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At least 541 records · Page 30Linked to original sources
USGS1996

Plant succession and greentree reservoir management: Implications for management and restoration of bottomland hardwood wetlands

Bottomland hardwood forests are distributed along rivers and streams throughout the central and eastern United States, with the greatest concentration in the Southeast. Past and projected losses of bottomland hardwoods and degradation of remaining stands suggest that habitat management and/or restoration strategies that target multiple species and multiple uses will be necessary to maintain, enhance, and restore flora and fauna within bottomland hardwood wetlands. A greentree reservoir is a current management strategy that entails manipulating water regimes to provide habitat for wintering waterfowl. We conducted a literature review and synthesis to determine the potential impacts of greentree reservoir management on plant succession within bottomland hardwood wetlands. Greentree reservoirs can impact vegetation establishment through several processes. Despite shortcomings of greentree reservoirs, designs similar to them could be very beneficial in restoring bottomland hardwood plant and animal communities from degraded forests provided water-level control and maintenance are substantially improved. Emulation of natural hydrologic regimes, including natural variability, could produce diverse bottomland hardwood plant communities and provide habitat for a variety of wildlife species.

Wetlands↗
USGS1998

Long-term hydrologic effects on marsh plant community structure in the southern Everglades

Although large-scale transformation of Everglades landscapes has occurred during the past century, the patterns of association among hydrologic factors and southern Everglades freshwater marsh vegetation have not been well-defined. We used a 10-year data base on the aquatic biota of Shark Slough to classify vegetation and describe plant community change in intermediate- to long-hydroperiod Everglades marshes. Study area marsh vegetation was quantitatively grouped into associations dominated by 1) Cladium jamaicense , 2) a group of emergents including Eleocharis cellulosa, Sagittaria lancifolia , and Rhyncospora tracyi , 3) taxa associated with algal mats ( Utricularia spp. and Bacopa caroliniana ), and 4) the grasses Panicum hemitomon and Paspalidium geminatum . During the decade evaluated, the range of water depths that characterized our study sites approached both extremes depicted in the 40-year hydrologic record for the region. Water depths were near the long-term average during the mid-1980s, declined sharply during a late 1980s drought, and underwent a prolonged increase from 1991 through 1995. Overall macrophyte cover varied inversely with water depth, while the response of periphyton was more complex. An ordination analysis, based on plant species abundance, revealed that study area vegetation structure was associated with hydrologic patterns. Marsh plant community structure showed evidence of cyclic interannual variation corresponding to hydrologic change over the decade evaluated. Lower water depths, the occurrence of marl substrates, and high periphyton cover were correlated. These factors contributed to reduced macrophyte cover in portions of the study area from which water had been diverted.

Florida↗
USGS2001

Plant community composition and biomass in Gulf Coast Chenier Plain marshes: Responses to winter burning and structural marsh management

Many marshes in the Gulf Coast Chenier Plain, USA, are managed through a combination of fall or winter burning and structural marsh management (i.e., levees and water control structures; hereafter SMM). The goals of winter burning and SMM include improvement of waterfowl and furbearer habitat, maintenance of historic isohaline lines, and creation and maintenance of emergent wetlands. Although management practices are intended to influence the plant community, effects of these practices on primary productivity have not been investigated. Marsh processes, such as vertical accretion and nutrient cycles, which depend on primary productivity may be affected directly or indirectly by winter burning or SMM. We compared Chenier Plain plant community characteristics (species composition and above- and belowground biomass) in experimentally burned and unburned control plots within impounded and unimpounded marshes at 7 months (1996), 19 months (1997), and 31 months (1998) after burning. Burning and SMM did not affect number of plant species or species composition in our experiment. For all three years combined, burned plots had higher live above-ground biomass than did unburned plots. Total above-ground and dead above-ground biomasses were reduced in burned plots for two and three years, respectively, compared to those in unburned control plots. During all three years, belowground biomass was lower in impounded than in unimpounded marshes but did not differ between burn treatments. Our results clearly indicate that current marsh management practices influence marsh primary productivity and may impact other marsh processes, such as vertical accretion, that are dependent on organic matter accumulation and decay.

