Revegetation Plots Research Articles

Composition and structure of soil fauna communities and their relationships with environmental factors in copper mine waste rock after re-vegetation

The re-vegetation of acid mine waste rock from the Dexing copper (Cu) mine in Shuilong mountain has been conducted for more than 10 years. However, few studies have assessed the composition of soil fauna communities in this restored ecosystem. Here, we investigated the relationship between the soil fauna communities and soil environmental factors in this area using two re-vegetation restoration types (shrub-dominated and herb-dominated vegetation types) and in one area without re-vegetation (control) and modified Tullgren and Baermann methods. The 3558 soil fauna individuals collected belonged to five classes, 13 orders, three suborders, and 29 families. The number of individuals and taxa of small- and medium-sized soil fauna were significantly influenced by the different re-vegetation types (P < 0.05). Soil temperature, organic carbon, total nitrogen, carbon-nitrogen ratio, total phosphorus, available phosphorus, as well as the number of individuals and taxa of soil fauna were higher in the shrub-dominated re-vegetated plots than in the herb-dominated re-vegetated plots. The number of taxa was significantly and positively correlated with soil available phosphorus (P < 0.05), and the number of taxa, diversity, and richness of the soil fauna were significantly and positively correlated with the content of cadmium (Cd) in the soil (P < 0.05). Redundancy analysis revealed that the effects exerted by soil temperature, total nitrogen, and carbon-nitrogen ratio on the main taxa of soil fauna were the most important (P < 0.05). Among the various heavy metals in the soil, Cd, lead, zinc, and Cu exerted the most significant effects on the main soil fauna taxa (P < 0.05). Our results showed that the re-vegetation types significantly influenced the community composition and diversity of soil fauna in the waste rock dump of the Dexing Cu mine in Shuilong mountain, and that soil properties and soil heavy metal content influenced soil fauna community structure.

Erosion‐reducing effects of revegetation and fish‐scale pits on steep spoil heaps under concentrated runoff on the Chinese Loess Plateau

AbstractMassive spoil heaps, formed during production and construction activities, have suffered from severe soil erosion, leading to land degradation and damaging the environment. Fish‐scale pits (FSPs) and revegetation (RG) are the most common measures for controlling soil erosion on spoil heaps on the Loess Plateau. To evaluate the effects of FSPs and RG on concentrated runoff erosion, scouring‐erosion experiments were conducted on FSP plots, RG plots, and bare plots (the control) in the field on two types of spoil heaps: low gravel content in soil (LGS) and high gravel content in soil (HGS) at various inflow rates. Mass movement was the main cause of the considerable fluctuations in erosion rate and sharply increased the sediment concentration, which could exceed 800 kg m−3 and cause hyperconcentrated flows. Conversely, the FSP and RG treatments observably reduced the sediment concentration and erosion rate. The erosion‐reducing benefits (ERBs) of both the FSPs and RG treatments were significant. However, the ERB of the FSPs treatment was superior to that of the RG treatment under concentrated runoff, especially high‐intensity concentrated runoff. The ERB of the FSP treatment was on average 78.5% and 80.9% for the LGS and HGS, respectively. The ERB of the RG treatment was on average 36.4% and 56.5% for the LGS and HGS, respectively. The ERBs of the FSPs and RG treatments for the HGS were greater than those for the LGS. Moreover, gravel inhibited concentrated flow erosion. Our results provide important guidance for preventing soil erosion on abandoned spoil heaps in semiarid regions.

Stand performance of revegetation of post coal mining

The success of revegetation can be monitored by an assessment of the performance of the revegetation stand. This study aims to analyze and comparing the performance of post-coal revegetation stands conventional cropping patterns and hydroseeding planting patterns. The research location is revegetation area of PT. Adaro Site Tanjung Tabalong. The research took place for 2 months from data collection, analysis of data and reporting article. Data is collected using nested plot, the main plot size used is 10 m x 40 m. The main plot is divided into 4 measuring plots measuring 10m x 10m. The main plot measuring 10m x 40m was purposively placed on 2 locations of conventional cropping revegetation stands and 4 locations for revegetation stands of hydroseeding planting patterns. Data collected are stand dimensions data in the form of individual numbers, diameter and height of trees. The composition of plant species was analyzed by tabulation matrix, the percentage of plant growth was calculated based on number of plant growth/ha, stand diversity was assessed by the Shanon-Wiener index (H’), stand volume was analyzed by volume formula, plant health was analyzed qualitatively from observations of visualization of revegetation stand. The composition of plant species used in revegetation is 6 species. The percentage of planting success for conventional planting patterns is 93.5%, while the hydroseeding planting pattern is can’t be determined by the percentage of growth. The number of revegetated plants compared to the two cropping patterns has exceeded the established revegetation success rules (625 individuals / ha). Conventional plants have fewer plants / ha than the hydroseeding pattern, but have a higher average diameter, height, stand volume and diversity index value. Based on visual observations, there was no difference in plant health between the two revegetation plots. The revegetation stand performance from the results of this study can be categorized as good.

