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
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

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

TEMPORAL AND SPATIAL VARIATION IN POLLINATION OF A MONTANE HERB: A SEVEN-YEAR STUDY.Price, Mary V.2005

TEMPORAL AND SPATIAL VARIATION IN POLLINATION OF A MONTANE HERB: A SEVEN-YEAR STUDY.

Keywords

field study;floral larcenists;floral visitation rates;flower-visitor community;hummingbirds;insects;Ipomopsis aggregata;long-term study;path analysis;plant population dynamics;pollen delivery;pollination services;structural equation modeling

Abstract

Pollination by animals is critical to sexual reproduction of most angiosperms. However, little is known about variation in pollination service to single plant species. We report results of a long-term study of Ipomopsis aggregata, a semelparous montane herb whose flowers are visited by hummingbird and insect pollinators as well as “floral larcenists.” We censused flower visitors over seven summers at permanent study sites separated by several hundred meters, and counted pollen delivered to flowers on a subset of plants observed for visitation. The species composition of the community of visitors varied significantly across years and within the flowering season; sites varied significantly only in the magnitude of parallel annual changes in the visitor community. Rates of flower visitation fluctuated over an order of magnitude or more. Variation in mean stigma pollen load among plants flowering in the same site and year was explained by a causal path model in which visitation rates by pollinators and larcenists had linear positive and negative effects, respectively. A simplified model including only pollinators explained almost as much variance as did the full model. However, qualitatively different parameter estimates were produced by an analogous causal model based on population means across site–year combinations. Discrepant results from within- and between-population levels of analysis suggest that pollen receipt is influenced by environmental factors that vary among sites and years, as well as by pollinator visit rates. We present a heuristic causal model that includes such factors, and we note its implications for ecological and evolutionary studies of pollination.

Authors

Price, Mary V., Nickolas M. Waser, Rebecca E. Irwin, Diane R. Campbell, and Alison K. Brody.

Year Published

2005

Publication

Ecology

Locations
DOI

10.1890/04-1274

This article contributed by:

Ecological Society of America

Long-term data collection at USDA experimental sites for studies of ecohydrologyMoran, M. Susan2008

Long-term data collection at USDA experimental sites for studies of ecohydrology

Keywords

ecohydrology; watersheds; forests; ranges; USDA; long-term

Abstract

The science of ecohydrology is characterized by feedbacks, gradual trends and extreme events that are best revealed with long-term experimental studies of hydrological processes and biological communities. fit this review, we identified 81 US Department of Agriculture (USDA) experimental watersheds. forests and ranges with data records of more than 20 years measuring important ecosystem dynamics such as variations in vegetation, precipitation, climate, runoff, water quality and soil moisture. Through a series of examples, we showed how USDA long-term data have been used to understand key ecohydrological issues, including (1) time lag between cause and effects, (2) critical thresholds and cyclic trends, (3) context of rare and extreme events and (4) mechanistic feedbacks for simulation modelling. New analyses of network-wide, long-term data from USDA experimental sites were used to illustrate the potential for multi-year, multi-site ecohydrological research. Three areas of investigation were identified to best exploit the unique spatial distribution and long-term data of USDA experimental sites: convergence, cumulative synthesis and autocorrelation. This review underscored the need for continuous, interdisciplinary data records spanning more than 20 years across a wide range of ecosystems within and Outside the conterminous USA to address major crosscutting problems facing ecohydrology. Conversely, the heightened interest in ecohydrology has impacted USDA experimental sites by encouraging new long-term data collection efforts and adapting existing long-term data collection networks to address new science issues. Copyright (C) 2008 John Wiley & Sons, Ltd.

Authors

Moran, M. Susan; Peters, Debra P. C.; McClaran, Mitchel P.; Nichols, Mary H.; Adams, Mary B.

