Keirith Snyder

• United States Department of Agriculture

Climate change is already resulting in changes in cold desert ecosystems, lending urgency to the need to understand climate change effects and develop effective adaptation strategies. In this review, we synthesize information on changes in climate and hydrologic processes during the past century for the Great Basin and Columbia Plateau and discuss...

Phenology of plants is important for ecological interactions. The timing and development of green leaves, plant maturity, and senescence affects biophysical interactions of plants with the environment. In this study we explored the agreement between land-based camera and satellite-based phenology metrics to quantify plant phenology and phenophases...

Pinyon (Pinus spp.) and juniper (Juniperus spp.) woodlands are an important vegetation type in the Great Basin, Colorado Plateau, and southwestern desert regions of the western US that is undergoing substantial changes associated with land management, altered disturbance regimes, and climate change. We synthesized literature on the ecohydrologic im...

• Plant phenology—timing of seasonal life cycle events—is a primary control on ecosystem productivity. • Phenology data can be used to design better management systems by adjusting the timing of grazing or managed burns relative to growth stages of key species and planning restoration activities, such as targeted grazing. • Tower-mounted digital ca...

In the arid and semiarid regions of North America, discrete precipitation pulses are important triggers for biological activity. The timing and magnitude of these pulses may differentially affect the activity of plants and microbes, combining to influence the C balance of desert ecosystems. Here, we evaluate how a "pulse" of water influences physio...

It has been postulated that stemflow, precipitation that flows from plant crowns down along branches and stems to soils, benefits plants that generate it because it increases plant-available soil water near the base of the plant; however, little direct evidence supports this postulation. Were plants’ crowns to preferentially route water to their ro...

Snow plays an important role in the hydrological and energy cycles. In agroecosystems, snow may be a beneficial source of plant-available water, a harmful source of flooding, a source of irrigation water supply (i.e., mountain snowpack filling reservoirs), and a determinant of seasonal timing, such as the onset of the planting or growing seasons. K...

Although each of the water quantity protocols developed for the USDA LTAR Common Experiment addresses specific issues concerning quality assurance (QA) and quality control (QC), basic QA/QC procedures apply to many of these protocols and have relevance in field research. QA is a set of processes or steps taken to ensure that protocols are developed...

Groundwater dependent systems are extremely important habitats for a wide variety of taxa in the Great Basin of North America. The impacts of grazing on these habitats cause shifts in resources and subsequent change in species composition. The Greater sage-grouse, a keystone species of Great Basin ecosystems, rear offspring in these areas during sp...

The U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists...

Groundwater-dependent ecosystems are biologically diverse and productive ecosystems but constitute a small fraction of total land area in semiarid regions. Efforts to link remotely sensed data from satellite-based platforms to measurements of vegetation structure and function at smaller spatial scales have increasingly received attention, due to th...

Understanding the relationship between water and production within and across agroecosystems is essential for addressing several agricultural challenges of the 21st century: providing food, fuel, and fiber to a growing human population, reducing the environmental impacts of agricultural production, and adapting food systems to climate change. Of al...

Successful conservation of threatened species and ecosystems in a rapidly changing world requires scientifically sound decision-making tools that are readily accessible to conservation practitioners. Physiological applications that examine how plants and animals interact with their environment are now widely used when planning, implementing and mon...

Canopy interception loss is an important component of the water budget for many ecosystems, and may be particularly influential in semi-arid shrublands where water is limiting. In this experiment, we quantified interception loss by mountain big sagebrush (Artemisia tridentata spp. vaseyana) using simulated rainfall events in the field. Various leve...

Riparian and ground-water dependent ecosystems found in the Great Basin of North America are heavily utilized by livestock and wildlife throughout the year. Due to this constant pressure, grazing can be a major influence on many groundwater dependent resources. It is important for land managers to understand how intensity and timing of grazing affe...

This synthesis reviews current knowledge of pinyon and juniper ecosystems, in both persistent and newly expanded woodlands, for managers, researchers, and the interested public. We draw from a large volume of research papers to centralize information on these semiarid woodlands. The first section includes a general description of both the Great Bas...

Biological control of Tamarix spp. (Tamarisk) with Diorhabda spp. (tamarisk beetle) was initiated in several states in the western United States in 2001. We analyzed twelve years of evapotranspiration (ET), net ecosystem production (NEP), and beetle abundance data from a tamarisk‐invaded site in western Nevada along the Truckee River. Diorhabda car...