Environmental Management↗
USGS2015

C 3 and C 4 plant responses to increased temperatures and altered monsoonal precipitation in a cool desert on the Colorado Plateau, USA

Dryland ecosystems represent >40 % of the terrestrial landscape and support over two billion people; consequently, it is vital to understand how drylands will respond to climatic change. However, while arid and semiarid ecosystems commonly experience extremely hot and dry conditions, our understanding of how further temperature increases or altered precipitation will affect dryland plant communities remains poor. To address this question, we assessed plant physiology and growth at a long-term (7-year) climate experiment on the Colorado Plateau , USA, where the community is a mix of shallow-rooted C 3 and C 4 grasses and deep-rooted C 4 shrubs. The experiment maintained elevated-temperature treatments (+2 or +4 °C) in combination with altered summer monsoonal precipitation (+small frequent precipitation events or +large infrequent events). Increased temperature negatively affected photosynthesis and growth of the C 3 and C 4 grasses, but effects varied in their timing: +4 °C treatments negatively affected the C 3 grass early in the growing season of both years, while the negative effects of temperature on the C 4 grass were seen in the +2 and +4 °C treatments, but only during the late growing season of the drier year. Increased summer precipitation did not affect photosynthesis or biomass for any species, either in the year the precipitation was applied or the following year. Although previous research suggests dryland plants, and C 4 grasses in particular, may respond positively to elevated temperature, our findings from a cool desert show marked declines in C 3 and C 4 photosynthesis and growth, with temperature effects dependent on the degree of warming and growing-season precipitation.

Utah↗
USGS2019

Environmental gradients influence differences in leaf functional traits between native and non-native plants

Determining the characteristics of non-native plants that can successfully establish and spread is central to pressing questions in invasion ecology. Evidence suggests that some non-native species establish and spread in new environments because they possess characteristics (functional traits) that allow them to either successfully compete with native residents or fill previously unfilled niches. However, the relative importance of out-competing native species vs. filling empty niche space as potential mechanisms of invasion may depend on environmental characteristics. Here, we measured plant functional traits, proxies indicative of competitive and establishment strategies, to determine if these traits vary among native and invasive species and if their prevalence is dependent on environmental conditions. Using a natural environmental gradient in Hawai’i Volcanoes National Park, we evaluated how functional traits differ between native and non-native plant communities and if these differences change along an environmental gradient from hot, dry to cool, wet conditions. Functional trait differences suggested that both competition and open niche space may be important for invasion. Non-native communities tended to have traits associated with faster growth strategies such as higher specific leaf area and lower leaf thickness. However, native and non-native community traits became more dissimilar along the gradient, suggesting that non-native species may be occupying previously unfilled niche space at the hot, dry end of the gradient. We also found that most of the variation in functional trait values amongst plots was due to species turnover rather than intraspecific variation. These results highlight the role of environmental context when considering invasion mechanisms.

Hawaii↗
USGS1998

Effects of flooding, salinity and herbivory on coastal plant communities, Louisiana, United States

Flooding and salinity stress are predicted to increase in coastal Louisiana as relative sea level rise (RSLR) continues in the Gulf of Mexico region. Although wetland plant species are adapted to these stressors, questions persist as to how marshes may respond to changed abiotic variables caused by RSLR, and how herbivory by native and non-native mammals may affect this response. The effects of altered flooding and salinity on coastal marsh communities were examined in two field experiments that simultaneously manipulated herbivore pressure. Marsh sods subjected to increased or decreased flooding (by lowering or raising sods, respectively), and increased or decreased salinity (by reciprocally transplanting sods between a brackish and fresh marsh), were monitored inside and outside mammalian herbivore exclosures for three growing seasons. Increased flooding stress reduced species numbers and biomass; alleviating flooding stress did not significantly alter species numbers while community biomass increased. Increased salinity reduced species numbers and biomass, more so if herbivores were present. Decreasing salinity had an unexpected effect: herbivores selectively consumed plants transplanted from the higher-salinity site. In plots protected from herbivory, decreased salinity had little effect on species numbers or biomass, but community composition changed. Overall, herbivore pressure further reduced species richness and biomass under conditions of increased flooding and increased salinity, supporting other findings that coastal marsh species can tolerate increasingly stressful conditions unless another factor, e.g., herbivory, is also present. Also, species dropped out of more stressful treatments much faster than they were added when stresses were alleviated, likely due to restrictions on dispersal. The rate at which plant communities will shift as a result of changed abiotic variables will determine if marshes remain viable when subjected to RSLR.

