the temporal, spatial and functional determinants of neighbourhood effects on lifetime fecundity is important for predicting not only individual plant fitness but also population and community dynamics in changing environments.

When disturbances favour species adapted to stressful soils: grazing may benefit soil specialists in gypsum plant communities

Background Herbivory and extreme soils are drivers of plant evolution. Adaptation to extreme soils often implies substrate-specific traits, and resistance to herbivory involves tolerance or avoidance mechanisms. However, little research has been done on the effect of grazing on plant communities rich in edaphic endemics growing on extreme soils. A widespread study case is gypsum drylands, where livestock grazing often prevails. Despite their limiting conditions, gypsum soils host a unique and highly specialised flora, identified as a conservation priority. Methods We evaluated the effect of different grazing intensities on the assembly of perennial plant communities growing on gypsum soils. We considered the contribution of species gypsum affinity and key functional traits of species such as traits related to gypsum specialisation (leaf S accumulation) or traits related to plant tolerance to herbivory such as leaf C and N concentrations. The effect of grazing intensity on plant community indices (i.e., richness, diversity, community weighted-means (CWM) and functional diversity (FD) indices for each trait) were modelled using Generalised Linear Mixed Models (GLMM). We analysed the relative contribution of interspecific trait variation and intraspecific trait variation (ITV) in shifts of community index values. Results Livestock grazing may benefit gypsum plant specialists during community assembly, as species with high gypsum affinity, and high leaf S contents, were more likely to assemble in the most grazed plots. Grazing also promoted species with traits related to herbivory tolerance, as species with a rapid-growth strategy (high leaf N, low leaf C) were promoted under high grazing conditions. Species that ultimately formed gypsum plant communities had sufficient functional variability among individuals to cope with different grazing intensities, as intraspecific variability was the main component of species assembly for CWM values. Conclusions The positive effects of grazing on plant communities in gypsum soils indicate that livestock may be a key tool for the conservation of these edaphic endemics.

Simultaneous niche expansion and contraction in plant–pollinator networks under drought

Global climate change threatens to substantially rearrange species interactions, yet we lack clear predictions on how these changes will cascade through communities. Many perturbations associated with climate change, such as droughts, will change resource levels, with consequences for species interactions and thus ecological network structure. Diet theory predicts foraging niche expansion when preferred resources are scarce, yet under severe resource reduction interspecific competition could alternatively increase niche partitioning. Such niche expansion and/or contraction could profoundly shape ecological network structure following perturbations, but whether these predictions hold at the community level is unclear. We studied the impacts of drought on plant–pollinator networks in long‐lived perennial plant communities in which drought affects flower and floral reward production. We assessed whether drought effects on available floral resources altered pollinator dietary niche breadth to drive higher network‐level generalization. Accounting for interaction abundance and species turnover, we compared plant–pollinator networks in two drought years and three non‐drought years. We found that drought restructured plant–pollinator networks, resulting in more generalization in terms of presence–absence of links, yet more specialization when accounting for quantitative network intensities. Our results support the application of diet theory to understanding how perturbations may impact ecological network structure.

Interaction network structure and spatial patterns influence invasiveness and invasibility in a stochastic model of plant communities

The factors governing invasiveness and invasibility are important for understanding invasions in plant communities, but most previous work does not incorporate network‐level interaction structure. We addressed this gap by simulating perennial plant communities at multiple life stages that varied in species richness and interaction network structures (transitive and intransitive), characteristics associated with species coexistence, using a stochastic lattice model that incorporated local competition, facilitation, and dispersal. Resident communities were invaded with alien species that varied in their fecundity, dispersal, and competitive abilities. We found that community structures that are known to promote coexistence also increased invasibility; communities with intransitive interaction networks on the whole were more invasible than transitive communities. However, the interaction between species richness and network structure was complex, as intransitive communities with few species were relatively resistant and transitive communities with many species were relatively invasible. Thus, simple rules linking intransitivity and diversity may not reflect the complex relationships between community structure and dynamics that occur in more realistic spatial systems. Spatial patterns of clustering and segregation were associated with higher invasibility and successful invaders intensified these patterns in communities, particularly at large spatial scales. Invasiveness and alien species abundance were associated with species‐level characteristics (fecundity and dispersal), but community‐level characteristics were also important, particularly competitive tolerance to the resident community. These results emphasize the importance of a community‐level approach, involving network‐level structure and spatial patterns, in adding nuance to our understanding of invasions in plant communities.

