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At least 73 records · Page 4Linked to original sources
USGS2013

Presence of indicator plant species as a predictor of wetland vegetation integrity

We fit regression and classification tree models to vegetation data collected from Ohio (USA) wetlands to determine (1) which species best predict Ohio vegetation index of biotic integrity (OVIBI) score and (2) which species best predict high-quality wetlands (OVIBI score >75). The simplest regression tree model predicted OVIBI score based on the occurrence of three plant species: skunk-cabbage (Symplocarpus foetidus), cinnamon fern (Osmunda cinnamomea), and swamp rose (Rosa palustris). The lowest OVIBI scores were best predicted by the absence of the selected plant species rather than by the presence of other species. The simplest classification tree model predicted high-quality wetlands based on the occurrence of two plant species: skunk-cabbage and marsh-fern (Thelypteris palustris). The overall misclassification rate from this tree was 13 %. Again, low-quality wetlands were better predicted than high-quality wetlands by the absence of selected species rather than the presence of other species using the classification tree model. Our results suggest that a species’ wetland status classification and coefficient of conservatism are of little use in predicting wetland quality. A simple, statistically derived species checklist such as the one created in this study could be used by field biologists to quickly and efficiently identify wetland sites likely to be regulated as high-quality, and requiring more intensive field assessments. Alternatively, it can be used for advanced determinations of low-quality wetlands. Agencies can save considerable money by screening wetlands for the presence/absence of such “indicator” species before issuing permits.

Ohio↗
USGS2013

Spatial contexts for temporal variability in alpine vegetation under ongoing climate change

A framework to monitor mountain summit vegetation (The Global Observation Research Initiative in Alpine Environments, GLORIA) was initiated in 1997. GLORIA results should be taken within a regional context of the spatial variability of alpine tundra. Changes observed at GLORIA sites in Glacier National Park, Montana, USA are quantified within the context of the range of variability observed in alpine tundra across much of western North America. Dissimilarity is calculated and used in nonmetric multidimensional scaling for repeated measures of vascular species cover at 14 GLORIA sites with 525 nearby sites and with 436 sites in western North America. The lengths of the trajectories of the GLORIA sites in ordination space are compared to the dimensions of the space created by the larger datasets. The absolute amount of change on the GLORIA summits over 5 years is high, but the degree of change is small relative to the geographical context. The GLORIA sites are on the margin of the ordination volumes with the large datasets. The GLORIA summit vegetation appears to be specialized, arguing for the intrinsic value of early observed change in limited niche space.

Montana↗
USGS2015

Core-satellite species hypothesis and native versus exotic species in secondary succession

A number of hypotheses exist to explain species’ distributions in a landscape, but these hypotheses are not frequently utilized to explain the differences in native and exotic species distributions. The core-satellite species (CSS) hypothesis predicts species occupancy will be bimodally distributed, i.e., many species will be common and many species will be rare, but does not explicitly consider exotic species distributions. The parallel dynamics (PD) hypothesis predicts that regional occurrence patterns of exotic species will be similar to native species. Together, the CSS and PD hypotheses may increase our understanding of exotic species’ distribution relative to natives. We selected an old field undergoing secondary succession to study the CSS and PD hypotheses in conjunction with each other. The ratio of exotic to native species (richness and abundance) was observed through 17 years of secondary succession. We predicted species would be bimodally distributed and that exotic:native species ratios would remain steady or decrease through time under frequent disturbance. In contrast to the CSS and PD hypotheses, native species occupancies were not bimodally distributed at the site, but exotic species were. The exotic:native species ratios for both richness (E:N richness ) and abundance (E:N cover ) generally decreased or remained constant throughout supporting the PD hypothesis. Our results suggest exotic species exhibit metapopulation structure in old field landscapes, but that metapopulation structures of native species are disrupted, perhaps because these species are dispersal limited in the fragmented landscape.

