Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Plant and Soil”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
USGS2012

Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage

The pollution of natural waters with metals derived from the oxidation of sulfide minerals like pyrite is a global environmental problem. However, the metal loading pathways and transport mechanisms associated with acid rock drainage reactions are often difficult to characterize using bulk chemical data alone. In this study, we evaluated the use of zinc (Zn) isotopes to complement traditional geochemical tools in the investigation of contaminated waters at the former Waldorf mining site in the Rocky Mountains, Colorado, U.S.A. Geochemical signatures and statistical analysis helped in identifying two primary metal loading pathways at the Waldorf site. The first was characterized by a circumneutral pH, high alkalinity, and high Zn/Cd ratios. The second was characterized by acidic pHs and low Zn/Cd ratios. Zinc isotope signatures in surface water samples collected across the site were remarkably similar (the δ 66 Zn, relative to JMC 3-0749-L, for most samples ranged from 0.20 to 0.30‰ ± 0.09‰ 2σ). This probably suggests that the ultimate source of Zn is consistent across the Waldorf site, regardless of the metal loading pathway. The δ 66 Zn of pore water samples collected within a nearby metal-impacted wetland area, however, were more variable, ranging from 0.20 to 0.80‰ ± 0.09‰ 2σ. Here the Zn isotopes seemed to reflect differences in groundwater flow pathways. However, a host of secondary processes might also have impacted Zn isotopes, including adsorption of Zn onto soil components, complexation of Zn with dissolved organic matter, uptake of Zn into plants, and the precipitation of Zn during the formation of reduced sulfur species. Zinc isotope analysis proved useful in this study; however, the utility of this isotopic tool would improve considerably with the addition of a comprehensive experimental foundation for interpreting the complex isotopic relationships found in soil pore waters.

Colorado↗
USGS2020

Warming of alpine tundra enhances belowground production and shifts community towards resource acquisition traits

Climate warming is expected to stimulate plant growth in high‐elevation and high‐latitude ecosystems, significantly increasing aboveground net primary production (ANPP). However, the effects of simultaneous changes in temperature, snowmelt timing, and summer water availability on total net primary production (NPP)—and elucidation of both above‐ and belowground responses—remain an important area in need of further study. In particular, measures of belowground net primary productivity (BNPP) are required to understand whether ANPP changes reflect changes in allocation or are indicative of a whole plant NPP response. Further, plant functional traits provide a key way to scale from the individual plant to the community level and provide insight into drivers of NPP responses to environmental change. We used infrared heaters to warm an alpine plant community at Niwot Ridge, Colorado, and applied supplemental water to compensate for soil water loss induced by warming. We measured ANPP, BNPP, and leaf and root functional traits across treatments after 5 yr of continuous warming. Community‐level ANPP and total NPP (ANPP + BNPP) did not respond to heating or watering, but BNPP increased in response to heating. Heating decreased community‐level leaf dry matter content and increased total root length, indicating a shift in strategy from resource conservation to acquisition in response to warming. Water use efficiency (WUE) decreased with heating, suggesting alleviation of moisture constraints that may have enabled the plant community to increase productivity. Heating may have decreased WUE by melting snow earlier and creating more days early in the growing season with adequate soil moisture, but stimulated dry mass investment in roots as soils dried down later in the growing season. Overall, this study highlights how ANPP and BNPP responses to climate change can diverge, and encourages a closer examination of belowground processes, especially in alpine systems, where the majority of NPP occurs belowground.

