Geology topics

Yuka Otsuki

Publications and source records attributed to Yuka Otsuki.

6 recordsLinked to original sources

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–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↗

USGS2001

Patterns of plant invasions: A case example in native species hotspots and rare habitats

Land managers require landscape-scale information on where exotic plant species have successfully established, to better guide research, control, and restoration efforts. We evaluated the vulnerability of various habitats to invasion by exotic plant species in a 100,000 ha area in the southeast corner of Grand Staircase-Escalante National Monument, Utah. For the 97 0.1-ha plots in 11 vegetation types, exotic species richness (log 10 ) was strongly negatively correlated to the cover of cryptobiotic soil crusts ( r = −0.47, P < 0.001), and positively correlated to native species richness ( r = 0.22, P < 0.03), native species cover ( r = 0.23, P < 0.05), and total nitrogen in the soil ( r = 0.40, P < 0.001). Exotic species cover was strongly positively correlated to exotic species richness ( r = 0.68, P < 0.001). Only 6 of 97 plots did not contain at least one exotic species. Exotic species richness was particularly high in locally rare, mesic vegetation types and nitrogen rich soils. Dry, upland plots ( n = 51) had less than half of the exotic species richness and cover compared to plots ( n = 45) in washes and lowland depressions that collect water intermittently. Plots dominated by trees had significantly greater native and exotic species richness compared to plots dominated by shrubs. For the 97 plots combined, 33% of the variance in exotic species richness could be explained by a positive relationship with total plant cover, and negative relationships with the cover of cryptobiotic crusts and bare ground. There are several reasons for concern: (1) Exotic plant species are invading hot spots of native plant diversity and rare/unique habitats. (2) The foliar cover of exotic species was greatest in habitats that had been invaded by several exotic species.(3) Continued disturbance of fragile cryptobiotic crusts by livestock, people, and vehicles may facilitate the further invasion of exotic plant species.

Biological Invasions↗

USGS2000

Using new video mapping technology in landscape ecology

Biological and ecological monitoring continues to play an important role in the conservation of species, natural communities, and landscapes ( Spellerberg 1991 ). Although resource-monitoring programs have advanced knowledge about natural ecosystems, weaknesses persist in our ability to rapidly transfer landscape-scale information to the public. Ecologists continue to search for new technologies to address this problem and to communicate natural resource information quickly and effectively. New video mapping technology may provide much-needed help. Ecologists realize that only a small portion of large nature reserves can be monitored because of cost and logistical constraints. However, plant and animal populations are usually patchily distributed in subpopulations scattered throughout heterogeneous landscapes, and they are often associated with rare habitats. These subpopulations and rare habitats may respond differently to climate change, land use, and management practices such as grazing, fire suppression, prescribed burning, or invasion of exotic species ( Stohlgren et al. 1997b ). In many national parks, monuments, and wildlife reserves, a few long-term monitoring plots are used to infer the status and trends of natural resources in much larger areas. To make defensible inferences about populations, habitats, and landscapes, it is necessary to extrapolate from a few monitoring plots (local scale) to the larger, unsampled landscape with known levels of accuracy and precision. Recent technological developments have given population biologists and landscape ecologists a unique tool for bridging the data gap between small, intensively sampled monitoring plots and the greater landscape and for transferring this information quickly to resource managers and the public. In this article, we briefly describe this tool, a hand-held video mapping system linked to a geographic information system (GIS). We provide examples of its use in quantifying patterns of native and exotic plant species and cryptobiotic crusts in the new Grand Staircase–Escalante National Monument, Utah, and in surveying aspen clones and regeneration in Rocky Mountain National Park, Colorado.

