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At least 163 records · Page 9Linked to original sources

USGS2015

Quantifying water requirements of riparian river red gum ( Eucalyptus camaldulensis ) in the Murray-Darling Basin, Australia: Implications for the management of environmental flows

Water resource development and drought have altered river flow regimes, increasing average flood return intervals across floodplains in the Murray-Darling Basin, Australia, causing health declines in riparian river red gum ( Eucalyptus camaldulensis ) forests and woodlands. Environmental flow allocations helped to alleviate water stress during the recent Millennium Drought (1997–2010), however, quantification of the flood frequency required to support healthy E. camaldulensis communities is still needed. We quantified water requirements of E. camaldulensis for two years across a flood gradient (trees inundated at frequencies of 1:2, 1:5 and 1:10 years) at Yanga National Park, New South Wales to help inform management decision-making and design of environmental flows. Sap flow, evaporative losses and soil moisture measurements were used to determine transpiration, evapotranspiration and plant-available soil water before and after flooding. A formula was developed using plant-available soil water post-flooding and average annual rainfall, to estimate maintenance time of soil water reserves in each flood frequency zone. Results indicated that soil water reserves could sustain 1:2 and 1:5 trees for 15 months and six years, respectively. Trees regulated their transpiration rates, allowing them to persist within their flood frequency zone, and showed reduction in active sapwood area and transpiration rates when flood frequencies exceeded 1:2 years. A leaf area index of 0.5 was identified as a potential threshold indicator of severe drought stress. Our results suggest environmental water managers may have greater flexibility to adaptively manage floodplains in order to sustain E. camaldulensis forests and woodlands than has been appreciated hitherto.

New South Wales↗

USGS2012

Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15 N tracer field studies

Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15 N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15 N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15 N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (<1 week after 15 N tracer application), total ecosystem 15 N recovery was negatively correlated with fine-root and soil 15 N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3–18 months after 15 N tracer application), total ecosystem 15 N retention was negatively correlated with foliar natural-abundance 15 N but was positively correlated with mineral soil C and N concentration and C: N, showing that plant and soil natural-abundance 15 N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15 N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15 N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15 N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N·ha -1 ·yr -1 above which most ecosystems showed net losses of applied 15 N tracer in response to N fertilizer addition.

Ecology↗

USGS1994

Degradation of trifluoroacetate in oxic and anoxic sediments

THE deleterious effect of chlorofluorocarbons on stratospheric ozone has led to international cooperation to end their use. The search for acceptable alternatives has focused on hydrofluorocarbons (HFCs) or hydrochlorofluorocarbons (HCFCs) which are attractive because they have relatively short atmospheric residence times. HFCs and HCFCs are attacked by tropospheric hydroxyl radicals, leading to the formation of trifluoroacetate (TFA). Most of the atmospheric TFA is deposited at the Earth's surface, where it is thought to be highly resistant to bacterial attack. Therefore, use of HCFCs and HFCs may lead to accumulation of TFA in soils, where it could prove toxic or inhibitory to plants and soil microbial communities. Although little is known about the toxicity of TFA, monofluoroacetate, which occurs at low levels in some plants and which is susceptible to slow attack by aerobic soil microbes, is known to be acutely toxic. Here we report that TFA can be rapidly degraded microbially under anoxic and oxic conditions. These results imply that significant microbial sinks exist in nature for the elimination of TFA from the environment. We also show that oxic degradation of TFA leads to the formation of fluoroform, a potential ozone-depleting compound with a much longer atmospheric lifetime than the parent compounds.The deleterious effect of chlorofluorcarbons on stratospheric ozone has led to international cooperation to end their use. The search for acceptable alternatives has focused on hydroflnorocarbons (HFCs) or hydrochloroflnorcarbons (HCFs) which are attractive because they have relatively short atmospheric residence times. HFCs and HCFs are attacked by tropospheric hydroxyl radicals, leading to the formation of trifluoroacetate (TFA). Most of the atmospheric TFA is deposited at the Earth's surface, where it is thought to be highly resistant to bacterial attack. Therefore, use of HCFs and HCFs may lead to accummulation of TFA in soils, where it could prove toxic or inhibitory to plants and soil microbial communities. Although little is known about the toxicity of TFA, monofluoracetate, which occurs at low levels in some plants and which is susceptible to slow attack by aerobic soil microbes, is known to be acutely toxic. Here we report that TFA can be rapidly degraded microbially under anoxic and oxic conditions. These results imply that significant microbial sinks exist in nature for the elimination of TFA from the environment. We also show that oxic degradation of TFA leads to the formation of fluoroform, a potential ozone-depleting compound with a much longer atmospheric lifetime than the parent compounds.