Year Published

2008

Publication

Ecohydrology

Locations
DOI

10.1002/eco.24

Population and clonal level responses of a perennial grass following fire in the northern Chihuahuan DesertDrewa, Paul B.2006

Population and clonal level responses of a perennial grass following fire in the northern Chihuahuan Desert

Keywords

Bouteloua eriopoda; fire intensity; grazing; precipitation; resprouting

Abstract

Relationships involving fire and perennial grasses are controversial in Chihuahuan Desert grasslands of southern New Mexico, USA. Research suggests that fire delays the resprouting of perennial grasses well after two growing seasons. However, such results are confounded by livestock grazing, soil erosion, and drought. Additionally, post-fire grass responses may depend on initial clone size. We evaluated the effects of fire, grazing, and clone size on Bouteloua eriopoda (black grama) in southern New Mexico grasslands. Four 2-ha plots were established in each of four sites. Fire and grazing were applied or not applied in 1999 such that four treatment combinations were assigned randomly to plots within each site. Within each plot, small (0-10 cm(2) basal area), medium (10-30 cm(2)), and large (> 30 cm(2)) clones were initially mapped in five 0.91-m(2) quadrats where grass attributes and litter cover were evaluated before and at the end of two growing seasons following fire. Maximum fire temperature was also measured. At a population level, canopy and litter cover were each approximately 50% less in burned than unburned areas. However, compared to initial levels, canopy height had increased by 10% at the end of the study, regardless of fire. At a clonal level, basal cover reductions were attributed mostly to large clones that survived fire. Smaller clone densities had decreased by as much as 19% in burned compared to unburned areas, and fire reduced the basal cover of medium clones. Basal and canopy cover, recruitment, and clone basal area decreased with increased fire temperatures. Almost all responses were independent of grazing, and interactive effects of grazing and fire were not detected. Fire did not kill all perennial grass clones, regardless of size. However, rapid responses were likely influenced by above-average precipitation after fire. Future studies in desert grasslands should examine how perennial grass dynamics are affected by fire, precipitation patterns, and interactions with grazing.

Authors

Drewa, Paul B.; Peters, Debra P. C.; Havstad, Kris M.

Year Published

2006

Publication

Oecologia

Locations
DOI

10.1007/s00442-006-0502-4

Aboveground net primary production dynamics in a northern Chihuahuan Desert ecosystemMuldavin, Esteban H.2008

Aboveground net primary production dynamics in a northern Chihuahuan Desert ecosystem

Keywords

aboveground net primary production; Bouteloua eriopoda; chihuahuan desert; desert grassland; desert shrubland

Abstract

Aboveground net primary production (ANPP) dynamics are a key element in the understanding of ecosystem processes. For semiarid environments, the pulse-reserve framework links ANPP to variable and unpredictable precipitation events contingent on surficial hydrology, soil moisture dynamics, biodiversity structure, trophic dynamics, and landscape context. Consequently, ANPP may be decoupled periodically from processes such as decomposition and may be subjected to complex feedbacks and thresholds at broader scales. As currently formulated, the pulse-reserve framework may not encompass the breadth of ANPP response to seasonal patterns of precipitation and heat inputs. Accordingly, we examined a 6-year (1999-2004), seasonal record of ANPP with respect to precipitation, soil moisture dynamics, and functional groups in a black grama (Bouteloua eriopoda) grassland and a creosotebush (Larrea tridentata) shrubland in the northern Chihuahuan Desert. Annual ANPP was similar in the grassland (51.1 g/m(2)) and shrubland (59.2 g/m(2)) and positively correlated with annual precipitation. ANPP differed among communities with respect to life forms and functional groups and responses to abiotic drivers. In keeping with the pulse-reserve model, ANPP in black grama grassland was dominated by warm-season C-4 grasses and subshrubs that responded to large, transient summer storms and associated soil moisture in the upper 30 cm. In contrast, ANPP in creosotebush shrubland occasionally responded to summer moisture, but the predominant pattern was slower, non-pulsed growth of cool-season C-3 shrubs during spring, in response to winter soil moisture accumulation and the breaking of cold dormancy. Overall, production in this Chihuahuan Desert ecosystem reflected a mix of warm-temperate arid land pulse dynamics during the summer monsoon and non-pulsed dynamics in spring driven by winter soil moisture accumulation similar to that of cool-temperate regions.

Authors

Muldavin, Esteban H.; Moore, Douglas I.; Collins, Scott L.; Wetherill, Karen R.; Lightfoot, David C.

