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Expanding global commerce may be increasing the likelihood of exotic earthworm invasions, which could have negative implications for soil processes, other animal and plant species, and importation of certain pathogens. [...]

Wetlands in agroecosystems provide multiple ecosystem services, including provisioning services such as forage production. Here, we examine how pasture management intensity (semi‐natural pastures vs. highly managed pastures (fertilized, heavily drained, planted with productive grasses), cattle exclusion (grazed vs. fenced), prescribed fire (burned vs. unburned), and their interactions affect provisioning services provided by small, isolated, and seasonally flooded wetlands in subtropical pastures and rangelands. We used a replicated, full‐factorial experiment on 40 seasonally flooded wetlands located in Florida (USA), and measured standing plant biomass and annual net primary productivity in each wetland. Biomass was sorted by species to calculate species abundance of palatable and unpalatable plants. We used general linear mixed models to evaluate the effect of treatments and their interactions on biomass quantity, plant tissue nutrients (% C, % N, and % P), and forage nutritive value (using in vitro organic matter digestibility). Plant standing biomass and productivity were greatest in wetlands embedded in highly managed pastures, but in grazed wetlands, a large proportion of this biomass was unpalatable to cattle. Excluding cattle from wetlands in highly managed pastures increased productivity, standing biomass, and the amount of palatable species (~6.3 t/ha) compared to grazed wetlands (~3.3 t/ha), especially when these wetlands were also exposed to prescribed fire. Total P in plant tissue was consistently higher in wetlands within highly managed pastures, but total N responses to treatments varied between years. In vitro digestibility was higher in vegetation from wetlands within highly managed pastures, but not in fenced wetlands despite the higher amount of palatable species, suggesting that palatability and digestibility were decoupled. Subtropical wetlands in agroecosystems provide substantial provisioning services, and our study suggests that targeted management can increase these services. However, the pasture type surrounding a wetland interacts with grazing and fire management to affect provisioning services. We propose that fencing off selected wetlands (specifically in highly managed pastures) followed by low‐intensity grazing with adequate resting periods could benefit ranchers and have less persistent impacts on this ecosystem. [ABSTRACT FROM AUTHOR]

Aims Understanding the drivers of grassland structure and function following livestock removal will inform grassland restoration and management. Here, we investigated the effects of fire and nutrient addition on structure and function in a subtropical semi-native grassland recently released from grazing in south-central Florida. We examined responses of soil nutrients, plant tissue nutrients, biomass of live, standing dead and litter, and plant species composition to experimental annual prescribed fire applied during different seasons (wet season vs. dry season), and nutrient additions (N, P and N + P) over 9 years. Methods Experimental plots were set up in a randomized block split-plot design, with season of prescribed fire as the main treatment and nutrient addition as the subplot treatment. Species cover data were collected annually from 2002 to 2011 and plant tissue and plant biomass data were collected in 2002-2006 and 2011. Soil nutrients were analyzed in 2004, 2006 and 2011. Important Findings Soil total phosphorus (P) levels increased substantially with P addition but were not influenced by prescribed fire. Addition of P and N led to increased P and N concentrations in live plant tissues, but prescribed fire reduced N in live tissue. Levels of tissue N were higher in all plots at the beginning of the experiment, an effect that was likely due to grazing activity prior to removal of livestock. Plant tissue N steadily declined over time in all plots, with annually burned plots declining faster than unburned plots. Prescribed fire was an important driver of standing dead and litter biomass and was important for maintaining grass biomass and percent cover. Nutrient addition was also important: the addition of both N and P was associated with greater live biomass and woody forbs. Removal of grazing, lack of prescribed fire, and addition of N + P led to a reduction of grass biomass and a large increase in biomass of a woody forb. Annual prescribed fire promoted N loss from the system by reducing standing dead and litter, but maintained desirable biomass of grasses. [ABSTRACT FROM AUTHOR]

In the USA, the United States Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS) has restored millions of acres of wetlands through its Wetland Reserve Easement (WRE) programs. However, few quantitative studies have explored whether WREs have enhanced wetland hydrology and wetland plant communities. Additionally, USDA Compatible Use Permits for cattle grazing and other management practices are sometimes issued for WREs, but little is known about potential benefits/detriments of such practice on the success of wetland restoration. In this study, we tested if hydrological restoration of previously drained species poor pastures increased water depth and hydroperiod. Restoration involved plugging key ditches, adding water control structures and a berm. We also tested if hydrological restoration increased plant diversity (alpha and beta), floristic quality (using coefficient of conservatism) and increased the cover of wetland species (using species wetland status). Finally, we tested if cattle grazing had an effect on the success of restoration by comparing grazed plots to fenced plots. We studied two conservation easements (a total of 748 acres) located on semi-native pastures in central Florida, USA. We monitored vegetation using permanent transects stratified by vegetation type before (2004–2005) and after (2012) the restoration (2008). We assessed wetland hydroperiod using groundwater wells set up in 2003 and located within and outside the boundaries of these two easements. We used linear mixed models and multivariate analyses to compare vegetation and hydroperiods pre- and post-restoration. Number of flooded days increased following restoration in one of the easements, but we did not detect significant changes in hydrology in the other easement. Floristic quality, beta diversity and cover of obligate wetland species increased in both conservation easements and in most vegetation types. These vegetation changes were likely due to restoration activities since annual rainfall was not significantly different pre- and post-restoration. Cattle grazing did not have a negative or positive effect on the success of restoration, nor did we detect any positive effect of grazing on the success of restoration. Overall, our study shows that hydrological restoration can enhance wetland hydroperiod, water depth and wetland vegetation, but more resources should be allocated to short- and long-term monitoring of the restoration success. [ABSTRACT FROM AUTHOR]