Oecologia↗
USGS2023

Modeling habitat suitability across different levels of invasive plant abundance

Predicting where invasive plants are likely to spread and become abundant is critical for informing invasive plant management. Species distribution models are a key tool for informing the geography of invasion risk, but most distribution models are limited by their use of presence data, including no information on invader population abundance. In this study, we ask how habitat suitability varies for different levels of abundance for three invasive plants: stiltgrass ( Microstegium vimineum ), sericea lespedeza ( Lespedeza cuneata ), and privet ( Ligustrum sinense ). For each species, we used an ensemble distribution modeling approach to compare suitability for invasion estimated from subsets of point location data: all presences vs. locations with percent cover ≥ 1%, ≥ 5%, ≥ 10%, ≥ 25%, and ≥ 50%. For all species, the total area predicted as suitable for abundant populations was 32%–68% less than the area predicted as suitable for presence. For stiltgrass and sericea lespedeza, the area suitable for invasion decreased when predicted from higher levels of abundance, whereas for privet, suitable area was similar across abundance levels. Stiltgrass and sericea lespedeza are therefore likely to become highly abundant in a smaller portion of their ranges, while privet could become highly abundant anywhere it can establish at low abundance. Different environmental predictors explained suitability for presence versus abundance, suggesting the environmental niche associated with presence differs from that associated with high population abundance. Analyses of more species and growth forms are still needed, but our results combined with previous studies consistently show that fitting distribution models to point locations with ≥ 5–10% cover refines range maps and can produce a more targeted assessment of invasion risk.

Biological Invasions↗
USGS2020

Salinity and inundation effects on productivity of brackish tidal marsh plants in the San Francisco Bay-Delta Estuary

Plant productivity is central to numerous ecosystem functions in tidal wetlands. We examined how productivity of brackish marsh plants in northern California responded to abiotic stress gradients of inundation and salinity using two experimental approaches. In a greenhouse study with varying salinity, shoot production and biomass of Juncus balticus , Schoenoplectus acutus and S. americanus all declined monotonically with higher salinity, with evidence of differences in sensitivity among species by their varied functional responses. Salinity also negatively affected fecundity for the one species ( S. americanus ) that produced enough inflorescences during the experiment for analysis. In a field manipulation of inundation and initial pore water salinity, total end-of-season biomass and other metrics of growth in the high marsh species, J. balticus , had unimodal relationships with inundation. Root production tended to be greater strongly impacted by greater inundation than shoot production. The salinity treatment quickly dissipated for treatments that were flooded more frequently but persisted at a higher marsh elevation where it suppressed plant growth. These results suggest that both increased flooding and salinity associated with climate change and sea-level rise may negatively impact productivity of brackish marsh species, but with variable effects by species and stressor.

California↗
USGS2018

Vertical zonation and niche breadth of tidal marsh plants along the Northeast Pacific coast

The distribution patterns of sessile organisms in coastal intertidal habitats typically exhibit vertical zonation, but little is known about variability in zonation among sites or species at larger spatial scales. Data on such heterogeneity could inform mechanistic understanding of factors affecting species distributions as well as efforts to assess and manage coastal species and habitat vulnerability to sea-level rise. Using data on the vertical distribution of common plant species at 12 tidal marshes across the US Pacific coast, we examined heterogeneity in patterns of zonation to test whether distributions varied by site, species, or latitude. Interspecific zonation was evident at most sites, but the vertical niches of co-occurring common species often overlapped considerably. The median elevation of most species varied across marshes, with site-specific differences in marsh elevation profiles more important than differences in latitude that reflect regional climate gradients. Some common species consistently inhabited lower or higher elevations relative to other species, but others varied among sites. Vertical niche breadth varied more than twofold among species. These results indicate that zonation varies by both site and species at the regional scale, and highlight the potential importance of local marsh elevation profiles to plant vertical distributions. Furthermore, they suggest that coastal foundation species such as marsh plants may differ in their vulnerability to sea-level rise by being restricted to specific elevation zones or by occurring in narrow vertical niches.

