高寒草毡层基本属性与固碳能力沿水分和海拔梯度的变化

高寒草毡层是高原寒区自然植被下形成的松软而坚韧且耐搬运的表土层,认识其生态功能是促进草牧业生产休养保护和工程施工主动利用的前提。通过对青藏高原东部若尔盖高原植被的广泛调查,在布设沼泽、退化沼泽、沼泽化草甸、湿草甸、干草甸和退化草甸水分梯度群落样地,以及亚高山草甸、亚高山灌丛草甸、高山灌丛草甸和高山草甸海拔梯度群落样地的基础上,通过对不同类型群落样地草毡层容重、土壤颗粒组成和土壤有机碳(SOC)含量的测定分析,比较了水分和海拔梯度下草毡层固碳能力。结果表明,草毡层厚度平均为30cm,沼泽湿地草毡层容重最小,SOC含量在300g/kg以上;退化草甸容重最高,SOC含量显著下降。不同群落草毡层SOC密度在10—24kg C/m~2之间,随着土壤水分有效性的降低而降低;高山灌丛草甸草毡层SOC密度比草甸高15%。研究得出,保持草毡层稳定的质量含水量阈值为30%,SOC含量阈值为30g/kg;高寒植被草毡层在沼泽到草甸的退化演替中,容重、紧实度变大,有机碳含量减少,碳密度和碳储量下降;灌丛草甸的固碳能力大于草甸,但灌丛草甸的生产功能降低;保持可持续发展的草地生产能力,维护固碳生态功能,需要防止草毡层退化,抑制草甸向灌丛草甸演替。     

Recovery of small denuded patches of the dominant NSW coastal saltmarsh species (Sporobolus virginicus and Sarcocornia quinqueflora) and implications for restoration using donor sites

Summary Efforts to restore coastal saltmarsh habitats through transplantation of saltmarsh species from donor sites are becoming more frequent. As sections removed are generally small there is little information on the ability of these areas to recover naturally after removal. The present study provides an understanding of the potential of dominant saltmarsh species in NSW (Saltcouch, Sporobolus virginicus and Samphire, Sarcocornia quinqueflora) to regenerate naturally after such small‐scale removal (25 cm × 25 cm plots) at separate sites for each species. The increase in percentage cover of vegetation within the denuded plots was measured over 21 months along a gradient within the marsh (between the mangrove and terrestrial boundaries) and then compared to non‐denuded plots. Recovery of Saltcouch was slow with an estimate of 5–6 years to reach the surrounding cover levels. Similarly, recovery of Samphire on upper levels of the shore is estimated at 4–5.5 years. On the lower level on the shore, however, Samphire had reached a cover that was within the range of the surrounding vegetation by the end of the 21‐month study period.     

Regeneration of a Gentiana pneumonanthe population in an oligotrophic wet meadow

Abstract. The aim of this study was to evaluate the critical phases of the life cycle of Gentiana pneumonanthe, the marsh gentian, a threatened species of the Bohemian flora. The effect of various conditions on germination and seedling establishment and the possible effect of competition on the performance of the species were tested. Seeds were sown in plots which were subjected to four treatments in a randomized complete blocks experiment: unmanaged meadow, mown meadow, burned meadow, and meadow with cut sod. The significantly highest recruitment was found in plots with cut sod, the lowest in the unmanaged control plots. Seedling survival also differed among the treatments. In the following year surviving individuals were only found in plots with cut sod. The influence of neighbouring vegetation on target gentian individuals was evaluated by removing the surrounding vegetation and comparing the performance of these individuals with controls. The initial height of each individual was measured and used as a covariable. No significant effect of neighbouring vegetation on performance was detected. Thus, the establishment phase appears to be critical for population persistence and is also more influenced by the management regime than other stages of the life cycle.     

