Arid Lands Ecology Research Articles

El Niño Southern Oscillation and enhanced arid land vegetation productivity in NW South America

El Niño Southern Oscillation (ENSO) is a periodic disruption of coupled oceanic-atmospheric conditions in the tropical Pacific, which changes global precipitation regimes. One area strongly affected by positive (el Niño) phases is the Pacific Coast of South America. The specific effects of ENSO on Andean ecological communities have received little attention, however. We examine vegetation gross primary productivity (GPP) on Peru's north coast arid-lands during a recent (2016–2017) el Niño, using a time series of Sentinel 2 imagery. By comparing GPP time-series in three agricultural subregions and three endemic desert vegetation communities, we demonstrate that levels of primary productivity in desert regions during ENSO-positive phases meet or exceed thresholds of adjacent agricultural lands. These results, the first that quantify and spatialize changing GPP between ENSO-neutral and ENSO-positive phases for South American arid-land biomes, both outline the scale and distribution of the el Niño effects on terrestrial ecosystems and highlight the resulting opportunities for human inhabitants. The dramatic changes to endemic vegetation on the normally hyperarid coastal desert of Peru revealed by reconstructed GPP suggest that periodic el Niño precipitation plays a critical role in arid land ecodynamics by enhancing establishment, green growth, and seedbank development. These findings improve our understanding of ENSO's net effects and highlight the roles of abrupt climate events in the arid land ecology of NW South America.

From the Divine to the Desertified: The Foundational Case of Deserts in the Middle East

Abstract Deserts in the Middle East have been crucial to our understanding of arid lands since the ancient Greek and Roman period if not before. Long viewed as a region that contained certain riches but that was hot, sandy/rocky and difficult for travel, key changes in western perceptions of Middle Eastern deserts took place during eighteenth and nineteenth centuries. These changes (which cast deserts as deforested, overgrazed spaces) were driven by geopolitics, political economy and imperialism as much as by developments in natural history. As a result of European interactions with the Ottoman Empire and other parts of the Middle East, deserts came to be equated with mismanagement resulting in desertification. Advancements in arid lands ecology, however, undermine these common understandings of deserts around the world and instead point to new ways of living sustainably in the highly variable arid lands of our globe.

Progress and trend of development of restoration ecology research in the arid regions of China

In this paper, the development process and characteristics of restoration ecology research in the arid regions of China were reviewed, and the research frontiers and development trends were analyzed systemically.The study on restoration ecology in arid regions has been promoted by national demands. Revegetation was the main method and approach for ecological recovery and restoration. Future study should focus on vegetation zonal distribution, soil habitat restoration, interaction of arid land ecology and hydrology, plant water relation, biological soil crust, projection based on models and modeling, and so on. The interaction and integration of geography and biology provide a new way of thinking and approach for both theoretical and practical innovations in the development of restoration ecology.

Establishing soil and surficial geologic habitat criteria for presumed gypsophiles — The example of Eriogonum corymbosum var. nilesii, Mojave Desert, U.S.A.

Detailed soil and surficial geologic data are needed for ecological interpretations, yet are often absent or incomplete in published studies of arid land ecology or biogeography. Clear, edaphic habitat definitions are needed for gypsophilic plants including the Las Vegas buckwheat, E. corymbosum var. nilesii (LVB), a rare shrub endemic to the Mojave Desert. As a case study, we use soil profile data and high resolution (1:3000 scale) surficial geologic maps to identify likely edaphic controls of LVB habitat, potential habitat, and non-habitat distributions. We confirm gypsiferous substrates lacking hard, physical surface crusts as a boundary condition in most, but not all population clusters, but find that fine-grained, carbonate-rich soil lacking gypsum is also viable habitat, as is shallow (<1m) sandy alluvium overlying gypsiferous sediments. Deep (>1m), coarse-grained alluvium and/or surfaces with tightly interlocking desert pavement exclude LVB. Our results challenge the view of this target species as a true gypsophile, however, it remains unclear whether carbonate-rich habitats represent ideal conditions or refugia. This study underscores the important merits of surficial geologic mapping and soil morphological description for ecological research, conservation, restoration, and land management in arid environments, especially gypsum soils, worldwide.

