Geology topics

J.B. Grace

Publications and source records attributed to J.B. Grace.

At least 37 records · Page 2Linked to original sources

USGS2007

Occurrence of oral deformities in larval anurans

We quantified deformities in the marginal papillae, tooth rows, and jaw sheaths of tadpoles from 13 population samples representing three families and 11 sites in the southeastern United States. Oral deformities were observed in all samples and in 13.5-98% of the specimens per sample. Batrachochytrium dendrobatidis (chytrid) infections were detected in three samples. There was high variability among samples in the pattern and number of discovered deformities. Pairwise associations between oral structures containing deformities were nonrandom for several populations, especially those with B. dendrobatidis infections or high total numbers of deformities. Comparisons of deformities among samples using multivariate analyses revealed that tadpole samples grouped together by family. Analyses of ordination indicated that three variables, the number of deformities, the number of significant associations among deformity types within populations, and whether populations were infected with B. dendrobatidis, were significantly correlated with the pattern of deformities. Our data indicate that the incidence of oral deformities can be high in natural populations and that phylogeny and B. dendrobatidis infection exert a strong influence on the occurrence and type of oral deformities in tadpoles. ?? by the American Society of Ichthyologists and Herperologists.

Copeia↗

USGS2007

Species richness and soil properties in Pinus ponderosa forests: A structural equation modeling analysis

Question: How are the effects of mineral soil properties on understory plant species richness propagated through a network of processes involving the forest overstory, soil organic matter, soil nitrogen, and understory plant abundance? Location: North-central Arizona, USA. Methods: We sampled 75 0.05-ha plots across a broad soil gradient in a Pinus ponderosa (ponderosa pine) forest ecosystem. We evaluated multivariate models of plant species richness using structural equation modeling. Results: Richness was highest at intermediate levels of understory plant cover, suggesting that both colonization success and competitive exclusion can limit richness in this system. We did not detect a reciprocal positive effect of richness on plant cover. Richness was strongly related to soil nitrogen in the model, with evidence for both a direct negative effect and an indirect non-linear relationship mediated through understory plant cover. Soil organic matter appeared to have a positive influence on understory richness that was independent of soil nitrogen. Richness was lowest where the forest overstory was densest, which can be explained through indirect effects on soil organic matter, soil nitrogen and understory cover. Finally, model results suggest a variety of direct and indirect processes whereby mineral soil properties can influence richness. Conclusions: Understory plant species richness and plant cover in P. ponderosa forests appear to be significantly influenced by soil organic matter and nitrogen, which are, in turn, related to overstory density and composition and mineral soil properties. Thus, soil properties can impose direct and indirect constraints on local species diversity in ponderosa pine forests. ?? IAVS; Opulus Press.

Journal of Vegetation Science↗

USGS2007

Habitat relationships of birds overwintering in a managed coastal prairie

Grassland birds are considered to be rapidly declining in North America. Management approaches for grassland birds frequently rely on prescribed burning to maintain habitat in suitable condition. We evaluated the relationships among years since burn, vegetation structure, and overwintering grassland bird abundance in coastal prairie. Le Conte's Sparrows (Ammodramus leconteii) were most common in areas that had: (1) been burned within the previous 2 years, (2) medium density herbaceous vegetation, and (3) sparse shrub densities. Savannah Sparrows (Passerculus sandwichensis) were associated with areas: (1) burned within 1 year, (2) with sparse herbaceous vegetation, and (3) with sparse shrub densities. Sedge Wrens (Cistothorus platensis) were most common in areas that had: (1) burned greater than 2 years prior and (2) dense herbaceous vegetation. Swamp Sparrows (Melospiza georgiana): (1) were most common in areas of dense shrubs, (2) not related to time since burnings, and (3) demonstrated no relationship to herbaceous vegetation densities. The relationships to fire histories for all four bird species could be explained by the associated vegetation characteristics indicating the need for a mosaic of burn rotations and modest levels of woody vegetation.