Vegetation Cover,Tidal Amplitude and Land Area Predict Short-Term Marsh Vulnerability in Coastal Louisiana

The loss of coastal marshes is a topic of great concern, because these habitats provide tangible ecosystem services and are at risk from sea-level rise and human activities. In recent years, a significant effort has gone into understanding and modeling the relationships between the biological and physical factors that contribute to marsh stability. Simulation-based process models suggest that marsh stability is the product of a complex feedback between sediment supply, flooding regime and vegetation response, resulting in elevation gains sufficient to match the combination of relative sea-level rise and losses from erosion. However, there have been few direct, empirical tests of these models, because long-term datasets that have captured sufficient numbers of marsh loss events in the context of a rigorous monitoring program are rare. We use a multi-year dataset collected by the Coastwide Reference Monitoring System that includes transitions of monitored vegetation plots to open water to build and test a predictive model of near-term marsh vulnerability. We found that despite the conclusions of previous process models, elevation change had no ability to predict the transition of vegetated marsh to open water. However, we found that the processes that drive elevation change were significant predictors of transitions. Specifically, vegetation cover in prior year, land area in the surrounding 1 km² (an estimate of marsh fragmentation) and the interaction of tidal amplitude and position in tidal frame were all significant factors predicting marsh loss. This suggests that (1) elevation change is likely better a predictor of marsh loss at timescales longer than we consider in this study and (2) the significant predictive factors affect marsh vulnerability through pathways other than elevation change, such as resistance to erosion. In addition, we found that, while sensitivity of marsh vulnerability to the predictive factors varied spatially across coastal Louisiana, vegetation cover in prior year was the best single predictor of subsequent loss in most sites followed by changes in percent land and tidal amplitude. The model’s predicted land loss rates correlated well with land loss rates derived from satellite data, although agreement was spatially variable. These results indicate (1) monitoring the loss of small-scale vegetation plots can inform patterns of land loss at larger scales, (2) the drivers of land loss vary spatially across coastal Louisiana, and (3) relatively simple models have potential as highly informative tools for bioassessment, directing future research and management planning.     

Invasive species removal increases species and phylogenetic diversity of wetland plant communities

Plant invasions result in biodiversity losses and altered ecological functions, though quantifying loss of multiple ecosystem functions presents a research challenge. Plant phylogenetic diversity correlates with a range of ecosystem functions and can be used as a proxy for ecosystem multifunctionality. Laurentian Great Lakes coastal wetlands are ideal systems for testing invasive species management effects because they support diverse biological communities, provide numerous ecosystem services, and are increasingly dominated by invasive macrophytes. Invasive cattails are among the most widespread and abundant of these taxa. We conducted a three‐year study in two Great Lakes wetlands, testing the effects of a gradient of cattail removal intensities (mowing, harvest, complete biomass removal) within two vegetation zones (emergent marsh and wet meadow) on plant taxonomic and phylogenetic diversity. To evaluate native plant recovery potential, we paired this with a seed bank emergence study that quantified diversity metrics in each zone under experimentally manipulated hydroperiods. Pretreatment, we found that wetland zones had distinct plant community composition. Wet meadow seed banks had greater taxonomic and phylogenetic diversity than emergent marsh seed banks, and high‐water treatments tended to inhibit diversity by reducing germination. Aboveground harvesting of cattails and their litter increased phylogenetic diversity and species richness in both zones, more than doubling richness compared to unmanipulated controls. In the wet meadow, harvesting shifted the community toward an early successional state, favoring seed bank germination from early seral species, whereas emergent marsh complete removal treatments shifted the community toward an aquatic condition, favoring floating‐leaved plants. Removing cattails and their litter increased taxonomic and phylogenetic diversity across water levels, a key environmental gradient, thereby potentially increasing the multifunctionality of these ecosystems. Killing invasive wetland macrophytes but leaving their biomass in situ does not address their underlying mechanism of dominance and is less effective than more intensive treatments that also remove their litter.     