Trajectories of change in sagebrush steppe vegetation communities in relation to multiple wildfires

Repeated perturbations, both biotic and abiotic, can lead to fundamental changes in the nature of ecosystems, including changes in state. Sagebrush steppe communities provide important habitat for wildlife and grazing for livestock. Fire is an integral part of these systems, but there is concern that increased ignition frequencies and invasive species are fundamentally altering them. Despite these issues, the majority of studies of fire effects in systems dominated by Artemisia tridentata wyomingensis have focused on the effects of single burns. The Arid Lands Ecology Reserve (ALE), in south-central Washington (USA), was one of the largest contiguous areas of sagebrush steppe habitat in the state until large wildfires burned the majority of it in 2000 and 2007. We analyzed data from permanent vegetation transects established in 1996 and resampled in 2002 and 2009. Our objective was to describe how the fires, and subsequent postfire restoration efforts, affected communities' successional pathways. Plant communities differed in response to repeated fire and restoration; these differences could largely be ascribed to the functional traits of the dominant species. Low-elevation communities, previously dominated by obligate seeders, moved furthest from their initial composition and were dominated by weedy, early-successional species in 2009. Higher-elevation sites with resprouting shrubs, native bunchgrasses, and few invasive species were generally more resilient to the effects of repeated disturbances. Shrub cover has been almost entirely removed from ALE, although there was some recovery where communities were dominated by resprouters. Bromus tectorum dominance was reduced by herbicide application in areas where it was previously abundant, but it increased significantly in untreated areas. Several resprouting species, notably Phlox longifolia and Poa secunda, expanded remarkably following competitive release from shrub canopies and/or abundant B. tectorum. Our results suggest that community dynamics can be understood through a state and transition model with two axes (shrub/grass and native/invasive abundance), although such models also need to account for differences in plant functional traits and disturbance regimes. We use our results to develop a conceptual model that will be validated with further research.

Trajectories of change in sagebrush steppe vegetation communities in relation to multiple wildfires

Repeated perturbations, both biotic and abiotic, can lead to fundamental changes in the nature of ecosystems, including changes in state. Sagebrush steppe communities provide important habitat for wildlife and grazing for livestock. Fire is an integral part of these systems, but there is concern that increased ignition frequencies and invasive species are fundamentally altering them. Despite these issues, the majority of studies of fire effects in systems dominated by Artemisia tridentata wyomingensis have focused on the effects of single burns. The Arid Lands Ecology Reserve (ALE), in south-central Washington (U.S.A.), was one of the largest contiguous areas of sagebrush steppe habitat in the state until large wildfires burned the majority of it in 2000 and 2007. We analyzed data from permanent vegetation transects established in 1996 and resampled in 2002 and 2009. Our objective was to describe how the fires, and subsequent postfire restoration efforts, affected communities' successional pathways. Plant communities differed in response to repeated fire and restoration; these differences could largely be ascribed to the functional traits of the dominant species. Low-elevation communities, previously dominated by obligate seeders, moved furthest from their initial composition and were dominated by weedy, early-successional species in 2009. Higher-elevation sites with resprouting shrubs, native bunchgrasses, and few invasive species were generally more resilient to the effects of repeated disturbances. Shrub cover has been almost entirely removed from ALE, although there was some recovery where communities were dominated by resprouters. Bromus tectorum dominance was reduced by herbicide application in areas where it was previously abundant, but it increased significantly in untreated areas. Several resprouting species, notably Phlox longifolia and Poa secunda, expanded remarkably following competitive release from shrub canopies and/or abundant B. tectorum. Our results suggest that community dynamics can be understood through a state and transition model with two axes (shrub/grass and native/invasive abundance), although such models also need to account for differences in plant functional traits and disturbance regimes. We use our results to develop a conceptual model that will be validated with further research.