Colonization of woodland species during restoration: seed or safe site limitation?

A strategy of assisted natural regeneration uses selective restoration interventions to remove potential barriers to passive natural regeneration and succession toward target ecosystems. In woodland restoration, this may involve the planting of woodland clusters that serve as seed sources for further colonization and/or site amelioration to enhance colonization and growth of the target species. We tested the importance of seed and safe site limitations for the colonization of birch and willows in experimental treatments representing a matrix of revegetation (+/−) and planted birch and willow clusters (+/−) on an eroded area in South Iceland. The revegetation was initiated in the fall of 1999 and clusters of birch and willows planted in 2002. Density of birch and willow seedlings and their distribution among microsites was surveyed in 2005, 2006, 2010, and 2015. Willow seedlings were first noted in 2006 but birch seedlings in 2010. In 2015, seedling density in revegetated plots with planted clusters was over 20 times greater than that of revegetated plots without clusters, indicating a strong seed limitation. No seedlings were found in plots that had not been revegetated, showing very strong microsite limitation. However, revegetation increased the cover of biological soil crust and other microsites favorable for seedling establishment. The results demonstrate that both seed and safe site limit the colonization of birch and willows, key species in woodland restoration, and highlight the importance of identifying barriers to spontaneous succession before selecting restoration strategies.

Secondary Invasion and Reinvasion after Russian-Olive Removal and Revegetation

Russian-olive is a nitrogen-fixing tree invading riparian corridors in western North America. The premise of revegetation after weed removal is that revegetation is required to return native species to a removal site and that revegetation improves site resistance to invasion or reinvasion via competitive exclusion. Therefore, we expected that revegetation would reduce invasive species cover and increase native species cover compared with non-revegetated controls. Native understory species diversity increased with time since removal. We recorded 18.2 native species in 2012, and 28.2 native species in 2016. Out of 22 planted species, 2 did not establish. Diversity in revegetated plots did not differ from unplanted controls, likely because species spread quickly across plot boundaries. Native perennial grass, seeded species, and annual bromes increased over time, while nonnative forbs and native forbs decreased over time. Only invasive perennial grass cover responded to the revegetation treatment with cover much higher in controls compared with revegetated plots (25.7% vs. 7.7%); this was likely a response to a preplanting herbicide treatment. All categories of species diversity except invasive species diversity increased over time. Only 4% of Russian-olive stumps resprouted in the first year of removal, less than 1% resprouted 2 yr after removal. There was no Russian-olive emergence from seed in the removal year, and seed emergence varied exponentially among following years. Seeded native species did not have trouble establishing once adequate spring moisture occurred in the second growing season after Russian-olive removal, indicating that removal did not present substantial obstacles to successful revegetation. Follow-up control of Russian-olive is critical after initial treatment.

The role of mangrove revegetation as a means of restoring macrofaunal communities along degraded coasts

As coastal habitats face unprecedented pressure globally, there is a need to better understand how revegetation can fortify or restore biodiversity. We examined the early-stage outcomes of mangrove revegetation efforts for benthic invertebrate communities within degraded mangrove habitats in south eastern Brazil. We followed changes in macrofaunal abundance and species richness within small-scale Avicennia schaueriana revegetation plots over a 12month period. The assemblages of revegetation plots (RP) became progressively more diverse when compared to structural (SC) and blank controls (BC). The trajectory of change also differed with RP communities demonstrating convergence with those of remnant mangrove forest. After 12months, RP had greater abundances of crustaceans (41%) and polychaetes (13%) as well as higher but variable numbers of gastropods and bivalves than both SC and BC. A spatial examination of revegetation outcomes showed that success may vary across sheltered vs. exposed coastal microhabitats. Indeed, subsequent analysis using generalised linear mixed models pointed to a stronger influence of tidal height, than many of the commonly attributed sedimentary variables such as grain-size and organic matter content as determinants of community structure. Given the encouraging results of this study, we advocate an intensification of revegetation initiatives to augment natural recovery, increase benthic biodiversity and restore ecosystems services to degraded coasts.