Illinois↗
USGS2015

Local climate and cultivation, but not ploidy, predict functional trait variation in Bouteloua gracilis (Poaceae)

Efforts to improve the diversity of seed 18 resources for important restoration species has become a high priority for land managers in many parts of the world. Relationships between functional trait values and the environment from which seed sources are collected can provide important insights into patterns of local adaptation and guidelines for seed transfer. However, little is known about which functional traits exhibit genetic differentiation across populations of restoration species and thus may contribute to local adaptation. Here, we report the results of a common garden experiment aimed at assessing genetic (including ploidy level) and environmental regulation of several functional traits among populations of Bouteloua gracilis, a dominant C4 grass and the most highly utilized restoration species across much of the Colorado Plateau. We found that leaf size and specific leaf area (SLA) varied significantly among populations, and were strongly correlated with the source population environment from which seeds were collected. However, variation in ploidy level had no significant effect on functional traits. Leaves of plants grown from commercial seed releases were significantly larger and had lower SLA than those from natural populations, a result that is concordant with the overall relation between climate and these two functional traits. We suggest that the patterns of functional trait variation shown here may extend to other grass species in the western USA, and may serve as useful proxies for more extensive genecology research. Furthermore, we argue that care should be taken to develop commercial seed lines with functional trait values that match those of natural populations occupying climates similar to target restoration sites.

Plant Ecology↗
USGS2017

Aridity increases below-ground niche breadth in grass communities

Aridity is an important environmental filter in the assembly of plant communities worldwide. The extent to which root traits mediate responses to aridity, and how they are coordinated with leaf traits, remains unclear. Here, we measured variation in root tissue density (RTD), specific root length (SRL), specific leaf area (SLA), and seed size within and among thirty perennial grass communities distributed along an aridity gradient spanning 190–540 mm of climatic water deficit (potential minus actual evapotranspiration). We tested the hypotheses that traits exhibited coordinated variation (1) among species, as well as (2) among communities varying in aridity, and (3) functional diversity within communities declines with increasing aridity, consistent with the “stress-dominance” hypothesis. Across communities, SLA and RTD exhibited a coordinated response to aridity, shifting toward more conservative (lower SLA, higher RTD) functional strategies with increasing aridity. The response of SRL to aridity was more idiosyncratic and was independent of variation in SLA and RTD. Contrary to the stress-dominance hypothesis, the diversity of SRL values within communities increased with aridity, while none of the other traits exhibited significant diversity responses. These results are consistent with other studies that have found SRL to be independent of an SLA–RTD axis of functional variation and suggest that the dynamic nature of soil moisture in arid environments may facilitate a wider array of resource capture strategies associated with variation in SRL.

Plant Ecology↗
USGS2017

The role of salinity tolerance and competition in the distribution of an endangered desert salt marsh endemic

Rare plants are often associated with distinctive soil types, and understanding why endemic species occur in unique environments is fundamental for their management. At Ash Meadows National Wildlife Refuge in southern Nevada, USA, we evaluated whether the limited distribution of endangered Amargosa niterwort (Nitrophila mohavensis) is explained by this species’ tolerance of saline soils on salt-encrusted mud flats compared with the broadly distributed desert saltgrass (Distichlis spicata var. stricta). We simultaneously explored whether niterwort distribution is restricted from expanding due to interspecific competition with saltgrass. Surface soils collected throughout niterwort’s range were unexpectedly less saline with lower extractable Na, seasonal electroconductivity, and Na absorption ratio, and higher soil moisture than in adjacent saltgrass or mixed shrub habitats. Comparison of niterwort and saltgrass growth along an experimental salinity gradient in a greenhouse demonstrated lower growth of niterwort at all but the highest NaCl concentrations. Although growth of niterwort ramets was similar when transplanted into both habitats at the refuge below Crystal Reservoir, niterwort reproductive effort was considerably higher in saltgrass compared to its own habitat, implying reallocation of resources to sexual reproduction to maximize fitness when the probability of ramet mortality increases with greater salinity stress. Saltgrass was not a demonstrated direct competitor of niterwort; however, this species is known to increase soil salinity by exuding salt ions and through litterfall. Niterwort conservation will benefit from protecting hydrological processes that reduce salinity stress and preventing saltgrass colonization into niterwort habitat.