A chemical and bio‐herbicide mixture increased exotic invaders, both targeted and non‐targeted, across a diversely invaded landscape after fire

AbstractQuestionsInvasive‐plant treatments often target a single or few species, but many landscapes are diversely invaded. Exotic annual grasses (EAGs) increase wildfires and degrade native perennial plant communities in cold‐desert rangelands, and herbicides are thus sprayed to inhibit EAG germination and establishment. We asked how EAG target and non‐target species responded to an herbicide mixture sprayed over a large, topographically diverse landscape after wildfire. We focused on how whole‐community and natural EAG‐pathogen treatment responses varied over years and physical properties of sites.LocationSagebrush steppe of southwest Idaho, USA.MethodsWe monitored plant cover and diversity in 41 pairs of plots located inside or outside areas (486 ha total) treated with a combined aerial broadcast spray of pre‐emergent herbicide (imazapic) and weed‐suppressive bacteria (Pseudomonas fluorescens, “MB906”) to target EAGs after wildfires.ResultsEAG cover and exotic species richness were initially less in treated plots but increased to levels similar to or greater than those of untreated plots by the third post‐treatment year. The EAG pathogen Ustilago bullata was not directly affected by the treatment. The treatment increased exotic perennial forb cover in all plots and exotic annual forb cover in cooler/wetter plots but reduced exotic annual forb cover in warmer/drier plots. Cover of the invasive biennial grass Poa bulbosa decreased more across study years in untreated than treated plots. Among natives, the treatment reduced perennial grass cover and annual forb presence but led to marginal increases in perennial forb cover and, on soils with less gravel, increased shrub presence.ConclusionsA treatment targeting a single plant functional group did not achieve lasting success in these diversely invaded communities. Spraying alone did not release native perennials sufficiently to counteract the simultaneous release of secondary invaders and the return of target invaders. Planting or seeding may also be needed to achieve management goals.

Community‐level responses to increasing dryness vary with plant growth form across an extensive aridity gradient

AbstractAimPerennial plant communities are crucial for regulating ecological processes and maintaining ecosystem functions. Variation in community structure is driven by both biotic and abiotic factors, reflecting adaptation strategies of plant communities to various environments. Although much is known about the response of individual perennial plants to drier climates, empirical evidence of the community‐level responses to increasing dryness is limited.LocationEastern Australia; 1500 km gradient.TaxonPerennial plants.MethodsWe measured the abundance and size distribution (median, skewness and variance) of perennial plant communities from different growth forms (trees, shrubs and grasses), the spatial arrangement of trees in the overstorey and both biotic (competition) and abiotic (climate, soil properties) factors at 150 sites along an extensive aridity gradient from humid to arid areas. We used regression analyses and linear models to explore variation in community structure with increasing aridity and key driving factors for different perennial plant communities.ResultsVariation in community structure differed with growth form. As aridity increased, trees had wider canopies and were spatially aggregated, shrubs became miniaturised, but highly variable in size, and grasses comprised more larger individuals. Biotic and abiotic factors exerted different effects on different growth forms, with trees and shrubs consistently affected by competition and aridity, respectively, whereas grasses were weakly affected by aridity, summer rainfall and soil texture.Main conclusionsOur study highlights the idiosyncratic adaptation strategies used by trees, shrubs and grasses in response to drying climates at the community level through their effect on the size distribution or spatial aggregation. The structure of different perennial growth forms was influenced by different effects from either biotic (competition) or abiotic (climate, soil) factors. Under forecasted drier climates, canopy expansion and greater aggregation of trees might enhance resource sinks and shelter for diverse biota, potentially shielding plant communities against predicted aridification.