RECOLONIZATION OF SMALL DISTURBANCE PATCHES IN A NEW ENGLAND SALT MARSH

Availability of colonizers and edaphic conditions were tested in relation to rates of recolonization of open patches in salt marsh vegetation. The density of buried viable seeds was estimated by counting seedlings in undisturbed vegetation and germinating seeds in the laboratory. A low density of viable seeds (<50 per m²) found in these salt marsh soils indicated the absence of an important viable seed bank in this system. Rates of recolonization in natural open patches were monitored for three years. Vegetative expansion of Spartina alterniflora, at approximately 12 cm per year, accounted for most of the recolonization of open patches, although some colonization of annual Salicornia spp. occurred from seeds. Salinity and sulfide and ammonium concentrations were measured in pore water samples from depths of 2–7 cm and 10–15 cm of soil. Comparison of the concentrations from disturbed and undisturbed plots in the marsh did not show significant differences, indicating that none of the edaphic conditions measured would be more inhibitory to plant growth in the disturbed than the undisturbed plots. Therefore, the rate at which small open patches become recolonized is primarily controlled by proximity of Spartina alterniflora and its capacity for vegetative expansion.     

Growing season carbon gas exchange from peatlands used as a source of vegetation donor material for restoration

The moss layer transfer technique removes the top layer of vegetation from donor sites as a method to transfer propagules and restore degraded or reclaimed peatlands. As this technique is new, little is known about the impacts of moss layer transfer on vegetation and carbon fluxes following harvest. We monitored growing season carbon dioxide (CO₂) and methane (CH₄) fluxes as well as plant communities at donor sites and neighbouring natural peatland sites in an ombrotrophic bog and minerotrophic fen in Alberta, Canada from which material was harvested between 1 and 6 years prior to the study. Plant recovery at all donor sites was rapid with an average of 72% total plant cover one growing season after harvest at the fen and an average of 87% total plant cover two growing seasons after harvest at the bog. Moss cover also returned, averaging 84% 6 years after harvest at the bog. The majority of natural peatlands in western Canada are treed and tree recruitment at the donor sites was limited. Methane emissions were higher from donor sites compared to natural sites due to the high water table and greater sedge cover. Carbon budgets suggested that the donor fen and bog sites released higher CO₂ and CH₄ over the growing season compared to adjacent natural sites. However, vegetation re-establishment on donor sites was rapid, and it is possible that these sites will return to their original carbon-cycle functioning after disturbance, suggesting that donor sites may recover naturally without implementing management strategies.     

Power analysis to determine sample size for monitoring vegetation change in salt marsh habitats

Numerous initiatives are underway throughout New England and elsewhere to quantify salt marsh vegetation change, mostly in response to habitat restoration, sea level rise, and nutrient enrichment. To detect temporal changes in vegetation at a marsh or to compare vegetation among different marshes with a degree of statistical certainty an adequate sample size is required. Based on sampling 1 m² vegetation plots from 11 New England salt marsh data sets, we conducted a power analysis to determine the minimum number of samples that were necessary to detect change between vegetation communities. Statistical power was determined for sample sizes of 5, 10, 15, and 20 vegetation plots at an alpha level of 0.05. Detection of subtle differences between vegetation data sets (e.g., comparing vegetation in the same marsh over two consecutive years) can be accomplished using a sample size of 20 plots with a reasonable probability of detecting a difference when one truly exists. With a lower sample size, and thus lower power, there is an increased probability of not detecting a difference when one exists (e.g., Type II error). However, if investigators expect to detect major changes in vegetation (e.g., such as those between an un-impacted and a highly impacted marsh) then a sample size of 5, 10, or 15 plots may be appropriate while still maintaining adequate power. Due to the relative ease of collecting vegetation data, we suggest a minimum sample size of 20 randomly located 1 m² plots when developing monitoring designs to detect vegetation community change of salt marshes. The sample size of 20 plots per New England salt marsh is appropriate regardless of marsh size or permanency (permanent or non-permanent) of the plots.     

