Collection of published works by members of the Southwest Chapter of the Ecological Society of America

Description

This collection was established to engage Southwest Chapter members and facilitate interaction between them and to enhance discovery of relevant ecological research.

latest article added on December 2013

ArticleFirst AuthorPublished
Responses to chronic N fertilization of ectomycorrhizal pinon but not arbuscular mycorrhizal juniper in a pinon-juniper woodlandAllen, Michael F.2010

Responses to chronic N fertilization of ectomycorrhizal pinon but not arbuscular mycorrhizal juniper in a pinon-juniper woodland

Keywords

Drought; Juniper; Mortality; Mycorrhiza; Nitrogen; Pinon pine

Abstract

Responses of mature trees to chronic N additions are poorly understood in ecosystems with high seasonal and spatial variability. To determine the effects of increased N deposition on mature conifers, we fertilized a pinon-juniper woodland in New Mexico at a rate equivalent to the urban interface. Fertilization (10 g m(-2) y(-1)) reduced numbers of mycorrhizae and increased leaf production in the ectomy-corrhizal (EM) pinon but not in arbuscular mycorrhizal (AM) juniper. Based on N fractionation between EM fungal sporocarps and pH-ion, EM in pinon utilized 20% of the net primary production in control plots. No sporocarps were produced in fertilized plots. N uptake by pinon could be accounted for by fertilization without mycorrhizae. Leaf N and size increased with fertilization in both species, and positively correlated with leaf delta(13)C. Leaf N:P increased in pinon but not juniper. Pinon mortality commenced in the N-fertilized plots in 2001, a year before the widespread die-off in western conifers, and continued through 2003. No mortality was observed in control plots or in junipers. The coupling of N enrichment and mycorrhizal decline could affect pinon production and mortality in semi-arid woodlands in the western US. (C) 2010 Elsevier Ltd. All rights reserved.

Authors

Allen, Michael F.; Allen, Edith B.; Lansing, Jennifer L.; Pregitzer, Kurt S.; Hendrick, Ron L.; Ruess, Roger W.; Collins, Scott L.

Year Published

2010

Publication

Journal of Arid Environments

Locations
DOI

10.1016/j.jaridenv.2010.05.001

Soil Heterogeneity Effects on Tallgrass Prairie Community Heterogeneity: An Application of Ecological Theory to Restoration Ecology.Baer, Sara G.2005

Soil Heterogeneity Effects on Tallgrass Prairie Community Heterogeneity: An Application of Ecological Theory to Restoration Ecology.

Keywords

grassland;Panicum virgatum;restoration;soil heterogeneity;Switchgrass;tallgrass prairie

Abstract

Spatial heterogeneity of resources can influence plant community composition and diversity in natural communities. We manipulated soil depth (two levels) and nutrient availability (three levels) to create four heterogeneity treatments (no heterogeneity, depth heterogeneity, nutrient heterogeneity, and depth + nutrient heterogeneity) replicated in an agricultural field seeded to native prairie species. Our objective was to determine whether resource heterogeneity influences species diversity and the trajectory of community development during grassland restoration. The treatments significantly increased heterogeneity of available inorganic nitrogen (N), soil water content, and light penetration. Plant diversity was indirectly related to resource heterogeneity through positive relationships with variability in productivity and cover established by the belowground manipulations. Diversity was inversely correlated with the average cover of the dominant grass, Switchgrass (Panicum virgatum), which increased over time in all heterogeneity treatments and resulted in community convergence among the heterogeneity treatments over time. The success of this cultivar across the wide range of resource availability was attributed to net photosynthesis rates equivalent to or higher than those of the native prairie plants in the presence of lower foliar N content. Our results suggest that resource heterogeneity alone may not increase diversity in restorations where a dominant species can successfully establish across the range of resource availability. This is consistent with theory regarding the role of ecological filters on community assembly in that the establishment of one species best adapted for the physical and biological conditions can play an inordinately important role in determining community structure.

Authors

Baer, Sara G., Scott L Collins, John M. Blair, Alan K. Knapp and Anna K. Fiedler.