The expansion of piñon and juniper trees into sagebrush steppe and the infilling of historic woodlands has caused a reduction in the cover and density of the understory vegetation. Water is the limiting factor in these systems; therefore, quantifying redistribution of water resources by tree species is critical to understanding the dynamics of thes...

The extent and heterogeneity of rangelands in the state of Nevada (United States) pose a challenging situation for land managers when determining stocking levels for livestock grazing. Overutilization can cause lasting environmental damage, while underutilization can create unnecessary economic hardship for livestock operators. An improved ability...

Plant phenology is recognized as important for ecological dynamics. There has been a recent advent of phenology and camera networks worldwide. The established PhenoCam Network has sites in the United States, including the western states. However, there is a paucity of published research from semi-arid regions. In this study, we demonstrate the util...

•Ecological sites often occur at scales too small for application in planning large-scale vegetation treatments or post-fire rehabilitation.•Disturbance Response Groups (DRGs) are used to scale up ecological sites by grouping ecological sites based on their responses to disturbances.•A state-and-transition model (STM) is created for the DRG and ref...

This research highlights development and application of an integrated hydrologic model (GSFLOW) to a semiarid, snow-dominated watershed in the Great Basin to evaluate Pinyon-Juniper (PJ) and temperature controls on mountain meadow shallow groundwater. The work used Google Earth Engine Landsat satellite and gridded climate archives for model evaluat...

Groundwater dependent ecosystems (GDEs) rely on near-surface groundwater. These systems are receiving more attention with rising air temperature, prolonged drought, and where groundwater pumping captures natural groundwater discharge for anthropogenic use. Phreatophyte shrublands, meadows, and riparian areas are GDEs that provide critical habitat f...

QuestionsHow does performance of a native early seral seed mix during early life stages compare to that of a late seral mix when seeded with Bromus tectorum or Taeniatherum caput-medusae? Does either mix reduce survival of exotic annual grasses during early life stages, and does this effect differ with soil type? Is exotic performance stronger in o...

Cellulose δ18O and δD can provide insights on climates and hydrological cycling in the distant past and how these factors differ spatially. However, most studies of plant cellulose have used only one isotope, most commonly δ18O, resulting in difficulties partitioning variation in δ18O of precipitation vs. evaporative conditions that affect leaf wat...

Cellulose delta O-18 and delta D can provide insights on climates and hydrological cycling in the distant past and how these factors differ spatially. However, most studies of plant cellulose have used only one isotope, most commonly delta O-18, resulting in difficulties partitioning variation in delta O-18 of precipitation vs. evaporative conditio...

Re-seeding efforts to restore or rehabilitate Great Basin rangelands invaded by exotic annual grasses are expensive and have generally achieved limited success. There is a need to identify new strategies to improve restoration outcomes. We tested the performance of a native early seral seed mix (annual forbs, early seral grasses and shrubs) with th...

Restoration of abandoned agricultural lands to create resilient ecosystems in arid and semi-arid ecosystems typically requires seeding or transplanting native species, improving plant soil water relations, and controlling invasive species. We asked if improving water relations via irrigation or surface mulch would result in negative tradeoffs betwe...

We investigated impacts of biocontrol of Tamarix spp. by Diorhabda carinulata on soil nitrogen (N) transformations by surveying organic and mineral soils from three sites. Potential net N mineralization was assayed using laboratory incubations. Results partially supported our hypothesis that herbivory would result in stimulated net N mineralization...

Biological control of Tamarix spp. (saltcedar) with Diorhabda carinulata (the northern tamarisk beetle) is currently underway in several western states U.S.A. through historical releases and the natural migration of this insect. Given the widespread dispersal of this biological control agent and its many unknown consequences, this study examines a...

Background/Question/Methods Use of native annual and early seral species in Great Basin rangeland reseeding efforts may increase invasion resistance and facilitate succession to desired vegetation, thus improving restoration/rehabilitation success. Early serals may be similar to exotic annual grasses in growth and resource acquisition strategies....

Background/Question/Methods Tamarix spp. (saltcedar) has invaded many river systems in the western United States with detrimental impacts to flora and fauna. Traditional methods of invasive plant control have been ineffective or costly. Therefore, insect biological control of Tamarix with Diorhabda spp. (tamarisk leaf beetles) was initiated in fi...