Above and below-ground nutrient cycling: a criteria for assessing the biogeochemical functioning of a constructed fen

Recent peatland restoration studies have highlighted the need to modify the conventional approach of monitoring the recovery of biogeochemical functions through above-ground processes by integrating below-ground components, which are potentially sensitive indicators of reclamation trajectory in long-term monitoring programs. In this study, the recovery of nutrient cycling processes were assessed from both above and below-ground perspectives in a fen constructed on a post-mining landscape in the Athabasca oil sands region, Canada. The goal of this study was to understand if and how different revegetation strategies (seedlings (SDL); moss layer transfers (MLT); seedlings with moss transfer (SMLT) and a control treatment (CTRL)) influence the evolution of biogeochemical functions in the constructed fen relative to a natural reference (REF). The treatments were replicated 6 times and monitored over 2 growing seasons. Our results showed that revegetation facilitated both above-ground productivity and the cycling of below-ground nutrients, especially in the species-rich SMLT plots. Supply of labile substrates in the re-vegetated plots increased microbial potential activity. This was reflected in higher rates of respiration (c.7.8g CO2m−2day−2), nutrient acquisition (net immobilization) and productivity (c. −16.3g CO2m−2day−2) among revegetated plots relative to the CTRL. Nutrient dynamics within the constructed fen suggest that phosphorus limitation (N:P ratio>20) could hamper the establishment of a diverse plant community, whereas the build-up of microbial biomass appears to be NO3− limited. Our results also emphasize the need to track the evolution of nutrients cycling processes through long-term monitoring programs, and identify the potential use of ammonification, nitrogen mineralization and phosphorus availability as functional indicators of a fen’s recovery trajectory towards conditions present in natural fens.

Effects of grazing on leaf area index, fractional cover and evapotranspiration by a desert phreatophyte community at a former uranium mill site on the Colorado Plateau

This study employed ground and remote sensing methods to monitor the effects of grazing on leaf area index (LAI), fractional cover (fc) and evapotranspiration (ET) of a desert phreatophyte community over an 11 year period at a former uranium mill site on the Colorado Plateau, U.S. Nitrate, ammonium and sulfate are migrating away from the mill site in a shallow alluvial aquifer. The phreatophyte community, consisting of Atriplex canescens (ATCA) and Sarcobatus vermiculatus (SAVE) shrubs, intercepts groundwater and could potentially slow the movement of the contaminant plume through evapotranspiration (ET). However, the site has been heavily grazed by livestock, reducing plant cover and LAI. We used livestock exclosures and revegetation plots to determine the effects of grazing on LAI, fc and ET, then projected the findings over the whole site using multi-platform remote sensing methods. We show that ET is approximately equal to annual precipitation at the site, but when ATCA and SAVE are protected from grazing they can develop high fc and LAI values, and ET can exceed annual precipitation, with the excess coming from groundwater discharge. Therefore, control of grazing could be an effective method to slow migration of contaminants at this and similar sites in the western U.S.

How Does Restoration of Native Canopy Affect Understory Vegetation Composition? Evidence from Riparian Communities of the Hunter Valley Australia

Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.

The ratio of exotic-to-native dung beetles can indicate habitat quality in riparian restoration