Colorado↗
USGS2010

Vegetation of eastern Unalaska Island, Aleutian Islands, Alaska

Plant communities of Unalaska Island in the eastern Aleutian Islands of western Alaska, and their relationship to environmental variables, were studied using a combined Braun-Blanquet and multivariate approach. Seventy relevés represented the range of structural and compositional variation in the matrix of vegetation and landform zonation. Eleven major community types were distinguished within six physiognomic–ecological groups: I. Dry coastal meadows: Honckenya peploides beach meadow, Leymus mollis dune meadow. II. Mesic meadows: Athyrium filix-femina – Aconitum maximum meadow, Athyrium filix-femina – Calamagrostis nutkaensis meadow, Erigeron peregrinus – Thelypteris quelpaertensis meadow. III. Wet snowbed meadow: Carex nigricans snowbed meadow. IV. Heath: Linnaea borealis – Empetrum nigrum heath, Phyllodoce aleutica heath, Vaccinium uliginosum – Thamnolia vermicularis fellfield. V. Mire: Carex pluriflora – Plantago macrocarpa mire. VI. Deciduous shrub thicket: Salix barclayi – Athyrium filix-femina thicket. These were interpreted as a complex gradient primarily influenced by soil moisture, elevation, and pH. Phytogeographical and syntaxonomical analysis of the plant communities indicated that the dry coastal meadows, most of the heaths, and the mire vegetation belonged, respectively, to the widespread classes Honckenyo–Elymetea, Loiseleurio–Vaccinietea, and Scheuchzerio–Caricetea, characterized by their circumpolar and widespread species. Amphi-Beringian species were likely diagnostic of amphi-Beringian syntaxa, many of these yet to be described.

Alaska↗
USGS2011

Strategy to control the invasive alien tree Miconia calvescens in Pacific islands: Eradication, containment or something else?

Miconia calvescens (Melastomataceae) is a notorious plant invader in the tropical islands of French Polynesia, Hawaii and New Caledonia. A small tree native to Central and South America, it was first introduced as an ornamental in private botanic gardens in Tahiti (1937), Honolulu (1961), and Nouméa (1970s) where it escaped, became naturalised, and formed dense monospecific stands. More than 80,000 ha are currently invaded in French Polynesia, 10,000 ha in the Hawaiian Islands and 140 ha in New Caledonia. Control programmes have been under way in the Hawaiian Islands (Oahu, Maui, Hawaii, Kauai) and French Polynesia (Raiatea, Tahaa, Nuku Hiva, Fatu Hiva) since the early 1990s, and in New Caledonia (Province Sud) since 2006. Despite more than 15 years of intensive control efforts and millions of plants destroyed, eradication has not been achieved in any of these islands, mainly because the species has multiple features that thwart its elimination (e.g., prolific seed production, active dispersal by alien and native frugivorous birds, large and persistent soil seed bank, shade-tolerance), combined with the difficulty of detecting and destroying plants on rough terrain and steep slopes, insufficient control frequency, and limited financial and human resources. Miconia’s life cycle requires at least four years growth from seedling to fruiting. Consequently, prevention of fruit production may be an effective management strategy for small populations. This “juvenilization” process may allow the eradication of small populations when carefully conducted over a quarter century.

French Polynesia, Hawai'i, New Caledonia↗
USGS2026

Biocrust and seed placement influence emergence rates of perennial grass Elymus elymoides across five North American deserts

1. Dryland vascular plant emergence is often limited by water availability especially with projected climate and precipitation changes. Biological soil crusts (biocrusts) can promote water retention and nutrient availability that benefit germination, and emergence yet can also act as a surface barrier preventing critical seed soil contact and hindering emergence. Alongside these factors, dryland fire frequency has increased with the inclusion of invasive species and vegetation structural changes. With enhanced continuous fine fuel distribution there is a high potential to disrupt biocrust-plant interactions and influence associated management actions. 2. This study explores the dynamic relationship between biocrusts and fire-related heating effects on seedling emergence across five North American deserts: the Chihuahuan Desert, Colorado Plateau, Great Basin, Mojave Desert and Sonoran Desert. We conducted a greenhouse-based seedling emergence experiment using Elymus elymoides (bottlebrush squirreltail), a common perennial grass, with biocrust and bare soil mesocosms in which half were heated to mimic the effects of wildfire temperature. 3. The variables that had the greatest influence on germination rate and germination timing were the presence of biocrust and seed placement (on top of vs within the biocrust/soil matrix). Emergence rate was greatest atop bare soil followed by seeds inserted into biocrust. Emergence timing was faster with biocrust present, but only when seeds were inserted into it. Desert origin of biocrust and soil collection also influenced germination where the probability of any one seed emerging was highest in the Chihuahuan and Mojave desert sites relative to the Sonoran desert site which showed the lowest probability. Heating had mixed effects whereby it increased the likelihood of emergence but did not affect the overall rate or timing. 4. Synthesis and applications . This study underscores the importance of healthy and impaired biocrusts in dryland systems and suggests ways in which the combination of biocrust and seed placement can influence plant establishment, in addition to providing insight into seeding strategies for managers and restoration practitioners working in dryland sites.