Fallow management in dryland agriculture: Explaining soil water accumulation using a pulse paradigm

The use of a fallow period to conserve rainfall as stored soil water is a long-established component of many dryland agricultural systems and there is general understanding that fallow management can play an important role in whole system water-use efficiency. Nevertheless there remain questions about the amount of residue required to make a difference and whether residue type or configuration matters. The magnitude of the observed effects on soil water accumulation has been variable, especially in short fallow systems. We present the results of field and lysimeter experiments of fallow management effects and extend these using simulation analyses to capture the impacts of climatic variability. The results allow identification of levels of evaporative demand and rainfall patterns that influence the effects of residue management and weed control. To move beyond whole-of-fallow, retrospective explanations of fallow management effects, we explain the results using a simple and easy to understand pulse paradigm approach adopted from the field of arid land ecology. Rainfall variability is viewed in terms of different possible sequences of rainfall events, which create pulses of soil water. By considering pulse size, frequency, duration and depth we explain the observed and simulated fallow management effects and provide a qualitative approach towards understanding and assessing soil water accumulation within the fallow period.

Seed germination of four Jordanian Stipa spp: differences in temperature regimes and seed provenances

Abstract Stipa steppes are considered to be an important model ecosystem in arid land ecology owing to their wide geographical distribution and their strong association with human activities. This paper presents data on the seed germination of four Jordanian Stipa species (Stipa capensis, Stipa parviflora, Stipa arabica and Stipa lagascae) that are widespread throughout various phytogeographical regions in Jordan. We studied variation in seed germination under laboratory conditions among populations and under various temperature regimes. There was significant variation in seed germination with temperature in all four species and seed provenance was significant for three out of the four species. The temperature levels that were most suitable for germination varied from low (8/4°C and 20/10°C) for S. lagascae to high (20/10°C and 32/20°C) for S. capensis; S. arabica and S. parviflora germinated equally well at all three temperature regimes. Variations among populations were species specific, but populations with the highest seed germination were always of arid and Saharan Mediterranean origin. Thus, seed germination was negatively correlated with annual precipitation. Such flexibility among temperatures and populations could be interpreted as an efficient survival strategy for species growing under unpredictable environmental conditions. Where artificial reseeding is necessary, differences among species and also among different seed provenances should be taken into account.

Controls over invasion of Bromus tectorum: The importance of climate, soil, disturbance and seed availability

AbstractQuestion: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi‐arid ecosystems where water is a limiting resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool‐season annual grass that has successfully colonized much of the U.S. Great Basin?Location: Short‐grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern Washington, USA; and the Patagonian steppe of the Chubut province in Argentina.Methods: We utilized a soil water model to simulate seasonal soil water dynamics in multiple combinations of climatic and soil properties. In addition, we utilized a gap dynamics model to simulate the impact of disturbance regime and seed availability on competition between B. tectorum and native plants.Results: Our results suggest that climate is very important, but that soil properties do not significantly influence the probability of observing conditions suitable for B. tectorum establishment. Results of the plant competition model indicate that frequent disturbance causes more Bromus tectorum in invaded areas and higher seed availability causes faster invasion.Conclusions: These results imply a general framework for understanding Bromus tectorum invasion in which climatic conditions dictate which areas are susceptible to invasion, disturbance regime dictates the severity of invasion and seed availability dictates the speed of invasion.

Controls over invasion of Bromus tectorum: The importance of climate, soil, disturbance and seed availability

Question: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi-arid ecosystems where water is a limiting resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool-season annual grass that has successfully colonized much of the U.S. Great Basin? Location: Short-grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern Washington, USA; and the Patagonian steppe of the Chubut province in Argentina. Methods: We utilized a soil water model to simulate seasonal soil water dynamics in multiple combinations of climatic and soil properties. In addition, we utilized a gap dynamics model to simulate the impact of disturbance regime and seed availability on competition between B. tectorum and native plants. Results: Our results suggest that climate is very important, but that soil properties do not significantly influence the probability of observing conditions suitable for B. tectorum establishment. Results of the plant competition model indicate that frequent disturbance causes more Bromus tectorum in invaded areas and higher seed availability causes faster invasion. Conclusions: These results imply a general framework for understanding Bromus tectorum invasion in which climatic conditions dictate which areas are susceptible to invasion, disturbance regime dictates the severity of invasion and seed availability dictates the speed of invasion.