. 1. Replanting natives on cleared riparian land is a common form of restoration. While most assessments of success are focussed on flora, the impact on fauna is often unknown. 2. We evaluated the effectiveness of revegetation for dung beetles in the riparian zone in a temperate Australian river. Total abundance, abundance of individual species, total species richness and species composition were compared using a chronosequence approach using four habitat types: unplanted; 1–3 and 7–10 year old revegetated plots, and mature native woodland. 3. A total of 1651 individuals and 20 species were trapped. Abundance and richness showed no trends across the chronosequence; however, changes in species composition appeared to be triggered by revegetation. Composition in older revegetation was more similar to mature woodland than the young revegetation or unplanted habitat. These shifts were largely due to a decline in the abundance and diversity of exotic dung beetles across the chronosequence. 4. Native revegetation also appeared to affect six species. Any of these six species could be used as indicators of progress in this region, but whether they are useful elsewhere cannot be guaranteed. This is a shortcoming of any study that recommends individual species as indicators. 5. Exotic-to-native ratios of plants are success indicators in restoration projects, and we suggest that this could also be used for monitoring success for invertebrate fauna. The exotic-to-native ratio has the advantage over single species indicators because the metric does not rely on those species being present in a particular region.

Long‐term effects of restoration on soil hydraulic properties in revegetation‐stabilized desert ecosystems

Improving structure of soils found at 0–5 cm depth, and increasing the thickness of biological soil crusts are both associated with sand dune revegetation‐stabilization in arid northwestern China. Since 1956, research on sand dune stabilization has included the use of straw chequer‐boards to facilitate development of soil structure. One method to gauge the degree of stabilization is to compare undisturbed soil hydraulic properties, including water retention [h(θ)] and hydraulic conductivity [K(h)] functions, with properties from stabilized sites of different ages. This study examined properties at five experimental sites of different ages since revegetation (51, 42, 34, 20 and 0 years). Saturated hydraulic conductivity (Ks) was determined in‐situ from all five sites, and the h(θ) curve was determined from samples collected from three sites. A significant negative correlation existed between Ks and the clay, silt and organic matter contents. Differences in most van Genuchten parameters for h(θ) were observed between the revegetated plots and the migrating sand dune area. Results of this long‐term study show that changes in soil hydraulic properties and improvement in soil structure were associated with migrating dune stabilization.

Abundance Patterns of Landbirds in Restored and Remnant Riparian Forests on the Sacramento River, California, U.S.A.

AbstractRiparian vegetation along the Sacramento River—California’s largest river—has been almost entirely lost, and several wildlife species have been extirpated or have declined as a result. Large‐scale restoration efforts are focusing on revegetating the land with native plants. To evaluate restoration success, we conducted surveys of landbirds on revegetated and remnant riparian plots from 1993 to 2003. Our objectives were to estimate population trends of landbirds, compare abundance patterns over time between revegetated and remnant riparian forests, and evaluate abundance in relation to restoration age. Of the 20 species examined, 11 were increasing, 1 was decreasing (Lazuli Bunting [Passerina amoena]), and 8 showed no trend. The negative trend for Lazuli Bunting is consistent with information on poor reproductive success and with Breeding Bird Survey results. There was no apparent guild association common to species with increasing trends. Nine species were increasing on revegetated and remnant plots, four were increasing on revegetated plots only, three were increasing on remnant plots only, the Lazuli Bunting was decreasing on both, and three species were stable on both. Although many species were increasing at a faster rate on revegetated plots, their abundance did not reach that of the remnant plots. For revegetated plots, “year since planting” was a strong predictor of abundance trends for 13 species: positive for 12, negative for 1. Our study shows that restoration activities along the Sacramento River are successfully providing habitat for a diverse community of landbirds and that results from bird monitoring provide a meaningful way to evaluate restoration success.

Long-term effects of revegetation on soil water content of sand dunes in arid region of Northern China

Desert is a challenging environment for organisms largely controlled by extreme abiotic factors including soil water content. The objectives of this study were to: (1) determine the effect of vegetative water utilization on soil water content; and (2) monitor the long-term vegetative response to the change of soil water content after establishing the revegetation of sand dunes of the Shapotou Region in the Tengger Desert, Northern China. The permanent revegetation plots were established in different sites in 1956, 1964, 1976 and 1982. Soil water content was monitored at 20 cm intervals of 10–300 cm in depth. Water content in sand dunes, was measured gravimetrically after 24-h desiccation at 105°C during the entire period of revegetation through the year to 2000. Our data show that soil water contents rapidly decreased at 9–10 years after revegetation, and similarly the vertical profile of soil water contents also decreased by depth. Annual precipitation is positively correlated with the water contents at depths 0–40 cm, although no clear-cut relationship was shown between precipitation and soil water at the deeper soil layers (from 40 to 300 cm). It is therefore concluded that water utilization of different plant species: shrub with deep-rooting system and annual plants with shallow-rooting system influences the spatial distribution of water inside the soil profile. Temporal and spatial variances of soil water also affected the changes in composition, coverage and biomass of vegetation. Vegetation composition of dominant species has successively changed from all shrub species, such as Caragana korshinskii and Hedysarum scoparaium to annual plants and shrub with shallow-rooting system ( Artemisia ordosica). The shrub biomass also changed along with soil water content, although the biomass of herb species increased over time. After 45 years, the shrub coverage decreased from the highest average 30.21% to the current level of 6%, whereas herb coverage increased over time. The soil water content was, however, kept relatively constant at lower level (1.23%) despite shrub coverage was reduced to about 6%. These results provide important baseline information for establishing vegetation and utilization of limited water resource in arid desert regions.

