Vegetation and soil recovery in wilderness campsites closed to visitor use

Recreational use of wilderness results in impacts to vegetation and soil in trails and campsites. Traditionally, campsite impact studies have compared campsites receiving various levels of use with unused control areas. Field studies in Sequoia National Park, California, indicate that the degree of impact to vegetation and soils also varies within campsites. The central areas of campsites, where trampling is concentrated, show lower plant species diversity, differences in relative species cover, more highly compacted soils, and lower soil nutrient concentrations than do peripheral, moderately trampled, and untrampled areas within the same campsite. Three years after closure to visitor use, the central areas show less increase in mean foliar plant cover, and soils remain more highly compacted than in previously moderately trampled areas of the same sites. Changes in relative species cover over time are used to assess both resiliency to trampling and species composition recovery within campsites closed to visitor use.     

Limits to Understory Plant Restoration Following Fuel-Reduction Treatments in a Piñon–Juniper Woodland

National fuel-reduction programs aim to reduce the risk of wildland fires to human communities and to restore forest and rangeland ecosystems to resemble their historical structure, function, and diversity. There are a number of factors, such as seed bank dynamics, post-treatment climate, and herbivory, which determine whether this latter goal may be achieved. Here, we examine the short-term (2 years) vegetation response to fuel-reduction treatments (mechanical mastication, broadcast burn, and pile burn) and seeding of native grasses on understory vegetation in an upland piñon–juniper woodland in southeast Utah. We also examine how wildlife herbivory affects the success of fuel-reduction treatments. Herbaceous cover increased in response to fuel-reduction treatments in all seeded treatments, with the broadcast burn and mastication having greater increases (234 and 160 %, respectively) in herbaceous cover than the pile burn (32 %). In the absence of seeding, herbaceous cover only increased in the broadcast burn (32 %). Notably, fuel-reduction treatments, but not seeding, strongly affected herbaceous plant composition. All fuel-reduction treatments increased the relative density of invasive species, especially in the broadcast burn, which shifted the plant community composition from one dominated by perennial graminoids to one dominated by annual forbs. Herbivory by wildlife reduced understory plant cover by over 40 % and altered plant community composition. If the primary management goal is to enhance understory cover while promoting native species abundance, our study suggests that mastication may be the most effective treatment strategy in these upland piñon–juniper woodlands. Seed applications and wildlife exclosures further enhanced herbaceous cover following fuel-reduction treatments.     

Assessing Degradation of Abandoned Farmlands for Conservation of the Monte Desert Biome in Argentina

Land abandonment is a major issue worldwide. In Argentina, the Monte Desert is the most arid rangeland, where the traditional conservation practices are based on successional management of areas excluded to disturbances or abandoned. Some areas subjected to this kind of management may be too degraded, and thus require active restoration. Therefore, the aim of this study was to assess whether passive succession-based management is a suitable approach by evaluating the status of land degradation in a protected area after 17–41 years of farming abandonment. Soil traits and plant growth forms were quantified and compared between sites according to time since abandonment and former land use (cultivation and grazing). Two variables were calculated using the CORINE-CEC method, i.e., potential (PSER) and actual (ASER) soil erosion risk. PSER indicates the erosion risk when no vegetation is present, while ASER includes the protective role of vegetation cover. Results showed that land use history had no significant effect on plant growth forms or soil traits (p > 0.05). After more than 25 years since abandonment of farming activities, soil conditions and vegetation cover had improved, thus having a lower ASER. Nevertheless, the present soil physical crusts may have delayed the full development of vegetation, enhancing erosion processes. Overall, this study indicates that succession-based management may not be the best practice in terms of conservation. Therefore, any effort for conservation in the Monte Desert should contemplate the current status of land degradation and potential vegetation recovery.     