Background/Question/Methods On a global basis, the area of abandoned agricultural land is growing. Modification of the environment for agriculture often results in degradation of the original ecosystem processes and a loss of the biotic and abiotic legacies necessary for recovery of the ecosystem. In arid and semi-arid ecosystems, low soil water...

Background/Question/Methods In water-limited ecosystems, soil profile characteristics can control plant community composition and production through their influence on spatial and temporal patterns of plant available water (PAW). Cemented parts of the soil profile typically are overlooked when evaluating available water holding capacity (AWHC) an...

Background/Question/Methods Quantification of ecosystem water-use efficiency (WUEe) in natural and managed ecosystems is important to address uncertainties related to the effects of global warming and land use change. This is especially important in arid ecosystems, where the impacts of these processes are expected to be high. We continuously mea...

Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decom...

The pattern of carbon (C) allocation among the different pools is an important ecosystem structural feature, which can be modified as a result of changes in environmental conditions that can occur gradually (e.g., climatic change) or abruptly (e.g., management practices). This study quantified the C pools of plant biomass, litter and soil in an ari...

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces di...

Insect herbivory can strongly influence ecosystem nutrient dynamics, yet the indirect effects of herbivore-altered litter quality on subsequent decomposition remain poorly understood. The northern tamarisk beetle Diorhabda carinulata was released across several western states as a biological control agent to reduce the extent of the invasive tree T...

Diurnal fluctuations of leaf water isotope ratios (δ18O and δD) were measured for Jeffrey (Pinus jeffreyi Balf.) and lodgepole (Pinus contorta Douglas ex Louden) pine. Two trees per species were sampled every few hours on 15–16 October 2005 and 19–20 June 2006. Diurnal gas exchange was measured during the summer sampling. In fall 2005, leaf water δ...

Encroachment of woody shrubs into historic desert grasslands is a major problem throughout the world. Conversion of grasslands to shrub-dominated systems may result in significant alteration of biogeochemical processes and reduced resource availability in shrub interspaces, making grassland recovery difficult. Soil petrocalcic horizons, which are c...

For most ecosystems, net ecosystem exchange of CO2 (NEE) varies within and among years in response to environmental change. We analyzed measurements of CO2 exchange from eight native rangeland ecosystems in the western United States (58 site-years of data) in order to determine the contributions of photosynthetic and respiratory (physiological) com...

Rangelands occupy 50% of Earth's land surface and thus are important in the terrestrial carbon (C) cycle. For rangelands and other terrestrial ecosystems, the balance between photosynthetic uptake of carbon dioxide (CO2) and CO2 loss to respiration varies among years in response to interannual variation in the environment. Variability in CO2 exchan...

Tamarisk species (genus Tamarix), also commonly known as saltcedar, are among the most successful plant invaders in the western United States. At the same time, tamarisk has been cited as having enormous economic costs. Accordingly, local, state, and federal agencies have undertaken considerable efforts to eradicate this invasive plant and restore...

Background/Question/Methods The effects of Diorhabda elongata (leaf beetle) herbivory on Tamarix ramosissima physiology are largely undocumented. Wounding by the beetle during consumption of leaf tissue and the laying of eggs (oviposition) could increase root and leaf respiration as carbohydrates are mobilized to regrow leaves. Photosynthesis per u...

Background/Question/Methods Saltcedar (Tamarix ramosissima) invasion and subsequent dominance in biologically and functionally diverse riparian ecosystems across the western U.S. has lead to release of the leaf beetle (Diorhabda elongata) as a biological control agent, and has resulted in large-scale rapid defoliation of saltcedar across several w...

Background/Question/Methods Natural ecosystems are in a state of constant fluctuation. However, most exist as a climax community represented by vegetation types based on soil, climate and other anthropogenic factors. These systems normally have tight nutrient cycling, with few nutrients in free abundance. Currently, many natural ecosystems are bei...

Our goal was to evaluate effects of broad-scale changes in vegetation from grasslands to shrublands over the past 150 years on near-surface atmosphere over the Jornada Experimental Range in the northern Chihuahuan Desert, using a regional climate model. Simulations were conducted using 1858 and 1998 vegetation maps, and data collected in the field....

Rangelands account for almost half of the earth's land surface and may play an important role in the global carbon (C) cycle. We studied net ecosystem exchange (NEE) of C on eight North American rangeland sites over a 6-yr period. Management practices and disturbance regimes can influence NEE; for consistency, we compared ungrazed and undisturbed r...