Restoration of riparian meadows degraded by livestock grazing: above- and belowground responses

Riparian meadows in the western US are highly productive areas withinthe riparian corridor that have been extensively utilized for livestock grazingand that are often degraded. This study aimed to increase our understanding ofboth the functional responses and restoration potential of mesic meadow systemsin central Nevada, USA. Nitrogen addition and clipping treatments were used toexamine grazing effects, while aeration and revegetation were included toevaluate potential restoration treatments. Belowground response was determinedby examining gravimetric soil water content and rooting depth and activity.Aboveground response was determined for two key mesic meadow species,Carex nebrascensis and Poa pratensis,by quantifying gas exchange and water relations. Large yearly and seasonaldifferences among water tables largely determined the rooting activity anddepthin these mesic meadows and influenced treatment responses. Little rootingactivity occurred within or at the surface of the water table and rooting depthincreased as water table level lowered during the growing season. In general,nitrogen addition decreased rooting activity and depth relative to controls. Itresulted in less negative water potentials and photosynthetic rates that werehigher early in the growing season, but lower later in the growing season. Theeffects of nitrogen addition could be attributed to accelerated phenology andearlier senescence. Clipping resulted in less negative plant water potentialsinCarex and Poa, andPoa had higher photosynthetic rates immediately afterclipping but only for certain dates and comparisons. Aeration increased rootingactivity and depth where there was no confounding effect of water table. Also,predawn and midday water potentials were generally less negative forCarex and Poa in aerated plots.Establishment on the revegetation plots was dominated by annual and early seralspecies and, consequently, these plots exhibited reduced rooting depth andactivity early in the growing season and high root turnover. Results indicatethat water table depth and its effects on soil water are dominant factors indetermining the functional processes and recovery potentials of these riparianmeadows. Clipping had minimal effects on above- and belowground responses,perhaps because clipping was performed late in the growing season after plantshad begun to senescence. Nitrogen addition decreased rooting activity andaltered phenology, indicating deleterious effects. Aeration was effective atovercoming some of the negative affects of overgrazing and may be an effectiverestoration treatment. However, revegetation may have limited potential due toestablishment constraints of the dominant species.

Long-Term Plant Community Development as Influenced by Revegetation Techniques

A revegetation techniques study was initiated during the fall of 1976 in northwestern Colorado in a disturbed sagebrush (Artemisia tridentata Nutt.) community. The study included 2 irrigation treatments, three seed mixtures, 2 seeding techniques, and 2 fertilization treatments. Short-term results were published and conclusions were made regarding the initial success of each treatment. The objective of the current study was to determine the effects of each treatment on plant community production, species composition, and species diversity after 20 years of plant community development. Among irrigated plots, the native seed mixture produced greater aboveground biomass compared to an introduced mixture and a mixture of both native and introduced species (combination seed mixture). The native seed mixture also resulted in greater total species richness than the introduced mixture when averaging over all other treatments. Altered seeding rate ratios among life forms as well as altered seeding methods (drill versus broadcast seeding) did not significantly alter plant community development after 20 years. However, a single application of nitrogen and phosphorus significantly increased grass production on plots seeded to the combination seed mixture. All revegetation plots have remained grass-dominated. However, shrub biomass was greater in the native and combination mixtures than in the introduced mixture under initial irrigated conditions in part due to successful establishment and growth of four-wing saltbush (Atriplex canescens Pursh Nutt.). Thus, the seed mixtures evaluated in this study have resulted in distinctly different plant communities and demonstrate that such initial treatments can influence long-term plant community development on severely disturbed rangelands. Broadcast seeding a native seed mixture that has been irrigated for 2 growing seasons without fertilization appears to be an effective long-term combination of cultural revegetation practices. DOI:10.2458/azu_jrm_v54i6_newman