Response of floodplain grassland plant communities to altered water regimes

Floodplain grasslands are often composed of a mosaic of plant communities controlled by hydrological regime. This article examines the sensitivity of floodplain grassland plant communities to water regime using reciprocal transplantation of an inundation grassland and a flood-meadow within an English floodplain. Experimental treatments comprised control, transplanted and lifted plots; the last treatment, in order to elucidate any disturbance effects of transplantation. Plant community response was analysed using species abundance and their ecological traits. Results from both communities showed substantial annual variations related to hydrology, including significant species changes, but generally, vegetation seemed to be responding to drier conditions following a major flood event. This ‘drying’ trend was characterised by increased species diversity, a greater abundance of competitive species and fewer typical wetland plants. Transplanted community composition increasingly resembled receptor sites and transplant effects were most pronounced the first year after treatment for both vegetation types. Differential responses to water regime were detected for the two plant communities. The inundation grassland community was particularly dynamic with a composition that rapidly reflected drying conditions following the major flood, but transplantation into a drier flood-meadow site prompted little additional change. The flood-meadow community appeared more resistant to post-inundation drying, but was sensitive to increased wetness caused by transplantation into inundation grassland, which significantly reduced six species while none were significantly favoured. The effects of disturbance caused by lifting the transplants were limited in both communities, although five species showed significant annual fluctuations. The study shows that small alterations in water regime can prompt rapid vegetation changes and significant plant species responses in floodplain grasslands, with effects probably magnified through competitive interactions. The dynamic properties of floodplain vegetation demonstrated by this study suggest that its classification, management and monitoring are challenging and ideally should be based on long-term studies.     

Variation in ecosystem carbon dynamics of saltwater marshes in the northern Gulf of Mexico

Wetlands are highly productive ecosystems that can sequester large quantities of carbon. However, variation in physiological potential can alter their capacity to sequester carbon. To examine variation in ecosystem physiological capacity, we established three coastal marsh sites in Mississippi and Alabama spanning a productivity gradient. Over 1 year, we measured ecophysiological activity and spectral indices in two vegetation zones within each marsh to develop a better understanding of variation in ecosystem responses and health. Gross ecosystem exchange of carbon and ecosystem respiration rates (R_eco) differed significantly among sites, with the highest activity at Grand Bay, Mississippi and Point Aux Pines, Alabama and lower ecophysiological activity at Dauphin Island, Alabama. Net ecosystem exchange was similar for all three study areas because greater carbon assimilation was negated by higher levels of respiration. Spectral indices and leaf area were significantly different by marsh vegetation zone, suggesting that alterations in species composition and plant productivity can have important implications for carbon sequestration. While limited to 1 year, this study establishes a foundation by which to evaluate future research conducted over greater temporal and spatial scales, thereby enhancing our understanding of marsh physiological activity.     

Restoration of Wet Dune Slacks on the Dutch Wadden Sea Islands: Recolonization After Large-Scale Sod Cutting

The effects of sod cutting were studied in a dune area on the Dutch Wadden Sea Island of Texel. Sod cutting was carried out in a range of different dune slacks in order to restore dune slack vegetation with many endangered Red List species. Sod cutting removed approximately 96% of the soil seed bank. Species abundant in the seed bank, notably Juncacea, also had a high frequency in the vegetation that established during the first year after the restoration measures. Many other species not registered in the seed bank or in the former vegetation also appeared. Species richness in the monitored plots exceeded that of uncut reference plots after a few years. Colonization rates were higher than extinction rates in most plots, indicating that a stable state has not been reached after 5 years. Differences in species richness between slacks appeared to be related to the occurrence of source areas nearby and availability of dispersal agents, such as flooding and animals.     

The natural regeneration of salt marsh on formerly reclaimed land

Question: Does the vegetation of restored salt marshes increasingly resemble natural reference communities over time? Location: The Essex estuaries, southeast England. Methods: Abandoned reclamations, where coastal defences had been breached in storm events, and current salt marsh recreation schemes were surveyed giving a chronosequence of salt marsh regeneration from 2 to 107 years. The presence, abundance and height of plant species were recorded and comparisons were made with adjacent reference salt marsh communities at equivalent elevations. Results: Of the 18 paired sites surveyed, 13 regenerated marshes had fewer species than their adjacent reference marsh, three had an equal number and two had more. The plant communities of only two de‐embankment sites matched that of the reference community. 0–50 year old sites and 51–100 year old sites had fewer species per quadrat than the 101+ year sites and the reference salt marshes. There was a weak relationship between differences in species richness for regenerated and reference marshes and the time since sites were first re‐exposed to tidal inundation. Cover values for the invasive and recently evolved Spartina anglica were greater within regenerated than reference marshes. Conclusions: Salt marsh plants will colonise formerly reclaimed land relatively quickly on resumption of tidal flooding. However, even after 100 years regenerated salt marshes differ in species richness, composition and structure from reference communities.     

