Percent Plant Cover Research Articles

The large‐scale restoration of fire and water regimes in Everglades National Park reveal little change in plant diversity along an elevational gradient

Quantifying the response of plant diversity to large‐scale restoration is essential for measuring management success. One of the world's largest restoration efforts began in 2000 in the Everglades ecosystem in Florida, United States, through the Comprehensive Everglades Restoration Plan. In coordination with ongoing fire management, this restoration effort aims to restore natural hydrologic and fire regimes in this dynamic ecosystem. Restored water and fire regimes in the Everglades interact along an elevational gradient between seasonally inundated marl prairie and frequently burned pine rockland on Long Pine Key in Everglades National Park. To determine the impact of management on plant community richness and composition, we resampled transects spanning the elevational gradient between marl prairie and pine rockland initially sampled prior to the implementation of current restoration efforts (circa 1997–1999). We measured percent plant cover and developed generalized linear mixed models to determine the effects of fire frequency, average water depth, and elevation on plant species richness and composition across the two time periods. Additionally, we used species‐level random effects to examine how individual species respond to each environmental variable. We failed to detect any systematic shifts in plant composition in response to fire and water management. However, we found that complex interactions between fire and water structure plant composition and maximize species richness along gradients of water depth and elevation, with low, moderate, and high burn frequencies increasing richness in wet, moderately wet, and dry sites, respectively.

Species-Specific Responses to Human Trampling Indicate Alpine Plant Size Is More Sensitive than Reproduction to Disturbance.

Human disturbance, such as trampling, is an integral component of global change, yet we lack a comprehensive understanding of its effects on alpine ecosystems. Many alpine systems are seeing a rapid increase in recreation and in understudied regions, such as the Coast Mountains of British Columbia, yet disturbance impacts on alpine plants remain unclear. We surveyed disturbed (trail-side) and undisturbed (off-trail) transects along elevational gradients of popular hiking trails in the T'ak't'ak'múy'in tl'a In'inyáxa7n region (Garibaldi Provincial Park), Canada, focusing on dominant shrubs (Phyllodoce empetriformis, Cassiope mertensiana, Vaccinium ovalifolium) and graminoids (Carex spp). We used a hierarchical Bayesian framework to test for disturbance by elevation effects on total plant percent cover, maximum plant height and diameter (growth proxies), and buds, flowers, and fruits (reproduction proxies). We found that trampling reduces plant cover and impacts all species, but that effects vary by species and trait, and disturbance effects only vary with elevation for one species' trait. Growth traits are more sensitive to trampling than reproductive traits, which may lead to differential impacts on population persistence and species-level fitness outcomes. Our study highlights that disturbance responses are species-specific, and this knowledge can help land managers minimize disturbance impacts on sensitive vegetation types.

Aphid biological control in arable crops via flower strips: The predominant role of food resources over diversity effects

Abstract Plant taxonomic and functional diversity promotes interactions at higher trophic levels, but the contribution of functional diversity effects to multitrophic interactions and ecosystem functioning remains unclear. In agroecosystems, flower strips can be sown to promote biodiversity and associated services, but their plant composition is poorly considered from a functional diversity perspective so as to promote multitrophic interactions. In a field experiment, aphid biological control was compared across contrasting flower strip mixtures, over a 4‐year arable crop rotation. The effects of plants providing food resources, that is nectar and legumes supporting alternative hosts and prey, and the effects of plant species richness and functional dispersion were investigated on the biological control of aphid populations. In general, increases in the percentage of plant cover providing nectar and alternative prey (Fabaceae) to natural enemies increased predator–prey ratios and aphid parasitism and decreased aphid population growth rates. These effects however depended on the crop species. Species richness and the functional dispersion of traits involved in plant–arthropod interactions were of lesser importance, and the directions of their effects were crop‐specific. Synthesis and applications. These findings provide useful insight for designing perennial plant mixtures for creating or restoring habitats supporting aphid regulation. It is not adequate to sow any mixture containing simply flowering plants. Plant mixtures should comprise a large proportion of plant species supporting alternative prey, like legumes, and species producing nectar being easily accessible to natural enemies (corollas with nondeep nectar). To be efficient over a crop rotation, with aphids being present at different seasons, these nectar resources should be provided throughout the year thanks to a diversity of plant flowering periods.

