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G.W. Chong

Publications and source records attributed to G.W. Chong.

13 recordsLinked to original sources
USGS2011

Greater sage-grouse of Grand Teton National Park: where do they roam?

Greater sage-grouse (Centrocercus urophasianus) population declines may be caused by range-wide degradation of sagebrush (woody Artemisia spp.) steppe ecosystems. Understanding how greater sage-grouse use the landscape is essential for successful management. We assessed greater sage-grouse habitat selection on a landscape level in Jackson Hole, Wyoming. We used a Geographic Information System (GIS) and radio-collared sage-grouse to compare habitat used and the total available landscape. Greater sage-grouse selected mountain big sagebrush (A. tridentata var. vaseyana) communities or mixed mountain big sagebrush–antelope bitterbrush (Purshia tridentata) communities and avoided low-sagebrush (A. arbuscula) dwarf shrubland. In spring and summer, sage-grouse primarily used sagebrush-dominated habitats on the valley floor and did not concentrate in mesic areas later in the summer as is typical of the species. The diversity of habitats used in winter exceeds that reported in the literature. In winter, Jackson Hole greater sage-grouse moved to hills, where they used various communities in proportion to their availability, including tall deciduous shrublands, cottonwood (Populus angustifolia) stands, exposed hillsides, and aspen (P. tremuloides) stands. Because seasonal habitat selection is not necessarily consistent across populations residing in different landscapes, habitat management should be specific to each population and landscape. This sage-grouse population provides an example that may offer insight into other species with seasonal habitat needs.

Grand Teton National Park↗
USGS2007

Species-area curves indicate the importance of habitats' contributions to regional biodiversity

We examined species-area curves, species composition and similarity (Jaccard's coefficients), and species richness in 17 vegetation types to develop a composite index of a vegetation type's contribution to regional species richness. We collected data from 1 to 1000 m2 scales in 147 nested plots in Rocky Mountain National Park, Colorado, USA to compare three species-area curve models' abilities to estimate the number of species observed in each vegetation type. The log(species)-log(area) curve had the largest adjusted coefficients of determination (r2 values) in 12 of the 17 types, followed by the species-log(area) curve with five of the highest values. When the slopes of the curves were corrected for species overlap among plots with Jaccard's coefficients, the species-log(area) curves estimated values closest to those observed. We combined information from species-area curves and measures of heterogeneity with information on the area covered by each vegetation type and found that the types making the greatest contributions to regional biodiversity covered the smallest areas. This approach may provide an accurate and relatively rapid way to rank hotspots of plant diversity within regions of interest.

Colorado↗
USGS2007

Rapid assessment of postfire plant invasions in coniferous forests of the western United States

Fire is a natural part of most forest ecosystems in the western United States, but its effects on nonnative plant invasion have only recently been studied. Also, forest managers are engaging in fuel reduction projects to lessen fire severity, often without considering potential negative ecological consequences such as nonnative plant species introductions. Increased availability of light, nutrients, and bare ground have all been associated with high-severity fires and fuel treatments and are known to aid in the establishment of nonnative plant species. We use vegetation and environmental data collected after wildfires at seven sites in coniferous forests in the western United States to study responses of nonnative plants to wildfire. We compared burned vs. unburned plots and plots treated with mechanical thinning and/or prescribed burning vs. untreated plots for nonnative plant species richness and cover and used correlation analyses to infer the effect of abiotic site conditions on invasibility. Wildfire was responsible for significant increases in nonnative species richness and cover, and a significant decrease in native cover. Mechanical thinning and prescribed fire fuel treatments were associated with significant changes in plant species composition at some sites. Treatment effects across sites were minimal and inconclusive due to significant site and site x treatment interaction effects caused by variation between sites including differences in treatment and fire severities and initial conditions (e.g., nonnative species sources). We used canonical correspondence analysis (CCA) to determine what combinations of environmental variables best explained patterns of nonnative plant species richness and cover. Variables related to fire severity, soil nutrients, and elevation explained most of the variation in species composition. Nonnative species were generally associated with sites with higher fire severity, elevation, percentage of bare ground, and lower soil nutrient levels and lower canopy cover. Early assessments of postfire stand conditions can guide rapid responses to nonnative plant invasions. ?? 2007 by the Ecological Society of America.

Western United States↗
USGS2006

Establishment of non-native plant species after wildfires: Effects of fuel treatments, abiotic and biotic factors, and post-fire grass seeding treatments

Establishment and spread of non-native species following wildfires can pose threats to long-term native plant recovery. Factors such as disturbance severity, resource availability, and propagule pressure may influence where non-native species establish in burned areas. In addition, pre- and post-fire management activities may influence the likelihood of non-native species establishment. In the present study we examine the establishment of non-native species after wildfires in relation to native species richness, fire severity, dominant native plant cover, resource availability, and pre- and post-fire management actions (fuel treatments and post-fire rehabilitation treatments). We used an information-theoretic approach to compare alternative hypotheses. We analysed post-fire effects at multiple scales at three wildfires in Colorado and New Mexico. For large and small spatial scales at all fires, fire severity was the most consistent predictor of non-native species cover. Non-native species cover was also correlated with high native species richness, low native dominant species cover, and high seeded grass cover. There was a positive, but non-significant, association of non-native species with fuel-treated areas at one wildfire. While there may be some potential for fuels treatments to promote non-native species establishment, wildfire and post-fire seeding treatments seem to have a larger impact on non-native species. ?? IAWF 2006.