Arizona, California, Colorado, Nevada, New Mexico↗
USGS2006

Integrating bioavailability approaches into waste rock evaluations

The presence of toxic metals in soils affected by mining, industry, agriculture and urbanization, presents problems to human health, the establishment and maintenance of plant and animal habitats, and the rehabilitation of affected areas. A key to managing these problems is predicting the fraction of metal in a given soil that will be biologically labile, and potentially harmful ('bioavailable'). The molecular form of metals and metalloids, particularly the uncomplexed (free) form, controls their bioavailability and toxicity in solution. One computational approach for determining bioavailability, the biotic ligand model (BLM), takes into account not only metal complexation by ligands in solution, but also competitive binding of hardness cations (Ca 2+,Mg 2+,) and metal ions to biological receptor sites. The more direct approach to assess bioavailability is to explicitly measure the response of an organism to a contaminant. A number of microbial enzyme tests have been developed to assess the impact of pollution in a rapid and procedurally simple way. These different approaches in making bioavailability predictions may have value in setting landuse priorities, remediation goals, and habitat reclamation strategies.

Conference Paper↗
USGS2021

Preserving soil organic carbon in prairie wetlands of central North America

Wetlands of the Prairie Pothole Region (PPR) in the Great Plains of central North America are numerous, densely distributed, and have highly productive plant and animal communities (Photo 49). When in a natural, unaltered condition, these wetlands store relatively large amounts of organic carbon in their soils (Photo 50). Human alterations, such as extensive drainage and land-use conversion for agriculture (Figure 7), have been linked with the loss of soil organic carbon (SOC) and associated emission of carbon dioxide (CO 2 ), as well as impacts to other ecosystem services provided by these wetlands, such as wildlife and waterfowl habitat, plant biodiversity, flood mitigation, groundwater recharge, nutrient removal and retention, and recreation (Gleason et al., 2011). It has been estimated that more than half of the wetlands of the PPR have been lost due to drainage and other disturbances, with losses approaching 90 percent in some areas (Dahl, 2014; Serran et al., 2018). The goal of this case study was to identify land-management strategies that are consistent with maintaining and increasing SOC stocks of PPR wetlands. Two overarching strategies generally are promoted to preserve and enhance SOC stocks of PPR wetlands: avoided drainage and rewetting or restoration. Avoided drainage involves protecting natural, unaltered wetlands from impacts of human actives with the purpose of retaining wetland functions and services such as carbon storage. Rewetting or restoration involves reestablishing natural hydrology and land use with the purpose of enhancing wetland functions and services that were previously lost due to human activities. Avoided drainage provides immediate and long-lasting benefits, while replenishing SOC through rewetting and restoration requires many decades. Both strategies are associated with higher methane (CH 4 ) emissions but lower CO 2 and nitrous oxide (N 2 O) emissions.

Alberta, Iowa, Manitoba, Minnesota, Montana, North↗
USGS1988

Gold and other metals in big sagebrush (Artemisia tridentata Nutt.) as an exploration tool, Gold Run District, Humboldt County, Nevada

Big sagebrush — a cold-desert species that dominates the terrain over large parts of western United States — was sampled along several traverses that crossed thermally metamorphosed limestone, phyllitic shale, and schist of the Middle and Upper Cambrian Preble Formation that host skarn-, disseminated gold and silver-, and hot springs gold-type mineral occurrences. Patterns of detectable levels of gold (8 to 28 ppb or ng g −1 ) in ash of new growth were consistent with areas affected by known or suspected gold mineralization. Soils collected along one of the traverses where a selenium-indicator plant was common contained no gold above background levels of 2ppb, but were consistently high in As, Sb, and Zn, and several samples were unusually high in Se (maximum 11 ppm or μg g −1 ). Sagebrush along this traverse contained Li at levels above norms for this species. We also found a puzzling geochemical anomaly at a site basinward from active hot springs along a range-front fault scarp. Sagebrush at this site contained a trace of gold and an unusually high concentration of Cd (13 ppm) and the soil had anomalous concentrations of Cd and Bi (3.2 and 6 ppm, respectively). The source of this anomaly could be either metal-rich waters from an irrigation ditch or leakage along a buried fault. Despite the limited nature of the study, we conclude that gold in sagebrush could be a cost-effective guide to drilling locations in areas where the geology seems favorable for disseminated and vein precious metals.