Bison wallows effect on soil properties, vegetation composition and structure in a recently reintroduced area

Bison are considered an ecologically keystone species of the North American grasslands because their activities influence ecosystem dynamics and interactions, particularly their wallowing behavior. In 2009, 23 bison were reintroduced within a 1,500 ha private native semi-arid grassland in Janos, Chihuahua. Our objective was to evaluate the effect of bison wallows on the composition and structure of the vegetation, on species composition of annual grasses, and soil properties. Soil and vegetation samples were taken from inside the wallows and were compared against the samples obtained outside the wallows from late August to early September. The percentage of plant cover and the height of the foliage were measured inside and outside the wallow. Soil cores were taken, and the presence of soluble salts, moisture retention capacity, percentage of clay, and concentration of nutrients was determined. The three associations preferred by bison for wallowing were toboso grassland, vine mesquite and annual grassland. Of the 27 species of grasses and forbs recorded in the three plant associations mostly used for wallowing, we found that 17 species were present inside and outside wallows. Five different species were found only inside wallows and another five, only outside of wallows. The annual grassland plants had a greater height outside the wallows. The toboso grassland association presented higher soil moisture, likely related to the higher percentage of clay, and the annual grassland presented the highest bulk density (BD) inside the wallows, which limited plant growth in this association. Soils in other associations did not show significant differences in BD among them, mainly due to their finer texture. No significant effect of the wallows on nutrient concentrations was recorded. The lack of significant differences related to bison activities could be related to the brief period since the herd was reintroduced to the site. These differences might become apparent over time with a larger herd. For this reason, we conclude that the current differences in the soil properties are mainly due to geomorphological processes. That is, at this stage after the reintroduction, the grasslands are responding to soil characteristics, and not to the activity of the bison.

Effects of Agricultural Management Practices on the Temporal Variability of Soil Temperature under Different Crop Rotations in Bad Lauchstaedt-Germany

To investigate the effects of management practices on the dynamics of soil temperature, during 2014–2017, a field experiment was carried out in Bad Lauchstaedt, Germany. In this study, four management systems are compared for determining management-induced changes in soil temperature at different depths: (i) conventional tillage (TC) with the standard rate of N fertilizer (P1N1), (ii) conventional tillage with the half-standard rate of N fertilizer (P1N0), (iii) reduced tillage (TR) with the standard rate of N fertilizer (P0N1), and iv) reduced tillage with the half-standard rate of N fertilizer (P0N0). Temporal analysis of soil temperature is assessed to examine data observed at a specific time to achieve a better understanding of the soil temperature dynamic that occurs at different time scales. The results showed that the soil temperature has decreasing amplitudes and increasing phase shifts with increasing soil depth, i.e., the deeper the measurement depth, the smoother the soil temperature changes cycle and the smaller the variability. Results showed that the diurnal temperature variation is found up to 45 cm depth of soil whereas annual temperature variation is up to a depth of 180 cm. The results, moreover, revealed that soil temperature dynamic was affected by tillage systems and fertilization and a time lag is observed between the temperature fluctuations at the surface and deeper layers, due to induced management effects on plant cover, residues, and soil properties. Although higher soil temperature at the sowing stage under TR is contributed to higher amounts of surface crop residues in crop rotations, the effect of residues on soil temperature variation reduces with an increase in percent plant cover and shading of soil, which happens in the last stage of plant growth. At the last stage of crop development regardless of tillage systems, applying more N fertilization increased crop yield, resulting in cooling soil temperature.