Nature↗

USGS2015

Nutrient-enhanced decomposition of plant biomass in a freshwater wetland

We studied soil decomposition in a Panicum hemitomon (Schultes)-dominated freshwater marsh located in southeastern Louisiana that was unambiguously changed by secondarily-treated municipal wastewater effluent. We used four approaches to evaluate how belowground biomass decomposition rates vary under different nutrient regimes in this marsh. The results of laboratory experiments demonstrated how nutrient enrichment enhanced the loss of soil or plant organic matter by 50%, and increased gas production. An experiment demonstrated that nitrogen, not phosphorus, limited decomposition. Cellulose decomposition at the field site was higher in the flowfield of the introduced secondarily treated sewage water, and the quality of the substrate (% N or % P) was directly related to the decomposition rates. We therefore rejected the null hypothesis that nutrient enrichment had no effect on the decomposition rates of these organic soils. In response to nutrient enrichment, plants respond through biomechanical or structural adaptations that alter the labile characteristics of plant tissue. These adaptations eventually change litter type and quality (where the marsh survives) as the % N content of plant tissue rises and is followed by even higher decomposition rates of the litter produced, creating a positive feedback loop. Marsh fragmentation will increase as a result. The assumptions and conditions underlying the use of unconstrained wastewater flow within natural wetlands, rather than controlled treatment within the confines of constructed wetlands, are revealed in the loss of previously sequestered carbon, habitat, public use, and other societal benefits.

Louisiana↗

USGS2022

Water-budget accounting for tropical regions model (WATRMod) documentation

Regional groundwater recharge commonly is estimated using a threshold-type water-budget approach in which groundwater recharge is assumed to occur when water in the plant-root zone exceeds the soil’s moisture storage capacity. A water budget of the plant-soil system accounts for water inputs (rainfall, fog interception, irrigation, septic-system leachate, and other inputs), water outputs (runoff, evaporation, transpiration, and recharge), and changes in stored water during a specified time interval. Water budgets can be computed on any desired interval, including annual, monthly, daily, and subdaily intervals. In general, uncertainty in recharge estimates is expected to be lower using daily or subdaily intervals relative to monthly and annual intervals. Average recharge rates computed over a period of a year or multiple years are commonly determined from water budgets computed using a daily computation interval capable of capturing rainfall and land-cover changes during the period. This report documents the Water-budget Accounting for Tropical Regions Model, or WATRMod, code that can be used to estimate spatially variable, daily water-budget components in tropical-island and other appropriate settings. The purpose of this report is to provide descriptions of WATRMod’s (1) approach to computing a daily water budget, (2) represented processes, (3) limitations, and (4) execution procedure, input requirements, output files, and example files. The model computes a daily water budget for each hydrologically independent subarea within the overall study area. A subarea is defined by its climatic, soil, land-cover, and human-related (for example, adding irrigation or other water) characteristics. The water-budget model can represent processes including rainfall, fog interception, irrigation, septic-system leachate, direct recharge that bypasses the plant-soil system, runoff, canopy evaporation in forested areas, evapotranspiration, and groundwater recharge. The water-budget model can represent either one of the following different accounting orders: (1) accounting for loss of water by evapotranspiration before accounting for recharge, and (2) accounting for recharge before accounting for evapotranspiration. WATRMod’s limitations include: (1) uncharacterized, subdaily transient changes in water inputs and outputs from the plant-soil system, (2) unrepresented precipitation in the form of snow and sublimation, and (3) routing runoff from one subarea to an adjacent subarea that is not directly represented.