Wilson Journal of Ornithology↗

USGS2006

A multivariate model of plant species richness in forested systems: Old-growth montane forests with a long history of fire

Recently, efforts to develop multivariate models of plant species richness have been extended to include systems where trees play important roles as overstory elements mediating the influences of environment and disturbance on understory richness. We used structural equation modeling to examine the relationship of understory vascular plant species richness to understory abundance, forest structure, topographic slope, and surface fire history in lower montane forests on the North Rim of Grand Canyon National Park, USA based on data from eighty-two 0.1 ha plots. The questions of primary interest in this analysis were: (1) to what degree are influences of trees on understory richness mediated by effects on understory abundance? (2) To what degree are influences of fire history on richness mediated by effects on trees and/or understory abundance? (3) Can the influences of fire history on this system be related simply to time-since-fire or are there unique influences associated with long-term fire frequency? The results we obtained are consistent with the following inferences. First, it appears that pine trees had a strong inhibitory effect on the abundance of understory plants, which in turn led to lower understory species richness. Second, richness declined over time since the last fire. This pattern appears to result from several processes, including (1) a post-fire stimulation of germination, (2) a decline in understory abundance, and (3) an increase over time in pine abundance (which indirectly leads to reduced richness). Finally, once time-since-fire was statistically controlled, it was seen that areas with higher fire frequency have lower richness than expected, which appears to result from negative effects on understory abundance, possibly by depletions of soil nutrients from repeated surface fire. Overall, it appears that at large temporal and spatial scales, surface fire plays an important and complex role in structuring understory plant communities in old-growth montane forests. These results show how multivariate models of herbaceous richness can be expanded to apply to forested systems. Copyright ?? Oikos 2006.

Oikos↗

USGS2006

Evaluation of non-destructive methods for estimating biomass in marshes of the upper Texas, USA coast

The estimation of aboveground biomass is important in the management of natural resources. Direct measurements by clipping, drying, and weighing of herbaceous vegetation are time-consuming and costly. Therefore, non-destructive methods for efficiently and accurately estimating biomass are of interest. We compared two non-destructive methods, visual obstruction and light penetration, for estimating aboveground biomass in marshes of the upper Texas, USA coast. Visual obstruction was estimated using the Robel pole method, which primarily measures the density and height of the canopy. Light penetration through the canopy was measured using a Decagon light wand, with readings taken above the vegetation and at the ground surface. Clip plots were also taken to provide direct estimates of total aboveground biomass. Regression relationships between estimated and clipped biomass were significant using both methods. However, the light penetration method was much more strongly correlated with clipped biomass under these conditions (R2 value 0.65 compared to 0.35 for the visual obstruction approach). The primary difference between the two methods in this situation was the ability of the light-penetration method to account for variations in plant litter. These results indicate that light-penetration measurements may be better for estimating biomass in marshes when plant litter is an important component. We advise that, in all cases, investigators should calibrate their methods against clip plots to evaluate applicability to their situation. ?? 2006, The Society of Wetland Scientists.

Wetlands↗

USGS2006

Habitat associations of chorusing anurans in the Lower Mississippi River Alluvial valley

Amphibian populations have declined worldwide. To pursue conservation efforts adequately, land managers need more information concerning amphibian habitat requirements. To address this need, we examined relationships between anurans and habitat characteristics of wetlands in the Lower Mississippi River Alluvial Valley (LMAV). We surveyed chorusing anurans in 31 wetlands in 2000 and 28 wetlands in 2001, and measured microhabitat variables along the shoreline within the week following each survey. We recorded 12 species of anurans during our study. Species richness was significantly lower in 2000 than 2001 ( t -test, P < 0.001) and correlated with an ongoing drought. We found species richness to be significantly greater at lake sites compared to impoundment, swale, and riverine sites (ANOVA, P = 0.002). We used stepwise regression to investigate the wetland types and microhabitat characteristics associated with species richness of chorusing anurans. Microhabitat characteristics associated with species richness included dense herbaceous vegetation and accumulated litter along the shoreline. Individual species showed species-specific habitat associations. The bronze frog, American bullfrog, and northern cricket frog were positively associated with lake sites (Fisher’s Exact Test, P < 0.05), however wetland type did not significantly influence any additional species. Using bivariate correlations, we found that six of the seven most common species had significant associations with microhabitat variables. Overall, our findings support the view that conservation and enhancement of amphibian communities in the LMAV and elsewhere requires a matrix of diverse wetland types and habitat conditions.