Extreme drought induces rapid declines in co‐occurring native Bouteloua eriopoda and invasive Eragrostis lehmanniana

AbstractGlobal climate change is expected to result in increased temperatures and variation in precipitation. In the Desert Southwest region of the United States, climate change may result in drier conditions. Eragrostis lehmanniana (Lehmann lovegrass) is an invasive species that has extensively colonized the southwestern United States, including Bouteloua eriopoda (black grama) grasslands. While both E. lehmanniana and B. eriopoda evolved in arid conditions, drier conditions may influence this invader–native system in unforeseen ways. Using a combination of precipitation pivot point (PPP) and drought sensitivity (DS) analysis, we compared responses of B. eriopoda and E. lehmanniana to altered precipitation regimes including long‐term drought treatments in the northern Chihuahuan Desert, New Mexico. We defined PPP as the critical point in precipitation amount below which plant percent cover decreased and above which it increased. We used DS, defined as the square millimeters of cover lost when precipitation decreased by 1 mm, to elucidate the direct response of biomass to drought on either side of the PPP. We estimated mean monsoon PPPs of 62.5 and 63.7 mm for B. eriopoda and E. lehmanniana, respectively. We estimated mean annual (1 October–30 September) PPPs of 108.6 and 108.5 mm for B. eriopoda and E. lehmanniana, respectively. Bouteloua eriopoda mean DS was 4.71 mm2/mm. Eragrostis lehmanniana mean DS was 1.56 mm2/mm. Results suggest that it is unlikely that extended drought will benefit E. lehmanniana over B. eriopoda and both species may decline under extreme drought.

Restoring Fringing Tidal Marshes for Ecological Function and Ecosystem Resilience to Moderate Sea-level Rise in the Northern Gulf of Mexico.

Tidal marshes are increasingly vulnerable to degradation or loss from eutrophication, land-use changes, and accelerating sea-level rise, making restoration necessary to recover ecosystem services. To evaluate effects of restoration planting density and sea-level rise on ecosystem function (i.e., nitrogen removal), we restored three marshes, which differed in elevation, at Weeks Bay National Estuarine Research Reserve, Alabama, USA and planted them with Juncus roemerianus sods at 0, 25, 50, 75, or 100% initial cover. We simulated future sea level using passive weirs that increased flooding during low tide. Because additional species emerged shortly after transplantation, we also tested for treatment effects on community structure. In all marshes, species richness increased following restoration, regardless of treatments, while relative abundances of new species tended to increase with increasing initial cover. Plant percent cover increased with increasing initial cover in all marshes, with similar vegetated cover at 50, 75, and 100% after 3 years in the highest elevation marsh. Porewater dissolved inorganic nitrogen concentrations ([DIN]) decreased with increasing initial cover in all marshes, and were significantly lower in 50, 75, and 100% treatments than 0 or 25% after 1 year. Furthermore, [DIN] was similarly low among 50, 75, and 100% treatments when elevation capital was highest. These results suggest that intermediate initial cover (50%) can recover plant cover and promote nitrogen removal when elevation capital is adequate at relatively lower labor and material costs than planting at higher cover, thereby maximizing restoration outcomes in the face of low to moderate sea-level rise.

Effect of soil carbon amendments in reversing the legacy effect of plant invasion