Abstract: Livestock significantly affect wetland soils and vegetation but their impacts on wetland nutrient dynamics are poorly understood. We set up a full factorial laboratory experiment to assess the effects of Juncus effusus, grazing exclusion, and flooding on P flux from intact cores collected from seasonal wetlands in cattle pastures in south Florida. We collected intact cores from Juncus tussocks and plant interspaces inside and outside 4-year grazing exclosures in five replicate wetlands. We incubated the cores for 50 days under continuous flooding or weekly 1-day flooding cycles and measured P concentrations in surface and pore water. Grazing exclosures had less Juncus (17%) and bare ground (2%) than adjacent grazed areas (Juncus, 48%; bare ground, 12%), but did not affect P fluxes. Initial fluxes of soluble reactive P (SRP) were much higher in cores with Juncus (242±153mgPm−2 day−1) than without Juncus (14±20mgPm−2 day−1). In weekly flooded cores P fluxes fell to 19.7±13.4mgPm−2 day−1 in cores with and 2.7±2.6 in cores without Juncus. The strong effect of Juncus on P flux was an indirect effect of cattle grazing, but 4 years of grazing exclusion did not have a significant effect on P fluxes. [Copyright &y& Elsevier]

Abstract: The 9th biennial meeting of the Soil Ecology Society held in Palm Springs, CA in May 2003, addressed the theme of “Invasive species and soil ecology”. This meeting prompted interest in pursuing this special issue of Applied Soil Ecology, which includes papers presented at the meeting and other papers contributed after the meeting. This paper highlights some of the major issues addressed at the meeting and in the subsequent papers published in this special issue, and also provides a conceptual framework for examining interactions between aboveground and belowground invasions. [Copyright &y& Elsevier]

We compared the biogeochemical cycling of phosphorus (P) in northern hardwood forest plots invaded by exotic earthworms versus adjacent uninvaded reference plots. In three of the six pairs of plots, earthworm invasion resulted in significantly more total P in the upper 12 cm of soil. The finding of increased amounts of unavailable and occluded inorganic P forms in the invaded plots suggests that earthworm activity mobilized unweathered soil particles from deeper layers of the soil, increasing the stocks of total P in surface soils. In two pairs of plots, the earthworm-invaded soils had less total P than the reference soils. In these plots, earthworm activity resulted in augmented rates of P cycling and alteration of the physical structure of the soil that increased loss of P in leaching water, reducing the total amount of P. We hypothesize that the different effects of earthworm invasion on the soil P cycle result from unique characteristics of the ecological groups of earthworms dominating each site. The invaded plots with increased total P were dominated by the anecic species Lumbricus terrestris, a large earthworm that constructs deep, vertical burrows and is effective at moving soil materials from and to deeper layers of the profile. In contrast, the earthworm-invaded plots where the total P in the surface soil decreased were dominated by the epiendogeic species L. rubellus, which feeds and lives in the upper organic layers of the soil. In these plots, earthworms significantly increased the amount of readily exchangeable P in the soil, increasing the loss of this element in leaching water. [ABSTRACT FROM AUTHOR]

Long-term exposure of native vegetation to elevated atmospheric CO2 concentrations is expected to increase C inputs to the soil and, in ecosystems with seasonally dry periods, to increase soil moisture. We tested the hypothesis that these indirect effects of elevated CO2 (600 μl l−1 vs 350 μl l−1) would improve conditions for microbial activity and stimulate emissions of nitrous oxide (N2O), a very potent and long-lived greenhouse gas. After two growing seasons, the mean N2O efflux from monoliths of calcareous grassland maintained at elevated CO2 was twice as high as that measured from monoliths maintained at current ambient CO2 (70 ± 9 vs 37 ± 4 μg N2O m−2 h−1 in October, 27 ± 5 vs 13 ± 3 μg N2O m−2 h−1 in November after aboveground harvest). The higher N2O emission rates at elevated CO2 were associated with increases in soil moisture, soil heterotrophic respiration, and plant biomass production, but appear to be mainly attributable to higher soil moisture. Our results suggest that rising atmospheric CO2 may contribute more to the total greenhouse effect than is currently estimated because of its plant-mediated effects on soil processes which may ultimately lead to increased N2O emissions from native grasslands. [ABSTRACT FROM AUTHOR]