Louisiana↗

USGS2006

Invasion in a diversity hotspot: Exotic cover and native richness in the Californian serpentine flora

Exotic species have been observed to be more prevalent in sites where the richness of native species is highest, possibly reflecting variation among sites in resources, propagule supply, heterogeneity, or disturbance. However, such a pattern leaves unclear whether natives at species-rich sites are subject to especially severe impacts from exotics as a result. We considered this question using path models in which relationships between exotic cover and native richness were evaluated in the presence of correlated environmental factors. At 109 sites on serpentine soils across California, USA, exotic cover was positively correlated with total native herbaceous richness and was negatively correlated with the richness of both serpentine-endemic and rare native herbs. However, in path models that accounted for the influences of soil chemistry, disturbance, overstory cover, and regional rainfall and elevation, we found no indication that exotic cover reduced any component of native herb richness. Rather, our results indicated similarities and differences in the conditions favoring exotic, native, endemic, and rare species. Our results suggest that, in spite of some localized impacts, exotic species are not exerting a detectable overall effect on the community richness of the unique native flora of Californian serpentine. ?? 2006 by the Ecological Society of America.

California↗

USGS2006

Regional and local species richness in an insular environment: Serpentine plants in California

We asked how the richness of the specialized (endemic) flora of serpentine rock outcrops in California varies at both the regional and local scales. Our study had two goals: first, to test whether endemic richness is affected by spatial habitat structure (e.g., regional serpentine area, local serpentine outcrop area, regional and local measures of outcrop isolation), and second, to conduct this test in the context of a broader assessment of environmental influences (e.g., climate, soils, vegetation, disturbance) and historical influences (e.g., geologic age, geographic province) on local and regional species richness. We measured endemic and total richness and environmental variables in 109 serpentine sites (1000-m2 paired plots) in 78 serpentine-containing regions of the state. We used structural equation modeling (SEM) to simultaneously relate regional richness to regionalscale predictors, and local richness to both local-scale and regional-scale predictors. Our model for serpentine endemics explained 66% of the variation in local endemic richness based on local environment (vegetation, soils, rock cover) and on regional endemic richness. It explained 73% of the variation in regional endemic richness based on regional environment (climate and productivity), historical factors (geologic age and geographic province), and spatial structure (regional total area of serpentine, the only significant spatial variable in our analysis). We did not find a strong influence of spatial structure on species richness. However, we were able to distinguish local vs. regional influences on species richness to a novel extent, despite the existence of correlations between local and regional conditions. ?? 2006 by the Ecological Society of America.

California↗

USGS2006

A structural equation model analysis of postfire plant diversity in California shrublands

This study investigates patterns of plant diversity following wildfires in fire‐prone shrublands of California, seeks to understand those patterns in terms of both local and landscape factors, and considers the implications for fire management. Ninety study sites were established following extensive wildfires in 1993, and 1000‐m 2 plots were used to sample a variety of parameters. Data on community responses were collected for five years following fire. Structural equation modeling (SEM) was used to relate plant species richness to plant abundance, fire severity, abiotic conditions, within‐plot heterogeneity, stand age, and position in the landscape. Temporal dynamics of average richness response was also modeled. Richness was highest in the first year following fire, indicating postfire enhancement of diversity. A general decline in richness over time was detected, with year‐to‐year variation attributable to annual variations in precipitation. Peak richness in the landscape was found where (1) plant abundance was moderately high, (2) within‐plot heterogeneity was high, (3) soils were moderately low in nitrogen, high in sand content, and with high rock cover, (4) fire severity was low, and (5) stands were young prior to fire. Many of these characteristics were correlated with position in the landscape and associated conditions. We infer from the SEM results that postfire richness in this system is strongly influenced by local conditions and that these conditions are, in turn, predictably related to landscape‐level conditions. For example, we observed that older stands of shrubs were characterized by more severe fires, which were associated with a low recovery of plant cover and low richness. These results may have implications for the use of prescribed fire in this system if these findings extrapolate to prescribed burns as we would expect.