Abstract Invasive plants are key drivers of global environmental changes leading to the disruption of ecosystems. Many invasive species engage in novel niche construction through plant–soil feedbacks that are driven by plant secondary compounds. These compounds can persist in the soil even after removing the invader, thus creating a legacy effect that inhibits the return of native flora and fauna. The formulation of active intervention strategies that can reverse niche construction is therefore critical for the restoration of these invaded ecosystems. We conducted this study in an old‐field in Massachusetts, USA, that has been invaded by Japanese knotweed (Polygonum cuspidatum) for >20 years. We chose knotweed as a model system as it alters soil chemistry and microbial community through the input of polyphenols such as tannins that creates a legacy effect. Following the removal of knotweed biomass, we investigated the effect of two soil carbon (C) amendments (biochar and activated carbon) on the growth and establishment of newly seeded native and prairie species. We measured the percent plant cover and above‐ground biomass to assess the establishment of the native and prairie species. We also measured soil and microbial characteristics including nutrient availability, extracellular enzyme activities and fungal biomass to elucidate the effect of C amendments in reversing the legacy effect. Eventhough the native species did not respond positively to C amendments, the biomass of the prairie species was 80% higher in activated carbon and biochar amended plots than the non‐amended control plots. The nitrate content of the C amended plots was five times higher than the non‐amended plots indicating an increased N mineralisation in the C amended plots. This could be potentially due to the amelioration of phenolic compounds by activated carbon and biocharthrough sorption. The phenol peroxidase activity also increased in the activated carbon and biochar amended plots potentially due to the less inhibition by phenolic compounds. With the decrease in polyphenols, the fungal biomass decreased in C amended plots that may have resulted in faster nutrient cycling and increased availability of soil N. Synthesis and applications. The phenolic compounds from the litter of invasive species that persist in soil C fractions can negatively affect the germination and growth of the native or non‐invasive plant species. The polyphenols such as tannins from the litter can complex nitrogenous compounds in soils making the N unavailable to the native or non‐invasive species. Our results revealed the potential of soil C amendments in reversing niche construction and legacy effects of polyphenol‐rich invasive species and indicated that biochar could be a more economically feasible alternative to activated carbon in restoring invaded ecosystems. These results also emphasise thatunderstanding the mechanisms through which invasive species create a legacy effect is pivotal in formulating suitable knowledge‐based practices for restoring invaded ecosystems.

Benefits of conservation-driven mowing for the EU policy species Gladiolus palustris Gaudin in mountain fen meadows: a case-study in the European Alps

The sword lily Gladiolus palustris Gaudin is protected on European level and listed in Annexes II and IV of the EC Habitat Directive 92/43/EEC. It grows in nutrient-poor, calcareous meadows in central and eastern Europe. Tree encroachment in montane meadows of the European Alps as a result of recent land use changes and the abandonment of traditional farming practices threaten the survival of this species. Conservation-driven mowing is considered a feasible conservation measure for maintaining high species diversity in abandoned semi-natural grasslands. To assess the effects of ten years of biennial mowing on a grassland community in the Dolomiti Bellunesi National Park, Italy (Site of Community Importance, Natura 2000 network), ten 25 m2 plots were established whereby four plots were placed in the mowed area, four in the non-mowed area and two in a small non-mowed patch of grassland inside the mowed area. In each plot the following variables were recorded, total percentage of plant cover, percentage cover of woody species, percentage cover of herbaceous species, percentage cover and number of flowering ramets of G. palustris and a complete list of species and their percentage abundance. Mowed plots showed a higher species richness than non-mowed plots. The number of G. palustris flowering ramets and percentage cover increased manifold in mowed plots compared to non-mowed plots. The resumption of mowing for conservation purposes undertaken by the managing authority halted the process of tree encroachment and avoided a drastic change in plant composition. Periodic mowing (every second or third year) was demonstrated to be a cost-effective conservation measure in non-productive grasslands to keep grasses at bay in favour of forbs of high conversation value.

Wetland Plant Communities of the Eastern Himalayan Highlands in Northern Bhutan

The study was conducted to characterize previously unexplored wetland vegetation in lower montane areas of the Himalaya (1597–2538 m above sea level) of Jigme Dorji National Park, Gasa District, Northern Bhutan. A random quadrat sampling method was employed to assess percent plant cover and environmental data were collected following standard procedures. Cluster and indicator species analyses using plant cover data were used to define the species composition of plant communities. Differences in community composition along gradients of elevation, slope, soil pH, available phosphorus, and peat/soil depth were analyzed using Canonical Correspondence Analysis (CCA). The wetlands supported 120 vascular plant species from 84 genera and 51 families. Analyses identified four plant communities, I to IV, each named from the three most prominent species. The key indicator species of four plant communities, Acorus calamus, Carex diandra, Equisetum ramosissimum, and Carex capillacea, dominate shallow fresh marsh, seasonally flooded basin of flat, fresh water meadow, and poor fen, respectively. Elevation and soil phosphorus were the most important environmental variables in explaining the variation in wetland vegetation. The findings can be used to support the work of conservation agencies to identify and conserve these plant communities and their habitats in the Himalaya.