Year Published

2008

Publication

Oecologia

Locations
DOI

10.1007/s00442-007-0880-2

Above- and belowground responses to nitrogen addition in a Chihuahuan Desert grasslandLadwig, Laura M.2012

Above- and belowground responses to nitrogen addition in a Chihuahuan Desert grassland

Keywords

Semiarid grassland; N deposition; Aboveground production; Belowground production; Species richness

Abstract

Increased available soil nitrogen can increase biomass, lower species richness, alter soil chemistry and modify community structure in herbaceous ecosystems worldwide. Although increased nitrogen availability typically increases aboveground production and decreases species richness in mesic systems, the impacts of nitrogen additions on semiarid ecosystems remain unclear. To determine how a semiarid grassland responds to increased nitrogen availability, we examined plant community structure and above- and belowground net primary production in response to long-term nitrogen addition in a desert grassland in central New Mexico, USA. Plots were fertilized annually (10 g N m(-2)) since 1995 and NPP measured from 2004 to 2009. Differences in aboveground NPP between fertilized and control treatments occurred in 2004 following a prescribed fire and in 2006 when precipitation was double the long-term average during the summer monsoon. Presumably, nitrogen only became limiting once drought stress was alleviated. Belowground NPP was also related to precipitation, and greatest root growth occurred the year following the wettest summer, decreasing gradually thereafter. Belowground production was unrelated to aboveground production within years and unrelated to nitrogen enrichment. Species richness changed between years in response to seasonal precipitation variability, but was not altered by nitrogen addition. Community structure did respond to nitrogen fertilization primarily through increased abundance of two dominant perennial grasses. These results were contrary to most nitrogen addition studies that find increased biomass and decreased species richness with nitrogen fertilization. Therefore, factors other than nitrogen deposition, such as fire or drought, may play a stronger role in shaping semiarid grassland communities than soil fertility.

Authors

Ladwig, Laura M.; Collins, Scott L.; Swann, Amaris L.; Xia, Yang; Allen, Michael F.; Allen, Edith B.

Year Published

2012

Publication

Oecologia

Locations
DOI

10.1007/s00442-011-2173-z

Post-Fire Resource Redistribution in Desert Grasslands: A Possible Negative Feedback on Land DegradationRavi, Sujith2009

Post-Fire Resource Redistribution in Desert Grasslands: A Possible Negative Feedback on Land Degradation

Keywords

land degradation; drylands; soil erosion; fire; water repellency; shrub encroachment

Abstract

Desert grasslands, which are very sensitive to external drivers like climate change, are areas affected by rapid land degradation processes. In many regions of the world the common form of land degradation involves the rapid encroachment of woody plants into desert grasslands. This process, thought to be irreversible and sustained by biophysical feedbacks of global desertification, results in the heterogeneous distribution of vegetation and soil resources. Most of these shrub-grass transition systems at the desert margins are prone to disturbances such as fires, which affect the interactions between ecological, hydrological, and land surface processes. Here we investigate the effect of prescribed fires on the landscape heterogeneity associated with shrub encroachment. Replicated field manipulation experiments were conducted at a shrub-grass transition zone in the northern Chihuahuan desert (New Mexico, USA) using a combination of erosion monitoring techniques, microtopography measurements, infiltration experiments, and isotopic studies. The results indicate that soil erosion is more intense in burned shrub patches compared to burned grass patches and bare interspaces. This enhancement of erosion processes, mainly aeolian, is attributed to the soil-water repellency induced by the burning shrubs, which alters the physical and chemical properties of the soil surface. Further, we show that by enhancing soil erodibility fires allow erosion processes to redistribute resources accumulated by the shrub clumps, thereby leading to a more homogeneous distribution of soil resources. Thus fires counteract or diminish the heterogeneity-forming dynamics of land degradation associated with shrub encroachment by enhancing local-scale soil erodibility.

Authors

Ravi, Sujith; D'Odorico, Paolo; Wang, Lixin; White, Carleton S.; Okin, Gregory S.; Macko, Stephen A.; Collins, Scott L.