Restoring Degraded Riparian Meadows: Biomass and Species Responses

Riparian meadows in central Nevada are highly productive and have been extensively utilized for livestock grazing. Consequently, many have been severely degraded resulting in changes in species composition and decreases in productivity. During a 3 year study, we examined the responses of mesic meadow systems to yearly nitrogen addition (100 kg ha(-1)) and clipping (8-10 cm stubble height) to increase our understanding of grazing effects. We also examined the effects of a one-time, fall aeration (10 cm deep by 2 cm wide holes spaced 20 cm apart) and revegetation (removal of existing vegetation and reseeding) to evaluate the restoration potential of these sites. Changes in total biomass, species aerial cover and frequency, and surface basal cover were used to evaluate treatment responses. Clipping had no effect on total biomass, possibly because it was conducted late in the growing season. In contrast, nitrogen addition plus clipping increased biomass in all 3 years when treatments were compared across sites and for 1 out of 3 years when treatments were compared across a single site. Aeration had no effect on above ground biomass, but has been shown to increase rooting activity in these same meadows. Due to a dry, hot spring, early seral and weedy species had higher establishment than the seeded natives in the revegetation plots, and biomass was low the first year after treatment. Individual species varied in their treatment responses. The cover of low-growing forb species (western aster (Aster occidentalis [Nutt.] Torrey and A. Gray), long-stalk starwort (Stellania Longipes Goldie), and common dandelion (Taraxacum officinale Wigg.) declined through time for all treatments, presumably due to increased grass cover and shading following release from grazing and above average precipitation and water table levels in 1998. Examination of the key graminoids showed that Kentucky bluegrass (Poa pratensis ssp. pratensis L.), an increaser species, did not increase in response to release from grazing, but increased in response to clipping and nitrogen addition. Nebraska sedge (Carex nebrascensis Dewey), a desirable native, increased in response to both release from grazing and nitrogen addition. The results were influenced by high spatial and temporal variability in water table elevations within these systems. DOI:10.2458/azu_jrm_v54i3_martin

Long-term plant community development as influenced by revegetation techniques

A revegetation techniques study was initiated during the fall of 1976 in northwestern Colorado in a disturbed sagebrush (Artemisia tridentata Nutt.) community. The study included 2 irrigation treatments, three seed mixtures, 2 seeding techniques, and 2 fertilization treatments. Short-term results were published and conclusions were made regarding the initial success of each treatment. The objective of the current study was to determine the effects of each treatment on plant community production, species composition, and species diversity after 20 years of plant community development. Among irrigated plots, the native seed mixture produced greater aboveground biomass compared to an introduced mixture and a mixture of both native and introduced species (combination seed mixture). The native seed mixture also resulted in greater total species richness than the introduced mixture when averaging over all other treatments. Altered seeding rate ratios among life forms as well as altered seeding methods (drill versus broadcast seeding) did not significantly alter plant community development after 20 years. However, a single application of nitrogen and phosphorus significantly increased grass production on plots seeded to the combination seed mixture. All revegetation plots have remained grass-dominated. However, shrub biomass was greater in the native and combination mixtures than in the introduced mixture under initial irrigated conditions in part due to successful establishment and growth of four-wing saltbush (Atriplex canescens Pursh Nutt.). Thus, the seed mixtures evaluated in this study have resulted in distinctly different plant communities and demonstrate that such initial treatments can influence long-term plant community development on severely disturbed rangelands. Broadcast seeding a native seed mixture that has been irrigated for 2 growing seasons without fertilization appears to be an effective long-term combination of cultural revegetation practices.