Nevada↗
USGS2017

The influence of soil resources and plant traits on invasion and restoration in a subtropical woodland

It has been shown in some cases that nitrogen (N) addition to soil will increase abundance of plant invaders because many invaders have traits that promote rapid growth in response to high resource supply. Similarly, it has been suggested, and sometimes shown, that decreasing soil N via carbon (C) additions can facilitate native species recovery. Yet all species are unlikely to respond to resource supply in the same way. We asked how soil nutrients and competition affect native and exotic woody species in a restoration experiment where we added N or C, and crossed soil manipulation with the manipulation of dominant exotic grass abundance in a Hawaiian subtropical woodland. We related changes in survival and growth of outplanted individuals to native/exotic status and plant traits. As a group, N-fixers showed reduced survival compared to non-fixers in response to added N, with Morella faya (exotic) and Acacia koa (native) having dramatic negative responses. Among non-fixers, species with greater foliar %N had more positive survival responses to increasing soil N. Specific leaf area was not predictive of responses to nutrients or competition. In general, responses to carbon addition were weak, although reducing competition from existing exotic grasses was beneficial for all outplanted species, with N-fixers showing the most positive response. We conclude that commonly used restoration strategies to clear exotic species or lower soil resources with C addition will most greatly benefit N-fixing species, which themselves may be unwanted invaders. Thus statements about the influence of increased soil N on invasions should be carefully dissected by considering the traits (such as N-fixation status) of the regional species pool.

Hawai'i↗
USGS2018

Changes in structure and physiological functioning due to experimentally enhanced precipitation seasonality in a widespread shrub species

Semi-arid shrub steppe occupies a vast geographic range that is characterized in part by distinct seasonal patterns in precipitation. Few studies have evaluated how variability in both the amount and timing of precipitation affect the structure and physiology of shrubs in these systems. We quantified changes in foliar crown parameters, xylem anatomy, gas exchange, and hydraulic transport capacity in deep-rooted Artemisia tridentata shrubs following 20 years of experimental manipulations in amount and seasonal timing of precipitation. We hypothesized that shrub growth (total leaf area per shrub and cover of shrub community), hydraulic transport efficiency, and gas exchange would increase in shrubs in irrigated plots compared to non-irrigated control plots, especially for irrigation applied in winter rather than summer. We also predicted similar changes in xylem anatomy (ring width, vessel size and frequency). Most treatment responses entailed changes in plant structure, and were generally consistent with our hypotheses: total-shrub leaf area, shrub basal area, canopy cover, and maximum sapwood-specific branch hydraulic conductivity were more than 2× greater in shrubs in winter-irrigated compared to control plots, while summer irrigation had few effects on these variables. Irrigation in either season did not affect xylem vessel size, but did increase xylem ring width by ~ 2 × and decreased xylem vessel frequency by about half. Anatomical, morphological, and stand-level abundance of A. tridentata appeared much more responsive to irrigation than state changes in gas exchange, particularly when the extra water is received during winter. Thus, it appears for sagebrush that seasonal timing is at least as important as the amount of precipitation, and that responses to changes in precipitation timing occur through changes in carbon allocation more so than changes in leaf-level carbon gain.

Plant Ecology↗
USGS2018

Scale dependence of diversity in alpine tundra, Rocky Mountains, USA

Drivers of alpine plant community composition have been observed to vary with scale. Diversity of alpine tundra across four regions of the Rocky Mountains and among plots within one region was examined relative to temperature and precipitation variables. For regional scale analyses, averages of three metrics of plot-level species diversity relative to environmental variables and regional gamma diversity were examined for a subset of 60 plots from a stratified random sample in each region. For local scale analyses, additional soil and climate variables were included at 96 plots from one of the four regions. Correlations and visual examination of bivariate plots elucidated possible controls of cold temperatures and gamma diversity on average diversity metrics among the four regions and of precipitation and/or location on plot-level metrics within the single region. For the latter, the bivariate graph indicated a triangular distribution in which all levels of diversity exist at low precipitation but only low diversity at higher precipitation. We propose that change in drivers with scale is a general result of the relative importance of temperature and water in seed production (temperature > water) and seedling establishment (vice versa) and the logical priority of seed production over seedling establishment.