Hawaii↗

USGS2016

Nitrogen enrichment regulates calcium sources in forests

Nitrogen (N) is a key nutrient that shapes cycles of other essential elements in forests, including calcium (Ca). When N availability exceeds ecosystem demands, excess N can stimulate Ca leaching and deplete Ca from soils. Over the long term, these processes may alter the proportion of available Ca that is derived from atmospheric deposition vs. bedrock weathering, which has fundamental consequences for ecosystem properties and nutrient supply. We evaluated how landscape variation in soil N, reflecting long-term legacies of biological N fixation, influenced plant and soil Ca availability and ecosystem Ca sources across 22 temperate forests in Oregon. We also examined interactions between soil N and bedrock Ca using soil N gradients on contrasting basaltic vs. sedimentary bedrock that differed 17-fold in underlying Ca content. We found that low-N forests on Ca-rich basaltic bedrock relied strongly on Ca from weathering, but that soil N enrichment depleted readily weatherable mineral Ca and shifted forest reliance toward atmospheric Ca. Forests on Ca-poor sedimentary bedrock relied more consistently on atmospheric Ca across all levels of soil N enrichment. The broad importance of atmospheric Ca was unexpected given active regional uplift and erosion that are thought to rejuvenate weathering supply of soil minerals. Despite different Ca sources to forests on basaltic vs. sedimentary bedrock, we observed consistent declines in plant and soil Ca availability with increasing N, regardless of the Ca content of underlying bedrock. Thus, traditional measures of Ca availability in foliage and soil exchangeable pools may poorly reflect long-term Ca sources that sustain soil fertility. We conclude that long-term soil N enrichment can deplete available Ca and cause forests to rely increasingly on Ca from atmospheric deposition, which may limit ecosystem Ca supply in an increasingly N-rich world.

Global Change Biology↗

USGS2007

Assessing exotic plant species invasions and associated soil characteristics: A case study in eastern Rocky Mountain National Park, Colorado, USA, using the pixel nested plot design

Rocky Mountain National Park (RMNP), Colorado, USA, contains a diversity of plant species. However, many exotic plant species have become established, potentially impacting the structure and function of native plant communities. Our goal was to quantify patterns of exotic plant species in relation to native plant species, soil characteristics, and other abiotic factors that may indicate or predict their establishment and success. Our research approach for field data collection was based on a field plot design called the pixel nested plot. The pixel nested plot provides a link to multi-phase and multi-scale spatial modeling-mapping techniques that can be used to estimate total species richness and patterns of plant diversity at finer landscape scales. Within the eastern region of RMNP, in an area of approximately 35,000 ha, we established a total of 60 pixel nested plots in 9 vegetation types. We used canonical correspondence analysis (CCA) and multiple linear regressions to quantify relationships between soil characteristics and native and exotic plant species richness and cover. We also used linear correlation, spatial autocorrelation and cross correlation statistics to test for the spatial patterns of variables of interest. CCA showed that exotic species were significantly (P < 0.05) associated with photosynthetically active radiation (r = 0.55), soil nitrogen (r = 0.58) and bare ground (r = -0.66). Pearson's correlation statistic showed significant linear relationships between exotic species, organic carbon, soil nitrogen, and bare ground. While spatial autocorrelations indicated that our 60 pixel nested plots were spatially independent, the cross correlation statistics indicated that exotic plant species were spatially associated with bare ground, in general, exotic plant species were most abundant in areas of high native species richness. This indicates that resource managers should focus on the protection of relatively rare native rich sites with little canopy cover, and fertile soils. Using the pixel nested plot approach for data collection can facilitate the ecological monitoring of these vulnerable areas at the landscape scale in a time- and cost-effective manner. ?? 2006 Elsevier B.V. All rights reserved.

Applied Soil Ecology↗

USGS2015

Long-term plant responses to climate are moderated by biophysical attributes in a North American desert

Recent elevated temperatures and prolonged droughts in many already water-limited regions throughout the world, including the southwestern U.S., are likely to intensify according to future climate-model projections. This warming and drying can negatively affect perennial vegetation and lead to the degradation of ecosystem properties. To better understand these detrimental effects, we formulate a conceptual model of dryland ecosystem vulnerability to climate change that integrates hypotheses on how plant species will respond to increases in temperature and drought, including how plant responses to climate are modified by landscape, soil, and plant attributes that are integral to water availability and use. We test the model through a synthesis of fifty years of repeat measurements of perennial plant species cover in large permanent plots across the Mojave Desert, one of the most water-limited ecosystems in North America. Plant species ranged in their sensitivity to precipitation in different seasons, capacity to increase in cover with high precipitation, and resistance to decrease in cover with low precipitation. Our model successfully explains how plant responses to climate are modified by biophysical attributes in the Mojave Desert. For example, deep-rooted plants were not as vulnerable to drought on soils that allowed for deep water percolation, whereas shallow-rooted plants were better buffered from drought on soils that promoted water retention near the surface. Synthesis. Our results emphasize the importance of understanding climate-vegetation relationships in the context of biophysical attributes that influence water availability and provide an important forecast of climate-change effects, including plant mortality and land degradation in dryland regions throughout the world.