BioScience↗

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↗

USGS1998

Riparian zones as havens for exotic plant species in the central grasslands

In the Central Grasslands of the United States, we hypothesized that riparian zones high in soil fertility would contain more exotic plant species than upland areas of low soil fertility. Our alternate hypothesis was that riparian zones high in native plant species richness and cover would monopolize available resources and resist invasion by exotic species. We gathered nested-scale vegetation data from 40 1 m2subplots (nested in four 1000 m2 plots) in both riparian and upland sites at four study areas in Colorado, Wyoming, and South Dakota (a total of 320 1 m2subplots and 32 1000 m2 plots). At the 1 m2 scale, mean foliar cover of native species was significantly greater (P < 0.001) in riparian zones (36.6% ?? 1.7%) compared to upland sites (28.7% ?? 1.5%), but at this small scale there were no consistent patterns of native and exotic species richness among the four management areas. Mean exotic species cover was slightly higher in upland sites compared to riparian sites (9.0% ?? 3.8% versus 8.2% ?? 3.0% cover). However, mean exotic species richness and cover were greater in the riparian zones than upland sites in three of four management areas. At the 1000 m2 scale, mean exotic species richness was also significantly greater (P < 0.05) in riparian zones (7.8 ?? 1.0 species) compared to upland sites (4.8 ?? 1.0 species) despite the heavy invasion of one upland site. For all 32 plots combined, 21% of the variance in exotic species richness was explained by positive relationships with soil % silt (t = 1.7, P = 0.09) and total foliar cover (t = 2.4, P = 0.02). Likewise, 26% of the variance in exotic species cover (log10 cover) was explained by positive relationships with soil % silt (t = 2.3, P = 0.03) and total plant species richness (t = 2.4, P = 0.02). At landscape scales (four 1000 m2 plots per type combined), total foliar cover was significantly and positively correlated with exotic species richness (r = 0.73, P < 0.05) and cover (r = 0.74, P < 0.05). Exotic species cover (log10 cover) was positively correlated with log10% N in the soil (r = 0.61, P = 0.11) at landscape scales. On average, we found that 85% (??5%) of the total number of exotic species in the sampling plots of a given management area could be found in riparian zones, while only 50% (??8%) were found in upland plots. We conclude that: (1 species-rich and productive riparian zones are particularly invasible in grassland ecosystems; and (2) riparian zones may act as havens, corridors, and sources of exotic plant invasions for upland sites and pose a significant challenge to land managers and conservation biologists.

Plant Ecology↗

USGS1998

Comparison of rangeland vegetation sampling techniques in the Central Grasslands

Maintaining native plant diversity, detecting exotic species, and monitoring rare species are becoming important objectives in rangeland conservation. Four rangeland vegetation sampling techniques were compared to see how well they captured local pant diversity. The methods tested included the commonly used Parker transects, Daubenmire transects as modified by the USDA Forest Service, a new transect and 'large quadrat' design proposed by the USDA Agricultural Research Service, and the Modified-Whittaker multi-scale vegetation plot. The 4 methods were superimposed in shortgrass steppe, mixed grass prairie, northern mixed prairie, and tallgrass prairie in the Central Grasslands of the United States with 4 replicates in each prairie type. Analysis of variance tests showed significant method effects and prairie type effects, but no significant method X type interactions for total species richness, the number of native species, the number of species with less than 1 % cover, and the time required for sampling. The methods behaved similarly in each prairie type under a wide variety of grazing regimens. The Parker, large quadrat, and Daubenmire transects significantly underestimated the total species richness and the number of native species in each prairie type, and the number of species with less than 1 % cover in all but the tallgrass prairie type. The transect techniques also consistently missed half the exotic species, including noxious weeds, in each prairie type. The Modified-Whittaker method, which included an exhaustive search for plant species in a 20 x 50 m plot, served as the baseline for species richeness comparisons. For all prairie types, the Modified-Whittaker plot captured an average of 42. ( ± 2.4; 1 S.E.) plant species per site compared to 15.9 ( ± 1.3), 18.9 ( ± 1.2), and 22.8 ( ± 1.6) plant species per site using the Parker, large quadrat, and Daubenmire transect methods, respectively. The 4 methods captured most of the dominant species at each site and thus produced similar results for total foliar cover and soil cover. The detection and measurement of exotic plant species were greatly enhanced by using ten 1 m 2 subplots in a multi-scale sampling design and searching a larger area (1,000 m 2 ) at each site. Even with 4 replicate sites, the transect methods usually captured, and thus would monitor, 36 to 66 % of the plant species at each site. To evaluate the status and trends of common, rare, and exotic plant species at local, regional, and national scales, innovative, multi-scale methods must replace the commonly used transect methods to the past.

Journal of Range Management↗