Climate-driven range shifts reduce persistence of competitors in a perennial plant community.

Forecasting the impacts of climate change on species persistence in diverse natural communities requires a way to account for indirect effects mediated through species interactions. In particular, we expect species to experience major changes in competition as they track favorable climates. Here, we combine experimental data with a recently developed theoretical framework based on coexistence theory to measure the impact of climate-driven range shifts on alpine plant persistence under climate change. We transplanted three co-dominant alpine perennial species to five elevations, creating a maximum of 5°C increase in average growing-season temperature. We statistically modeled species' demographic rates in response to the environment and interpolated species' intrinsic ranges-the environmental mapping of reproduction in the absence of competition. We used low-density population growth rates-species' initial rate of invasion into an established community-as a metric of persistence. Further analysis of low-density growth rates (LGRs) allowed us to parse the direct impacts of climate change from indirect impacts mediated by shifting competition. Our models predict qualitatively different range shifts for each species based on the climate conditions under which growth rates are maximized and where they are zero. Overall, climate change is predicted to increase the intrinsic (competition free) growth rates of all species, as warmer and wetter conditions increase the favorability of alpine habitat. However, these benefits are entirely negated by increased competition arising from greater overlap between competitors in their intrinsic ranges. Species were highly dispersal limited, which can prevent species from tracking shifting intrinsic ranges by reducing population spread rates. Yet dispersal limitation also promoted species' persistence because it promotes persistence mechanisms. Our study demonstrates the complex pathways by which climate change impacts species' persistence by altering their competitive environment, and highlights how a persistence framework based on LGRs can help disentangle impacts.

Larger aboveground neighbourhood scales maximise similarity but do not eliminate discrepancies with belowground plant diversity in a Mediterranean shrubland

An unresolved question in plant ecology is whether diversity of the aboveground and belowground compartments of a plant community is similar at different neighbourhood scales. We investigated how the similarity between both compartments varies with the aboveground sampling grain and if significant discrepancies exist between aboveground and belowground plant diversity at the maximum similarity scale. We fully mapped the aboveground perennial plant community of a 64 m2 plot in a Mediterranean shrubland and analysed this compartment by assessing diversity in 5 to 50 cm radii circles centred in soil cores. We sampled 2.5 cm radius root cores at two different depths and identified plant species by using DNA metabarcoding to characterise the belowground compartment. We quantified differences in species richness, composition and species’ spatial distribution above- and belowground. The differences between aboveground and belowground communities were affected by the size of the aboveground sampling grain and were minimised when considering a circle of 20 cm radius in the aboveground. We found a significant dissimilarity in richness and composition between the two compartments, with larger differences when considering the deeper soil layer only. Our results showed that the spatial grain selected to sample a plant community aboveground and belowground is critical to characterise them in a comparable manner. Although their composition is related, species distribution patterns strongly differ, suggesting the simultaneous action of different assembly mechanisms. Our results call for caution when studying community assembly considering only the standing vegetation, since total plant diversity can be underappreciated.

Effect of aridity on species assembly in gypsum drylands: a response mediated by the soil affinity of species.