Modifying the 'pulse-reserve' paradigm for deserts of North America: precipitation pulses, soil water, and plant responses.

The 'pulse-reserve' conceptual model--arguably one of the most-cited paradigms in aridland ecology--depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of 'pulses', 'triggers' and 'reserves' are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse-reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant 'rainfall pulse', (2) how do rainfall pulses translate into usable 'soil moisture pulses', and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant 'pulses' of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October-March) or summer (July-September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.

Arid lands management: toward ecological sustainability

'As living systems change, so research priorities and decisions about resource management must change and adapt. By relating various kinds of ecological systems to the question of sustainability in arid lands, Arid Lands Management offers new directions for both research and management. The earth's surface currently is undergoing massive land-use changes as a component of human-accelerated environmental change. Loss of biodiversity, invasion of exotic species, global climate change, toxification of the biosphere, and stratospheric ozone depletion are the consequences of land-use changes that lead to a deterioration of vital resources. Fragile arid and semi-arid ecosystems are particularly vulnerable.Arid Lands Management gathers the insights and expertise of an international consortium of scientists to assess the current status of ecological sciences and arid lands ecology. This volume provides an overview of the arid and semi-arid land situation in three major arid systems: the Negev of Israel, the Sonoran-Chiuahuan deserts of North America, and the arid lands of Australia. Contributors provide a framework for understanding ecological sustainability, assess progress toward it, and outline essential principles of arid lands management.They suggest promising areas of research as well as management approaches that take account of interactions among three ecological criteria or levels of organization: population, community, and ecosystem. They also address the implications for these criteria of human-induced local and global environmental changes and investigate how to expand the conventional definition of sustainability - the use of resources by humans with the intention of protecting those resources for future populations of humans - to encompass also the reliance of other organisms on these resources.

Elk Habitat Use Patterns in the Shrub-Steppe of Washington

Spatial and temporal habitat use patterns of elk (Cervus elaphus) in the shrub-steppe of Washington were studied from March through October 1983 and 1984. Four male and 4 female radio-collared elk were relocated a total of 782 times. Female elk preferred low elevation sagebrush associations during spring, late summer, and fall and riparian areas during the calving period and late summer months. Sagebrush stands were important bedding areas, particularly during late summer. Male elk selected sagebrush types during spring, summer, and fall. Elk preferred low elevation topographic zones. The distribution of natural springs was an important determinant of habitat use patterns for lactating female elk, but bull elk habitat use was less constrained by free water. Elk were active nocturnally. In the absence of extensive thermal cover, elk decreased thermoregulatory costs by bedding in sagebrush stands and by limiting major diurnal foraging bouts. The behavior of this population suggested that elk can be successful with limited cover under conditions of infrequent disturbance and adequate forage. J. WILDL. MANAGE. 50(4):664-669 North American elk have historically occupied a variety of habitats, but the desert and semi-desert regions of the West may not have supported elk in the past (Skovlin 1982). Presumably, low forage quality and quantity, scarcity of water, and high energetic costs of thermoregulation in the absence of extensive thermal cover made these regions poor elk habitat (Skovlin 1982). In contrast, a small nonmigratory herd of Rocky Mountain elk (C. e. nelsoni) colonized the Arid Lands Ecology (ALE) Reserve, a treeless shrub-steppe region of southcentral Washington in 1972 (Rickard et al. 1977); the population currently numbers approximately 55 elk. Summer use of steppe habitats by elk is atypical and exposes these animals to a thermal environment that is extreme compared to that experienced by most summering elk populations. Most Rocky Mountain elk populations are associated with coniferous forests (Bryant and Maser 1982), and the importance of forest cover has previously been shown (Beall 1976, Marcum 1976, Lyon 1979). Forest cover provides elk with thermoregulatory advantages in winter and summer (Beall 1976, Skovlin 1982) and security from disturbance (Morgantini and Hudson 1979). We studied the habitat relationships and behavior of elk on the ALE Reserve from March through October 1983 and 1984. In this paper we report on their spatial and temporal habitat use patterns. This work was supported by the U.S. Dep. Energy (Contract DE-AC06-76RLO 1830). We gratefully acknowledge the support of the Northwest Coll. and Univ. Assoc. for Sci. (NORCUS) and the Pacific Northwest Lab. We thank W. H. Rickard for his support and L. E. Eberhardt for assistance in the early stages of this investigation.

