Past Projects

Select past projects & publications


Fire Ecology & Invasive Species Ecology

Picture 003.jpgPlant community recovery along a fire chronosequence

Large fires are increasingly common across desert landscapes, especially after exotic annual grasses accumulate following years with above average rainfall. The goals for this study were to associate biotic and abiotic factors with plant community recovery and reveal landscape level patterns for which factors influence community recovery. To do this, we quantified the foliar cover of perennial species and related their presence and abundance to abiotic site characteristics, soil chemistry, and adjacent unburned plant community composition. Results demonstrate legacy impacts of fire on Mojave Desert communities. In blackbrush (Coleogyne ramosissima) communities the dominant species fail to return for at least 20 years, creosote bush (Larrea tridentata)- and yucca-dominated communities recover more quickly with dominant species capable of reestablishing or resprouting, but still not in pre-fire abundances.

Abella SR, Engel EC. 2013. Influences of wildfires on organic carbon, total nitrogen, and other properties of desert soils. Soil Science Society of America Journal 77:1806-1817.

Engel EC, Abella SR. 2011. Vegetation recovery in a desert landscape after wildfires: influences of community type, time since fire and contingency effects. Journal of Applied Ecology 48:1401-1410.

Post-fire restoration and invasive management

Wildfires have been increasing in frequency and severity in the Mojave Desert since the introduction of exotic annual grasses Bromus rubens and Schismus spp.  Only a few native desert species are adapted to fires. After fire most native species require years to decades to reestablish, leaving communities vulnerable to the invasive annual grasses which perpetuate the grass-fire cycle. Revegetation efforts are needed to break the cycle and help native communities reestablish. However, not much is known about how native plants compete with the exotic annual grasses. Are there native species that can 1) reliably establish, and 2) successfully compete with exotics in post-fire environments?



Jurand BS, Abella SR. 2013. Soil seed banks of the exotic annual grass Bromus rubens on a burned desert landscape. Rangeland Ecology and Management 66:157-163.

Juand BS, Abella SR, Suazo AA. 2013. Seed bank longevity and carry over of the exotic annual grass Bromus rubens in the Mojave Desert, USA. Journal of Arid Environments 94:68-75.

Abella SR, Craig DJ, Suazo AA. 2012. Outplanting but not seeding establishes native desert perennials. Native Plants Journal 13:81-89.

Abella SR, Craig DJ, Smith SD, Newton AC. 2012. Identifying native vegetation for reducing exotic species during the restoration of desert ecosystems. Restoration Ecology  20:781-787.

Abella SR, Embrey TM, Schmid SM, Prengaman KA. 2012. Biophysical correlates with the distribution of the invasive annual red brome (Bromus rubens) on a Mojave Desert landscape. Invasive Plant Science and Management 5:47-56.

Abella SR, Prengaman KA, Embrey TM, Schmid SM, Newton AC, Merkler DJ. 2012. A hierarchical analysis of vegetation on a Mojave Desert landscape, USA. Journal of Arid Environments 78:135-143.

Abella SR, Craig DJ, Chiquoine LP, Prengaman KA, Schmid SM, Embrey TM. 2011. Relationships of native desert plants with red brome (Bromus rubens): toward identifying invasion-reducing species. Invasive Plant Science and Management 4:115-124

Abella SR, Engel EC, Lund CL, Spencer JE. 2009. Early post-fire plant establishment on a Mojave Desert burn. Mandroño 56:137-148.

Emerging invasive plant management, anticipating fire

20110322112514.jpgUnderstanding the ecological characteristics of areas invaded and not invaded by exotic plants is a priority for invasive plant science and management. Buffelgrass is an invasive perennial species that managers view as a major threat to indigenous ecosystems of conservation lands in Australia, Mexico, the United States, and other locations where the species is not native.

Abella SR, Chiquoine LP, Backer DM. 2012. Ecological characteristics of sites invaded by buffelgrass (Pennisetum ciliare). Invasive Plant Science and Management 5:443-453.

