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
Response of an aridland ecosystem to interannual climate variability and prolonged droughtPennington, Deana D.2007

Response of an aridland ecosystem to interannual climate variability and prolonged drought

Keywords

aridland ecosystems; drought; grasslands; New Mexico; NDVI

Abstract

Water is a key driver of ecosystem processes in aridland ecosystems. Thus, changes in climate could have significant impacts on ecosystem structure and function. In the southwestern US, interactions among regional climate drivers (e.g., El Nino Southern Oscillation) and topographically controlled convective storms create a spatially and temporally variable precipitation regime that governs the rate and magnitude of ecosystem processes. We quantified the spatial and temporal distribution of reduced grassland greenness in response to seasonal and annual variation in precipitation at two scales at the Sevilleta Long Term Ecological Research site in central New Mexico, using Normalized Difference Vegetation Index (NDVI) values from bi-weekly AVHRR data and seasonal ETM data from 1989 to 2005. We used spatially explicit NDVI Z-scores to identify times and places of significantly reduced greenness and related those to interactions between plant functional type, seasonal climate variation, and topography. Seasonal greenness was bimodal with a small peak in spring and a stronger peak following the summer monsoon. Greenness was generally spatially homogeneous in spring and more spatially variable in summer. From 2001 through spring 2002, drought effects were evidenced by a 4-fold increase in the number of pixels showing significantly low greenness. Spatial distribution of low greenness was initially modulated by topographic position, but as the drought intensified spread throughout the study area. Vegetation green up occurred rapidly when drought conditions ceased. We conclude that drought effects vary spatially over time, pervasive drought reduces broad-scale spatial heterogeneity, and greenness patterns recover rapidly when drought conditions end.

Authors

Pennington, Deana D.; Collins, Scott L.

Year Published

2007

Publication

Landscape Ecology

Locations
DOI

10.1007/s10980-006-9071-5

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

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

Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grasslandThomey, Michell L.2011

Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland

Keywords

carbon cycle; desert grasslands; leaf gas exchange; precipitation variability; primary production; soil respiration

Abstract

Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water-limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (theta), soil respiration (R-s), along with leaf-level photosynthesis (A(net)), predawn leaf water potential (Psi(pd)), and seasonal aboveground net primary productivity (ANPP) of the dominant C-4 grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil theta which corresponded with a significant increase in R-s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.

Authors

Thomey, Michell L.; Collins, Scott L.; Vargas, Rodrigo; Johnson, Jennifer E.; Brown, Renee F.; Natvig, Donald O.; Friggens, Michael T.

Year Published

2011

Publication

Global Change Biology

Locations
DOI

10.1111/j.1365-2486.2010.02363.x

Directional climate change and potential reversal of desertification in arid and semiarid ecosystemsPeters, Debra P. C.2012

Directional climate change and potential reversal of desertification in arid and semiarid ecosystems

Keywords

extreme events; grasslands; regime shift; shrublands; spatial context; wet-dry climatic periods

Abstract

Our objective was to determine if long-term increases in precipitation can maintain grasslands susceptible to desertification, and initiate a reversal of historic regime shifts on desertified shrublands. Perennial grass production and species richness in a multi-year wet period were hypothesized to be greater than expected based on precipitation in a sequence of dry years. These responses were expected to differ for grasslands and shrublands with different dominant species and topo-edaphic properties. Long-term trends in desertification were documented using vegetation maps beginning in 1858, 1915, 1928, and 1998). These trends were compared with herbaceous and woody species responses to a sequence of dry (19942003) and wet years (20042008) for two grassland (uplands, playas) and three desertified shrubland types (honey mesquite, creosotebush, tarbush) in the Chihuahuan Desert. Analyses showed that both types of grasslands decreased in spatial extent since 1858 whereas areas dominated by mesquite or creosotebush increased. Production of upland grasslands in the wet period was greater than expected based on responses during the dry period whereas the relationships between species richness and precipitation was the same for both periods. Precipitation was not important to responses in playa grasslands in either period. For all ecosystem types, the production response in wet years primarily was an increase in herbaceous plants, and the most pronounced responses occurred on sandy sites (upland grasslands, mesquite shrubland). Results suggest that multiple wet years are needed to initiate a sequence of grass establishment and survival processes that can maintain upland grasslands without management inputs and lead to a state change reversal in desertified shrublands. Restoration strategies need to take advantage of opportunities provided by future climates while recognizing the importance of ecosystem type.