California, Nevada↗

USGS2011

Carbon gas fluxes in re-established wetlands on organic soils differ relative to plant community and hydrology

We measured CO 2 and CH 4 fluxes for 6 years following permanent flooding of an agriculturally managed organic soil at two water depths (~25 and ~55 cm standing water) in the Sacramento–San Joaquin Delta, California, as part of research studying C dynamics in re-established wetlands. Flooding rapidly reduced gaseous C losses, and radiocarbon data showed that this, in part, was due to reduced oxidation of "old" C preserved in the organic soils. Both CO 2 and CH 4 emissions from the water surface increased during the first few growing seasons, concomitant with emergent marsh establishment, and thereafter appeared to stabilize according to plant communities. Areas of emergent marsh vegetation in the shallower wetland had greater net CO 2 influx (-485 mg Cm -1 h -1 ), and lower CH 4 emissions (11.5 mg Cm -2 h -1 ), than in the deeper wetland (-381 and 14.1 mg Cm -2 h -1 , respectively). Areas with submerged and floating vegetation in the deeper wetland had CH 4 emissions similar to emergent vegetation (11.9 and 12.6 mg Cm -2 h -1 , respectively), despite lower net CO 2 influx (-102 gC m -2 h -1 ). Measurements of plant moderated net CO 2 influx and CH 4 efflux indicated greatest potential reduction of greenhouse gases in the more shallowly flooded wetland.

California↗

USGS2019

Soil texture and precipitation seasonality influence plant community structure in North American temperate shrub steppe

In drylands, the coexistence of grasses and woody plants has been attributed to soil‐water resource partitioning. Soil texture and precipitation seasonality can influence the amount and distribution of water in the soil, and their interaction may play an important role in determining the relative importance of grasses and woody plants. We investigated the influence of this interaction on plant functional types across a broad range of precipitation regimes and soil textures in western North America by analyzing plant‐cover data collected at 2,084 plots that included the widespread shrub big sagebrush ( Artemisia tridentata Nutt.). We characterized how the significance of the inverse‐texture effect varies across soil conditions by quantifying relationships between precipitation and foliar cover on finer‐ vs. coarser‐textured soils across a range of potential texture divisions represented by sand content. We found evidence of the inverse‐texture effect for every plant functional type (except for cheatgrass) that we examined with at least one component of precipitation (annual, warm, or cold season), and provide the first evidence for this effect in locations with cold‐season‐dominated precipitation regimes. The texture and precipitation combinations that exhibited the inverse‐texture effect varied with plant functional type, presumably because of effects of soil texture on water availability at different soil depths with season. Furthermore, we found an inverse‐texture effect that was remarkably similar for shrub cover with cold‐season precipitation and grass cover with warm‐season precipitation. These results provide new insight into how the inverse‐texture effect interacts with precipitation seasonality to influence plant functional type composition in drylands, and further suggest that quantifying the soil‐texture division at which the inverse‐texture effect is relevant under a given set of environmental conditions may provide support for the effect across dryland plant communities.

Arizona, California, Colorado, Idaho, Montana, New↗

USGS2020

Components and predictors of biological soil crusts vary at the regional vs. plant community scales

Although biological soil crusts (biocrusts) occur globally in arid and semi-arid environments, most of our knowledge of biocrust cover and ecology is from a relatively small number of locations worldwide. Some plant communities are known to have high cover of biocrusts, but the abundance of biocrusts is largely undocumented in most plant communities. Using a data driven approach, we identified 16 plant communities based on plant cover from the Assessment, Inventory, and Monitoring Strategy data from the Bureau of Land Management (AIM, 5,200 plots). We found that abundance of lichens and mosses varies among communities, but that both components of biocrusts are present in all plant communities. Biocrusts are indicators of two of these communities: one that is defined by high cover of mosses and basin big sagebrush and one that is defined by high cover of lichens and shadscale saltbush. Using non-parametric multiplicative regression, we evaluated a suite of abiotic and disturbance variables to assess the degree to which climate and soils are associated with the abundance of lichens and mosses at the regional scale. At the regional scale, soil depth and maximum vapor pressure deficit were found to be strongly associated with the abundance of lichens and January minimum temperature dictated the abundance of mosses. At the scale of plant communities, community specific metrics of soils and climate were better able to explain the abundance of biocrusts. Our demonstration of the presence of biocrusts across the western US suggests that studies on ecosystem function could include these organisms because they are present in all plant communities, maintain arguably stronger associations with climatic variation, are directly associated with soils, and contribute to ecosystem functions that are not solely maintained by vascular plants.