Dryland forests: impacts by invasive species 

Invasions by exotic plant species can threaten forest ecosystems in numerous ways. Theories on relationships of exotic species invasions with native vegetation, resource availability, and disturbance could assist in managing exotic plants by identifying parts of the landscape and ecological conditions most susceptible to invasion. Generality of these theories is complicated by considerable variation among landscapes and ecology of individual species. We assessed hypotheses on relationships of exotic plant communities with native vegetation, environmental (soil, topographic, and climate), and disturbance (roads and grazing) variables using data from 66 plots within a 110,000-ha Pinus ponderosa forest landscape in northern Arizona, USA. We further assessed exotic plant relationships with ecosystem classification, which has a long history of use in forest ecology and management but has been underutilized for understanding exotic species distributions. Plots contained a total of 251 native and 20 exotic plant species. As hypothesized for distributional studies, native and exotic species were positively correlated, but the correlation varied with scale for species richness and was weaker for cover. Multiple regression, including native vegetation and environmental variables, accounted for similar amounts of variation in exotic species richness and cover. Exotic species richness, cover, and community composition were strongly related to the ecosystem classification. As hypothesized, moist ecosystems were generally most invaded. However, also considering factors such as past management of the ecosystems and literature on the introduction histories (e.g., intentional seeding for range improvement) of the species, we hypothesize that the ecosystem classification integrated co-varying environmental, disturbance, and management variables related to exotic plant communities. Ecosystem classification was a useful framework for understanding distributions of exotic plant communities across the landscape.

Abella SR, Engel EC, Springer JD, Covington WW. 2012. Relationships of exotic plant communities with native vegetation, environmental factors, disturbance, and landscape ecosystems of Pinus ponderosa forests, USA. Forest Ecology and Management 271: 65-74.

Community Ecology 

Desert woodland communities

P1070354.JPGWoodlands of Acacia greggii, Prosopis glandulosa, and Prosopis pubescens are of conservation-priority in the Mojave Desert because of their wildlife and watershed values. We measured plant community composition, environmental variables and ecological condition within Lake Mead National Recreation Area in the eastern Mojave Desert in Arizona-Nevada. We classified community types, analyzed vegetation-environment relationships, developed ecological species groups and evaluated woodland condition.

Abella SR, Chittick KL. 2014. Ecology and conservation of Acacia and Prosopis (Fabaceae) woodlands of the Mojave Desert, U.S.A. Journal of the Botanical Research Institute of Texas 8:175-195.

Soil seed bank assessments

Estimates of soil seed banks are important to many ecological investigations and plant conservation, yet seed banks are among the most difficult plant community attributes to accurately quantify. Additionally, seed bank assessment methods and selection of microsites for seed bank sample collection
can impact assessment results.


Phacelia palmeri

Multifactor approaches that balance several effectiveness measures (e.g., both seed density and species detection at multiple scales) and procedural challenges are most likely to accurately represent complexity in tradeoffs for choosing methods to quantify soil seed banks.

Abella SR, Chiquoine LP, Backer DM. 2013. Soil, vegetation, and seed bank of a Sonoran Desert ecosystem along an exotic plant (Pennisetum ciliare) treatment gradient. Environmental Management 52:946-957.

Abella SR, Chiquoine LP, Vanier CH. 2013. Characterizing soil seed banks and relationships to plant communities. Plant Ecology 214:703-715.

Rare plant ecology

Phenological study of Anulocaulis leiosolenus var. leisolenus. The species A. leiosolenus (Ringstem) has been described but little is known about its natural history.  Therefore, we designed studies with the goal of understanding the vegetative and reproductive phenology of the species.


Anulocaulis leiosolenus var. leisolenus Lake Mead National Recreation Area

Since 2008 we have been documenting information about the duration of flowering per plant, how many flowers and fruits a plant may produce, if leaf number is related to timing of bolting and flowering, and whether leaf number and stem length determine reproductive output. Ringstem flowers are short-lived, open in the evening, and wither in the morning. We conducted some initial pollinator observations and have observed that the main nighttime pollinator appears to be Celerio lineate (white-lined sphinx moth), however flowers are also visited by a generalist bee (species unknown) in the early evening and morning.