Effects of Wild Pig Disturbance on Forest Vegetation and Soils

ABSTRACTIn North America, wild pigs (Sus scrofa; feral pigs, feral swine, wild boars) are a widespread exotic species capable of creating large‐scale biotic and abiotic landscape perturbations. Quantification of wild pig environmental effects has been particularly problematic in northern climates, where they occur only recently as localized populations at low densities. Between 2016 and 2017, we assessed short‐term (within ~2 yrs of disturbance) effects of a low‐density wild pig population on forest features in the central Lower Peninsula of Michigan, USA. We identified 16 8‐ha sites using global positioning system locations from 7 radio‐collared wild pigs for sampling. Within each site, we conducted fine‐scale assessments at 81 plots and quantified potential disturbance by wild pigs. We defined disturbance as exposure of overturned soil, often resulting from rooting behavior by wild pigs. We quantified ground cover of plants within paired 1‐m2 frames at each plot, determined effects to tree regeneration using point‐centered quarter sampling, and collected soil cores from each plot. We observed less percent ground cover of native herbaceous plants and lower species diversity, particularly for plants with a coefficient of conservatism ≥5, in plots disturbed by wild pigs. We did not observe an increase in colonization of exotic plants following disturbance, though the observed prevalence of exotic plants was low. Wild pigs did not select for tree species when rooting, and we did not detect any differences in regeneration of light‐ and heavy‐seeded tree species between disturbed or undisturbed plots. Magnesium and ammonium content in soils were lower in disturbed plots, suggesting soil disturbance accelerated leaching of macronutrients, potentially altering nitrogen transformation. Our study suggested that disturbances by wild pigs, even at low densities, alters short‐term native herbaceous plant diversity and soil chemistry. Thus, small‐scale exclusion of wild pigs from vulnerable and rare plant communities may be warranted. © 2020 The Wildlife Society.

Pine savanna plant community disassembly after fire suppression

AbstractQuestionsBiodiversity is being lost rapidly due to anthropogenic changes in land use, climate, and other environmental conditions. In fire‐maintained ecosystems, altered fire regimes accelerate native species loss — community disassembly — and promote recruitment of fire‐sensitive species. In this study, we ask whether fire suppression results in changes over time in functional trait composition of ground‐layer species and whether these changes differ in longleaf pine savannas invaded by hardwoods from those invaded by sand pines.LocationFive Floridian locations on the southeastern coastal plain of the United States.MethodsAt each location we selected a fire‐maintained and fire‐suppressed savanna and measured percent plant cover by ground‐story species in 1,000 m2 plots. For 102 of these species, we measured 10 functional traits — height, growth form, specific leaf area, leaf dry matter content (LDMC), leaf water content, leaf ignition time, leaf mass consumed by fire, light compensation points (LCPs), non‐structural carbohydrate concentrations in under‐ground organs, and seed mass.ResultsFire exclusion was associated with reductions in both functional diversity and species richness. We identified 38 species exclusive to frequently burned sites: these species showed high LDMC values, high LCPs, high leaf mass consumed, and low leaf ignition time values. Lack of fire was associated with loss of 6 of the 12 C4 native grass species. Species and functional trait composition were affected by both time‐since‐fire and whether post‐fire communities were invaded by broadleaved trees (Quercus spp. and Liquidambar styraciflua) or by sand pine (Pinus clausa).ConclusionsWe demonstrated the effects of altered disturbance regimes on savanna plant species and functional trait composition. This trait‐based approach advanced our understanding of how altered disturbance regimes can alter plant communities. Although 38 shade‐intolerant and flammable native savanna species were absent by 10 years since fire, 12 such species persisted even 40 years after fire exclusion.