California↗

USGS2005

Fine-scale spatial variation in plant species richness and its relationship to environmental conditions in coastal marshlands

Previous studies have shown that variations in environmental conditions play a major role in explaining variations in plant species richness at community and landscape scales. In this study, we considered the degree to which fine-scale spatial variations in richness could be related to fine-scale variations in abiotic and biotic factors. To examine spatial variation in richness, grids of 1 m 2 plots were laid out at five sites within a coastal riverine wetland landscape. At each site, a 5 × 7 array of plots was established adjacent to the river’s edge with plots one meter apart. In addition to the estimation of species richness, environmental measurements included sediment salinity, plot microelevation, percent of plot recently disturbed, and estimated community biomass. Our analysis strategy was to combine the use of structural equation modeling (path modeling) with an assessment of spatial association. Mantel’s tests revealed significant spatial autocorrelation in species richness at four of the five sites sampled, indicating that richness in a plot correlated with the richness of nearby plots. We subsequently considered the degree to which spatial autocorrelations in richness could be explained by spatial autocorrelations in environmental conditions. Once data were corrected for environmental correlations, spatial autocorrelation in residual species richness could not be detected at any site. Based on these results, we conclude that in this coastal wetland, there appears to be a fine-scale mapping of diversity to microgradients in environmental conditions.

Louisiana↗

USGS2004

Multivariate control of plant species richness and community biomass in blackland prairie

Recent studies have shown that patterns of plant species richness and community biomass are best understood in a multivariate context. The objective of this study was to develop and evaluate a multivariate hypothesis about how herbaceous biomass and richness relate to gradients in soil conditions and woody plant cover in blackland prairies. Structural equation modeling was used to investigate how soil characteristics and shade by scattered Juniperus virginiana trees relate to standing biomass and species richness in 99 0.25 m2 quadrats collected in eastern Mississippi, USA. Analysis proceeded in two stages. In the first stage, we evaluated the hypothesis that correlations among soil parameters could be represented by two underlying (latent) soil factors, mineral content and organic content. In the second stage, we evaluated the hypothesis that richness and biomass were related to (1) soil properties, (2) tree canopy extent, and (3) each other (i.e. reciprocal effects between richness and biomass). With some modification to the details of the original model, it was found that soil properties could be represented as two latent variables. In the overall model, 51% and 53% of the observed variation in richness and biomass were explained. The order of importance for variables explaining variations in richness was (1) soil organic content, (2) soil mineral content, (3) community biomass, and (4) tree canopy extent. The order of importance for variables explaining biomass was (1) tree canopy and (2) soil organic content, with neither soil mineral content nor species richness explaining significant variation in biomass. Based on these findings, we conclude that variations in richness are uniquely related to both variations in soil conditions and variations in herbaceous biomass. We further conclude that there is no evidence in these data for effects of species richness on biomass.

Oikos↗

USGS2004

Temporal dynamics of leafy spurge (Euphorbia esula) and two species of flea beetles (Aphthona spp.) used as biological control agents

The goal of this study was to evaluate the biological control program of leafy spurge ( Euphorbia esula ) in a large natural area, Theodore Roosevelt National Park, western North Dakota, USA. Aphthona lacertosa and Aphthona nigriscutis have been released at more than 1800 points in the 18,600-ha South Unit of the park beginning in 1989; most releases have occurred since 1994. We established permanent vegetation plots throughout the infested area of the park and determined stem counts and biomass of leafy spurge and abundance of the two flea beetle species at these plots each year from 1999 to 2001. Both biomass and stem counts declined over the 3 years of the study. Both species of flea beetle are well established within the park and have expanded into areas where they were not released. A. nigriscutis was more abundant than A. lacertosa in the grassland areas we surveyed, but in all other habitats abundances were similar. Using structural equation models, only A. lacertosa could be shown to have a significant effect on counts of mature stems of leafy spurge. A. nigriscutis numbers were positively correlated with stem counts of mature stems. Previous year’s stem counts had the greatest influence on change in stem counts over each 2-year time step examined with structural equation models.