Journal of Geochemical Exploration↗
USGS2020

Projected climate and land use changes drive plant community composition in agricultural wetlands

Playa wetlands in the Great Plains, USA support a wide variety of plant species not found elsewhere in this agriculturally-dominated region due to the ephemeral presence of standing water and hydric soils within playas. If longer dry periods occur due to climate change or if changes in surrounding land use alter sediment accumulation rates and water storage capacity in playas, plant communities could experience decreased diversity, with lasting effects on ecosystem services provided by playas in the Great Plains and at a continental-level in North America. We quantified potential changes in playa wetland plant community composition associated with predicted changes in precipitation and land use in the Great Plains through the end of the 21 st century. We conducted two six-month greenhouse experiments mimicking field conditions using intact mesocosms collected from playas in Nebraska and Texas. In the precipitation experiment, treatments derived from historical precipitation observations and three future moderate emissions (CMIP5 RCP4.5) downscaled climate projections were applied to mesocosms. For the land use experiment, treatments were simulated by nitrogen (N) applications to soil ranging from 0 to 100 mg-N L -1 with each precipitation event under historical rainfall patterns, representing increasing and decreasing area in agricultural use in playa watersheds. Plant communities tended to shift toward more native species under projected future climate conditions, but as N runoff increased, native species richness decreased. Agricultural land-use surrounding playas may have a greater effect on wetland plant communities than future alterations to hydrology based on climate change in the Great Plains; thus, efforts to reduce nutrient runoff into playas would likely mitigate loss in ecosystem function in the coming decades.

Nebraska, Texas↗
USGS1991

Effect of phosphorus deficiency on spectral reflectance and morphology of soybean plants

Soybean plants were grown in hydroponic solutions having three concentration levels of phosphorus. Spectral reflectance changes included higher reflectance in the green and yellow portions of the electromagnetic spectrum in phosphorus-deficient plants and a difference in position of the long wavelength edge (the red edge) of the chlorophyll absorption band centered near 0.68 ??m. Plants having the least phosphorus in the growing medium did not show the normal shift of the red edge to longer wavelength which occurs as leaves mature. Shoot and root biomass were significantly lower in the phosphorus-deficient plants. These results are consistent with those obtained when soybean plants are dosed with elevated concentrations of metallic elements. We hypothesize that nutrient imbalances or anomalous metal concentrations in the soil set up physiological conditions at the soil/root interface that are responsible for the reflectance differences observed in laboratory and field studies of plants growing in substrates enriched in metallic elements.

Remote Sensing of Environment↗
USGS2002

Patton's tracks in the Mojave Desert, USA: An ecological legacy

Recovery of soil properties from World War II-era military training exercises in the Mojave Desert was measured approximately 55 years following disturbance. Tracks from military vehicles were still visible, particularly in areas of desert pavement. Soil penetrability was much lower in visible tracks than outside the tracks. Soils in tracks had fewer rocks in the top 10cm of the soil profile than adjacent untracked soils. Larger particles (> 4.8mm) formed a moderately well-developed pavement outside of the tracks, while smaller, loose particles ( h 4.8mm) dominated the surface of the tracks. The time required to restore the desert pavement is likely to be measured in centuries. Based on biomass estimates, the cyanobacterial component of biological soil crusts had recovered 46-65% in tracks, compared to outside the tracks. Overall recovery of lichen cover has been much slower. Under plant canopies, cover of Collema tenax was not significantly different between areas inside and outside the tracks; however, recovery of Catapyrenium squamulosum was only 36%. In plant interspaces with less favorable moisture and temperature conditions, C. tenax showed a 6% recovery and C. squamulosum a 3% recovery. Assuming recovery of the biological soil crust is linear, and complete only when the most sensitive species ( C. squamulosum ) has fully recovered in the most limiting microhabitats (plant interspaces), it may require almost two millennia for full recovery of these areas.