The Effect of Visitors on the Properties of Vegetation of Calcareous Grasslands in the Context of Width and Distances from Tourist Trails

Over the last decades, valuable natural areas considered as zones of silence and rest have been increasingly struggling with the problem of mass tourism. In this study, an investigation of the effect of visitors on the properties of vegetation of calcareous grasslands in the context of width and distances from tourist trails is performed. The study was conducted in seven localities in Cracow (southern Poland) involving calcareous grasslands impacted by tourist trails. The results show that the lower height of plants, the greater number of species and the greater percentage of plant cover damaged by trampling in plots located close to the edge of tourist trails, as well as lower total plant cover and greater mean cover-abundance degree per species along narrow pathways. The dominance of meadow and grassland species, as well as the prevalence of native species, suggests that the composition of the examined vegetation has not been drastically changed. In the majority of the study plots, the dominance of hemicryptophytes and chamaephytes, inconsiderable share of phanerophytes and therophytes, as well as the low share of geophytes, were observed. The infrequent occurrence of species presenting Bidens dispersal type along narrow pathways, as well as in plots located close to the edge of tourist trails, suggests low external transport of epizoochorous seeds by passing people, while the prevalence of species presenting Cornus type in plots located away from the edge of tourist trails might be the effect of dung deposition by animals.

Changes in grassland bird communities and breeding success after a fire in the Argentinian Pampas

Fire is responsible for the structure and composition of the biological communities in grasslands, despite this, few studies evaluate the effects of fire on bird communities, especially in the southern cone of South America. We compared the structure and composition of vegetation, bird communities, density of nests and predation rates between burnt and unburnt areas in grassland habitats in the Argentine Pampas during two reproductive seasons following a fire. The abundance, richness and diversity of birds were lower in the burnt areas and followed a pattern of interannual recovery associated with the increase in vegetation cover. The density of nests and the number of nesting species was higher in the controls only during the first season. The risk of predation of artificial nests in burnt areas was greater 1 year after the fire in respect to the controls, this difference decreased over time in inverse relationship with the percentage of plant cover surrounding the nests. Our results highlight the importance of a good vegetation structure and cover to support abundant and species-rich bird communities, as well as high values of nest density and reproductive success, and the ability of vegetation and bird communities to recover after the fire. However, this successional and temporary loss of habitats of high nesting value should be analyzed on a larger scale in order to consider the effect of the total reduction, and the fragmentation of the grasslands in a good state of conservation, on the population dynamics of grassland birds.

Shifts in Vegetation Cover of Southern California Deserts in Response to Recent Climate Variations

In the deserts of Southern California, air temperatures have been rising and precipitation variability has been increasing over the past several decades. These recent climate shifts may have begun to threaten the survival of certain plant and animal species in these arid ecosystems. This study was designed to quantify and characterize variations in vegetation canopy density using more than 30 consecutive years of Landsat satellite image data across the western Lower Colorado (Sonoran) and southern Mojave Desert region. Mapping of the normalized difference vegetation index (NDVI) from Landsat images (1985 to 2017), which has been closely correlated with percent cover measurements of green vegetation canopies in a variety of arid ecosystems, was used to detect periodic upslope and downslope shifts in plant cover. The change in Landsat NDVI between 1985 and 2017 within the Santa Rosa Mountains Wilderness at four elevation zones between 500 m and 2500 m showed that vegetation green cover dropped notably in below-average precipitation periods, whereas green cover increased sharply in above-average precipitation years. This same temporal pattern of shifting in NDVI was detected along steep elevation gradients in the Anza-Borrego Desert State Park and in the Little San Bernardino Mountains of Joshua Tree National Park. Although the distribution of the dominant plant species along elevation gradients may have increased by more than 60 m over several decades (prior to 2007), we found no evidence that upslope shifts in percent plant cover have yet become a permanent pattern at these mountainous desert sites.