Soil, Vegetation, and Seed Bank of a Sonoran Desert Ecosystem Along an Exotic Plant (Pennisetum ciliare) Treatment Gradient

Ecological conditions following removal of exotic plants are a key part of comprehensive environmental management strategies to combat exotic plant invasions. We examined ecological conditions following removal of the management-priority buffelgrass (Pennisetum ciliare) in Saguaro National Park of the North American Sonoran Desert. We assessed soil, vegetation, and soil seed banks on seven buffelgrass site types: five different frequencies of buffelgrass herbicide plus hand removal treatments (ranging from 5 years of annual treatment to a single year of treatment), untreated sites, and non-invaded sites, with three replicates for each of the seven site types. The 22 measured soil properties (e.g., pH) differed little among sites. Regarding vegetation, buffelgrass cover was low (≤1 % median cover), or absent, across all treated sites but was high (10–70 %) in untreated sites. Native vegetation cover, diversity, and composition were indistinguishable across site types. Species composition was dominated by native species (>93 % relative cover) across all sites except untreated buffelgrass sites. Most (38 species, 93 %) of the 41 species detected in soil seed banks were native, and native seed density did not differ significantly across sites. Results suggest that: (1) buffelgrass cover was minimal across treated sites; (2) aside from high buffelgrass cover in untreated sites, ecological conditions were largely indistinguishable across sites; (3) soil seed banks harbored ≥12 species that were frequent in the aboveground vegetation; and (4) native species dominated post-treatment vegetation composition, and removing buffelgrass did not result in replacement by other exotic species.     

Restoration of Mountain Big Sagebrush Steppe Following Prescribed Burning to Control Western Juniper

Western juniper (Juniperus occidentalis ssp. occidentalis Hook) encroachment into mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) steppe has reduced livestock forage production, increased erosion risk, and degraded sagebrush-associated wildlife habitat. Western juniper has been successfully controlled with partial cutting followed by prescribed burning the next fall, but the herbaceous understory and sagebrush may be slow to recover. We evaluated the effectiveness of seeding perennial herbaceous vegetation and sagebrush at five sites where juniper was controlled by partially cutting and prescribed burning. Treatments tested at each site included an unseeded control, herbaceous seed mix (aerially seeded), and the herbaceous seed mix plus sagebrush seed. In the third year post-treatment, perennial grass cover and density were twice as high in plots receiving the herbaceous seed mix compared to the control plots. Sagebrush cover and density in the sagebrush seeded plots were between 74- and 290-fold and 62- and 155-fold greater than the other treatments. By the third year after treatment, sagebrush cover was as high as 12 % in the sagebrush seeded plots and between 0 % and 0.4 % where it was not seeded. These results indicate that aerial seeding perennial herbaceous vegetation can accelerate the recovery of perennial grasses which likely stabilize the site. Our results also suggest that seeding mountain big sagebrush after prescribed burning encroaching juniper can rapidly recover sagebrush cover and density. In areas where sagebrush habitat is limited, seeding sagebrush after juniper control may increase sagebrush habitat and decrease the risks to sagebrush-associated species.     

Effects of Long-Term Trampling on the Above-Ground Forest Vegetation and Soil Seed Bank at the Base of Limestone Cliffs

Exposed limestone cliffs in central Europe harbor a highly divers flora with many rare and endangered species. During the past few decades, there has been increasing recreational use of these cliffs, which has caused local environmental disturbances. Successful restoration strategies hinge on identifying critical limitations. We examined the composition of aboveground forest vegetation and density and species composition of seeds in the soil seed bank at the base of four limestone cliffs in mixed deciduous forests that are intensively disturbed by human trampling and at four undisturbed cliffs in the Jura Mountains in northwestern Switzerland. We found that long-term human trampling reduced total aboveground vegetation cover at the base of cliffs and caused a significant shift in the plant-species composition. Compared with undisturbed cliffs, total seed density was lower in disturbed cliffs. Human trampling also altered the species composition of seeds in the soil seed bank. Seeds of unintentionally introduced, stress-tolerant, and ruderal species dominated the soil seed bank at the base of disturbed cliffs. Our findings indicate that a restoration of degraded cliff bases from the existing soil seed bank would result in a substantial change of the original unique plant composition. Active seed transfer, or seed flux from adjacent undisturbed forest areas, is essential for restoration success.     