Arid Land Research and Management↗
USGS2016

Transport of atrazine and dicamba through silt and loam soils

The objectives of this research were to determine the role of preferential flow paths in the transport of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) and dicamba (3-6-dichloro-2-methoxybenzoic acid) through silt and loam soils overlying the High Plains aquifer in Nebraska. In a previous study, 3 of 6 study areas demonstrated high percentages of macropores; those three areas were used in this study for analysis of chemical transport. As a subsequent part of the study, 12 intact soil cores (30-cm diameter by 40-cm height), were excavated sequentially, two from each of the following depths: 0-40cm and 40-80cm. These cores were used to study preferential flow characteristics using dye staining and to determine hydraulic properties. Two undisturbed experimental field plots, each with a 3-m2 surface area, were installed in three study areas in Nebraska. Each was instrumented with suction lysimeters and tensiometers at depths of 10cm to 80cm in 10-cm increments. Additionally, each plot was planted with corn (Zea mays). A neutron probe access tube was installed in each plot to determine soil w ater content at 15-cm intervals. All plots were enclosed w ith a raised frame (of 8-cm height) to prevent surface runoff. All suction lysimeters were purged monthly for three months and were sampled immediately prior to pre-plant herbicide application to obtain background chemical concentrations. Atrazine and dicamba moved rapidly through the soil, but only after a heavy rainfall event, probably owing to the presence of preferential flow paths and lack of microbial degradation in these soil areas. Staining of laboratory cores showed a positive correlation between the percent area stained by depth and the subsequent breakthrough of Br- in the laboratory and leaching of field-applied herbicides owing to large rainfall events. Suction lysimeter samples in the field showed increases in concentrations of herbicides at depths where laboratory data indicated greater percentages of what appeared to be preferential flow paths. Concentrations of atrazine and dicamba exceeding 0.30 and 0.05µg m1-1 were observed at depths of 10-30cm and 50-70cm after two months following heavy rainfall events. It appears from the laboratory experiment that preferential flow paths were a significant factor in transport of atrazine and dicamba.

Nebraska↗
USGS2022

Plant community context controls short- vs. medium-term effects of pre-emergent herbicides on target and non-target species after fire

Questions: Selective herbicide application is a common restoration strategy to control exotic invaders that interfere with native plant recovery after wildfire. Whether spraying with preemergent or bioherbicides releases native plants from competition with exotics (“spray-and-release” strategy) and can make communities resistant to re-invasion by exotic annual grasses (e.g., cheatgrass, medusahead), without risks to non-target native plants or secondary invasion, is a major question for land managers of semiarid plant communities. Location: Sagebrush steppe of southwest Idaho, USA Methods We applied chemical herbicides (imazapic, rimsulfuron) and weed-suppressive bacteria ( Pseudomonas fluorescens strains MB906 and D7) to three sagebrush-steppe communities after fire.We measured plant cover prior to burning and for four years (five for exotic annual grasses) post-treatment. Results Both chemical herbicides significantly reduced exotic annual grass cover in all communities in the first post-spraying year, but rimsulfuron plots were re-invaded after 1-2 years, while imazapic plots continued to resist re-invasion 4 and even 5 years post-spraying, well after the herbicide should have degraded. We did not detect any increase in native perennial grass cover with either herbicide, and herbicides had both positive and negative effects on individual bunchgrass basal diameter, depending on species and plant community. Rimsulfuron was more damaging than imazapic to shallow-rooted perennial bunchgrasses. Moss and lichen cover, key components of soil integrity, increased with chemical herbicide treatments in some communities. Both herbicides increased secondary invaders (exotic forbs or grasses), which varied by plant community and herbicide. Weed-suppressive bacteria treatments had no significant effects on cover of any functional group. Conclusions While short-term effects of chemical herbicides that target exotic annual grasses were relatively consistent and predictable, longer-term effects were specific to the herbicide and plant community. The “spray and release” strategy may confer resistance to re-invasion by exotic annual grasses if herbicides prevent re-invasion for an extended period.