North Dakota↗

USGS2004

Effects of invasive alien plants on fire regimes

Plant invasions are widely recognized as significant threats to biodiversity conservation worldwide. One way invasions can affect native ecosystems is by changing fuel properties, which can in turn affect fire behavior and, ultimately, alter fire regime characteristics such as frequency, intensity, extent, type, and seasonality of fire. If the regime changes subsequently promote the dominance of the invaders, then an invasive plant–fire regime cycle can be established. As more ecosystem components and interactions are altered, restoration of preinvasion conditions becomes more difficult. Restoration may require managing fuel conditions, fire regimes, native plant communities, and other ecosystem properties in addition to the invaders that caused the changes in the first place. We present a multiphase model describing the interrelationships between plant invaders and fire regimes, provide a system for evaluating the relative effects of invaders and prioritizing them for control, and recommend ways to restore pre-invasion fire regime properties.

BioScience↗

USGS2003

The roles of community biomass and species pools in the regulation of plant diversity

Considerable debate has developed over the importance of community biomass and species pools in the regulation of community diversity. Attempts to explain patterns of plant diversity as a function of community biomass or productivity have been only partially successful and in general, have explained only a fraction of the observed variation in diversity. At the same time studies that have focused on the importance of species pools have led some to conclude that diversity is primarily regulated in the short term by the size of the species pool rather than by biotic interactions. In this paper, I explore how community biomass and species pools may work in combination to regulate diversity in herbaceous plant communities. To address this problem, I employ a simple model in which the dynamics of species richness are a function of aboveground community biomass and environmentally controlled gradients in species pools. Model results lead to two main predictions about the role of biomass regulation: (1) Seasonal dynamics of richness will tend to follow a regular oscillation, with richness rising to peak values during the early to middle portion of the growing season and then declining during the latter part of the season. (2.) Seasonal dieback of aboveground tissues facilitates the long-term maintenance of high levels of richness in the community. The persistence of aboveground tissues and accumulation of litter are especially important in limiting the number of species through the suppression of recruitment. Model results also lead to two main predictions about the role of species pools: (1) The height and position of peak richness relative to community biomass will be influenced by the rate at which the species pool increases as available soil resources increase. (2) Variations in nonresource environmental factors (e.g. soil pH or soil salinity) have the potential to regulate species pools in a way that is uncorrelated with aboveground biomass. Under extreme conditions, such nonresource effects can create a unimodal envelope of biomass-richness values. Available evidence from the literature provides partial support for these predictions, though additional data are needed to provide more convincing tests.

Oikos↗

USGS2001

Difficulties with estimating and interpreting species pools and the implications for understanding patterns of diversity

Evidence has been accumulating that species pools play a major role in regulating variations in small-scale diversity. However, our ability to unambiguously estimate and interpret species pools remains a major impediment to understanding the processes that control patterns of diversity. Two main approaches have been employed to evaluate the relationships between species pools and species diversity. The direct approach has been to estimate the actual sizes of species pools by sampling discrete areas at larger spatial scales and then relating these estimates to samples taken at smaller scales. The indirect approach has been to search for correlations between abiotic environmental factors and patterns of diversity that are indicative of gradients in species pools. Both of these approaches have substantial predictive capability but also have limitations that impair our ability to draw unambiguous interpretations about causal factors. A primary difficulty for the direct approach is in deciding which species in the larger pool of potential species are actually capable of living in a sample. In this regard, the indirect approach requires fewer assumptions and has the ability to detect previously unsuspected gradients in species pools. As with the direct approach, assessing the causes for observed gradients in species pools remains a limitation for the indirect approach. Consideration of experimental studies of potential niches suggests that it may be valuable to distinguish between potential and observed species pools if the role of competitive exclusion is to be fully assessed. This paper concludes by arguing for (1) an increased use of multivariate studies that examine the effects of species pools indirectly and (2) further experimental studies designed to determine potential species pools.