Colorado, Montana, New Mexico, Wyoming↗
USGS2019

Postfire population dynamics of a fire-dependent cypress

Tecate cypress ( Hesperocyparis forbesii ) is a rare species restricted to four metapopulations in southern California, USA and a few isolated stands in northern Baja California, Mexico. It is a closed-cone, fire-dependent tree of conservation concern due to an increase in human-caused wildfires that have shortened the interval between fires in many of their populations. In 2003 the Mine/Otay Fire burned 70% of the Tecate cypress on Otay Mountain in San Diego County, California providing an opportunity to evaluate the immaturity risk of this species and to examine its recruitment, survivorship, and reproductive maturity over a 14-year period from 2004 to 2017. Sixteen plots were established in burned stands of Tecate cypress with prefire ages that ranged from 7 to 53 years old. After 14 years the overall density of Tecate cypress was still higher than before the fire, however the areal extent of the species decreased due to the loss of locations where either there was low cone production or fire intensity was too high. The immaturity risk for this species, while a function of prefire stand age, is confounded by other factors including the reproductive capacities of trees based on their density and size and the climatic variables affecting their growth over time. The future management of Tecate cypress and other fire-dependent species requires a knowledge of all factors impacting their immaturity risk, as well as an understanding of the potential fire-climate interactions that may impact their persistence in a future of climate change and altered fire regimes.

California↗
USGS2020

Influence of soil microbiota on Taxodium distichum seedling performance during extreme flooding events

Plant associations with soil microbiota can modulate tree seedling growth and survival via mutualistic or antagonistic interactions. It is uncertain, however, whether soil microbiota influence seedling growth of coastal trees when exposed to extreme flooding regimes. We evaluated the role of soil microbes in promoting baldcypress ( Taxodium distichum ) seedling performance under different inundation scenarios and determined the influence of flooding on the colonization of in planta beneficial microbes. Seedlings reared in sterile and non-sterile soil were exposed to three different flooding regimes historically experienced in Louisiana swamps. Seedling growth was assessed, and the colonization by beneficial symbionts such as arbuscular mycorrizhal fungi (AMF), and dark septate endophytes (DSE) was evaluated in harvested roots. Seedlings grown in sterile soil had six times higher growth than seedlings reared in non-sterile soil. As a result, we evaluated pathogen load in the roots by assessing oomycete colonization. Flooding influenced the in planta colonization of DSE and oomycetes, but did not affect the colonization of mutualist AMF fungi. DSE and oomycetes were rarer in flooded conditions, while AMF remained abundant. Seedling biomass production was not correlated with in planta fungal colonization or pathogen load. Soil microbiota can negatively influence baldcypress seedling growth, and no growth benefit was evidenced from the root colonization of mutualist fungi. Flooding can modify baldcypress-fungal interactions by diminishing colonization of DSE. Overall, baldycpress seedlings were more sensitive to the presence of microbiota than flooding, and thus restoration efforts should focus on having a better understanding of plant–microbe interactions in swamps.

Louisiana↗
USGS2020

Architecture of remnant trees influences native woody plant recruitment in abandoned Hawaiian pastures

Abandoned tropical pastures offer opportunities for passive and active restoration of native forest communities. Tree architecture of remnant canopy trees may be one important factor that can facilitate native plant recruitment in abandoned pastures but has largely been overlooked. Here, we evaluated patterns of native woody plant recruitment under remnant trees in abandoned pastures on Hawai’i Island and how these might be related to both tree architectural features and landscape variables. We measured native woody stems (excluding sprouts of the tree itself) in a 5 m radius around the base of each tree and modeled total basal area of native stems as a function of tree architectural characteristics. Recruitment was positively correlated with tree height as well as horizontal woody area below 1 m (tree structure that occurred below 1 m and was < 45° angle from the ground) around the base of trees. Tall trees likely attract more avian seed dispersers due to their higher visibility on the landscape and increased crown volume. Horizontal woody area likely provides establishment microsites that are above the pasture grass layer, similar to how dead or decaying logs act as nurse substrates. Unlike previous studies, we found little evidence that landscape variables such as distance to the intact forest or nearest canopy neighbor influenced understory recruitment. Tree architectural characteristics can be important predictors of native plant recruitment in abandoned tropical pastures and should be considered in addition to local and landscape-level variables.