Recreational impacts on backcountry campsites in Grand Canyon National Park,Arizona, USA

Backcountry campsites were studied in three desert vegetation types (pinyon-juniper, catclaw, and desert scrub) in Grand Canyon National Park, Arizona. Relationships between amount of use and amount of impact were examined within each vegetation type. The area disturbed was small, but impacts were generally severe. Important impacts were increased soil compaction and associated decreases in infiltration rates and soil moisture content; these were substantially more pronounced on high than low use sites. The only impact parameter that differed significantly between vegetation types was core area. The types of impact identified are similar to those found in the coniferous forests studied elsewhere, as is the logarithmic relationship between amount of use and amount of impact. However, Grand Canyon sites can support more visitor use before reaching near-maximum levels of impact for important impact parameters.     

Native Grasses as a Management Alternative on Vegetated Closure Caps

Capped waste sites often are vegetated with commercial turf grasses to increase evapotranspiration and prevent erosion and possible exposure of the barrier. Fertilizer, frequent watering, and mowing may be required to establish the turf grass and prevent invasion by trees and shrubs. Oldfield vegetation of grasses and forbs is a possible sustainable alternative to turf grass communities. To determine if oldfield vegetation can establish on caps, we (1) compared establishment of a dominant oldfield grass and a commercial turf grass under different combinations of new closure cap management: spring or summer planting and presence or absence of amendments to alleviate drought (watering, mulch) or increase soil fertility (fertilizer, lime, a nitrogen-fixing legume); (2) surveyed existing caps to determine if oldfield species establish naturally; and (3) performed a greenhouse experiment to compare growth of two native grasses under low and amended (added water, soil nutrients) conditions. Both the commercial grass and oldfield species established under new cap conditions; fertilizer, water, and mulch improved vegetation establishment in spring or summer, but legumes decreased grass cover. In the greenhouse, both native grasses grew best with amendments; however, substantial stem and root length were obtained with no fertilizer and only once-weekly watering. Existing vegetated caps supported planted grasses and naturally established oldfield species. Overall, the results indicate native grasses can establish on new caps and oldfields can serve as a management model; further work is needed to determine the management strategy to maintain herbaceous vegetation and slow woody species invasion.     

Assessment of Vegetation Establishment on Tailings Dam at an Iron Ore Mining Site of Suburban Beijing, China, 7 Years After Reclamation with Contrasting Site Treatment Methods

Strip-mining operations greatly disturb soil, vegetation and landscape elements, causing many ecological and environmental problems. Establishment of vegetation is a critical step in achieving the goal of ecosystem restoration in mining areas. At the Shouyun Iron Ore Mine in suburban Beijing, China, we investigated selective vegetation and soil traits on a tailings dam 7 years after site treatments with three contrasting approaches: (1) soil covering (designated as SC), (2) application of a straw mat, known as “vegetation carpet”, which contains prescribed plant seed mix and water retaining agent (designated as VC), on top of sand piles, and (3) combination of soil covering and application of vegetation carpet (designated as SC+VC). We found that after 7 years of reclamation, the SC+VC site had twice the number of plant species and greater biomass than the SC and VC sites, and that the VC site had a comparable plant abundance with the SC+VC site but much less biodiversity and plant coverage. The VC site did not differ with the SC site in the vegetation traits, albeit low soil fertility. It is suggested that application of vegetation carpet can be an alternative to introduction of topsoil for treatment of tailings dam with fine-structured substrate of ore sands. However, combination of topsoil treatment and application of vegetation carpet greatly increases vegetation coverage and plant biodiversity, and is therefore a much better approach for assisting vegetation establishment on the tailings dam of strip-mining operations. While application of vegetation carpet helps to stabilize the loose surface of fine-structured mine wastes and to introduce seed bank, introduction of fertile soil is necessary for supplying nutrients to plant growth in the efforts of ecosystem restoration of mining areas.     