Pacific Coast↗
USGS2023

Inundation tolerance, rather than drought tolerance, predicts riparian plant distributions along a local hydrologic gradient

Riparian vegetation varies along hydrologic gradients, along which inundation and drought tend to be inversely correlated. Differentiating effects of inundation and drought on plant distributions is critical for predicting impacts of changes to baseflows and designing flow patterns to achieve vegetation objectives in regulated river systems. To this end, we conducted a greenhouse experiment where we decreased, increased, or maintained constant water levels experienced by a suite of riparian plant species. We related changes in new root growth and stomatal conductance under experimental conditions to species hydrologic niches in the field, specifically the median elevation at which they occur above the channel, along the regulated Colorado River in Grand Canyon. We found a significant negative relationship between root growth response to experimental inundation with increasing elevation above the channel in the field, and a negative response of stomatal conductance to inundation among the most xeric-adapted species. Drought responses were idiosyncratic with respect to hydrologic niche, and instead seemed to vary in relation to clonality and rooting depth. Several Salicaceae tree species that are uncommon along regulated rivers exhibited consistently negative responses to both drought and inundation relative to other species, which may explain their rarity. The results of this study suggest that riparian plant distributions along hydrologic gradients have been shaped primarily by current and past levels of inundation. However, future anticipated declines in the water table are likely to produce species-specific responses based on drought tolerance that may in part be predicted from the results of this experiment.

Wetlands↗
USGS1982

Distribution and status of Vicia menziesii Spreng. (Leguminosae): Hawai'i's first officially listed endangered plant species

Vicia menziesii Spreng., Hawai'i's first officially listed endangered plant species, formerly occurred across a large area in the upper montane-mesic forest habitat on the windward side of the island of Hawai'i. Until this species was ‘rediscovered’ in 1974, it had last been seen in 1915, and it was presumed to be extinct. The population is presently thought to number 150–300 plants, most of which are seedlings. These are located within a 200 ha area on the eastern flank of Mauna Loa volcano. The primary factors responsible for the decline of V. menziesii are habitat loss and excessive predation on the plants by introduced ungulates. Continued logging and cattle grazing within its remnant range are major threats to its existence. Enhancing the survival of V. menziesii may best be accomplished by stabilizing its remaining habitat and allowing the population to reestablish itself naturally.

Hawai'i↗
USGS2009

Sediment losses and gains across a gradient of livestock grazing and plant invasion in a cool, semi-arid grassland, Colorado Plateau, USA

Large sediment fluxes can have significant impacts on ecosystems. We measured incoming and outgoing sediment across a gradient of soil disturbance (livestock grazing, plowing) and annual plant invasion for 9 years. Our sites included two currently ungrazed sites: one never grazed by livestock and dominated by perennial grasses/well-developed biocrusts and one not grazed since 1974 and dominated by annual weeds with little biocrusts. We used two currently grazed sites: one dominated by annual weeds and the other dominated by perennial plants, both with little biocrusts. Precipitation was highly variable, with years of average, above-average, and extremely low precipitation. During years with average and above-average precipitation, the disturbed sites consistently produced 2.8 times more sediment than the currently undisturbed sites. The never grazed site always produced the least sediment of all the sites. During the drought years, we observed a 5600-fold increase in sediment production from the most disturbed site (dominated by annual grasses, plowed about 50 years previously and currently grazed by livestock) relative to the never grazed site dominated by perennial grasses and well-developed biocrusts, indicating a non-linear, synergistic response to increasing disturbance types and levels. Comparing sediment losses among the sites, biocrusts were most important in predicting site stability, followed by perennial plant cover. Incoming sediment was similar among the sites, and while inputs were up to 9-fold higher at the most heavily disturbed site during drought years compared to average years, the change during the drought conditions was small relative to the large change seen in the sediment outputs. ?? 2009 Elsevier B.V. All rights reserved.