Year Published

2005

Publication

Restoration Ecology

Locations
DOI

10.1111/j.1526-100X.2005.00051.x

Bottom-up regulation of plant community structure in an aridland ecosystemBaez, Selene2006

Bottom-up regulation of plant community structure in an aridland ecosystem

Keywords

Chihuahuan desert; grassland; long-term study; precipitation; shrubland; small mammals

Abstract

We conducted a long-term rodent exclosure experiment in native grass- and shrub-dominated vegetation to evaluate the importance of top-down and bottom-up controls on plant community structure in a low-productivity aridland ecosystem. Using multiple regressions and analysis of covariance, we assessed how bottom-up precipitation pulses cascade through vegetation to affect rodent populations, how rodent populations affect plant community structure, and how rodents alter rates of plant community change over time. Our findings showed that bottom-up pulses cascade through the system, increasing the abundances of plants and rodents, and that rodents exerted no control on plant community structure and rate of change in grass-dominated vegetation, and only limited control in shrub-dominated vegetation. These results were discussed in the context of top-down effects on plant communities across broad gradients of primary productivity. We conclude that bottom-up regulation maintains this ecosystem in a state of low primary productivity that constrains the abundance of consumers such that they exert limited influence on plant community structure and dynamics.

Authors

Baez, Selene; Collins, Scott L.; Lightfoot, David; Koontz, Terri L.

Year Published

2006

Publication

Ecology

Locations
DOI

10.1890/0012-9658(2006)87[2746:BROPCS]2.0.CO;2

This article contributed by:

Ecological Society of America

Does shrub invasion indirectly limit grass establishment via seedling herbivory? A test at grassland-shrubland ecotonesBestelmeyer, Brandon T.2007

Does shrub invasion indirectly limit grass establishment via seedling herbivory? A test at grassland-shrubland ecotones

Keywords

alternative state; Bouteloua eriopoda; Chihuahuan Desert; desertification; Dipodomys; foraging behavior; Lepus californicus; restoration; small mammal

Abstract

Question: Does shrub invasion at ecotones indirectly limit grass establishment by increasing mammalian seedling herbivory? Location: Chihuahuan Desert, New Mexico, USA. Methods: We tested the hypothesis that herbivore-related mortality of seedlings of the dominant perennial grass Bouteloua eriopoda would be highest in shrub-dominated portions of grassland-shrubland ecotones. We tested the hypothesis in two Chihuahuan Desert sites featuring similar shrub encroachment patterns but different shrub species, grass cover, and different abundances of small mammals. Within each site we transplanted B. eriopoda seedlings to grass-dominated, middle, and shrub-dominated positions of replicate ecotones during the time of year (mid-summer) when they would naturally appear and monitored seedling fates. We estimated population size/activity of putative small mammal herbivores. Results: Seedlings were killed by mammals in greater numbers in shrubland than in grassland or middle ecotone positions at the site with large herbivore numbers. At the site with low herbivore numbers, most seedlings were killed in middle ecotone positions. The abundance patterns of herbivores did not parallel patterns of seedling herbivory across the ecotones or between sites. Conclusions: Seedling herbivory is an important process and is related to vegetation composition, but the mechanisms underlying the relationship are not clear. We speculate that variation in small mammal foraging behavior may contribute to seedling herbivory patterns. Restoration strategies in the Chihuahuan Desert need to account for the abundance and/or behavior of native herbivores.

Authors

Bestelmeyer, Brandon T.; Kalil, N. I.; Peters, Debra P. C.

Year Published

2007

Publication

Journal of Vegetation Science

Locations
DOI

10.1111/j.1654-1103.2007.tb02548.x

State-and-Transition Models for Heterogeneous Landscapes: A Strategy for Development and ApplicationBestelmeyer, Brandon T.2009

State-and-Transition Models for Heterogeneous Landscapes: A Strategy for Development and Application

Keywords

climate, dynamic soil properties, ecological sites, inventory, monitoring, quantile regression, soils, state-and-transition models, threshold