Authors

Peters, Debra P. C.; Yao, Jin; Sala, Osvaldo E.; Anderson, John P.

Year Published

2012

Publication

Global Change Biology

Locations
DOI

10.1111/j.1365-2486.2011.02498.x

Precipitation variability and fire influence the temporal dynamics of soil CO2 efflux in an arid grasslandVargas, Rodrigo2012

Precipitation variability and fire influence the temporal dynamics of soil CO2 efflux in an arid grassland

Keywords

carbon cycle; climate change; disturbance; extreme pulses; grasslands; net primary production; precipitation variability; soil respiration; wavelet analysis

Abstract

Climate models suggest that extreme rainfall events will become more common with increased atmospheric warming. Consequently, changes in the size and frequency of rainfall will influence biophysical drivers that regulate the strength and timing of soil CO2 efflux a major source of terrestrial carbon flux. We used a rainfall manipulation experiment during the summer monsoon season (JulySeptember) to vary both the size and frequency of precipitation in an arid grassland 2 similar to years before and 2 similar to years after a lightning-caused wildfire. Soil CO2 efflux rates were always higher under increased rainfall event size than under increased rainfall event frequency, or ambient precipitation. Although fire reduced soil CO2 efflux rates by nearly 70%, the overall responses to rainfall variability were consistent before and after the fire. The overall sensitivity of soil CO2 efflux to temperature (Q10) converged to 1.4, but this value differed somewhat among treatments especially before the fire. Changes in rainfall patterns resulted in differences in the periodicity of soil CO2 efflux with strong signals at 1, 8, and 30 similar to days. Increased rainfall event size enhanced the synchrony between photosynthetically active radiation and soil CO2 efflux over the growing season before and after fire, suggesting a change in the temporal availability of substrate pools that regulate the temporal dynamics and magnitude of soil CO2 efflux. We conclude that arid grasslands are capable of rapidly increasing and maintaining high soil CO2 efflux rates in response to increased rainfall event size more than increased rainfall event frequency both before and after a fire. Therefore, the amount and pattern of multiple rain pulses over the growing season are crucial for understanding CO2 dynamics in burned and unburned water-limited ecosystems.

Authors

Vargas, Rodrigo; Collins, Scott L.; Thomey, Michell L.; Johnson, Jennifer E.; Brown, Renee F.; Natvig, Donald O.; Friggens, Michael T.

Year Published

2012

Publication

Global Change Biology

Locations
DOI

10.1111/j.1365-2486.2011.02628.x

Pulse dynamics and microbial processes in aridland ecosystemsCollins, Scott L.2008

Pulse dynamics and microbial processes in aridland ecosystems

Keywords

aridland ecosystems; decomposition; decoupled systems; fungal loop; net primary production; pulse-dynamics; soil carbon; soil nitrogen