Frontiers in Ecology and Evolution↗

USGS2020

How plants influence resilience of salt marsh and mangrove wetlands to sea-level rise

This review evaluates the importance of plants and associated biological processes in determining the vulnerability of coastal wetlands to sea-level rise. Coastal wetlands occur across a broad sedimentary continuum from minerogenic to biogenic, providing an opportunity to examine the relative importance of biological processes in wetland resilience to sea-level rise. We explore how plants influence sediment accretion, elevation capital (vertical position in the tidal frame), and compaction or erosion of deposited material. We focus on salt marsh and mangrove wetlands, which occupy a similar physiographic niche and display similar physical and biological controls on resilience to sea-level rise. In both habitats, plants stabilize emergent mudflats and help sustain the wetland position in the tidal frame relative to ocean height through both surface and subsurface process controls on soil elevation. Plants influence soil elevations by modifying (1) mineral sediment deposition and retention, (2) organic matter contributions to soil volume, and (3) resistance to compaction and erosion. Recognition of the importance of plants in coastal wetland resilience to sea-level rise is key to accurate predictions about the future fate of salt marshes and mangrove forests and for development of effective management and restoration plans.

Estuaries and Coasts↗

USGS1989

Copper deficiency in Tule Elk at Point Reyes, California

Tule elk ( Cervus elaphus nannodes ) reintroduced to Point Reyes, Calif., in 1978 exhibited gross signs of copper deficiency by June 1979. Copper levels in liver (x=5.9 ppm) and serum (0.42 ppm) of elk in Point Reyes were below levels in adult tule elk from other locations in California (liver, x=80 ppm; serum, x=1.4 ppm). These levels were consistent with documented copper deficiencies in wild and domestic ruminants. Copper serum levels increased in response to copper enriched dietary supplements and declined after the elk stopped eating the supplements. Analysis of plant and soil samples showed both are deficient in copper and normal in molybdenum and sulfur-sulfates. Deficiency in plants and soils at Point Reyes are probably due to low copper levels in the underlying granitic parent material.

California↗

USGS2015

A framework to assess biogeochemical response to ecosystem disturbance using nutrient partitioning ratios

Disturbances affect almost all terrestrial ecosystems, but it has been difficult to identify general principles regarding these influences. To improve our understanding of the long-term consequences of disturbance on terrestrial ecosystems, we present a conceptual framework that analyzes disturbances by their biogeochemical impacts. We posit that the ratio of soil and plant nutrient stocks in mature ecosystems represents a characteristic site property. Focusing on nitrogen (N), we hypothesize that this partitioning ratio (soil N: plant N) will undergo a predictable trajectory after disturbance. We investigate the nature of this partitioning ratio with three approaches: (1) nutrient stock data from forested ecosystems in North America, (2) a process-based ecosystem model, and (3) conceptual shifts in site nutrient availability with altered disturbance frequency. Partitioning ratios could be applied to a variety of ecosystems and successional states, allowing for improved temporal scaling of disturbance events. The generally short-term empirical evidence for recovery trajectories of nutrient stocks and partitioning ratios suggests two areas for future research. First, we need to recognize and quantify how disturbance effects can be accreting or depleting, depending on whether their net effect is to increase or decrease ecosystem nutrient stocks. Second, we need to test how altered disturbance frequencies from the present state may be constructive or destructive in their effects on biogeochemical cycling and nutrient availability. Long-term studies, with repeated sampling of soils and vegetation, will be essential in further developing this framework of biogeochemical response to disturbance.

Ecosystems↗

USGS2021

Behaviorally-mediated trophic cascade attenuated by prey use of risky places at safe times

The mere threat of predation may incite behavioral changes in prey that lead to community-wide impacts on productivity, biodiversity, and nutrient cycling. The paucity of experimental manipulations, however, has contributed to controversy over the strength of this pathway in wide-ranging vertebrate systems. We investigated whether simulated gray wolf ( Canis lupus ) presence can induce behaviorally-mediated trophic cascades, specifically, whether the ‘fear’ of wolf olfactory cues alone can change deer foraging behavior in ways that affect plants and soils. Wolves were recently removed from the Cedar Creek Ecosystem Science Reserve (Minnesota, USA), such that consumptively mediated predator effects were negligible. At 32 experimental plots, we crossed two nested treatments: wolf urine application and herbivore exclosures. We deployed camera traps to quantify how white-tailed deer ( Odocoileus virginianus ) adjusted their spatiotemporal habitat use, foraging, and vigilance in response to wolf cues and how these behavioral changes affected plant productivity, plant communities, and soil nutrients. Weekly applications of wolf urine significantly altered deer behavior, but deer responses did not cascade to affect plant or soil properties. Deer substantially reduced crepuscular activity at wolf-simulated sites compared to control locations. As wolves in this area predominantly hunted during mornings and evenings, this response potentially allows deer to maximize landscape use by accessing dangerous areas when temporal threat is low. Our experiment suggests that prey may be sensitive to ‘dynamic’ predation risk that is structured across both space and time and, consequentially, prey use of risky areas during safe times may attenuate behaviorally-mediated trophic cascades at the predator–prey interface.