Hawaii↗
USGS2023

Divergent physiological responses of hydric and mesic riparian plant species to a Colorado River experimental flow

Riparian plant species can differ in their responses to streamflow variation in ways that strongly influence the composition and functioning of riparian plant communities. Quantifying these differences and the potential asymmetry of responses to low- versus high-flow phases of stream fluctuations is important for predicting and managing vegetation responses to variation in flow regimes. We measured the physiological response of two riparian plant species with different habitat preferences to an experimental flow that progressed from a low-flow to high-flow phase. Schedonorous arundinaceus , a hydric grass growing in near-channel habitat, exhibited significant and biologically substantial declines in stem water potential (SWP) during the low-flow phase of the experiment and a saturating increase in leaf relative water content (LRWC) during the high-flow phase. These patterns are consistent with cavitation risk in response to low-flow anomalies and saturating responses to high-flow anomalies in this hydric species. Pluchea sericea , a mesic shrub growing at intermediate elevations above the channel, exhibited a decrease in LRWC during the low-flow phase and an increase in SWP during the high-flow phase. These patterns are consistent with protection from stem cavitation risk during drought through leaf dehydration and opportunistic increases in water status in response to high-flow anomalies in this mesic species. The asymmetrical responses of both species to low- versus high-flow phases demonstrate unique physiological responses to flow anomalies of contrasting directions attributable to species habitat preferences and functional strategies that can be used by managers to predict non-linear vegetation responses to flow variation.

Plant Ecology↗
USGS2025

Blowing in the wind: Anemochory in blackbrush habitat of South Texas

Wind dispersal has the potential to carry seeds long-distances and could inform the management and restoration of natural vegetation along the U.S.-Mexico Border. Plant species with the potential to disperse seeds in arid landscapes fragmented by border barrier infrastructure include foundational native, invasive, and federally endangered plant species. Wind dispersal traps constructed of cloth were set facing into the prevailing wind direction (SE) to characterize the role of wind in transporting soil particles, pebbles, plant debris, and seeds in blackbrush habitat during maximum events of wind speed (km per hour), and precipitation (cm). Shrubs, native grasses, the invasive Pennisetum ciliare (buffelgrass), soil particles, and pebbles dispersed in the wind, especially during maximum wind and/or precipitation events. Natural blackbrush areas supported the wind dispersal of twelve native species including grasses and woody shrubs. Sites disturbed by border infrastructure (barrier, roads, waterways) had higher seed numbers of invasive species such as P. ciliare captured in the wind traps. While modifications in passages through waterways and other structures have been proposed to improve the movement of organisms influenced by the barrier, the restoration of native plant species in damaged areas might further aid in the maintenance of blackbrush ecosystems by reducing invasive plant species dispersal into natural habitats.

Texas↗
USGS2025

Reproductive output of the rare plant Arctomecon californica does not appear to be limited by its floral visitor community

The majority of plants rely on animal-mediated pollination for reproduction. Reductions in pollinator visitations can lead to pollen limitation and declines in seed production. Arctomecon californica, the Las Vegas bearpoppy, is a rare plant native to the northeastern Mojave Desert. It is pollinator dependent for reproduction as it is self-incompatible, but associated pollinator populations can fluctuate greatly year to year. We therefore investigated if the reproductive output of A. californica is reduced in a year with lower pollinator visitation (2022) compared to a year when visitors were more abundant (2023). We documented the visiting bee community across both years and compared rates of A. californica seed fertilization and development across populations and between the two years. We collected and identified bees from 18 genera visiting A. californica flowers over the two years, with significant differences in the bee communities between years. There were significantly fewer overall bee visits to A. californica flowers in 2022 compared to 2023, but we found no impact on reproductive output, with overall high rates of seed production in both years.