Quantifying ecosystem rejuvenation: foliar nutrient concentrations and vegetation communities across a dust gradient and a chronosequence

Background and aims

Due to long-term weathering of land surfaces, aeolian nutrient contributions can become essential to maintain ecosystem fertility and avoid retrogression. However, studies that consider the qualitative and quantitative effects of dust deposition on ecosystem development are rare. We addressed this knowledge gap by studying an active Holocene dust flux gradient along a 6,500 year old dune ridge and a nearby chronosequence outside the influence of dust deposition in a super-humid, high leaching environment, on the west coast of the South Island in New Zealand.

Methods

Along both sequences we measured foliar nutrients of two main tree species (Dacrydium cupressinum, Prumnopitys ferruginea) and analysed vegetation communities in survey plots.

Results

Along the dust gradient, foliar phosphorus (P) concentrations increased up to 50 % with increasing dust flux. Across the nearby chronosequence a rapid decline of up to 50 % in foliar [P] occurred within the first 2,000 years after which it plateaued. At the highest dust flux rate, closest to the dust source, foliar [P] matched those of surfaces that are 5,702 to 6,098 years younger than the 6,500 year old dune. Vegetation communities along the dust gradient showed increasing relative abundance of species typical for successional communities on immature soils (Entisols, Inceptisols), while canopy cover and basal area (total, angiosperms, conifers) did not respond to increasing dust deposition. Tree fern basal area, however, positively responded to the dust flux.

Conclusion

We conclude that naturally occurring dust deposition can fertilise ecosystems significantly, creating a foliar nutrient status normally found on land surfaces that are up to 94 % younger and vegetation communities that are typical for successional stages on young soils (Entisols, Inceptisols). We suspect that these observations mainly reflect more plant-available P in the ecosystem as a result of dust fertilisation. Thus, dust deposition can be an important mechanism to avoid or retard the development of an ecosystem toward natural retrogression. This is the first study to directly quantify the fertilising capacity of natural dust deposition by calibrating its rejuvenating effect against a well-dated successional vegetation sequence.     

Vegetation change from chronic stress events: Detection of the effects of tide gate removal and long‐term drought on a tidal marsh

Question: Chronic stress events are defined as disturbance events that exceed the lifespan of the dominant plant species, fluctuate in intensity and lack abruptness or physical destruction of biomass. Can the effects of chronic stress events be measured on vegetation communities? Did two chronic stress events, the removal of a tide gate and a four year drought, cause a temporary or permanent shift in the vegetation communities of a tidal marsh? Location: Tidal marsh in southeastern United States. Methods: Change in species composition and dominance and community change on a landscape level salinity gradient were measured between time periods ranging from four months to seven years to construct a statistical baseline reference community at freshwater, oligohaline, and mesohaline sections of a tidal marsh. Statistical shifts in the plant community were defined as changes in the plant community that fell outside of the defined baseline reference community. Results: Plant community changes outside of the reference community occurred in 13 out of 378 community comparisons. Removal of the tide gate had a greater effect on interstitial salinity levels than the drought and was most intense in the oligohaline marsh, where between 20 to 45% of the freshwa‐ter/oligohaline community types permanently converted to oligohaline community types. However, community shifts in the freshwater and oligohaline marsh induced by the drought were temporary, lasting from 1 to 3+ years. Neither chronic stress event permanently altered the mesohaline plant communities. Conclusion: The effects of chronic stress events could be detected; an extended historical record of vegetation change (18 years) was necessary to identify community shifts outside of a reference condition of the community and to determine if those shifts were permanent or temporary.     