Abstract

Interpretation of assessment and monitoring data requires information about how reference conditions and ecological resilience vary in space and time. Reference conditions used as benchmarks are often specified via potential-based land classifications (e.g., ecological sites) that describe the plant communities potentially observed in an area based on soil and climate. State-and-transition models (STMs) coupled to ecological sites specify indicators of ecological resilience and thresholds. Although general concepts surrounding STMs and ecological sites have received increasing attention, strategies to apply and quantify these concepts have not. In this paper, we outline concepts and a practical approach to potential-based land classification and STM development. Quantification emphasizes inventory techniques readily available to natural resource professionals that reveal processes interacting across spatial scales. We recommend a sequence of eight steps for the co-development of ecological sites and STMs, including 1) creation of initial concepts based on literature and workshops; 2) extensive, low-intensity traverses to refine initial concepts and to plan inventory; 3) development of a spatial hierarchy for sampling based on climate, geomorphology, and soils; 4) stratified medium-intensity inventory of plant communities and soils across a broad extent and with large sample sizes; 5) storage of plant and soil data in a single database; 6) model-building and analysis of inventory data to test initial concepts; 7) support and/or refinement of concepts; and 8) high-intensity characterization and monitoring of states. We offer a simple example of how data assembled via our sequence are used to refine ecological site classes and STMs. The linkage of inventory to expert knowledge and site-based mechanistic experiments and monitoring provides a powerful means for specifying management hypotheses and, ultimately, promoting resilience in grassland, shrubland, savanna, and forest ecosystems.

Authors

Herrick, Jeffrey E., Bestelmeyer, Brandon T., Havstad, Kris M., Tugel, Arlene J., Peacock, George L., Robinett, Daniel G., Shaver, Pat L., Brown, Joel R. and Sanchez, Homer

Year Published

2009

Publication

Rangeland Ecology & Management

Locations
DOI

10.2111/08-146

Spatial patterns of grassland-shrubland state transitions: a 74 year record on grazed and protected areasBrowning, Dawn2014

Spatial patterns of grassland-shrubland state transitions: a 74 year record on grazed and protected areas

Keywords

point pattern analysis, spatial ecology, pair correlation function, Ripley’s K, Moran’s I, spatial autocorrelation, LISA, livestock exclusion, Sonoran Desert, Prosopis velutina

Abstract

Tree and shrub abundance has increased in many grasslands, causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns, little is known about (i) how they develop; (ii) how they are influenced by grazing; or (iii) the extent to which intraspecific interactions dictate them. We addressed these questions by quantifying changes in the spatial distribution of Prosopis velutina (mesquite) shrubs over 74 years on grazed and protected grasslands. Livestock are effective agents of mesquite dispersal and mesquite has lateral roots extending well beyond its canopy. We therefore hypothesized that mesquite distributions would be (a) random on grazed areas and clustered on protected areas; and (b) that clustered or random distributions at early stages of encroachment would give way to regular distributions as stands matured and density-dependent interactions intensified. Assessments in 1932, 1948 and 2006 supported the first hypothesis, but we found no support for the second. In fact, clustering intensified with time on the protected area and the pattern remained random on the grazed site. Although shrub density increased on both areas between 1932 and 2006, we saw no progression toward a regular distribution indicative of density-dependent interactions. We propose that processes related to seed dispersal, grass-shrub seedling interactions, and hydrological constraints on shrub size interact to determine vegetation structure in grassland-to-shrubland state changes with implications for ecosystem function and management

Authors

Browning, Dawn, Franklin, Janet, Archer, Steven R., Gillan, Jeffrey K. and Guertin, D.Phillip

Year Published

2014

Publication

Ecological Applications

Locations
DOI

10.1890/13-2033.1

This article contributed by:

Ecological Society of America

Vegetation Index Differencing for Broad-Scale Assessment of Productivity Under Prolonged Drought and Sequential High Rainfall ConditionsBrowning, Dawn2013

Vegetation Index Differencing for Broad-Scale Assessment of Productivity Under Prolonged Drought and Sequential High Rainfall Conditions

Keywords

change detection, rangeland monitoring, Landsat, ecological state, state-and-transition models, phenology

Abstract

Spatially-explicit depictions of plant productivity over large areas are critical to monitoring landscapes in highly heterogeneous arid ecosystems. Applying radiometric change detection techniques we sought to determine whether: (1) differences between pre- and post-growing season spectral vegetation index values effectively identify areas of significant change in vegetation; and (2) areas of significant change coincide with altered ecological states. We differenced NDVI values, standardized difference values to Z-scores to identify areas of significant increase and decrease in NDVI, and examined the ecological states associated with these areas. The vegetation index differencing method and translation of growing season NDVI to Z-scores permit examination of change over large areas and can be applied by non-experts. This method identified areas with potential for vegetation/ecological state transition and serves to guide field reconnaissance efforts that may ultimately inform land management decisions for millions of acres of federal lands.