Nevada↗
USGS2022

CO2 uptake offsets other greenhouse gas emissions from salt marshes with chronic nitrogen loading

Coastal wetlands are known for exceptional productivity, but they also receive intense land-based nitrogen (N) loading. In Narragansett Bay, RI (USA), coastal ecosystems have received anthropogenic N inputs from wastewater for more than two centuries. Greenhouse gas fluxes were studied throughout a growing season (2016) in three coastal wetlands with contrasting histories of nitrogen loading. The wetland with the highest historic N load (Mary’s Creek, Warwick, RI) had significantly greater nitrous oxide (N 2 O) and methane (CH 4 ) emissions than the other two sites. However, the two marshes with historic N loads (Mary’s Creek and Mary Donovan, Little Compton, RI) also had greater rates of CO 2 uptake than the reference site (Nag Marsh, Prudence Island, RI). Their CO 2 uptake rates far outpaced their other greenhouse gas emissions. Mary’s Creek had the greatest above- and below-ground plant biomass, vertical accretion rates, and carbon content of soils. Spartina alterniflora height was greatest at Mary’s Creek and Mary Donovan marsh. The following growing season (2017), greenhouse gases were compared across four plant-defined ecological zones in Mary’s Creek. Higher rates of CO 2 uptake and CH 4 emissions were found in the S. alterniflora -vegetated creekbank compared to high marsh zones or bare mudflats. Potential denitrifying enzyme activity did not significantly differ across the four zones nor between Mary’s Creek and Nag Marsh, suggesting a consistently high capacity to completely reduce N loads. These results support efforts to protect and restore these coastal ecosystems for their carbon sequestration function even despite prevalence of anthropogenic N loading.

Rhode Island↗
USGS2023

Genetic analysis of North American Phragmites australis guides management approaches

Phragmites australis subsp. australis is an invasive and ecologically detrimental plant in multiple regions of North America. Its co-occurrence with the native subspecies, and multiple instances of hybridization, has created the need to differentiate Phragmites subspecies or haplotypes so that management can be appropriately targeted to the invader. We compiled a review of current genetic discrimination methods among the three Phragmites subspecies inhabiting the United States and Canada, and discussed how each method can contribute to control of the introduced subspecies while preserving the two endemic subspecies. We also discussed various control tools and the implications of Phragmites genetics for implementation. The Phragmites subspecies endemic to North America have environmental or infrastructure significance (e.g., habitat sustainability, biodiversity, storm surge and erosion protection). Thus, faster and more accurate differentiation among the endemic and introduced subspecies is needed. Additionally, more in-depth genetic information on Phragmites subspecies could support better management decisions, as well as the development of improved control treatments. This review highlights technologies and approaches currently available for genetic identification, recently collected genomic, transcriptomic and proteomic information, and implications for biological control and herbicide treatments.

Aquatic Botany↗
USGS2011

Lianas escape self-thinning: Experimental evidence of positive density dependence in temperate lianas Celastrus orbiculatus and C. scandens

The neighborhood density of plants strongly affects their growth, reproduction, and survival. In most cases, high density increases competition and negatively affects a focal plant in predictable ways, leading to the self-thinning law. There are, however, situations in which high densities of plants facilitate focal plant performance, resulting in positive density dependence. Despite their importance in forest gap dynamics and distinctive growth form, there have been very few studies of the effect of density on lianas or vines. We grew an invasive ( Celastrus orbiculatus ) and a native ( Celastrus scandens ) liana species together in three different density treatments, while also manipulating the light and support availability. We found that across treatment conditions, C. orbiculatus always out-performed C. scandens , showing greater relative growth rate in height and diameter, greater biomass and higher survival. Both species responded similarly to the density treatments: with plants in high density not showing a decrease in relative height growth rate compared to medium density. Aboveground biomass for C. scandens was not affected by density, while for C. orbiculatus , the most massive plants were growing in medium density without support. More surprisingly, survival analysis indicated that the two species both had significantly lower mortality rates in the highest density treatment; this trend held true across the other treatments of light and supports. More generally, this study demonstrates that these lianas can escape the consequences of high density and thus the self-thinning law that affects self-supporting plants. This suggests a broader hypothesis about lianas in general: their greater flexibility in allocating growth resources allows them to grow taller and thinner without collapsing and thereby potentially escape shading and mortality even at high densities.

Perspectives in Plant Ecology, Evolution and Syste↗