Within-field variation of mycotoxin contamination of winter wheat is related to indicators of soil moisture

Forest areas have increased in the Mediterranean basin over the last two decades, due to the abandonment of agriculture. This and the occurrence of intense drought periods have led to an increase in the frequency and intensity of fires. Fire and drought can increase short-term soil organic C accumulation as a result of increased plant residues. In this study, we examined the changes in the soil organic C and the effects of fire and drought during a 12-year period in two Mediterranean grasslands and a shrubland. Thus, we established 6 plots for each of the three vegetation type and we set 18 experimental fires. Soils were sampled 3 days, 9 months, 6 years and 12 years after the fires and were analyzed for organic C. We used the RothC-26.3 model to help interpret the changes we observed. Three days after the fire, the amount of organic C was higher in burned plots than in unburned plots down to a depth of 5 cm. This was true in all plant communities under study and was probably due to burned plant deposition after the fires. However, these differences disappeared in the following years. In some cases, organic C from burned and unburned plots showed a large increase between years 6 and 12, which coincided with an extended 4-year drought period. Our results indicate that in Mediterranean shrublands and mixed shrub-grasslands the influence of drought periods could produce transient pulses of C that are much larger than the pulses produced by fire. The pulses of C caused by drought should be considered when studying the soil organic C dynamics in the frame of global warming.     

Temporal Variability of CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O Flux Spatial Patterns at a Mowed and a Grazed Grassland

Spatial patterns of ecosystem processes constitute significant sources of uncertainty in greenhouse gas flux estimations partly because the patterns are temporally dynamic. The aim of this study was to describe temporal variability in the spatial patterns of grassland CO₂ and N₂O flux under varying environmental conditions and to assess effects of the grassland management (grazing and mowing) on flux patterns. We made spatially explicit measurements of variables including soil respiration, aboveground biomass, N₂O flux, soil water content, and soil temperature during a 4-year study in the vegetation periods at grazed and mowed grasslands. Sampling was conducted in 80 × 60 m grids of 10 m resolution with 78 sampling points in both study plots. Soil respiration was monitored nine times, and N₂O flux was monitored twice during the study period. Altitude, soil organic carbon, and total soil nitrogen were used as background factors at each sampling position, while aboveground biomass, soil water content, and soil temperature were considered as covariates in the spatial analysis. Data were analyzed using variography and kriging. Altitude was autocorrelated over distances of 40–50 m in both plots and influenced spatial patterns of soil organic carbon, total soil nitrogen, and the covariates. Altitude was inversely related to soil water content and aboveground biomass and positively related to soil temperature. Autocorrelation lengths for soil respiration were similar on both plots (about 30 m), whereas autocorrelation lengths of N₂O flux differed between plots (39 m in the grazed plot vs. 18 m in the mowed plot). Grazing appeared to increase heterogeneity and linkage of the spatial patterns, whereas mowing had a homogenizing effect. Spatial patterns of soil water content, soil respiration, and aboveground biomass were temporally variable especially in the first 2 years of the experiment, whereas spatial patterns were more persistent (mostly significant correlation at p < 0.05 between location ranks) in the second 2 years, following a wet year. Increased persistence of spatial patterns after a wet year indicated the recovery potential of grasslands following drought and suggested that adequate water supply could have a homogenizing effect on CO₂ and N₂O fluxes.     