Previous studies found that plant communities on infertile soils are relatively resistant to climatic variation due to stress tolerance adaptations. However, the species assemblies in gypsum soil habitats require further investigation. Thus, we considered the following questions. (1) Do harsher arid conditions determine the characteristics of the species that form plant assemblages? (2) Is the selection of the species that assemble in arid conditions mediated by their ability to grow on gypsum soils? (3) Is the selection of species that assemble in harsher conditions related to phylogenetically conserved functional traits? Perennial plant communities were analysed in 89 gypsum-soil sites along a 400 km climate gradient from the central to southeastern Iberian Peninsula. Each local assemblage was analysed in 30 × 30 m plots and described based on taxonomic, functional (soil plant affinity) and phylogenetic parameters. The mean maximum temperatures in the hottest month, mean annual precipitation and their interaction terms were used as surrogates for the aridity conditions in generalized linear models. In the hottest locations, the gypsophily range narrowed and the mean gypsophily increased at the community level, thereby suggesting the filtering of species and the dominance of soil specialists in the actual plant assemblies. Drier sites had higher taxonomic diversity. The species that formed the perennial communities were close in evolutionary terms at the two ends of the aridity gradient. The mean maximum temperatures in the hottest month had the main abiotic filtering effect on perennial plant communities, which was mediated by the ability of species to grow on gypsum soils, and thus gypsum specialists dominated the species assemblies in the hottest locations. In contrast, the perennial communities on gypsum soils were relatively resistant to changes in precipitation. Our findings suggest that the warmer environmental conditions predicted by global change models will favour gypsum specialists over generalists.

Evaluating Restoration Methods A Cross A Range of Plant Communities Dominated by Invasive Annual Grasses to Native Perennial Grasses

The objectives of the study were to determine whether there are differences in plant community response to restoration methods & to create awareness among the pastoralists/ agro-pastoralists on how to restore degraded rangeland. Six treatments were established: (1) ripping, mulching and seeding (2) ripping, manuling and seeding (3) ripping, mulching, manuling and seeding (4) control. The treatments were arranged in a randomized complete block design with factorial and replicated three times in each plant community. Each treatment plot was 3m by 6m, and depending on the treatment assigned to the plot, measurements for the vegetations were taken from those plots. Seeds of perennials, large tufted and palatable grass species were selected for reseeding purpose i.e., Andropogon canaliculatus, Tetrapogon cenchriformis, Panicum coloratum and Chrysopogon plumolosus. The study was carried out over the last three rainy seasons from 2015/16 and 2017/ 2018. Data were collected from germination to dry matter yield within three years of the experimental years. Accordingly, the result showed as variation clearly observed among the restoration treatments to different plant community. There is a significant difference at (P<0.05) rangeland parameters collected in all Restoration methods in each seasons. A total of 18 species of grasses were identified in the study district. Of the grass species 11(61.1%) species were perennials and 7 (38.9%) species were annuals. In Perennial plant community with Restoration Methods of Ri+Ma+Mu+Se was significant difference at (P<0.05) in the three consecutive seasons in Biomass production. The highest Biomass production was observed in the third season of implementation time which was 2.37 ton/ha while the lowest biomass production was observed in the first season of implementation period in control one which was 1 ton/ha. In Mixed plant community with Restoration Methods of Ri+Ma+Mu+Se was significant difference at (P<0.05) in the three consecutive seasons in Biomass production. The highest Biomass production was observed in the third season of implementation time which was 1.75 ton/ha while the lowest biomass production was observed in the first season of implementation period in control one which was 0.83 ton/ha. Therefore, we conclude that from this finding, perennial plant community with Restoration methods of Ri+Ma+Mu+Se is more effective method to rehabilitate denuded rangeland areas in semi-arid areas and also Annual plant community with Restoration methods of Ri+Ma+Mu+Se has shown dramatic result to improved range resources within short period of time. However, continuous onsite training & practical demonstration was very crucial to enhance the adoption rate of those Restoration methods. Keywords: Restoration Methods, plant community, Germination, Basal cover & Biomass Yield DOI : 10.7176/JBAH/9-19-01 Publication date :October 31 st 2019