Water movement from roots to soil at night in the process of hydraulic lift (redistribution) rehydrates the rhizosphere and has been proposed to improve plant nutrient acquisition. Another process that has now been found in many plant species is nighttime transpiration and this could also affect nutrient relations by influencing supply of mobile nu...

The genus Populus relies on shallow groundwater for successful recruitment and is often the focus of riparian restoration efforts. Under some circumstances mature trees take up a substantial proportion of their water from unsaturated soil water derived from growing season rainfall, but it is unknown how Populus saplings may alter root allocation pa...

This chapter describes general characteristics and components of the energy and water balances in arid regions, with specific examples from the Jornada Basin. Various research efforts to characterize the energy and water balances and resultant carbon dioxide fluxes in the Jornada Basin are detailed. We provide a brief overview of how plant physiolo...

The Jornada Basin LTER is located in the Chihuahuan Desert, the largest in North America. This region of south central New Mexico has a history of nearly 100 years as the basis for scientific research. This work gives a thorough, encompassing review of the tremendous array of observations resulting from experiments conducted in this ecosystem. Begi...

The objective of this paper is to illustrate the importance of variation in water availability to temporal variation in vegetation dynamics in arid and semi-arid ecosystems. We hypothesize that fine-scale pulses of precipitation interact with longer scale variation in climate and weather to generate temporal variation in plant community composition...

Increases in the abundance or density of woody plants in historically semiarid and arid grassland ecosystems have important ecological, hydrological, and socioeconomic implications. Using a simplified water-balance model, we propose a framework for con- ceptualizing how woody plant encroachment is likely to affect components of the water cycle with...

Plant species and functionally related species groups from arid and semi-arid habitats vary in their capacity to take up summer precipitation, acquire nitrogen quickly after summer precipitation, and subsequently respond with ecophysiological changes (e.g. water and nitrogen relations, gas exchange). For species that respond ecophysiologically, the...

Increases in the abundance or density of woody plants in historically semiarid and arid grassland ecosystems have important implications for hydrology, ecology, and society. Using a simplified water-balance model, we propose a framework for conceptualizing how woody plant encroachment is likely to affect components of the water cycle within these e...

1. Prosopis velutina Woot. (Velvet Mesquite) at a site with limited groundwater availability derived a greater percentage of water from shallow soil at the onset of the summer rainy season than did trees at a site with greater availability of groundwater. Predawn leaf water potentials (Ypd) were not a strong indicator of shallow water use for this...

Significant night‐time stomatal conductance and transpiration were found for 11 out of 17 species with a range of life histories (herbaceous annual, perennial grass, shrub, tree), photosynthetic pathways (C3, C4), and habitats in the western United States. Across species and habitats, higher night‐time conductance and transpiration were associated...

The USDA/ARS Jornada Experimental Range (JER) (738 km2), north of Las Cruces, NM, was

Predicted changes in regional precipitation patterns and soil moisture caused by anthropogenic trace gas emissions may affect the distribution and abundance of woody plants in arid and semiarid regions. To test the response of woody plants to potential changes in precipitation regimes, we manipulated summer and winter precipitation on plots that co...

The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, multi-national research effort that seeks to evaluate the consequences of natural and human-induced environmental change in semi-arid regions. The ultimate goal of SALSA is to advance scientific understanding of the semi-arid portion of the hydrosphere–biosphere interface in o...

Variation in the sources of water used by tree species has important ramifications for forest water balances. The fraction of tree transpiration water derived from the unsaturated soil zone and groundwater in a riparian forest was quantified for Populus fremontii, Salix gooddingii, and Prosopis velutina across a gradient of groundwater depth and st...

In many semi-arid basins during extended periods when surface snowmelt or storm runoff is absent, groundwater constitutes the primary water source for human habitation, agriculture and riparian ecosystems. Utilizing regional groundwater models in the management of these water resources requires accurate estimates of basin boundary conditions. A cri...

1. ABSTRACT This research investigated physiological and environmental controls on plant water-use and transpiration loss at the species-level. We identified water sources (precipitation, stream, soil moisture and/or groundwater) utilized by cottonwood (Populus fremontii), willow (Salix goodingii) and mesquite (Prosopis velutina) in relation to pat...