Colorado, New Mexico↗
USGS2006

A 21st century perspective on postfire seeding

Wildfires elicit a perceived need for emergency action to stabilize denuded landscapes. Aerial seeding of rapidly growing nonnative grasses is used routinely in an attempt to control postfire erosion, despite limited scientific basis for its effectiveness and with little consideration for its unintended ecological impacts. As fire size and magnitude have increased in recent decades, so has the prevalence and cost of postfire seeding and the potential footprint of its unintended impacts. We see a growing consensus in the research community on two important points: this management practice often is not cost-effective and it appears to create more problems than it solves.

Journal of Forestry↗
USGS2006

Evaluating plant invasions from both habitat and species perspectives

We present an approach to quantitatively assess nonnative plant invasions at landscape scales from both habitat and species perspectives. Our case study included 34 nonnative species found in 142 plots (0.1 ha) in 14 vegetation types within the Grand Staircase&ndash;Escalante National Monument, Utah. A plot invasion index, based on nonnative species richness and cover, showed that only 16 of 142 plots were heavily invaded. A species invasive index, based on frequency, cover, and number of vegetation types invaded, showed that only 7 of 34 plant species were highly invasive. Multiple regressions using habitat characteristics (moisture index, elevation, soil P, native species richness, maximum crust development class, bare ground, and rock) explained 60% of variation in nonnative species richness and 46% of variation in nonnative species cover. Three mesic habitats (aspen, wet meadow, and perennial riparian types) were particularly invaded (31 of 34 nonnative species studied were found in these types). Species-specific logistic regression models for the 7 most invasive species correctly predicted occurrence 89% of the time on average (from 80% for Bromus tectorum , a habitat generalist, to 93% for Tamarix spp., a habitat specialist). Even with such a modest sampling intensity (<0.1% of the landscape), this multiscale sampling scheme was effective at evaluating habitat vulnerability to invasion and the occurrence of the 7 most invasive nonnative species. This approach could be applied in other natural areas to develop strategies to document invasive species and invaded habitats.

Utah↗
USGS2006

Scale and plant invasions: A theory of biotic acceptance

We examined the relationship between native and alien plant species richness, cover, and estimated biomass at multiple spatial scales. The large dataset included 70511-m2 subplots, 1443 10-m2 subplots, and 727100-m2 subplots, nested in 727 1000-m2 plots in 37 natural vegetation types in seven states in the central United States. We found that native and alien species richness (averaged across the vegetation types) increased significantly with plot area. Furthermore, the relationship between native and alien species richness became increasingly positive and significant from the plant neighbourhood scale (1-m2) to the 10-m2, 100-m2, and the 1000-m2 scale where over 80% of the vegetation types had positive slopes between native and alien species richness. Both native and alien plant species may be responding to increased resource availability and/or habitat heterogeneity with increased area. We found significant positive relationships between the coefficient of variation of native cover in 1-m2 subplots in a vegetation type (i.e. a measure of habitat heterogeneity), and both the relative cover and relative biomass of alien plant species. At the 1000-m2 scale, we did find weak negative relationships between native species richness and the cover, biomass, and relative cover of alien plant species. However, we found very strong positive relationships between alien species richness and the cover, relative cover, and relative biomass of alien species at regional scales. These results, along with many other field studies in natural ecosystems, show that the dominant genera pattern in invasion ecology at multiple spatial scales is one of "biotic acceptance" where natural ecosystems tend to accommodate the establishment and coexistence of introduced species despite the presence and abundance of native species.

Preslia↗
USGS2005

Life-history habitat matching in invading non-native plant species

We briefly reviewed the literature on habitat matching in invading non-native plant species. Then we hypothesized that the richness and cover of native annual and perennial plant species integrate complex local information of vegetation and soils that would help to predict invasion success by similarly adapted non-native plant species. We tested these ‘life-history habitat matching’ relationships in 603 0.1-ha plots, including 294 plots in Colorado, which were relatively high for the cover of native perennial plant species, and for 309 0.1-ha plots in southern Utah, which were relatively high in the cover of native annual plant species. We found strong positive relationships between the richness and foliar cover for both native and non-native species, whether they were annual or perennial species (0.34 > r 2 < 0.53; P < 0.0001). We also found significant positive relationships between the cover of native annual species at a site and the richness ( r 2 = 0.13; P < 0.0001) and the foliar cover ( r 2 = 0.06; P < 0.0001) of non-native annual species. The proportion of non-native annual species in the flora of a plot also increased significantly with the foliar cover of native annual species. Conversely, the richness and cover of non-native annual species were significantly negatively associated with the foliar cover of native perennial species ( r 2 = 0.05 and 0.06, respectively; P < 0.0001). The cover of non-native annual or perennial species was not significantly correlated with soil texture variables, %N, or %C. We conclude that there may be a high degree of life-history habitat matching by non-native annual species in these study sites. Information on native annual and perennial species richness and cover may help characterize the complex soils, climate, and disturbance environment in which similarly adapted non-native plant species establish and gain foliar cover.