Year Published

2009

Publication

Ecosystems

Locations
DOI

10.1007/s10021-009-9233-9

Spatiotemporal Patterns of Production Can Be Used to Detect State Change Across an Arid LandscapeWilliamson, Jeb C.2012

Spatiotemporal Patterns of Production Can Be Used to Detect State Change Across an Arid Landscape

Keywords

aboveground net primary production; normalized difference vegetation index; precipitation; remote sensing; Chihuahuan Desert; state change; shrub encroachment; grassland; shrubland

Abstract

Methods to detect and quantify shifts in the state of ecosystems are increasingly important as global change drivers push more systems toward thresholds of change. Temporal relationships between precipitation and aboveground net primary production (ANPP) have been studied extensively in arid and semiarid ecosystems, but rarely has spatial variation in these relationships been investigated at a landscape scale, and rarely has such information been viewed as a resource for mapping the distribution of different ecological states. We examined the broad-scale effects of a shift from grassland to shrubland states on spatiotemporal patterns of remotely sensed ANPP proxies in the northern Chihuahuan Desert. We found that the normalized difference vegetation index (NDVI), when averaged across an eight-year period, did not vary significantly between these states, despite changes in ecosystem attributes likely to influence water availability to plants. In contrast, temporal relationships between precipitation and time-integrated NDVI (NDVI-I) modeled on a per-pixel basis were sensitive to spatial variation in shrub canopy cover, a key attribute differentiating ecological states in the region. The slope of the relationship between annual NDVI-I and 2-year cumulative precipitation was negatively related to, and accounted for 71% of variation in, shrub canopy cover estimated at validation sites using high spatial resolution satellite imagery. These results suggest that remote sensing studies of temporal precipitation-NDVI relationships may be useful for deriving shrub canopy cover estimates in the region, as well as for mapping other ecological state changes characterized by shifts in long-term ANPP, plant functional type dominance, or both.

Authors

Williamson, Jeb C.; Bestelmeyer, Brandon T.; Peters, Debra P. C.

Year Published

2012

Publication

Ecosystems

Locations
DOI

10.1007/s10021-011-9490-2

Multi-scale factors and long-term responses of Chihuahuan Desert grasses to droughtYao, Jin2006

Multi-scale factors and long-term responses of Chihuahuan Desert grasses to drought

Keywords

arid grasslands; desertification; drought; grazing; perennial grasses; transport processes

Abstract

Factors with variation at broad (e.g., climate) and fine scales (e.g., soil texture) that influence local processes at the plant scale (e.g., competition) have often been used to infer controls on spatial patterns and temporal trends in vegetation. However, these factors can be insufficient to explain spatial and temporal variation in grass cover for and and semiarid grasslands during an extreme drought that promotes woody plant encroachment. Transport of materials among patches may also be important to this variation. We used long-term cover data (19152001) combined with recently collected field data and spatial databases from a site in the northern Chihuahuan Desert to assess temporal trends in cover and the relative importance of factors at three scales (plant. patch, landscape unit) in explaining spatial variation in grass cover. We examined cover of five important grass species from two topographic positions before, during, and after the extreme drought of the 1950s. Our results show that dynamics before, during, and after the drought varied by species rather than by topographic position. Different factors were related to cover of each species in each time period. Factors at the landscape unit scale (rainfall, stocking rate) were related to grass cover in the pre- and post-drought periods whereas only the plant-scale factor of soil texture was significantly related to cover of two upland species during the drought. Patch-scale factors associated with the redistribution of water (microtopography) were important for different species in the pre- and post-drought period. Another patch-scale factor, distance from historic shrub populations, was important to the persistence of the dominant grass in uplands (Bouteloua eriopoda) through time. Our results suggest the importance of local processes during the drought, and transport processes before and after the drought with different relationships for different species. Disentangling the relative importance of factors at different spatial scales to spatial patterns and long-term trends in grass cover can provide new insights into the key processes driving these historic patterns, and can be used to improve forecasts of vegetation change in and and semiarid areas.

Authors

Yao, Jin; Peters, Debra P. C.; Havstad, Kris M.; Gibbens, Robert P.; Herrick, Jeffrey E.

Year Published

2006

Publication

Landscape Ecology

Locations
DOI

10.1007/s10980-006-0025-8

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