Geology topics

Dana L. Witwicki

Publications and source records attributed to Dana L. Witwicki.

7 recordsLinked to original sources

USGS2022

Geologic, geomorphic, and edaphic underpinnings of dryland ecosystems: Colorado Plateau landscapes in a changing world

Drylands represent more than 41% of the global land surface and are at degradation risk due to land use and climate change. Developing strategies to mitigate degradation and restore drylands in the face of these threats requires an understanding of how drylands are shaped by not only soils and climate, but also geology and geomorphology. However, few studies have completed such a comprehensive analysis that relates spatial variation in plant communities to all aspects of the geologic–geomorphic–edaphic–plant–climate system. The focus of this study is the Colorado Plateau, a high-elevation dryland in the southwestern United States, which is particularly sensitive to future change due to climate vulnerability and increasing land-use pressure. Here, we examined 135 long-term vegetation-monitoring sites in three national parks and characterized connections between geology, geomorphology, soils, climate, and dryland plant communities. To first understand the geologic and geomorphic influences on soil formation and characteristics, we explore associations between soil pedons, bedrock geology, and geomorphology. Then, we characterize principal axes of variation in plant communities and ascertain controls and linkages between components of the edaphic–geomorphic system and plant community ordinations. Geologic and geomorphic substrate exerted controls on important properties of the soil profile, particularly depth, water-holding capacity, rockiness, salinity, and fine sands. Ordination identified five distinct plant communities and three primary axes of variation, representing gradients of woody- to herbaceous-dominated communities (Axis 1), saline scrublands to C 3 grasslands (Axis 2), and annual to perennial communities (Axis 3). Geology, geomorphology, and soil explained a large proportion of variation in Axis 1 (74%), while climate variables largely explained Axis 2 (68%), and Axis 3 was not well explained by the random forest models. The variables identified as most influential to each axis were, respectively: (1) soil depth; (2) aridity, lithology, and soil salinity; and (3) temperature and precipitation. We posit that Axis 3 represents a land degradation gradient due to historic grazing, likely exacerbated by dry conditions. Results provide a novel framework that links the geologic and geomorphic evolution of landscapes, with the distribution of soils and plant communities that can guide ecosystem management, exemplifying an approach applicable to drylands globally.

Arizona, Colorado, New Mexico, Utah↗

USGS2022

Southeast Utah Group climate and drought adaptation report: Exposure and perennial grass sensitivity

National Park Service (NPS) managers face growing challenges resulting from the effects of climate change. In particular, as temperatures rise in coming decades, natural resource management in the western United States must cope with expectations for elevated severity and frequency of droughts. These challenges are particularly pronounced for vegetation managers in dryland environments. Developing adaptive strategies requires specific information about the expected magnitude of change in climate and drought conditions as well as insights into how those changes will affect important vegetation resources. This report describes research focused on Southeast Utah Group (SEUG) park units designed to provide information about exposure and sensitivity of perennial grasses to aridification. Analyses at larger regional scales are also reported for context and comparison. This report is a product of an ongoing climate adaptation collaboration between the U.S. Geological Survey (USGS), NPS, and Northern Arizona University. The study it summarizes contributes quantitative ingredients for vulnerability assessments that are needed in the Climate-Smart Conservation framework. As such, the results informed a series of climate adaptation workshops conducted between 2018 and 2021 for Colorado Plateau scientists and managers. This is a giant step forward in science-informed management. The information in this report can be used to craft management strategies that can be implemented at the right place and time for individual species of concern.