Private lands conservation: A vision for the future

ABSTRACTAgricultural production, including croplands, pasture, and timber, dominates private‐land use and land cover across much of the contiguous lower 48 states. These private lands are essential to achieving the goals of national conservation initiatives such as the Northern Bobwhite Conservation Initiative (bobwhite [Colinus virginianus]), Sage Grouse Initiative, and North American Waterfowl Management Plan. Effective conservation delivery in managed landscapes requires 1) an understanding of landowner priorities and ownership objectives, 2) knowledge of the economic and environmental costs and benefits of conservation, and 3) natural resource professionals who understand the business of agriculture and forestry as well as principles of habitat management and wildlife conservation. We make the case for a new vision of multifunctional working landscapes that include designed components of natural and seminatural noncrop perennial plant communities (wetlands, grasslands, riparian areas, field margins, pine [Pinus spp.] grasslands, savannas, etc.) embedded in a matrix of row‐crop, pasture, rangeland, and forested working lands that produce sustainable food, fiber, and fuel. Producing sustainable, multifunctional landscapes will require effective conservation delivery that is intentional, objective‐driven, targeted, science‐based, and landscape scale. We contend that it will also require a new kind of natural resource professional. We consider the specific and novel skill sets that will be required among natural resource professionals to deliver conservation to private owners–producers of working lands. © 2019 The Wildlife Society.

Persistence and turnover in desert plant communities during a 37‐yr period of land use and climate change

AbstractUnderstanding long‐term changes in ecological communities during global change is a priority for 21st‐century ecology. Deserts, already at climatic extremes, are of unique interest because they are projected to be ecosystems most responsive to global change. Within a 500‐km2 landscape in the Mojave Desert, USA, we measured perennial plant communities at 100 sites three times (1979, 2008, and 2016) during 37 yr to evaluate six hypotheses of community change. These hypotheses encompassed shifts in community measures (e.g., diversity, cover) and species elevational distributions, biotic homogenization, disproportionately large change at the highest elevations, relationships between turnover and species’ responses to disturbance and drought, and that environmental refugia (e.g., moist topographic positions) would receive species during climatic warming and drying. Most community measures changed temporally, such as species density (species/600 m2) increasing 23% and plant cover doubling between 1979 and 2016. There was no increase in nonnative species and minimal evidence for biotic homogenization. High‐elevation communities did not display greater change than low‐elevation communities. Moreover, environmental refugia factored little in species shifts. While species distributional changes were unrelated to affinity for disturbance, the six most persistent species (persisting on >80% of sites) were long‐lived shrubs not associated with disturbance. Overall, seemingly paradoxically, climatic warming and drying was associated with increasing plant abundance. Comparing the 1970s to 2007–2016, precipitation in the study area declined 16% from 17 to 14 cm/yr and average daily minimum temperature rose 13% (1.2°C). The current climate with fewer freezes, together with reduced grazing, could be among the most optimal for desert perennials in the past century, although potential response lags to continuing warming and drying are uncertain. This study of long‐term elevational shifts in communities during global change is among few in deserts, and the average upward elevational shift of 6 m/decade for species in our study is within the range reported for temperate biomes. However, the 41% of species moving downslope is unusually high. We propose that dynamics within desert perennial communities follow a core‐transient species model where a site's species are either highly persistent or transient in approximately equal proportions.

Regenerating Agricultural Landscapes with Perennial Groundcover for Intensive Crop Production

The Midwestern U.S. landscape is one of the most highly altered and intensively managed ecosystems in the country. The predominant crops grown are maize (Zea mays L.) and soybean [Glycine max (L.) Merr]. They are typically grown as monocrops in a simple yearly rotation or with multiple years of maize (2 to 3) followed by a single year of soybean. This system is highly productive because the crops and management systems have been well adapted to the regional growing conditions through substantial public and private investment. Furthermore, markets and supporting infrastructure are highly developed for both crops. As maize and soybean production have intensified, a number of concerns have arisen due to the unintended environmental impacts on the ecosystem. Many areas across the Midwest are experiencing negative impacts on water quality, soil degradation, and increased flood risk due to changes in regional hydrology. The water quality impacts extend even further downstream. We propose the development of an innovative system for growing maize and soybean with perennial groundcover to recover ecosystem services historically provided naturally by predominantly perennial native plant communities. Reincorporating perennial plants into annual cropping systems has the potential of restoring ecosystem services without negatively impacting grain crop production and offers the prospect of increasing grain crop productivity through improving the biological functioning of the system.