Aeolian Research↗
USGS2015

Bistability of mangrove forests and competition with freshwater plants

Halophytic communities such as mangrove forests and buttonwood hammocks tend to border freshwater plant communities as sharp ecotones. Most studies attribute this purely to underlying physical templates, such as groundwater salinity gradients caused by tidal flux and topography. However, a few recent studies hypothesize that self-reinforcing feedback between vegetation and vadose zone salinity are also involved and create a bistable situation in which either halophytic dominated habitat or freshwater plant communities may dominate as alternative stable states. Here, we revisit the bistability hypothesis and demonstrate the mechanisms that result in bistability. We demonstrate with remote sensing imagery the sharp boundaries between freshwater hardwood hammock communities in southern Florida and halophytic communities such as buttonwood hammocks and mangroves. We further document from the literature how transpiration of mangroves and freshwater plants respond differently to vadose zone salinity, thus altering the salinity through feedback. Using mathematical models, we show how the self-reinforcing feedback, together with physical template, controls the ecotones between halophytic and freshwater communities. Regions of bistability along environmental gradients of salinity have the potential for large-scale vegetation shifts following pulse disturbances such as hurricane tidal surges in Florida, or tsunamis in other regions. The size of the region of bistability can be large for low-lying coastal habitat due to the saline water table, which extends inland due to salinity intrusion. We suggest coupling ecological and hydrologic processes as a framework for future studies.

Florida↗
USGS2011

Estimating site occupancy rates for aquatic plants using spatial sub-sampling designs when detection probabilities are less than one

Estimation of site occupancy rates when detection probabilities are <1 is well established in wildlife science. Data from multiple visits to a sample of sites are used to estimate detection probabilities and the proportion of sites occupied by focal species. In this article we describe how site occupancy methods can be applied to estimate occupancy rates of plants and other sessile organisms. We illustrate this approach and the pitfalls of ignoring incomplete detection using spatial data for 2 aquatic vascular plants collected under the Upper Mississippi River's Long Term Resource Monitoring Program (LTRMP). Site occupancy models considered include: a naïve model that ignores incomplete detection, a simple site occupancy model assuming a constant occupancy rate and a constant probability of detection across sites, several models that allow site occupancy rates and probabilities of detection to vary with habitat characteristics, and mixture models that allow for unexplained variation in detection probabilities. We used information theoretic methods to rank competing models and bootstrapping to evaluate the goodness-of-fit of the final models. Results of our analysis confirm that ignoring incomplete detection can result in biased estimates of occupancy rates. Estimates of site occupancy rates for 2 aquatic plant species were 19–36% higher compared to naive estimates that ignored probabilities of detection <1. Simulations indicate that final models have little bias when 50 or more sites are sampled, and little gains in precision could be expected for sample sizes >300. We recommend applying site occupancy methods for monitoring presence of aquatic species.

Aquatic Botany↗
USGS2019

Explaining harvests of wild-harvested herbaceous plants: American ginseng as a case study

Wild-harvested plants face increasing demand globally. As in many fisheries, monitoring the effect of harvesting on the size and trajectory of resource stocks presents many challenges given often limited data from disparate sources. Here we analyze American ginseng ( Panax quinquefolius L.) harvests from 18 states in the eastern U.S. 1978–2014 to infer temporal patterns and evidence of population declines, and we test the effects of local environmental and socioeconomic factors on ginseng harvesting at the county level 2000–2014. Despite rising prices, annual wild ginseng harvests decreased from a high point in the late 1980s to early 1990s, then, in most, increased after 2005 or 2010 - suggesting range-wide overexploitation notwithstanding federal regulations that, since 1999, restrict minimum harvest age. County-level harvest rates increased with available habitat, road density, poverty and unemployment, but decreased when public land formed a large proportion of county area. Harvests were largest in the Southern Appalachian region. Poverty and accessibility were strongly related to high levels of harvesting. A key implication is that to conserve valuable wild native plant products while also improving local livelihoods, wild cultivation and good stewardship practices must be strongly promoted. Our approach to assessing the condition of wild populations offers a broad template that could be adapted to other wild-harvested plants.