What factors influence colonization of lichens, liverworts, mosses and vascular plants on snags?

The dead standing trees i.e. snags are known as habitat for epiphytic and epixylic species including first of all lichens and bryophytes. The vascular plants are much rarer on this type of coarse woody debris (CWD). The eighty snags (CWD elements higher than 1.5 m) of Norway spruce Picea abies and beech Fagus sylvatica in the Karkonosze Mts. were examined for the presence of lichens, liverworts, mosses and vascular plants. The height of snags, their decomposition stage, cover of bark, diameter at breast height (DBH) as well as site conditions (elevation, slope and aspect, presence in forest community) were measured and noted. The percent cover of plants and lichens were estimated on each snag. Totally 99 taxa were recorded. There lichen species were dominant (44), followed by mosses (34), liverworts (13) and there were only 8 vascular plants. The total species richness varied from 1 to 22 taxa. The species composition growing on snags was subjected to canonical correspondence analysis and statistical analyses. They revealed that the species identity of snag is one of the most important factors influencing species composition. The number of species is positively correlated with DBH whereas decomposition stage, presence of bark, snag height are not significant factors. The species richness increases also with altitude what is connected with higher abundance of spruce snags. The occurrence of snags in this area is mainly associated with forest management practices in the past. Despite of some observed patterns in colonization of snags they are important habitat especially for lichens.

Grassland fragmentation and its influence on woody plant cover in the southern Great Plains, USA

Woodland and agricultural expansion are major causes of grassland fragmentation. Fire and rainfall play important roles in maintaining grasslands, however, fire activity has been reduced in fragmented landscapes. Quantify the degree to which basic landscape fragmentation metrics could be used as drivers of woody cover potential. Woody plant percent cover was calculated between 2004 and 2008 at > 2000 sites. At each site, we calculated these fragmentation metrics for grassland cover type (classified by the National Land Cover Database); # patches, landscape proportion, edge density, largest patch index, effective mesh size and patch cohesion index within 3 circular areas (10 km2, 360 km2 and 3600 km2) surrounding the sampling site. A quantile regression was performed to identify which metrics were useful at predicting the 25th, 50th, 75th or 95th quantile of woody cover distribution. Grassland proportion and edge density were significant predictors of the woody plant potential (75th and 95th quantile). Woody cover potential was positively associated with edge density suggesting that fragmented areas (i.e., areas with high number of edges) maintained higher woody cover, while grassland proportion was negatively associated with woody plant potential. We propose that in addition to a lack of fire, fragmented landscapes may facilitate further woodland expansion by reducing natural land and restricting grasslands to smaller, less connected patches, which can maintain higher woody cover. Given current trends in woodland expansion, special attention should be given to areas that are found within a fragmented landscape and climatically prone to woodland expansion.

Impacts and Best Management Practices for Erect Veldtgrass (Ehrharta erecta)

AbstractErect veldtgrass (Ehrharta erecta Lam.) is an invasive grass actively spreading in California that is capable of invading multiple habitats. Our objective is to contribute to a better understanding of the ecology, impacts, and potential for control of E. erecta in order to guide management practices. In a mixed-evergreen forest in Santa Cruz County, we measured impacts of E. erecta on native plant species richness and abundance in an observational comparison across 11 sites. Strikingly, we measured nearly four times greater total vegetation cover in plots invaded by E. erecta. However, native plants were not significantly less abundant in invaded plots than in reference plots, and native cover was not significantly predicted by E. erecta cover within invaded plots. We did, however, find evidence of change in community composition in response to E. erecta abundance. Our findings demonstrate that native species can persist in the presence of E. erecta, although the long-term impacts on populations of the perennial plants that dominate this forest understory are still unknown.We also compared the effectiveness of mechanical (hand pulling with volunteers) and chemical (glyphosate) management methods. Twenty-two months following management treatments, we found substantial reductions in E. erecta using both mechanical and herbicide treatments, but herbicide application also produced greater reductions in native species cover and species richness. Transplanting native yerba buena [Clinopodium douglasii (Benth.) Kuntze] into management plots following treatment did not slow regrowth of E. erecta. It did, however, increase total native plant percent cover in herbicide and pull treatments, although largely by increasing C. douglasii cover. Effective management is possible using either manual or chemical removal methods; the optimal method may depend on the availability of manual labor and the sensitivity of the habitat to non-target effects on native plants.