Wetland Waterbird Food Resources Increased by Harvesting Invasive Cattails

The conservation of many freshwater marsh waterbirds (i.e., waterfowl, shorebirds, wading birds, and secretive marshbirds) in the Laurentian Great Lakes requires managing invasive emergent macrophytes, which degrade waterbird habitat by creating dense, litter-clogged stands, and excluding plants that produce nutritionally balanced and high-energy food (seeds, tubers, and submerged aquatic vegetation). The most commonly used management approach in the United States Great Lakes region involves the application of herbicides, which can stimulate waterbird forage plants but does not address the accumulation of plant litter, the underlying cause of plant community diversity loss and habitat degradation. We experimentally evaluated the effects of an alternative approach, harvesting invasive plants and their litter followed by flooding, on plant communities, focusing on the effects of these treatments to increase the abundance of high-energy wetland plants. At the Shiawassee National Wildlife Refuge in Michigan, USA, we experimentally treated an invasive cattail (Typha × glauca)-dominated wetland in August and September of 2016, 2017, and 2018, using a randomized block design with 4 blocks and 3 treatments (sediment surface harvest, above ground harvest, and control). We monitored the effects of these treatments on the abundance and dominance of waterbird forage-producing plants, plant diversity, and plant communities prior to (Jul 2016) and during the summer following each treatment (late Jul or early Aug 2017, 2018, and 2019). Additionally, we used pre- and post-treatment waterbird use-day data collected at the unit scale and compared values with satellite imagery-derived land cover changes. Compared to control plots, 3 years of harvesting and flooding significantly increased plant species diversity, increased the abundance of waterbird seed- and tuber-producing plant species by 5 times, and increased annual plant dominance by more than 10 times, while substantially reducing all measures of cattail and its litter. Use-days increased for total waterbirds, including waterfowl and dabbling ducks, following treatment. Cattail cover decreased and open water and non-cattail emergent vegetation cover increased. Harvesting invasive plant biomass coupled with flooding promoted a plant community composition and structure beneficial to waterbirds. © 2020 The Wildlife Society.     

Relationship of different feeding groups of true bugs (Hemiptera: Heteroptera) with habitat and landscape features in Pannonic salt grasslands

Eastern European grasslands are still inhabited by a rich arthropod fauna, but the drivers and mechanisms influencing their communities have to be understood to ensure their future survival. Heteroptera communities were studied in 20 plot-pairs in Pannonic salt steppe–salt marsh mosaics in Hungary. The effects of vegetation characteristics, landscape diversity and the proportion of surrounding grasslands on the composition, species richness and abundance of different feeding groups of true bugs (carnivores, specialist and generalist herbivores) were examined using ordinations and mixed-effect models. We found distinct herbivorous assemblages corresponding to microtopography-driven differences in water regime and vegetation between steppe and marsh plots, but this pattern was less pronounced in carnivorous assemblages. A higher species richness of true bugs was found in the more diverse steppe vegetation than in the salt marsh vegetation, while the abundance pattern of true bugs was opposite. Landscape diversity had a positive effect on the species richness and abundance of generalist herbivores and carnivores. Our results suggested that generalist herbivores and carnivores appear to drive diversity patterns in the local landscape due to their high dispersal abilities and the broader range of resources they can utilize. Specialist herbivores strongly influence the local insect biomass in relation to the distribution and density of their host plants. The present study highlights the importance of both habitat and landscape diversity for local insect diversity in Pannonic salt grasslands and suggests that the main threats for arthropod diversity are those processes and activities that homogenize these areas.     

Controlling perennial pepperweed (<Emphasis Type="Italic">Lepidium latifolium</Emphasis>) in a brackish tidal marsh

Perennial pepperweed (Lepidium latifolium) is an aggressively invasive species that spreads by vegetative growth and seeds. Common methods for removal such as hand-pulling and mowing are impractical in brackish marsh environments. We evaluated the effects of two herbicide treatments (imazapyr and imazapyr + glyphosate) against a non-herbicide control (flower head removal) on invasive pepperweed and native vegetation in three habitats (bay edge, channel edge, and levee) in brackish marshes. Both herbicide treatments produced significantly better control of pepperweed than the control, but imazapyr alone took 2 years of treatment to produce levels of control that were similar to one year of the imazpyr + glyphosate treatment. Both herbicide treatments also reduced native cover, but the effects were more severe in plots treated with imazapyr + glyphosate than in plots treated with imazapyr alone. Effects on pepperweed were similar across the three habitats, but impacts on native vegetation were less severe in bay edge environments. Managers should consider the tradeoffs when choosing a treatment plan for pepperweed: the quick reduction of pepperweed achieved by the combination of imazapyr and glyphosate may come at the expense of creating opportunities for reinvasion by causing bare ground and/or patches of litter that are slowly recolonized by native species.