Colorado, Utah↗

USGS2018

Landscape pivot points and responses to water balance in national parks of the southwest US

A recent drying trend that is expected to continue in the southwestern US underscores the need for site‐specific and near real‐time understanding of vegetation vulnerability so that land management actions can be implemented at the right time and place. We related the annual integrated normalized difference vegetation index (iNDVI), a proxy for vegetation production, to water balance across landscapes of the Colorado Plateau. We determined how changes in production per unit of water (vegetation responses) and the water balance amounts at which production shifted from above to below average values (pivot points), varied across dominant vegetation and soil types. Precipitation (PRCP), actual evapotranspiration (AET), water deficit ( D ), and soil moisture (SM) explained 13%–82% of variation in vegetation production. Along an increasing water availability gradient, vegetation responses to PRCP and AET increased, responses to SM decreased, and responses to D became more negative. We found trade‐offs between vegetation responses and pivot points within and across all vegetation types that were mediated by soil properties. Synthesis and applications . The water needed by native vegetation to maintain production depends on plant traits. The water available to vegetation depends on climate and soil properties that change along environmental gradients. Tracking this biologically relevant water availability in relation to water need provides an indicator of vegetation growth or stress that can help guide the time and place for management actions.

Colorado, Utah↗

USGS2016

Effects of climate and water balance across grasslands of varying C 3 and C 4 grass cover

Climate change in grassland ecosystems may lead to divergent shifts in the abundance and distribution of C 3 and C 4 grasses. Many studies relate mean climate conditions over relatively long time periods to plant cover, but there is still much uncertainty about how the balance of C 3 and C 4 species will be affected by climate at a finer temporal scale than season (individual events to months). We monitored cover at five grassland sites with co-dominant C 3 and C 4 grass species or only dominant C 3 grass species for 6 yr in national parks across the Colorado Plateau region to assess the influence of specific months of climate and water balance on changes in grass cover. C 4 grass cover increased and decreased to a larger degree than C 3 grass cover with extremely dry and wet consecutive years, but this response varied by ecological site. Climate and water balance explained 10–49% of the inter-annual variability of cover of C 3 and C 4 grasses at all sites. High precipitation in the spring and in previous year monsoon storms influenced changes in cover of C 4 grasses, with measures of water balance in the same months explaining additional variability. C 3 grasses in grasslands where they were dominant were influenced primarily by longer periods of climate, while C 3 grasses in grasslands where they were co-dominant with C 4 grasses were influenced little by climate anomalies at either short or long periods of time. Our results suggest that future changes in spring and summer climate and water balance are likely to affect cover of both C 3 and C 4 grasses, but cover of C 4 grasses may be affected more strongly, and the degree of change will depend on soils and topography where they are growing and the timing of the growing season.

Ecosphere↗

USGS2016

Semi-arid vegetation response to antecedent climate and water balance windows

Questions Can we improve understanding of vegetation response to water availability on monthly time scales in semi-arid environments using remote sensing methods? What climatic or water balance variables and antecedent windows of time associated with these variables best relate to the condition of vegetation? Can we develop credible near-term forecasts from climate data that can be used to prepare for future climate change effects on vegetation? Location Semi-arid grasslands in Capitol Reef National Park, Utah, USA. Methods We built vegetation response models by relating the normalized difference vegetation index (NDVI) from MODIS imagery in Mar–Nov 2000–2013 to antecedent climate and water balance variables preceding the monthly NDVI observations. We compared how climate and water balance variables explained vegetation greenness and then used a multi-model ensemble of climate and water balance models to forecast monthly NDVI for three holdout years. Results Water balance variables explained vegetation greenness to a greater degree than climate variables for most growing season months. Seasonally important variables included measures of antecedent water input and storage in spring, switching to indicators of drought, input or use in summer, followed by antecedent moisture availability in autumn. In spite of similar climates, there was evidence the grazed grassland showed a response to drying conditions 1 mo sooner than the ungrazed grassland. Lead times were generally short early in the growing season and antecedent window durations increased from 3 mo early in the growing season to 1 yr or more as the growing season progressed. Forecast accuracy for three holdout years using a multi-model ensemble of climate and water balance variables outperformed forecasts made with a naïve NDVI climatology. Conclusions We determined the influence of climate and water balance on vegetation at a fine temporal scale, which presents an opportunity to forecast vegetation response with short lead times. This understanding was obtained through high-frequency vegetation monitoring using remote sensing, which reduces the costs and time necessary for field measurements and can lead to more rapid detection of vegetation changes that could help managers take appropriate actions.