Emerging and transitioning systems: the Lake Mead drawdown zone

P1020349Drawdown of Lake Mead from 1998 to 2011 reduced the lake’s perimeter by more than 400 km while exposing more than 25,000 ha of formerly submerged land. To evaluate primary plant succession and soil properties in this new shoreline habitat, we sampled surfaces last submerged 3, 6, 9, or 13 years before, sampling at 3 sites varying in topography and soil parent material. One of the priority invasives along the shoreline include the exotic saltcedar (Tamarix ramosissima), which was observed to declined with increasing surface age. Conversely, cover of native species was greatest overall on older surfaces across sites. Early successional native perennial species colonized the 13-year-old surface. Unexpectedly, multivariate soil properties did not differ between never-submerged and formerly submerged surfaces. Based on the first 13 years of plant colonization along the Lake Mead shoreline and previous research on longer term Mojave Desert vegetation succession, managers can likely anticipate (1) continued development of an early colonizing native shrubland persistent for several decades, and (2) eventual colonization by species of the mature vegetation inhabiting never-submerged surfaces.

Engel EC, Abella SR, Chittick KL. 2014. Plant colonization and soil properties on newly exposed shoreline during drawdown of Lake Mead, Mojave Desert. Lake and Reservoir Management 30:105-114.

Dryland forests: impacts of human disturbances

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Understanding temporal forest change across spatial biophysical gradients is fundamental to managing dynamic forests across variable landscapes. This is especially true for identifying how biophysical variation mediates forest development through multi-century changes in climate and eras of forest manipulation by humans. We examined 155 years of forest change across a 13,000-ha mixed conifer landscape in the Spring Mountains, Nevada, USA.

Know to locals as Mt. Charleston, the Spring Mountain National Recreation Area (SMNRA) is a part of Humboldt-Toiyabe National Forest. The Spring Mountains are located west of Las Vegas, NV and encompass vegetation communities that range from about 2,000 ft up to the highest point in southern Nevada on Mt Charleston at 11,918 feet. Upon entering the SMNRA, single-leaf pinion pine and Rocky Mountain juniper take over the lower elevation shrub-dominated communities. Continuing to higher elevations, one enters ponderosa pine systems that gradually transition to white fir and bristlecone pine. Ponderosa pine-dominated systems the potential to reflect historical forest structure and forest resource use. In many ponderosa pine-dominated systems within the southwestern United States, the fire-resistant bark of older ponderosa pines allows them to survive low intensity fires that assist with decreasing tree density and reducing competition, while supporting a greater biodiversity. 

SLoop2009 and2015However, these systems in the Spring Mountains have not been investigated to know how fire or other historical influences play a role in forest health. With funding support from the Ecological Restoration Institute at Northern Arizona University, we were able to conduct initial overstory vegetation and fire evidence surveys to assist with developing a current view on forest structure and possible legacy impacts on the forest systems.

Abella SR, Chiquoine LP, Sinanian PA. 2015. Forest change over 155 years along biophysical gradients of forest composition, environment, and anthropogenic disturbance. Forest Ecology and Management 348:196-207.


Invasive Species Management

Invasive plant management

The United States created national parks to conserve indigenous species, ecological processes, and cultural resources unimpaired for future generations. Curtailing impacts of exotic species is important to meeting this mission. This synthesis identified 56 studies reported in 60 publications that evaluated effects of exotic plant treatments on National Park Service lands. Studies encompassed 35 parks in 20 states and one U.S. territory and included 157 exotic plant species. Eighty-seven percent of studies reported that at least one treatment reduced focal exotic species. Of 30 studies evaluating response of native vegetation, 53% reported that natives increased, 40% reported neutral responses, and 7% reported that natives decreased. For at least some of the neutral cases, neutrality was consistent with management objectives. In other cases, insufficient time may have elapsed to thoroughly characterize responses, or restoration might be needed. Nonfocal exotic species increased in 44% of the 16 studies evaluating them, but the other 56% of studies reported no increase. Results suggest that: (1) a range of exotic species spanning annual forbs to trees have been effectively treated; (2) developing effective treatments often required extensive experimentation and balancing nontarget impacts; (3) presence of multiple exotic species complicated treatment efforts, highlighting importance of preventing invasions; and (4) placing treatment objectives and outcomes in context, such as pretreatment condition of native vegetation, is important to evaluating effectiveness. Attaining the goal in national parks of conserving native species and ecological processes minimally influenced by exotic species will likely require comprehensive management strategies inclusive of treatment interactions with focal exotic species, other potential invaders, and native species.

Abella, S.R. 2014. Effectiveness of exotic plant treatments on National Park Service lands in the United States. Invasive Plant Science and Management  7:147-163.