Authors

Browning, Dawn and Steele, Caitriana

Year Published

2013

Publication

Remote Sensing

Locations
DOI

10.3390/rs5010327

WOODY PLANTS IN GRASSLANDS: POST-ENCROACHMENT STAND DYNAMICS.Browning, Dawn M.2008

WOODY PLANTS IN GRASSLANDS: POST-ENCROACHMENT STAND DYNAMICS.

Keywords

aerial photography;dynamic equilibrium;edaphic constraints;encroachment phase;Prosopis velutina;;Santa Rita Experimental Range;shifting mosaic;shrub encroachment;stabilization phase;woody biomass

Abstract

Woody plant abundance is widely recognized to have increased in savannas and grasslands worldwide. The lack of information on the rates, dynamics, and extent of increases in shrub abundance is a major source of uncertainty in assessing how this vegetation change has influenced biogeochemical cycles. Projecting future consequences of woody cover change on ecosystem function will require knowledge of where shrub cover in present-day stands lies relative to the realizable maximum for a given soil type within a bioclimatic region. We used time-series aerial photography (1936, 1966, and 1996) and field studies to quantify cover and biomass of velvet mesquite (Prosopis velutina Woot.) following its proliferation in a semidesert grassland of Arizona. Mapping of individual shrubs indicated an encroachment phase characterized by high rates of bare patch colonization. Upon entering a stabilization phase, shrub cover increases associated with recruitment and canopy expansion were largely offset by contractions in canopy area of other shrub patches. Instances of shrub disappearance coincided with a period of below-average rainfall (1936–1966). Overall, shrub cover (mean ± SE) on sandy uplands with few and widely scattered shrubs in 1902 was dynamically stable over the 1936–1996 period averaging ~35% ± 5%. Shrub cover on clayey uplands in 1936 was 17% ± 2% but subsequently increased twofold to levels comparable to those on sandy uplands by 1966 (36% ± 7%). Cover on both soils then decreased slightly between 1966 and 1996 to 28% ± 3%. Thus, soil properties influenced the rate at which landscapes reached a dynamic equilibrium, but not the apparent endpoint. Although sandy and clayey landscapes appear to have stabilized at comparable levels of cover, shrub biomass was 1.4 times greater on clayey soils. Declines in shrub cover between 1966 and 1996 were accompanied by a shift to smaller patch sizes on both sandy and clayey landscapes. Dynamics observed during the stabilization phase suggest that density-dependent regulation may be in play. If woody cover has transitioned from directional increases to a dynamic equilibrium, biomass projections will require monitoring and modeling patch dynamics and stand structure rather than simply changes in total cover.

Authors

Browning, Dawn M., Steven R. Archer, Gregory P. Asner, Mitchel P. McClaran, and Carol A. Wessman.

Year Published

2008

Publication

Ecological Applications

Locations
DOI

10.1890/07-1559.1

This article contributed by:

Ecological Society of America

Hierarchical analysis of vegetation dynamics over 71 years: soil-rainfall interactions in a Chihuahuan Desert ecosystemBrowning, Dawn M.2012

Hierarchical analysis of vegetation dynamics over 71 years: soil-rainfall interactions in a Chihuahuan Desert ecosystem

Keywords

aerial photography; Chihuahuan Desert, New Mexico, USA; cross-scale linkages; ecological-state mapping; hierarchy theory; Jornada Basin LTER; object-based change detection; petrocalcic soil; Prosopis glandulosa; shrub patch dynamics; shrub proliferation; soil depth