Increasingly, agriculture is recognized as valuable not only for food production, but also for regulating and supporting ecosystem services such as those encompassing biodiversity and water. Various government programs provide incentives to farmers and ranchers to maintain ecosystem services, with an emerging focus on payment‐for‐ecosystem services (PES) programs. However, interactions among ecosystem services, including synergies or trade‐offs, at spatial scales relevant to land managers are not well understood. Here, we examined how a PES program for enhanced water retention on subtropical ranchlands in the headwaters of the Everglades affected seven indicators of ecosystem services and three indicators of disservices within wetlands (local scale) and among wetlands (wetland scale) at four different ranches. We used general linear mixed models and model selection to evaluate the feasibility of explicit, a priori hypotheses using data from 15 wetlands sampled across four participating ranches. Our study indicated that managing for increased water retention could result in both synergies and trade‐offs among ecosystem services. Higher water retention increased wetland plants at both local and wetland scales and was associated with reduced mosquitoes. Trade‐offs included significant declines in forage plant cover and decreases in amphibian abundance with higher water retention. Unimodal non‐linear relationships described responses of macroinvertebrates, fish, mosquito, and non‐native plant abundance to increasing water retention. These complex relationships indicate that optimizing water retention, provisioning services, and wetland biodiversity in ranchlands may not be straightforward. Unimodal non‐linear relationships among water retention and biodiversity suggest there is a threshold of water retention that represents a trade‐off for also maintaining biodiversity. Land use was an important driver of ecosystem disservices, with more intensely managed ranches having a greater potential for ecosystem disservices such as increased cover of non‐native plants, abundant mosquitoes, and lower amphibian abundance. Multidisciplinary collaboration was required to design, implement, monitor, and assess this PES program for trade‐offs and synergies. [ABSTRACT FROM AUTHOR]

Recent studies have reported that earthworm invasions alter native communities and impact nutrient cycling in terrestrial ecosystems. We developed a simulation model to evaluate the potential impacts of earthworm invasions on carbon dynamics, taking into consideration earthworm feeding strategies and priming effects on the microorganisms through their casting activities. Responses of carbon stocks (forest litter, soil organic matter, microbial biomass and earthworm populations) and carbon fluxes (litter decomposition, earthworm consumption, and microbial respiration) were used to evaluate an earthworm invasion of a forest ecosystem. Data from a northern temperate forest (Arnot Forest, New York) were adapted for model calibration and evaluation. Simulation results suggest that the impact and outcome of earthworm invasions are affected by pre-invasion resource availability (litter and soil organic matter), invasive earthworm assemblages (particularly feeding strategy), and invasion history (associated with earthworm population dynamics). The abovementioned factors may also determine invasion progress of earthworm species. The accuracy of the model could be improved by the addition of environmental modules (e.g., soil water regimes), precise parameters accounting for individual species attributes under different environmental conditions (e.g. utilization ability of different types of food resources), as well as earthworm population dynamics (size and structure) and interactions with predators and other invasive/indigenous species during the invasion progress. Such an earthworm invasion model could provide valuable evaluation of the complicated responses of carbon dynamics to earthworm invasions in a range of forest ecosystems, particularly under global change scenarios. [Copyright &y& Elsevier]

Long-term exposure of native vegetation to elevated atmospheric CO 2 concentrations is expected to increase C inputs to the soil and, in ecosystems with seasonally dry periods, to increase soil moisture. We tested the hypothesis that these indirect effects of elevated CO 2 (600 μl l -1 vs 350 μl l -1 ) would improve conditions for microbial activity and stimulate emissions of nitrous oxide (N 2 O), a very potent and long-lived greenhouse gas. After two growing seasons, the mean N 2 O efflux from monoliths of calcareous grassland maintained at elevated CO 2 was twice as high as that measured from monoliths maintained at current ambient CO 2 (70 ± 9 vs 37 ± 4 μg N 2 O m -2  h -1 in October, 27 ± 5 vs 13 ± 3 μg N 2 O m -2  h -1 in November after aboveground harvest). The higher N 2 O emission rates at elevated CO 2 were associated with increases in soil moisture, soil heterotrophic respiration, and plant biomass production, but appear to be mainly attributable to higher soil moisture. Our results suggest that rising atmospheric CO 2 may contribute more to the total greenhouse effect than is currently estimated because of its plant-mediated effects on soil processes which may ultimately lead to increased N 2 O emissions from native grasslands.