Rainfall Response of Degraded Soil Following Reforestation in the Copper Basin, Tennessee, USA

2 Copper Basin in southeastern Tennessee became the site of increasingly extensive and successful reforestation efforts. To determine the effectiveness of more than 50 years of reforestation efforts, we compared rainfall infiltration, sediment detachment, and soil organic matter of reforested sites to those properties of unvegetated sites and forested reference sites outside the basin. Results of 54 rainfall simulation experiments conducted in zones of the basin known to have been planted during different decades demonstrate that hydrologic recovery of soils in the Copper Basin lags significantly behind the establishment of tree cover and the protection offered by vegetation against soil erosion. Soils in new “forests” have significantly less organic matter and lower infiltration than forests more than 50 years old. The long-term persistence of low infiltration rates serves as a reminder that, at sites where the A and B soil horizons have been lost, restoration of the hydrologic function of a landscape requires decades, at least.     

Restoring grassland savannas from degraded pinyon-juniper woodlands: effects of mechanical overstory reduction and slash treatment alternatives

Although the distribution and structure of pinyon-juiper woodlands in the southwestern United States are thought to be the result of historic fluctuations in regional climatic conditions, more recent increases in the areal extent, tree density, soil erosion rates and loss of understory plant diversity are attributed to heavy grazing by domestic livestock and interruption of the natural fire regime. Prior to 1850, many areas currently occupied by high-density pinyon-juniper woodlands, with their degraded soils and depauperate understories, were very likely savannas dominated by native grasses and forbs and containing sparse tree cover scattered across the landscape. The purpose of this study was to evaluate the effectiveness of mechanical overstory reduction and three slash treatment alternatives (removal, clustering and scattering) followed by prescribed fire as techniques for restoring grassland savannas from degraded woodlands. Plant cover, diversity, biomass and nutrient status, litter cover and soil chemistry and erosion rates were measured prior to and for two years following experimental treatment in a degraded pinyon-juniper woodland in central New Mexico. Treatment resulted in a significant increase in the cover of native grasses and, to a lesser degree, forbs and shrubs. Plant species richness and diversity increased most on sites where slash was either completely removed or scattered to serve as a mulch. Although no changes in soil chemistry or plant nutrient status were observed, understory biomass increased over 200% for all harvest treatments and was significantly greater than controls. While treatment increased litter cover and decreased soil exposure, this improvement did not significantly affect soil loss rates. Even though all slash treatment alternatives increased the cover and biomass of native grasses, scattering slash across the site to serve as a mulch appears most beneficial to improving plant species diversity and conserving site resources.     

Disturbance of natural vegetation by camping: Experimental applications of low-level stress

Previously undisturbed sites in four different vegetation types were camped on for one night and for four nights. Changes in vegetation cover and vegetation height were measured after camping and one year later. Results are presented separately for different campsite zones—parts of the site where campers slept, cooked meals, and stored their packs. Just one night of camping was sufficient to cause evident impact in all four vegetation types, although the amount of impact varied significantly between zones and between vegetation types. Vegetation impact on campsites used four nights was generally less than twice as severe as impact on the sites used one night. The effects of camping on vegetation were also predicted for 12 other vegetation types on the basis of vegetational responses to experimental trampling. These results suggest that impact can almost always be minimized by confining camping to a small number of campsites instead of dispersing use across many campsites.     

Do Postfire Mulching Treatments Affect Plant Community Recovery in California Coastal Sage Scrub Lands?

In recent years, the use of postfire mulch treatments to stabilize slopes and reduce soil erosion in shrubland ecosystems has increased; however, the potential effects on plant recovery have not been examined. To evaluate the effects of mulching treatments on postfire plant recovery in southern California coastal sage scrub, we conducted a field experiment with three experimental treatments, consisting of two hydromulch products and an erosion control blanket, plus a control treatment. The area burned in 2007, and treatments were applied to six plot blocks before the 2008 growing season. Treatment effects on plant community recovery were analyzed with a mixed effects ANOVA analysis using a univariate repeated measures approach. Absolute plant cover increased from 13 to 90% by the end of the second growing season, and the mean relative cover of exotic species was 32%. The two hydromulch treatments had no effect on any plant community recovery response variable measured. For the erosion control blanket treatment, the amount of bare ground cover at the end of the second growing season was significantly lower (P = 0.01), and greater shrub height was observed (P < 0.01). We conclude that postfire mulch treatments did not provide either a major benefit or negative impact to coastal sage scrub recovery on the study area.     