Invasive plant treatments

Ecological conditions following removal of exotic plants are a key part of comprehensive environmental management strategies to combat exotic plant invasions. Buffelgrass (Pennisetum ciliare) is an invasive perennial species that managers view as a major threat to indigenous ecosystems of conservation lands in Australia, Mexico, the United States, and other locations where the species is not native.

Abella SR, Chiquoine LP, Backer DM. 2013. Soil, vegetation, and seed bank of a Sonoran Desert ecosystem along an exotic plant (Pennisetum ciliare) treatment gradient. Environmental Management 52:946-957.


Ecological Restoration 

Restoration of native ecosystems after human disturbance

NS reveg 007Lake Mead NRA. Road construction can cause significant disturbance to ecosystems. However, they also provide unique opportunities to observe disturbance impacts to ecosystems and also provide locations to test restoration techniques. Within Lake Mead National Recreation Area, sections of Northshore Rd were impacted by road realignment and reconstruction. Within the proposed path of destruction, we salvaged perennial plants and biological soil crusts to use in restoration experiments. Specifically, we asked how native perennials respond to salvage and outplanting, and how biological soil crusts respond to salvage, storage, and application in restoration treatments.

Chiquoine LP, Abella SR, Bowker MA, 2016. Rapidly restoring biological soil crusts and ecosystem functions in a severely disturbed desert ecosystem. Ecological Applications 26:1260-1272.

Abella SR, Chiquoine LP, Newton AC, Vanier CH. 2015. Restoring a desert ecosystem using soil salvage, revegetation, and irrigation. Journal of Arid Environments 115:44-52.

DSCN2576Joshua Tree NP. Road repaving, such as that which occurred along Key’s View Road in Joshua Tree National Park, may result in a buffer of vegetation and soil disturbance along the roadsides. To restore and mask the disturbance, Joshua Tree NP planted perennial species salvaged from the path of destruction and applied salvaged topsoil along the disturbance corridor. Additionally, they also placed dead plants and branches (referred to as vertical mulch) to provide cover and habitat and promote natural revegetation.  We monitored the restoration sites to assess outplanting survival, seed bank structure, and established plant community composition among the restoration treatments.

Engel EC, Abella SR. 2010. Evaluating efficacy of restoration techniques, Keys View Road reconstruction, Joshua Tree National Park, California, U.S.A. Mojave Applied Ecology Notes 3(2):3-4.

Restoration of native ecosystems to counter exotic invasion


The upsurge of exotic annual grasses such as Bromus rubens (Bromus) spp. initiates a fire cycle that occurs at a greater frequency than the recovery time of the long-lived desert perennial community, predisposing the vegetation to become fire-controlled annual grassland. Management in as yet unburned landscapes (and burned landscapes to prevent re-burning) must intervene in this cycle for at least two reasons. First, fuels must be reduced on desert landscapes infested with exotic annual grasses, or the landscapes will eventually burn, as was demonstrated by the record 2005 fire season when nearly 3% of the entire Mojave Desert burned (Brooks and Matchett 2006). And second, some type of vegetation competitive with the exotic annual grasses must be established, to provide vegetative cover for purposes such as minimizing soil erosion, while hopefully reducing fire hazard. The reestablishment of native vegetation following fire could be a major biotic factor influencing the ability of exotic grasses to resurge and promote a grass-fire cycle. Our objectives included establishing a native plant materials program for the Grand Canyon-Parashant NM, to provide locally adapted native plant materials for landscape vegetative rehabilitation, with an emphasis on competitive ability with non-native invasive species.

20140812_103611_Richtone(HDR)Forage enhancement

Vegetation in habitat of the federally listed desert tortoise Gopherus agassizii in the Mojave and western Sonoran Desert is now partly or mostly dominated by nonnative annual plants, such as red brome. To improve forage quality and augment availability of perennial cover plants, we tested seeding (pelletized or bare seeding), watering, and fencing for increasing a native annual forage species, a perennial forage species, and two shrub species that provide cover in desert tortoise habitat of southern Nevada.


Abella SR, Chiquoine LP, Engel EC, Kleinick KE, Edwards FS. 2015. Enhancing quality of desert tortoise habitat: augmenting native forage and cover plants. Journal of Fish and Wildlife Management 6:278-289.