Fire season modifies the perennial plant community composition through a differential effect on obligate seeders in eastern Mediterranean woodlands

AbstractAimPlant species regenerate after fire either through vegetative growth (i.e., obligate resprouters) or seed germination (i.e., obligate seeders), with some species adopting both strategies (i.e., facultative seeders). Fire season can have important consequences for the relative abundance of plant species adopting these regeneration strategies. The present study aimed to test for differential effects of fire season on perennial plant community composition.LocationEastern Mediterranean woodland in the Judea Mountains, Israel.MethodsWe conducted, for the first time, a large‐scale field experiment, involving prescribed spring and autumn burns in a typical eastern Mediterranean woodland. We sampled the perennial plant community before and after the burns, quantifying temporal changes in community composition caused by seasonal fires.ResultsAlthough fire intensity and severity were consistent between the two seasonal fires, plant community composition differed between areas subjected to spring or autumn burns. The abundances of all common species, Pistacia lenticus (obligate resprouter), Cistus spp. (obligate seeders) and Teucrium divaricatum (facultative seeder), were all reduced by both fires. Yet, their dominance in the post‐fire perennial plant community was retained. Differential fire season effects were detected only among obligate seeders, which experienced a stronger reduction in abundance after spring than after autumn burns.ConclusionsDifferential fire season effects on the perennial plant community resulted from phenological rather than fire intensity/severity effects. Such changes in community composition may have important implications for plant community dynamics, because they affect the circle of “fire event–plant regeneration–fire reoccurrence”, determining the probability and intensity of future fires. Furthermore, even though the eastern mediterranean ecosystem is considered highly resilient to disturbances, increased spatio‐temporal variation in fire season, may result in a new vegetation mosaic, differing from the contemporary one, i.e., an alternative stable state.

Halophytic plant community patterns in Mediterranean saltmarshes: shedding light on the connection between abiotic factors and the distribution of halophytes

Establishing a vegetation-soil model in Mediterranean saltmarshes based on the relationships between the plant communities and the abiotic factors, considering temporary variation. Relationships between perennial plant species abundances and plant communities were analysed by DCAs. A CCA was performed to study the relationships between floristic composition and edaphic variables. Sixteen soil variables and Pearson correlations between them were considered. Marginal and conditional effects were supported by mixed ANOVA. Statistical analyses were performed to check temporary variation. DCAs results showed eight vegetation types. CCA showed E.C. as the main gradient, with the succulent halophyte communities growing in high E.C. soils. SAR and percentage of sand were considered as secondary gradients. Finally, the highest values of the edaphic variables were observed, in general, during the cold period. The main gradient of salinity, together with sodicity and texture gradients, would markedly influence the plant distribution in Mediterranean saltmarshes. Two principal plant zones were observed: succulent zone vs. non-succulent zone, with a specific edaphic distribution for each plant community and for the proposed Limonium morphotypes treatment. A plant-soil model based on these three gradients is here proposed. Our results would complement the previous knowledge about plant-soil relationships in Mediterranean saltmarshes.

Successional change in species composition alters climate sensitivity of grassland productivity.

Succession theory predicts altered sensitivity of ecosystem functions to disturbance (i.e., climate change) due to the temporal shift in plant community composition. However, empirical evidence in global change experiments is lacking to support this prediction. Here, we present findings from an 8-year long-term global change experiment with warming and altered precipitation manipulation (double and halved amount). First, we observed a temporal shift in species composition over 8years, resulting in a transition from an annual C3 -dominant plant community to a perennial C4 -dominant plant community. This successional transition was independent of any experimental treatments. During the successional transition, the response of aboveground net primary productivity (ANPP) to precipitation addition magnified from neutral to +45.3%, while the response to halved precipitation attenuated substantially from -17.6% to neutral. However, warming did not affect ANPP in either state. The findings further reveal that the time-dependent climate sensitivity may be regulated by successional change in species composition, highlighting the importance of vegetation dynamics in regulating the response of ecosystem productivity to precipitation change.