Impacts of Camping on Vegetation: Response and Recovery Following Acute and Chronic Disturbance

Experiments with controlled levels of recreational camping were conducted on previously undisturbed sites in two different plant communities in the subalpine zone of the Wind River Mountains, Wyoming, USA. The plant communities were coniferous forest with understory dominated by the low shrub Vaccinium scoparium and a riparian meadow of intermixed grasses and forbs, of which Deschampsia cespitosa was most abundant. Sites were camped on at intensities of either one or four nights per year, for either one (acute disturbance) or three consecutive years (chronic disturbance). Recovery was followed for three years on sites camped on for one year and for one year on sites camped on for three years. Reductions in vegetation cover and vegetation height were much more pronounced on sites in the forest than on sites in the meadow. In both plant communities, increases in vegetation impact were not proportional to increases in either years of camping or nights per year of camping. Close to the center of campsites, near-maximum levels of impact occurred after the first year of camping on forested sites and after the second year on meadow sites. Meadow sites recovered completely within a year, at the camping intensities employed in the experiments. Forest sites, even those camped on for just one night, did not recover completely within three years. Differences between acute and chronic disturbance were not pronounced.     

Remediation of heavy metal-contaminated forest soil using recycled organic matter and native woody plants

The main aim of this study was to determine how the application of a mulch cover (a mixture of household biocompost and woodchips) onto heavy metal-polluted forest soil affects (i) long-term survival and growth of planted dwarf shrubs and tree seedlings and (ii) natural revegetation. Native woody plants (Pinus sylvestris, Betula pubescens, Empetrum nigrum, and Arctostaphylos uva-ursi) were planted in mulch pockets on mulch-covered and uncovered plots in summer 1996 in a highly polluted Scots pine stand in southwest Finland. Spreading a mulch layer on the soil surface was essential for the recolonization of natural vegetation and increased dwarf shrub survival, partly through protection against drought. Despite initial mortality, transplant establishment was relatively successful during the following 10 yr. Tree species had higher survival rates, but the dwarf shrubs covered a larger area of the soil surface during the experiment. Especially E. nigrum and P. sylvestris proved to be suitable for revegetating heavy metal-polluted and degraded forests. Natural recolonization of pioneer species (e.g., Epilobium angustifolium, Taraxacum coll., and grasses) and tree seedlings (P. sylvestris, Betula sp., and Salix sp.) was strongly enhanced on the mulched plots, whereas there was no natural vegetation on the untreated plots. These results indicate that a heavy metal-polluted site can be ecologically remediated without having to remove the soil. Household compost and woodchips are low-cost mulching materials that are suitable for restoring heavy metal-polluted soil.     

Herbicide retention in soil as affected by sugarcane mulch residue

Reducing surface and subsurface losses of herbicides in the soil and thus their potential contamination of water resources is a national concern. This study evaluated the effectiveness of sugarcane (Saccharum spp.) residue (mulch cover) in reducing nonpoint-source contamination of applied herbicides from sugarcane fields. Specifically, the effect of mulch residue on herbicide retention was quantified. Two main treatments were investigated: a no-till treatment and a no-mulch treatment. The amounts of extractable atrazine [2-chloro-4-(isopropylamino)-6-ethylamino-s-triazine], metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], and pendimethalin [N-(ethylpropyl)-3,4-dimethyl-2,6-dinitroaniline] from the mulch residue and the surface soil layer were quantified during the 1999 and 2000 growing seasons. Significant amounts of applied herbicides were intercepted by the mulch residue. Extractable concentrations were at least one order of magnitude higher for the mulch residue compared with that retained by the soil. Moreover, the presence of mulch residue on the sugarcane rows was highly beneficial in minimizing runoff losses of the herbicides applied. When the residue was not removed, a reduction in runoff-effluent concentrations, as much as 50%, for atrazine and pendimethalin was realized. Moreover, the presence of mulch residue resulted in consistently lower estimates for rates of decay or disappearance of atrazine and pendimethalin in the surface soil.     