Stress and subsidy effects of seagrass wrack duration, frequency, and magnitude on salt marsh community structure.

Environmental perturbations can strongly affect community processes and ecosystem functions by acting primarily as a subsidy that increases productivity, a stress that decreases productivity, or both, with the predominant effect potentially shifting from subsidy to stress as the overall intensity of the perturbation increases. While perturbations are often considered along a single axis of intensity, they consist of multiple components (e.g., magnitude, frequency, and duration) that may not have equivalent stress and/or subsidy effects. Thus, different combinations of perturbation components may elicit community and ecosystem responses that differ in strength and/or direction (i.e., stress or subsidy) even if they reflect a similar overall perturbation intensity. To assess the independent and interactive effects of perturbation components, we experimentally manipulated the magnitude, frequency, and duration of wrack deposition, a common stress-subsidy in a variety of coastal systems. The effects of wrack perturbation on salt marsh community and ecosystem properties were assessed both in the short-term (at the end of a 12-week experimental manipulation) and long-term (6 months after the end of the experiment). In the short-term, plants and associated benthic invertebrates exhibited primarily stress-based responses to wrack perturbation. The extent of these stress effects on density of the dominant plant Spartina alterniflora, total plant percent cover, invertebrate abundance, and sediment oxygen availability were largely determined by perturbation duration. Yet, higher nitrogen content of Spartina, which indicates a subsidy effect of wrack, was influenced primarily by perturbation magnitude in the short-term. In the longer term, perturbation magnitude determined the extent of both stress and subsidy effects of wrack perturbation, with lower subordinate plant percent cover and snail density, and higher Spartina nitrogen content in high wrack biomass treatments. However, stress effects on the marsh community were generally less pronounced 6 months after the wrack perturbation, indicating capacity for recovery. Our results demonstrate that individual perturbation components can determine the degree to which its effects on the community elicit primarily stress- and/or subsidy-based responses. Further, the nature and extent of stress-subsidy effects can change over time, depending on species' relative ability to tolerate and/or recover from perturbation.

A Quarter-Century of Change Without Fire: The High-Elevation Pitch Pine Community on Panther Knob, Pendleton County, West Virginia

The Panther Knob Preserve is important in the Central Appalachians because it is the region's largest high-elevation pitch pine (Pinus rigida) community, containing numerous rare and threatened plants and animals. Plant community structure and evidence of fire in 2008 were quantified to (a) document successional changes since 1985, and (b) test the hypothesis of pitch pine regeneration failure without recent fire. Diameter at breast height (dbh) of trees and percent cover of plants within 19 plots, each 20 × 20 m, were measured. Increment borings were used to estimate stand age, and evidence of fire, such as bark charring and soil charcoal, was recorded. Mineral soil from the top 10 cm was collected to evaluate the connection between soil characteristics and plant composition. Cluster analysis of percent cover values identified four plant community types. Diameter distributions, age structure, and the presence of only seven seedlings indicated little recent pine regeneration on the plateau. Comparisons with Fleming's (1985) observations showed that pines are taller but declined in percent cover, that ericaceous shrubs are denser, and that the threatened variable sedge, Carex polymorpha, has declined. Charred woody debris, fire scars, or soil charcoal occurred at 16 of 19 sites. Plant community structure, represented by nonmetric multidimensional scaling (NMS) ordination axes, was not correlated directly with the presence of fire evidence or soil mineral nutrients (principal components analysis [PCA] axes). A new conceptual model of pine dynamics on Panther Knob is introduced. Successional pathways with and without fire are discussed in the context of management.