Idaho↗
USGS2015

Pulse-drought atop press-drought: unexpected plant responses and implications for dryland ecosystems

In drylands, climate change is predicted to cause chronic reductions in water availability (press-droughts) through reduced precipitation and increased temperatures as well as increase the frequency and intensity of short-term extreme droughts (pulse-droughts). These changes in precipitation patterns may have profound ecosystem effects, depending on the sensitivities of the dominant plant functional types (PFTs). Here we present the responses of four Colorado Plateau PFTs to an experimentally imposed, 4-year, press-drought during which a natural pulse-drought occurred. Our objectives were to (1) identify the drought sensitivities of the PFTs, (2) assess the additive effects of the press- and pulse-drought, and (3) examine the interactive effects of soils and drought. Our results revealed that the C 3 grasses were the most sensitive PFT to drought, the C 3 shrubs were the most resistant, and the C 4 grasses and shrubs had intermediate drought sensitivities. Although we expected the C 3 grasses would have the greatest response to drought, the higher resistance of C 3 shrubs relative to the C 4 shrubs was contrary to our predictions based on the higher water use efficiency of C 4 photosynthesis. Also, the additive effects of press- and pulse-droughts caused high morality in C 3 grasses, which has large ecological and economic ramifications for this region. Furthermore, despite predictions based on the inverse texture hypothesis, we observed no interactive effects of soils with the drought treatment on cover or mortality. These results suggest that plant responses to droughts in drylands may differ from expectations and have large ecological effects if press- and pulse-droughts push species beyond physiological and mortality thresholds.

Oecologia↗
USGS2023

Integrated rangeland fire management strategy actionable science plan completion assessment: Restoration topic, 2015–20

Loss and degradation of sagebrush rangelands due to an accelerated invasive annual grass-wildfire cycle and other stressors are substantial management, conservation, and economic issues in the western United States. These sagebrush rangelands comprise a unique biome spanning 11 states, support over 350 wildlife species, and provide important ecosystem services that include stabilizing the economies of western communities. Impacts to sagebrush ecosystem processes over large areas due to the annual grass-wildfire cycle necessitated the development of a coordinated, science-based strategy for improving efforts to achieve long-term protection, conservation, and restoration of sagebrush rangelands, which was framed in 2015 under the Integrated Rangeland Fire Management Strategy (IRFMS). Central to this effort was the development of an Actionable Science Plan (Plan) that identified 37 priority science needs (Needs) for informing the actions proposed under the 5 topics (Fire, Invasives, Restoration, Sagebrush and Sage-Grouse, Climate and Weather) that were part of the collective focus of the IRFMS. Notable keys to this effort were identification of the Needs co-produced by managers and researchers, and a focus on resulting science being “actionable.” Substantial investments aimed at fulfilling the Needs identified in the Plan have been made since its release in 2016. While the state of the science has advanced considerably, the extent to which knowledge gaps remain relative to identified Needs is relatively unknown. Moreover, new Needs have likely emerged since the original strategy as results from actionable science reveal new questions, and possible (yet untested) solutions. A quantifiable assessment of the progress made on the original science Needs can identify unresolved gaps and new information that can help inform prioritization of future research efforts. This report details a systematic literature review that evaluated how well peer-reviewed journal articles and formal technical reports published between January 1, 2015, and December 31, 2020, addressed 10 needs (hereinafter “Needs”) identified under the Restoration topic in the Plan. The topic outlined research Needs for improving restoration success in degraded sagebrush rangelands. We established the level of progress towards addressing each Need following a standardized set of criteria, and developed summaries detailing how research objectives nested within Needs identified in the Plan (“Next Steps”) were either addressed well, partially addressed or remain outstanding (that is, addressed poorly) in the literature through 2020. Our searches resulted in the inclusion of 371 science products that at least partially addressed a Need identified in the Restoration topic. The Needs that were well and partially addressed included: the development of methods to improve seeding success of native plants after fire; evaluation of short- and long-term plant responses relative to biotic and abiotic factors following restoration treatments; assessments of long-term effects on ecosystem processes following conifer removal treatments and development of decision support tools to aid in conifer management; determination of the costs of restoration treatments relative to the benefits to sage-grouse occupancy, survival, and populations; and assessments of the factors which contribute to soil degradation and development of soil enhancement methods that enhance seed germination and seedling survival while resisting nonnative plants. Needs that were not addressed well included: the development of methods for the rapid recovery of sagebrush and native herbaceous plants following wildfire and determination of whether treatments benefit sage-grouse and mitigate impacts from fires; determination of thresholds for successful restoration across a range of environmental conditions and development of decision support tools to assist with restoration effectiveness monitoring; and development and evaluation of the utility of seed transfer zones. The information provided in this assessment will assist updating the Plan along with other science strategies.