Backfilling canals to mitigate Wetland dredging in Louisiana coastal marshes

Returning canal spoil banks into canals, or backfilling, is used in Louisiana marshes to mitigate damage caused by dredging for oil and gas extraction. We evaluated 33 canals backfilled through July 1984 to assess the success of habitat restoration. We determined restoration success by examining canal depth, vegetation recolonization, and regraded spoil bank soils after backfilling. Restoration success depended on: marsh type, canal location, canal age, marsh soil characteristics, the presence or absence of a plug at the canal mouth, whether mitigation was on- or off-site, and dredge operator performance.Backfilling reduced median canal depth from 2.4 to 1.1 m, restored marsh vegetation on the backfilled spoil bank, but did not restore emergent marsh vegetation in the canal because of the lack of sufficient spoil material to fill the canal and time. Median percentage of cover of marsh vegetation on the canal spoil banks was 51.6%. Median percentage of cover in the canal was 0.7%. The organic matter and water content of spoil bank soils were restored to values intermediate between spoil bank levels and predredging marsh conditions.The average percentage of cover of marsh vegetation on backfilled spoil banks was highest in intermediate marshes (68.6%) and lowest in fresh (34.7%) and salt marshes (33.9%). Average canal depth was greatest in intermediate marshes (1.50 m) and least in fresh marshes (0.85 m). Canals backfilled in the Chenier Plain of western Louisiana were shallower (average depth = 0.61 m) than in the eastern Deltaic Plain (mean depth range = 1.08 to 1.30 m), probably because of differences in sediment type, lower subsidence rate, and lower tidal exchange in the Chenier Plain. Canals backfilled in marshes with more organic soils were deeper, probably as a result of greater loss of spoil volume caused by oxidation of soil organic matter. Canals ten or more years old at the time of backfilling had shallower depths after backfilling. Depths varied widely among canals backfilled within ten years of dredging. Canal size showed no relationship to canal depth or amount of vegetation reestablished. Plugged canals contained more marsh reestablished in the canal and much greater chance of colonization by submerged aquatic vegetation compared with unplugged canals. Dredge operator skill was important in leveling spoil banks to allow vegetation reestablishment. Wide variation in dredge performance led to differing success of vegetation restoration.Complete reestablishment of the vegetation was not a necessary condition for successful restoration. In addition to providing vegetation reestablishment, backfilling canals resulted in shallow water areas with higher habitat value for benthos, fish, and waterfowl than unfilled canals. Spoil bank removal also may help restore water flow patterns over the marsh surface. Increased backfilling for wetland mitigation and restoration is recommended.     