Applying a hydrogeomorphic channel classification to understand spatial patterns in riparian vegetation

Questions Hydrogeomorphic channel classifications are widely employed to understand natural phenomena in Earth sciences, but are rarely used in riparian vegetation studies. However, when these types of classifications correspond to physical process domains (discrete landscape units with consistent abiotic attributes), they may be useful in distinguishing habitat and vegetation types. We assessed the ecological significance of a hydrogeomorphic stream channel classification by addressing the following questions: (1) does perennial plant community composition differ among hydrogeomorphic channel types; (2) which species and functional groups contribute to compositional variation among channel types in the Sonoran Desert; and (3) what are the stream reach-scale geomorphic drivers of compositional variation? Location Sonoran Desert, Arizona, USA. Methods We compared perennial riparian plant community composition among five a priori hydrogeomorphic channel types at 86 stream reaches in arid ephemeral watersheds. Floristic differences among channel types were assessed using PERMANOVA. GLM were used to identify species and functional groups whose abundance differed among channel types. Abiotic drivers of compositional differences were identified through correlations among biotic and abiotic matrices. Results Community composition differed significantly among channel types, with distinctive vegetation in bedrock, piedmont headwater and braided channels. While different from other channel types, vegetation in bedrock with alluvium and incised alluvium channels was broadly similar, but could be distinguished by the abundance of common species and functional groups. The density of drought-deciduous subshrubs, as well as large woody plants with evergreen, drought-deciduous and photosynthetic stem phenology contributed to the observed compositional variance. Bed slope was the primary driver of compositional differences among channel types, with elevation providing additional explanatory power. Conclusions Hydrogeomorphic channel classifications corresponding to distinctive fluvial process domains are useful for understanding spatial variability in riparian habitats and resulting differences in plant community composition in the Sonoran Desert. Analogous spatial patterns of riparian plant communities previously reported from other arid regions suggest that these general channel types are broadly applicable.

Roadsides: an opportunity for biodiversity conservation

AbstractQuestionsHow do roadsides interact with patches of natural vegetation in shaping perennial plant communities in fragmented agricultural areas? Are the observed differences due to the type of roadside (i.e. roadcuts, embankments or road verges) or are there other factors driving community structure and composition?LocationStretch of motorway A3 and its surrounding area, central Spain.MethodsWe analysed the variation in perennial plant species composition and diversity among 92 plots (400 m2). The plots were located in five different environmental scenarios, three of them in a fragmented landscape (patches of natural vegetation, embankments and roadcuts) and two in an unfragmented landscape (natural vegetation and road verges). In each plot, the cover of each perennial plant species and eight soil variables were assessed. We used phi coefficient of correlation to determine the scenario preferences of each species, Kruskal–Wallis tests to compare the soil variables between landscape scenarios and eight descriptive variables of the community, and RDA and partial RDA to evaluate the relative importance of the type of environmental scenario on the floristic community.ResultsWe identified 130 species, with only 16 species never appearing on roadsides. Perennial total cover, species richness, inverse Simpson's index and number of protected species showed no significant differences between the five scenarios considered. In contrast, the number of nutrient‐demanding species and restricted‐range diversity had lower values in natural vegetation plots. Soil variables and the type of scenario together explained 28.5% of the species composition variation. Of this percentage, 6.8% was explained by soil variables, 12.1% by the type of scenario and 10.0% of the variation was shared between the two data sets.ConclusionsOur results show that almost all perennial species occurring in natural vegetation patches were also able to reach and settle in roadsides. However, soil conditions and other specific roadside variables generate different plant communities. In spite of the differences found between the perennial plant community of roadsides and their surrounding area, roadsides are excellent reservoirs of biodiversity.