Biological Conservation↗
USGS2016

Mosses in Ohio wetlands respond to indices of disturbance and vascular plant integrity

We examined the relationships between an index of wetland habitat quality and disturbance (ORAM score) and an index of vascular plant integrity (VIBI-FQ score) with moss species richness and a moss quality assessment index (MQAI) in 45 wetlands in three vegetation types in Ohio, USA. Species richness of mosses and MQAI were positively associated with ORAM and VIBI-FQ scores. VIBI-FQ score was a better predictor of both moss species richness and MQAI than was either ORAM score or vegetation type. This result was consistent with the strict microhabitat requirements for many moss species, which may be better assessed by VIBI-FQ than ORAM. Probability curves as a function of VIBI-FQ score were then generated for presence of groups of moss species having the same degree of fidelity to substrate and plant communities relative to other species in the moss flora (coefficients of conservatism, CCs). Species having an intermediate- or high degree of fidelity to substrate and plant communities (i.e., species with CC &ge; 5) had a 50% probability of presence (P 50 ) and 90% probability of presence (P 90 ) in wetlands with intermediate- and high VIBI-FQ scores, respectively. Although moss species richness, probability of presence of species based on CC, and MQAI may reflect wetland habitat quality, the 95% confidence intervals around P 50 and P 90 values may be too wide for regulatory use. Moss species richness, MQAI, and presence of groups of mosses may be more useful for evaluating moss habitat quality in wetlands than a set of &ldquo;indicator species.&rdquo;

Ohio↗
USGS2013

Predictive occurrence models for coastal wetland plant communities: delineating hydrologic response surfaces with multinomial logistic regression

Understanding plant community zonation along estuarine stress gradients is critical for effective conservation and restoration of coastal wetland ecosystems. We related the presence of plant community types to estuarine hydrology at 173 sites across coastal Louisiana. Percent relative cover by species was assessed at each site near the end of the growing season in 2008, and hourly water level and salinity were recorded at each site Oct 2007–Sep 2008. Nine plant community types were delineated with k-means clustering, and indicator species were identified for each of the community types with indicator species analysis. An inverse relation between salinity and species diversity was observed. Canonical correspondence analysis (CCA) effectively segregated the sites across ordination space by community type, and indicated that salinity and tidal amplitude were both important drivers of vegetation composition. Multinomial logistic regression (MLR) and Akaike's Information Criterion (AIC) were used to predict the probability of occurrence of the nine vegetation communities as a function of salinity and tidal amplitude, and probability surfaces obtained from the MLR model corroborated the CCA results. The weighted kappa statistic, calculated from the confusion matrix of predicted versus actual community types, was 0.7 and indicated good agreement between observed community types and model predictions. Our results suggest that models based on a few key hydrologic variables can be valuable tools for predicting vegetation community development when restoring and managing coastal wetlands.

Estuarine, Coastal and Shelf Science↗
USGS2019

The evolving threat of rapid Ohia death (ROD) to Hawaii’s native ecosystems and rare plant species

Hawai‘i’s most widespread native tree, ‘ōhi‘a lehua ( Metrosideros polymorpha ), has been dying across large areas of Hawai‘i Island mainly due to two fungal pathogens ( Ceratocystis lukuohia and Ceratocystis huliohia ) that cause a disease collectively known as Rapid ‘Ōhi‘a Death (ROD). Here we examine patterns of positive detections of C. lukuohia as it has been linked to the larger mortality events across Hawai‘i Island. Our analysis compares the environmental range of C. lukuohia and its spread over time through the known climatic range and distribution of ‘ōhi‘a. Analyses show this fungal pathogen generally encompassed the core, but not the extremes of the climatic range of ‘ōhi‘a. We further modeled the potential distribution of C. lukuohia across the Hawaiian Archipelago to estimate the risk of ROD to other islands. Given the potential for C. lukuohia to alter the structure of ‘ōhi‘a dominated forests, we used our projected potential distribution of C. lukuohia to assess the risk of ROD to threatened and endangered plant species across Hawai‘i. Many native plants are likely vulnerable to these types of large ‘ōhi‘a mortality events: of 234 endangered native plant species considered, 147 (62.8%) have more than half of their range within current and expanding C. lukuohia suitable areas. We also found evidence that protecting habitat by fencing out introduced feral ungulates reduces the prevalence of the disease likely by reducing physical damage caused by these animals to ‘ōhi‘a trees, a precondition for Ceratocystis infection. Given the ongoing spread of C. lukuohia , we developed a dynamic web portal to host our results online, where models and analyses are updated with new lab-confirmed detections to provide managers with a useful tool to help monitor and assess the risk of C. lukuohia as it continues to spread.

Hawaii↗