Minnesota↗

USGS2001

Soil N and 15N variation with time in a California annual grassland ecosystem

The %N and ??15N values of soils and plants were measured along a chronosequence spanning 3 to 3000 Ky in a California annual grassland. Total soil N decreased with increasing soil age (1.1 to 0.4 kg N m-2) while the mean ?? 15N values of the soil N increased by several ??? from the youngest to oldest sites (+3.5 to +6.2 ???). The ?? 15N values of plants varied along the gradient, reflecting changing soil N pools and differences in the form of N uptake. The decline in total N storage with time is hypothesized to be due to a shift from N to P limitation with increasing soil age. The general increase in ?? 15N values with time is interpreted using a N mass balance model, and appears to reflect a shift toward an increasing proportional losses of inorganic mineral forms of N (vs. organic forms) with increasing soil age. We develop a quantitative index of this trend (mineral vs. organic forms of N loss) using mass balance considerations and parameters. The %N and ?? 15N values along the California age gradient were compared to the published data for a comparably aged chronosequence in Hawaii. Most striking in this comparison is the observation that the California soil and plant ?? 15N values are several ??? greater than those on comparably aged Hawaiian sites. Multiple explanations are plausible, but assuming the sites have a similar range in ?? 15N values of atmospheric inputs, the isotopic differences suggest that N may be, at least seasonally, in greater excess in the strongly seasonal, semi-arid, California grassland. Copyright ?? 2001 Elsevier Science Ltd.

Geochimica et Cosmochimica Acta↗

USGS2023

Livestock removal increases plant cover across a heterogeneous dryland landscape on the Colorado Plateau

Livestock removal is increasingly used as a management option to mitigate the negative impacts of grazing-related disturbances on rangelands. Removal generally increases plant cover, but it is unclear when, where, and by how much plant and soil cover changes can be expected. On the Colorado Plateau, complex geology, topography, soils, and climate all interact to mediate the relationship between land cover, climate, and disturbance. In this study we used new developments in land cover mapping and analysis to assess landscape plant and bare soil cover up to 30 years after livestock removal from two grazing allotments in Capitol Reef National Park, Utah, USA. Results indicate that livestock removal increases plant cover 0.17-0.32% per year and reduces bare soil cover 0.34-0.41% per year, although these rates may be suppressed by warming temperatures. Soils, assessed through Soil Geomorphic Units, played a strong but complex role in mediating land cover changes through time. These results suggest that livestock removal is an effective strategy for increasing plant cover and reducing bare soil on the Colorado Plateau, but including soil information in decision making will enhance efficiency by improving manager's ability to prioritize management actions effectively across space and through time.

Environmental Research Letters↗

USGS2023

Symbiotic nitrogen fixation does not stimulate soil phosphatase activity under temperate and tropical trees

Symbiotic nitrogen (N)-fixing plants can enrich ecosystems with N, which can alter the cycling and demand for other nutrients. Researchers have hypothesized that fixed N could be used by plants and soil microbes to produce extracellular phosphatase enzymes, which release P from organic matter. Consistent with this speculation, the presence of N-fixing plants is often associated with high phosphatase activity, either in the soil or on root surfaces, although other studies have not found this association, and the connection between phosphatase and rates of N fixation—the mechanistic part of the argument—is tenuous. Here, we measured soil phosphatase activity under N-fixing trees and non-fixing trees transplanted and grown in tropical and temperate sites in the USA: two sites in Hawaii, and one each in New York and Oregon. This provides a rare example of phosphatase activity measured in a multi-site field experiment with rigorously quantified rates of N fixation. We found no difference in soil phosphatase activity under N-fixing vs. non-fixing trees nor across rates of N fixation, though we note that no sites were P limited and only one was N limited. Our results add to the literature showing no connection between N fixation rates and phosphatase activity.

Oecologia↗