Vegetation Response to Western Juniper Slash Treatments

The expansion of piñon–juniper woodlands the past 100 years in the western United States has resulted in large scale efforts to kill trees and recover sagebrush steppe rangelands. It is important to evaluate vegetation recovery following woodland control to develop best management practices. In this study, we compared two fuel reduction treatments and a cut-and-leave (CUT) treatment used to control western juniper (Juniperus occidentalis spp. occidentalis Hook.) of the northwestern United States. Treatments were; CUT, cut-and-broadcast burn (BURN), and cut-pile-and-burn the pile (PILE). A randomized complete block design was used with five replicates of each treatment located in a curl leaf mahogany (Cercocarpus ledifolius Nutt. ex Torr. & A. Gray)/mountain big sagebrush (Artemisia tridentata Nutt. spp. vaseyana (Rydb.) Beetle)/Idaho fescue (Festuca idahoensis Elmer) association. In 2010, 4 years after tree control the cover of perennial grasses (PG) [Sandberg’s bluegrass (Poa secunda J. Pres) and large bunchgrasses] were about 4 and 5 % less, respectively, in the BURN (7.1 ± 0.6 %) than the PILE (11.4 ± 2.3 %) and CUT (12.4 ± 1.7 %) treatments (P < 0.0015). In 2010, cover of invasive cheatgrass (Bromus tectorum L.) was greater in the BURN (6.3 ± 1.0 %) and was 50 and 100 % greater than PILE and CUT treatments, respectively. However, the increase in perennial bunchgrass density and cover, despite cheatgrass in the BURN treatment, mean it unlikely that cheatgrass will persist as a major understory component. In the CUT treatment mahogany cover increased 12.5 % and density increased in from 172 ± 25 to 404 ± 123 trees/ha. Burning, killed most or all of the adult mahogany, and mahogany recovery consisted of 100 and 67 % seedlings in the PILE and BURN treatments, respectively. After treatment, juniper presence from untreated small trees (<1 m tall; PILE and CUT treatments) and seedling emergence (all treatments) represented 25–33 % of pre-treatment tree density. To maintain recovery of herbaceous, shrub, and mahogany species additional control of reestablished juniper will be necessary.     

Heterogeneity of Thermal Extremes: Driven by Disturbance or Inherent in the Landscape

Ecologists are beginning to recognize the effect of heterogeneity on structure and function in arid and semiarid ecosystems. Additionally, the influences of temperature on ecosystems are widely documented, but landscape temperature patterns and relationships with vegetation are rarely reported in ecological studies. To better understand the importance of temperature patterns to the conservation and restoration of native ecosystems, we designed an experiment to investigate relationships among soil surface temperature, landscape heterogeneity, and grazing intensity. Grazing intensity did influence the vegetation structure and composition. Heavy treatments had the greatest bare ground and the least vertical structure. Ungrazed treatments had the most litter and live grass cover. However, average temperatures among the three grazing treatments were not different and ranged less than 2°C during midday summer periods. The temperature difference between riparian and upland landscapes within grazing treatments was 21°C. Landscape position (riparian vs. upland) did have a significant influence on soil surface temperature and produced a variation in temperature 11 times greater than grazing intensities. Thermal heterogeneity did not differ among grazing treatments. Lower soil surface temperatures (associated with riparian areas) may provide a critical thermal refuge for many animals in arid and semiarid ecosystems on hot summer days, when air temperatures can exceed 37°C. Riparian zones, specifically riparian vegetation, are an important component in ecosystem management.     

Effects of Disturbance Associated With Seismic Exploration for Oil and Gas Reserves in Coastal Marshes

Anthropogenic disturbances in wetland ecosystems can alter the composition and structure of plant assemblages and affect system functions. Extensive oil and gas extraction has occurred in wetland habitats along the northern Gulf of Mexico coast since the early 1900s. Activities involved with three-dimensional (3D) seismic exploration for these resources cause various disturbances to vegetation and soils. We documented the impact of a 3D seismic survey in coastal marshes in Louisiana, USA, along transects established before exploration began. Two semi-impounded marshes dominated by Spartina patens were in the area surveyed. Vegetation, soil, and water physicochemical data were collected before the survey, about 6 weeks following its completion, and every 3 months thereafter for 2 years. Soil cores for seed bank emergence experiments were also collected. Maximum vegetation height at impact sites was reduced in both marshes 6 weeks following the survey. In one marsh, total vegetation cover was also reduced, and dead vegetation cover increased, at impact sites 6 weeks after the survey. These effects, however, did not persist 3 months later. No effects on soil or water properties were identified. The total number of seeds that germinated during greenhouse studies increased at impact sites 5 months following the survey in both marshes. Although some seed bank effects persisted 1 year, these effects were not reflected in standing vegetation. The marshes studied were therefore resilient to the impacts resulting from 3D seismic exploration because vegetation responses were short term in that they could not be identified a few months following survey completion.