Abstract

1. Aridland ecosystems cover about one-third of terrestrial environments globally, yet the extent to which models of carbon (C) and nitrogen (N) cycling, developed largely from studies of mesic ecosystems, apply to aridland systems remains unclear. 2. Within aridland ecosystems, C and N dynamics are often described by a pulse-reserve model in which episodic precipitation events stimulate biological activity that generate reserves of biomass, propagules and organic matter that prime the ecosystem to respond rapidly to subsequent precipitation events. 3. The role of microbial C and N processing within the pulse-reserve paradigm has not received much study. We present evidence suggesting that fungi play a critical and underappreciated role in aridland soils, including efficient decomposition of recalcitrant C compounds, N-transformations such as nitrification, and nutrient storage and translocation of C and N between plants and biotic soil crusts. While fungi may perform some of these functions in other ecosystems, this 'fungal loop' assumes particular importance in the N cycle in aridlands because water availability imposes even greater restrictions on bacterial activity and physicochemical processes limit accumulation of soil organic matter (SOM). 4. We incorporate these findings into a Threshold-Delay Nutrient Dynamics (TDND) model for aridland ecosystems in which plant responses to pulsed precipitation events are mediated by a fungal loop that links C and N cycling, net primary production (NPP) and decomposition in aridland soils. 5. Synthesis. Arid ecosystems are highly sensitive to global environmental change including N deposition and altered precipitation patterns; yet, models from mesic ecosystems do not adequately apply to aridland environments. Our 'fungal loop' N cycle model integrates spatial structure with pulse dynamics and extends the pulse-reserve paradigm to include the key role of microbial processes in aridland ecosystem dynamics.

Authors

Collins, Scott L.; Sinsabaugh, Robert L.; Crenshaw, Chelsea; Green, Laura; Porras-Alfaro, Andrea; Stursova, Martina; Zeglin, Lydia H.

Year Published

2008

Publication

Journal of Ecology

Locations
DOI

10.1111/j.1365-2745.2008.01362.x

Woody plant invasion at a semi-arid/arid transition zone: importance of ecosystem type to colonization and patch expansionPeters, Debra P. C.2006

Woody plant invasion at a semi-arid/arid transition zone: importance of ecosystem type to colonization and patch expansion

Keywords

biome transition; Chilmalman Desert; ecotone; invasive species; patch dynamics; patch structure; shortgrass steppe

Abstract

Question: How do patterns in colonization and patch expansion of an invasive woody plant (Larrea tridentata, Zygophyllaceae) differ between two grassland ecosystems at a biome transition zone? Location: Semi-arid/arid transition zone in central New Mexico. Methods: Frequency of occurrence, height, and surface area of saplings (n = 134) and patches of adult plants (n = 247) of the invasive shrub, L. tridentata, were measured within a mosaic of ecosystems dominated either by the Chihuahuan Desert species, Bouteloua eriopoda (Poaceae),or the shortgrass steppe species, B. gracilis, located within I km of the L. tridentata-dominated ecosystem. Distances between L. tridentata patches and patch area were used to estimate connectivity as a measure of propagule pressure. Sapling age (estimated from height using previously established relationships) and distance to the L. tridentata-dominated ecosystem was used to evaluate patterns in dispersal. Cover by species or functional group inside each L. tridentata patch was compared with surrounding vegetation to estimate changes in species composition with patch expansion. Results: L. tridentata saplings (< 1%) and adult patches (15%) occurred less frequently in B. gracilis-dominated ecosystems than expected based on areal extent of this ecosystem type. Propagule pressure did not differ with distance from the core ecosystem dominated by L. tridentata. Evidence for both local and long-distance dispersal events was found. Similar relationships between number of plants and patch area in both grassland types indicate similar patterns in patch expansion. Cover of perennial forbs was higher and cover of dominant grasses was lower in L. tridentata patches compared with the surrounding vegetation for both ecosystem types. Conclusions: Spatial variation in L. tridentata saplings and patches at this biome transition zone is related to the different susceptibilities to invasion by two grassland ecosystems. The persistence of grasslands at this site despite region-wide expansion by L. tridentata may be related to the spatial distribution of B. gracilis-dominated ecosystems that resist or deter invasion by this woody plant.

Authors

Peters, Debra P. C.; Yao, Jin; Gosz, James R.

Year Published

2006

Publication

Journal of Vegetation Science

Locations
DOI

10.1111/j.1654-1103.2006.tb02459.x

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

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

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