Abstract

Proliferation of woody plants in grasslands and savannas is a persistent problem globally. This widely observed shift from grass to shrub dominance in rangelands worldwide has been heterogeneous in space and time largely due to cross-scale interactions among soils, climate, and land-use history. Our objective was to use a hierarchical framework to evaluate the relationship between spatial patterns in soil properties and long-term shrub dynamics in the northern Chihuahuan Desert of New Mexico, USA. To meet this objective, shrub patch dynamics from 1937 to 2008 were characterized at patch and landscape scales using historical imagery and a recent digital soils map. Effects of annual precipitation on patch dynamics on two soils revealed strong correlations between shrub growth on deep sandy soils and above-average rainfall years (r = 0.671, P = 0.034) and shrub colonization and below-average rainfall years on shallow sandy soils (r = 0.705, P = 0.023). Patch-level analysis of demographic patterns revealed significant differences between shrub patches on deep and shallow sandy soils during periods of above-and below-average rainfall. Both deep and shallow sandy soils exhibited low shrub cover in 1937 (1.0% +/- 2.3% and 0.3% +/- 1.3%, respectively [mean +/- SD]) and were characterized by colonization or appearance of new patches until 1960. However, different demographic responses to the cessation of severe drought on the two soils and increased frequency of wet years after 1960 have resulted in very different endpoints. In 2008 a shrubland occupied the deep sandy soils with cover at 19.8% +/- 9.1%, while a shrub-dominated grassland occurred on the shallow sandy soils with cover at 9.3% +/- 7.2%. Present-day shrub vegetation constitutes a shifting mosaic marked by the coexistence of patches at different stages of development. Management implications of this long-term multi-scale assessment of vegetation dynamics support the notion that soil properties may constrain grassland remediation. Such efforts on sandy soils should be focused on sites characterized by near-surface water-holding capacity, as those lacking available water-holding capacity in the shallow root zone pose challenges to grass recovery and survival.

Authors

Browning, Dawn M.; Duniway, Michael C.; Laliberte, Andrea S.; Rango, Albert

Year Published

2012

Publication

Ecological Applications

Locations
This article contributed by:

Ecological Society of America

Rapid plant community responses during the summer monsoon to nighttime warming in a northern Chihuahuan Desert grasslandCollins, Scott L.2010

Rapid plant community responses during the summer monsoon to nighttime warming in a northern Chihuahuan Desert grassland

Keywords

Bouteloua eriopoda; Bouteloua gracilis; Desert grassland; Nighttime warming; Nitrogen deposition; Soil moisture; Soil temperature

Abstract

Global environmental change is altering temperature, precipitation patterns, and resource availability in aridland ecosystems. In 2006, we established a multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric N deposition, and more frequent occurrence of El Nino years on plant community dynamics in a northern Chihuahuan Desert grassland. Here we only report the results of warming and N addition from the first monsoon growing season prior to the imposition of the precipitation treatments. Our passive nighttime warming treatment increased daily minimum temperatures by 1.4-3.0 degrees C. Fertilization increased NO(3)-N supply, as measured with Root Simulator Probes, by 28% and NO(3)-N supply in warmed plots was 12% higher than in control plots. After one monsoon season we found that warming significantly increased total plant cover. Responses among dominant species varied, however. Warming significantly increased cover of Bouteloua eriopoda (P < 0.05) and tended to increase cover of the shrub Gurierrezia sarothrae (P = 0.064), whereas N addition significantly increased the cover of Bouteloua gracilis (P < 0.05). Our results demonstrate that rapid soil and plant community responses can occur in response to nighttime warming and N fertilization during one monsoon season in this semi-arid desert grassland. The sensitivity of this desert system to key drivers of global environmental change suggests that further increases in temperature and atmospheric deposition will likely alter community structure and ecosystem functioning in this and other aridland ecosystems. (C) 2009 Elsevier Ltd. All rights reserved.

Authors

Collins, Scott L.; Fargione, Joseph E.; Crenshaw, Chelsea L.; Nonaka, Etsuko; Elliott, James R.; Xia, Yang; Pockman, William T.

Year Published

2010

Publication

Journal of Arid Environments

Locations
DOI

10.1016/j.jaridenv.2009.10.005

Recent Articles

Spatial Patterns of Grassland-Shrubland State Transitions: a 74 Year Record on Grazed and Protected Areas

by Browning, Dawn, Franklin, Janet, Archer, Steven R., Gillan, Jeffrey K. and Guertin, D.Phillip

Tree and shrub abundance has increased in many grasslands, causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns, little is known about (i) how they develop; (ii) how they are influenced by grazing; or (iii) the extent to which intraspecific interactions dictate them. We addressed these questi...

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Interpretation of High-Resolution Imagery for Detecting Woodland Cover Composition Change After Fuels Reduction Treatments

by Karl, Jason W., Gillan, Jeffrey K., Barger, Nichole N., Herrick, Jeffrey E. and Duniway, Michael C.

The use of very high resolution (VHR; ground sampling distances &lt; ~5cm) aerial imagery to estimate site vegetation cover and to detect changes from management has been well documented. However, as the purpose of monitoring is to document change over time, the ability to detect changes from imagery at the same or better level of accuracy and precision as those measured in situ must be assesse...

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