Plant and Soil↗
USGS2001

Rapid assessment of butterfly diversity in a montane landscape

We present the results of a rapid assessment of butterfly diversity in the 754 ha Beaver Meadows study area in Rocky Mountain National Park, Larimer County, Colorado. We measured butterfly species richness and relative abundance as part of a landscape-scale investigation of diversity patterns involving several groups of organisms. A stratified random sampling design was used to include replication in both rare and common vegetation types. We recorded 49 butterfly species from the twenty-four 0.1 ha plots that were sampled four times during June, July, and August 1996. Butterfly species richness, diversity, and uniqueness were highest in quaking aspen ( Populus tremuloides Michaux) groves and wet meadows, which occupy only a small proportion of the studied landscape. This result supports the suggestion that aspen areas represent ‘hotspots’ of biological diversity in this montane landscape. Patterns of butterfly species richness were positively correlated with total vascular plant species richness ( r = 0.69; P < 0.001), and native plant species richness ( r = 0.64; P < 0.001). However, exotic plant species richness ( r = 0.70; P < 0.001) and the cover of exotic plant species ( r = 0.70; P < 0.001) were the best predictors of butterfly species richness.

Colorado↗
USGS2001

New approaches for sampling and modeling native and exotic plant species richness

We demonstrate new multi-phase, multi-scale approaches for sampling and modeling native and exotic plant species to predict the spread of invasive species and aid in control efforts. Our test site is a 54,000-ha portion of Rocky Mountain National Park, Colorado, USA. This work is based on previous research wherein we developed vegetation sampling techniques to identify hot spots of diversity, important rare habitats, and locations of invasive plant species. Here we demonstrate statistical modeling tools to rapidly assess current patterns of native and exotic plant species to determine which habitats are most vulnerable to invasion by exotic species. We use stepwise multiple regression and modified residual kriging to estimate numbers of native species and exotic species, as well as probability of observing an exotic species in 30 × 30-m cells. Final models accounted for 62% of the variability observed in number of native species, 51% of the variability observed in number of exotic species, and 47% of the variability associated with observing an exotic species. Important independent variables used in developing the models include geographical location, elevation, slope, aspect, and Landsat TM bands 1-7. These models can direct resource managers to areas in need of further inventory, monitoring, and exotic species control efforts.

Western North American Naturalist↗
USGS1999

Exotic plant species invade hot spots of native plant diversity

Some theories and experimental studies suggest that areas of low plant species richness may be invaded more easily than areas of high plant species richness. We gathered nested-scale vegetation data on plant species richness, foliar cover, and frequency from 200 1-m 2 subplots (20 1000-m 2 modified-Whittaker plots) in the Colorado Rockies (USA), and 160 1-m 2 subplots (16 1000-m 2 plots) in the Central Grasslands in Colorado, Wyoming, South Dakota, and Minnesota (USA) to test the generality of this paradigm. At the 1-m 2 scale, the paradigm was supported in four prairie types in the Central Grasslands, where exotic species richness declined with increasing plant species richness and cover. At the 1-m 2 scale, five forest and meadow vegetation types in the Colorado Rockies contradicted the paradigm; exotic species richness increased with native-plant species richness and foliar cover. At the 1000-m 2 plot scale (among vegetation types), 83% of the variance in exotic species richness in the Central Grasslands was explained by the total percentage of nitrogen in the soil and the cover of native plant species. In the Colorado Rockies, 69% of the variance in exotic species richness in 1000-m 2 plots was explained by the number of native plant species and the total percentage of soil carbon. At landscape and biome scales, exotic species primarily invaded areas of high species richness in the four Central Grasslands sites and in the five Colorado Rockies vegetation types. For the nine vegetation types in both biomes, exotic species cover was positively correlated with mean foliar cover, mean soil percentage N, and the total number of exotic species. These patterns of invasibility depend on spatial scale, biome and vegetation type, spatial autocorrelation effects, availability of resources, and species-specific responses to grazing and other disturbances. We conclude that: (1) sites high in herbaceous foliar cover and soil fertility, and hot spots of plant diversity (and biodiversity), are invasible in many landscapes; and (2) this pattern may be more closely related to the degree resources are available in native plant communities, independent of species richness. Exotic plant invasions in rare habitats and distinctive plant communities pose a significant challenge to land managers and conservation biologists.

Ecological Monographs↗