Applied Vegetation Science↗

USGS2012

Nitrogen limitation, 15 N tracer retention, and growth response in intact and Bromus tectorum -invaded Artemisia tridentata ssp. wyomingensis communities

Annual grass invasion into shrub-dominated ecosystems is associated with changes in nutrient cycling that may alter nitrogen (N) limitation and retention. Carbon (C) applications that reduce plant-available N have been suggested to give native perennial vegetation a competitive advantage over exotic annual grasses, but plant community and N retention responses to C addition remain poorly understood in these ecosystems. The main objectives of this study were to (1) evaluate the degree of N limitation of plant biomass in intact versus B. tectorum -invaded sagebrush communities, (2) determine if plant N limitation patterns are reflected in the strength of tracer 15 N retention over two growing seasons, and (3) assess if the strength of plant N limitation predicts the efficacy of carbon additions intended to reduce soil N availability and plant growth. Labile C additions reduced biomass of exotic annual species; however, growth of native A. tridentata shrubs also declined. Exotic annual and native perennial plant communities had divergent responses to added N, with B. tectorum displaying greater ability to use added N to rapidly increase aboveground biomass, and native perennials increasing their tissue N concentration but showing little growth response. Few differences in N pools between the annual and native communities were detected. In contrast to expectations, however, more 15 N was retained over two growing seasons in the invaded annual grass than in the native shrub community. Our data suggest that N cycling in converted exotic annual grasslands of the northern Intermountain West, USA, may retain N more strongly than previously thought.

Arizona;California;Colorado;Idaho;Nevada;Oregon;Ut↗

USGS2007

Field Evaluations of Sampling Methods for Long-Term Monitoring of Upland Ecosystems on the Colorado Plateau

To inform planning for long-term ecological monitoring, we sampled vegetation and soil-surface attributes across a range of terrestrial ecosystems (physiognomic types) in seven National Park Service units on the Colorado Plateau. Primary objectives were (1) to evaluate a suite of sampling methods according to measures of repeatability, efficiency, and impacts on plot conditions; and (2) to characterize within- and among-plot variability in monitoring measures. This work was designed to support NPS staff in selecting the combination of methods that best meets their monitoring objectives and resource constraints. We found no differences among cover-estimation techniques in terms of repeatability between observers (measurement precision). Estimates for total live understory canopy cover, cover of individual species, and cover of soil-surface features were highly repeatable between observers for 10-m2 quadrats, 1-m2 quadrats, and line-point intercept sampling methods. Estimates of shrub and tree density in 10-m2 quadrats also were repeatable between observers, although sample sizes for were small for many species. At 10 of 11 ecological sites, we found that sampling with 10-m2 quadrats was the most efficient cover-estimation technique with respect to within-plot variability in cover estimates and numbers of subsamples required to estimate plot-level cover with 20 percent precision. According to these same measures, sampling with 1-m2 quadrats was the least efficient cover-estimation technique at eight of 11 ecological sites. The line-point technique was most efficient at eight of 11 ecological sites in terms of the amount of time required to estimate total plot-level cover with 20 percent precision - largely because 10-m2 quadrats were more time consuming and 1-m2 quadrats had greater within-plot variability relative to line-point sampling. However, there was no statistical difference among methods with respect to median subsampling times for 20 percent precision. There also were no differences among methods with respect to mean and median measures of among-plot variability in total live understory canopy cover. But among-plot variability was least for the line-point technique at seven of 11 ecological sites. Sampling activities had greatest impacts on plot conditions at macroplots where there was a high degree of cover by biological and physical soil crusts. Of all sampling procedures, 10-m2 quadrat sampling, line-point sampling, and gap-intercept sampling had the most impacts on soil conditions due to trampling of soil crusts by the field team.

Open-File Report↗