Recovery of Streamside Woody Vegetation after Exclusion of Livestock Grazing

Removal of livestock grazing along a small, perennial desert stream allowed the reestablishment of woody vegetation (Sulix amygdaloides) in the riparian zone within 10 years. Small spring/streams are widely distributed in the semiarid, sagebrush-steppe region of the northwestern United States. They are characteristically bordered by narrow corridors of deciduous trees especially cottonwoods (Populus spp.) and/or willows (Salix spp). The value of these wooded habitats of limited extent to bird populations is well recognized and has been especially well documented on the Arid Lands Ecology (ALE) reserve in south-central Washington (Rotenberry et. al. 1979). Historically, spring streams have also been the focal points of human habitation and the congregation areas for herds of domestic livestock that pasture in the surrounding sagebrush-steppe and trek back and forth to the few widely separated spring streams that serve as watering points. The physiological requirement for drinking water has tended to concentrate livestock at a few places, causing damage and even destruction of riparian woody vegetation (Thomas et al. 1979). Our paper reports on the self-recovery of woody vegetation along a small spring/ stream in south central Washington after exclusion of livestock by fencing.

Comparison of Soil Water Used by a Sagebrush-Bunchgrass and a Cheatgrass Community

Highlight: Two contrasting plant communities occur on the Arid Lands Ecology (ALE) Reserve in south-central Washington, one dominated by a mixture of sagebrush and bluebunch wheatgrass and the other by a nearly pure stand of cheatgrass. At the beginning of the spring growing season in 1974, a year of aboveaverage precipitation, both communities had about the same amount of soil water stored in the first 18 dm of the soil profile. During the growing season, the quantity of soil water used by the sagebrush-bunchgrass and cheatgrass communities was 15 and 8 cm, respectively. The difference in soil water used by the two communities is attributed to a deeper root system and a longer growing period by plants of the sagebrush-bunchgrass community.

Small Mammals, Their Parasites and Pathologic Lesions on the Arid Lands Ecology Reserve, Benton County, Washington

During May-June 1968 small mammals were sampled on the U. S. Atomic Energy Commission's Arid Lands Ecology Reserve in Benton Co., Washington. A total of 875 trap nights of effort were ex- pended capturing 302 small mammals in seven vegetation associations at seven elevations between 750 and 3500 ft. Species included Perognathus parvus, Peromyscus maniculatus, Lagurus curtatus, Spermophilus town- sendii, Eutamias minimus, Onychomys leucogaster, Thomomys tal- poides and Neotoma cinerea. Perognathus and Peromyscus were caught in most of the vegetation associations sampled, although pocket mice dominated mammalian fauna at lower elevations and deer mice became dominant at higher elevations. Onychomys was trapped only in the ArtemisialPoa association, while the other species, especially L. curtatus, showed a preference for Artemisia/Agropyron. Ten species of fleas and two species of ticks were collected. Meringis shannoni was the most abundant flea and occurred on five hosts. Thrassis bacchi johnsoni, potentially one of the most important flea vectors of sylvatic plague, was collected on L. curtatus. A spectrum of minor pathologic lesions and endoparasitic burdens was documented for Perognathus and Peromyscus.