Folia Geobotanica↗

USGS2001

Identifying determinants of nations' wetland management programs using structural equation modeling: An exploratory analysis

Integrated management and policy models suggest that solutions to environmental issues may be linked to the socioeconomic and political Characteristics of a nation. In this study, we empirically explore these suggestions by applying them to the wetland management activities of nations. Structural equation modeling was used to evaluate a model of national wetland management effort and one of national wetland protection. Using five predictor variables of social capital, economic capital, environmental and political characteristics, and land-use pressure, the multivariate models were able to explain 60% of the variation in nations' wetland protection efforts based on data from 90 nations, as defined by level of participation, in the international wetland convention. Social capital had the largest direct effect on wetland protection efforts, suggesting that increased social development may eventually lead to better wetland protection. In contrast, increasing economic development had a negative linear relationship with wetland protection efforts, suggesting the need for explicit wetland protection programs as nations continue to focus on economic development. Government, environmental characteristics, and land-use pressure also had a positive direct effect on wetland protection, and mediated the effect of social capital on wetland protection. Explicit wetland protection policies, combined with a focus on social development, would lead to better wetland protection at the national level.

Environmental Management↗

USGS2000

The effects of soil flooding on the establishment of cogongrass (Imperata cylindrica), a nonindigenous invader of the southeastern United States

Cogongrass ( Imperata cylindrica ), an invasive perennial introduced from Southeast Asia, is currently spreading throughout the southeastern United States from Florida to Louisiana. In the U.S., cogongrass is generally not considered a wetland species, although it’s range is expanding in regions with high wetland abundance. The objective of this study was to determine if excessive soil moisture might prevent cogongrass from establishing in areas with seasonaly flooded soils. In one greenhouse experiment, we examined cogongrass germination and seedling growth in soils that were freely drained, saturated, and inundated. We performed a second greenhouse experiment to evaluate growth and survival of cogongrass seedlings of four different size classes in five soil moisture treatments ranging from dry to inundated. Cogongrass germination was lowest when seeds were overtopped with water. There were no differences in germination between saturated and freely drained treatments; however, seedlings grew larget in freely drained soil and were smallest when immersed. In our second experiment, most cogongrass plantswsurvived except when given no water, but growth differed by watering treatment depending on seedling size. Increasing moisture was more detrimental to the growth of small seedlings compared to the growth of larger cogongrass plants. Overall, cogongrass was most sensitive to soil inundation in the earliest stages of establishment; thus, excessive moisture conditions in the spring, during early seedling development, could restrict invasion of cogongrass by seed. Once cogongrass is established, however, it tolerance of flooding appears to increase.

Alabama, Florida, Louisiana, Mississippi↗

USGS2000

Growth and invasive potential of Sapium sebiferum (Euphorbiaceae) within the coastal prairie region: the effects of soil and moisture regime

The introduced tree Sapium sebiferum (Euphorbiaceae) is considered a serious threat to the preservation of the coastal prairie region of Louisiana and Texas, although it is currently uncommon in the western part of the region. The objective of this study was to evaluate the potential effects of location, soils, and available moisture on the growth and survival of S. sebiferum in coastal prairie. In a field experiment, S. sebiferum mortality was significantly greater at a western site than at central and eastern sites. The greatest mortality and least growth of surviving plants occurred on a soil from the western region, regardless of site. A greenhouse study also found that S. sebiferum growth was lowest on the western soil. Watering frequency significantly affected S. sebiferum growth, except on the western soil. Sapium sebiferum growth responded to both nitrogen and phosphorum additions for all soils. Soil analyses revealed the highest sand, sodium, and phosphorus contents, and much higher electrical conductivity in the western soil. It is concluded that the soil examined from the western region is unfavorable for S. sebiferum growth, though not to the extent to preclude S. sebiferum completely. Evidence suggests that soil salinity may be the primary cause of the poor S. sebiferum growth at the western site.

Louisiana, Texas↗