Restoring degraded riparian meadows: Biomass and species responses

Riparian meadows in central Nevada are highly productive and have been extensively utilized for livestock grazing. Consequently, many have been severely degraded resulting in changes in species composition and decreases in productivity. During a 3 year study, we examined the responses of mesic meadow systems to yearly nitrogen addition (100 kg ha(-1)) and clipping (8-10 cm stubble height) to increase our understanding of grazing effects. We also examined the effects of a one-time, fall aeration (10 cm deep by 2 cm wide holes spaced 20 cm apart) and revegetation (removal of existing vegetation and reseeding) to evaluate the restoration potential of these sites. Changes in total biomass, species aerial cover and frequency, and surface basal cover were used to evaluate treatment responses. Clipping had no effect on total biomass, possibly because it was conducted late in the growing season. In contrast, nitrogen addition plus clipping increased biomass in all 3 years when treatments were compared across sites and for 1 out of 3 years when treatments were compared across a single site. Aeration had no effect on above ground biomass, but has been shown to increase rooting activity in these same meadows. Due to a dry, hot spring, early seral and weedy species had higher establishment than the seeded natives in the revegetation plots, and biomass was low the first year after treatment. Individual species varied in their treatment responses. The cover of low-growing forb species (western aster (Aster occidentalis [Nutt.] Torrey and A. Gray), long-stalk starwort (Stellania Longipes Goldie), and common dandelion (Taraxacum officinale Wigg.) declined through time for all treatments, presumably due to increased grass cover and shading following release from grazing and above average precipitation and water table levels in 1998. Examination of the key graminoids showed that Kentucky bluegrass (Poa pratensis ssp. pratensis L.), an increaser species, did not increase in response to release from grazing, but increased in response to clipping and nitrogen addition. Nebraska sedge (Carex nebrascensis Dewey), a desirable native, increased in response to both release from grazing and nitrogen addition. The results were influenced by high spatial and temporal variability in water table elevations within these systems.

The Wog Wog habitat fragmentation experiment: C. R. Margules, Environmental Conservation, 19(4), 1992, pp 316–325

This study employed ground and remote sensing methods to monitor the effects of grazing on leaf area index (LAI), fractional cover (fc) and evapotranspiration (ET) of a desert phreatophyte community over an 11 year period at a former uranium mill site on the Colorado Plateau, U.S. Nitrate, ammonium and sulfate are migrating away from the mill site in a shallow alluvial aquifer. The phreatophyte community, consisting of Atriplex canescens (ATCA) and Sarcobatus vermiculatus (SAVE) shrubs, intercepts groundwater and could potentially slow the movement of the contaminant plume through evapotranspiration (ET). However, the site has been heavily grazed by livestock, reducing plant cover and LAI. We used livestock exclosures and revegetation plots to determine the effects of grazing on LAI, fc and ET, then projected the findings over the whole site using multi-platform remote sensing methods. We show that ET is approximately equal to annual precipitation at the site, but when ATCA and SAVE are protected from grazing they can develop high fc and LAI values, and ET can exceed annual precipitation, with the excess coming from groundwater discharge. Therefore, control of grazing could be an effective method to slow migration of contaminants at this and similar sites in the western U.S.

Selected Trace Elements in Plants Grown on Retorted Oil Shales

AbstractWestern wheatgrass (Agropyron smithii Rydb. ‘Arriba’) and fourwing saltbush (Atriplex canescens (Pursh) Nutt.) were sampled from oil shale revegetation plots in northwestern Colorado. Plants were growing on two types of retorted shales: TOSCO II, produced by the Tosco Corporation; and USBM, produced by the U.S. Bureau of Mines. Various treatments included leaching and different depths of soil covering over the retorted shales. Plant samples were analyzed for B, Mo, As, Se, and F on a dry‐weight basis. Plant samples with elevated Mo concentrations were also analyzed for Cu.Boron in western wheatgrass from the TOSCO retorted shale ranged from 85 to 202 ppm, compared with ranges of 4 to 15 ppm B in plants from the soil control. Analysis of variance indicated significant differences in B content due to site, aspect, type of retorted shale, and amount of soil cover over retorted shale. The concentration of B in western wheatgrass growing on retorted shales, especially TOSCO retorted shale, could affect plant growth. Fourwing saltbush samples, growing on USBM retorted shales, contained levels of Mo averaging 28 ppm, and low‐to‐moderate Cu content (4.8–6.8 ppm). This combination could make this species unacceptable as forage for ruminants. The concentrations of As (0.03–0.44 ppm), Se (0.02–0.94 ppm); and F (0.5–10.0 ppm) in the plant species investigated in this study were below limits usually set for either plant or animal toxicities and appear to be of little environmental significance.