western United States↗
USGS2007

Forage nutritive quality in the Serengeti ecosystem: The roles of fire and herbivory

Fire and herbivory are important determinants of nutrient availability in savanna ecosystems. Fire and herbivory effects on the nutritive quality of savanna vegetation can occur directly, independent of changes in the plant community, or indirectly, via effects on the plant community. Indirect effects can be further subdivided into those occurring because of changes in plant species composition or plant abundance (i.e., quality versus quantity). We studied relationships between fire, herbivory, rainfall, soil fertility, and leaf nitrogen (N), phosphorus (P), and sodium (Na) at 30 sites inside and outside of Serengeti National Park. Using structural equation modeling, we asked whether fire and herbivory influences were largely direct or indirect and how their signs and strengths differed within the context of natural savanna processes. Herbivory was associated with enhanced leaf N and P through changes in plant biomass and community composition. Fire was associated with reduced leaf nutrient concentrations through changes in plant community composition. Additionally, fire had direct positive effects on Na and nonlinear direct effects on P that partially mitigated the indirect negative effects. Key mechanisms by which fire reduced plant nutritive quality were through reductions of Na-rich grasses and increased abundance of Themeda triandra, which had below-average leaf nutrients. ?? 2007 by The University of Chicago. All rights reserved.

American Naturalist↗
USGS1976

Relations among surficial materials, light intensity, and sycamore-seed germination along the Potomac River near Washington, D.C.

Seed of sycamore, a common tree on river flood plains, germinate in mineral soil exposed to high light intensities. Germination rates are low on surfaces covered with leaf litter, and seedlings die when shaded by closely spaced herbaceous plants. All germination rates were higher when seed were kept moist. Surflcial materials and light values in this study are similar to those on flood plains. Results were derived from counting seedlings after planting 1,000 seeds in each of several flats filled with different kinds of flood-plain and upland soils.

District of Columbia, Virginia↗
USGS2003

Roads as conduits for exotic plant invasions in a semiarid landscape

Roads are believed to be a major contributing factor to the ongoing spread of exotic plants. We examined the effect of road improvement and environmental variables on exotic and native plant diversity in roadside verges and adjacent semiarid grassland, shrubland, and woodland communities of southern Utah (U.S.A.). We measured the cover of exotic and native species in roadside verges and both the richness and cover of exotic and native species in adjacent interior communities (50 m beyond the edge of the road cut) along 42 roads stratified by level of road improvement (paved, improved surface, graded, and four-wheel-drive track). In roadside verges along paved roads, the cover of Bromus tectorum was three times as great (27%) as in verges along four-wheel-drive tracks (9%). The cover of five common exotic forb species tended to be lower in verges along four-wheel-drive tracks than in verges along more improved roads. The richness and cover of exotic species were both more than 50% greater, and the richness of native species was 30% lower, at interior sites adjacent to paved roads than at those adjacent to four-wheel-drive tracks. In addition, environmental variables relating to dominant vegetation, disturbance, and topography were significantly correlated with exotic and native species richness and cover. Improved roads can act as conduits for the invasion of adjacent ecosystems by converting natural habitats to those highly vulnerable to invasion. However, variation in dominant vegetation, soil moisture, nutrient levels, soil depth, disturbance, and topography may render interior communities differentially susceptible to invasions originating from roadside verges. Plant communities that are both physically invasible (e.g., characterized by deep or fertile soils) and disturbed appear most vulnerable. Decision-makers considering whether to build, improve, and maintain roads should take into account the potential spread of exotic plants.

Conservation Biology↗