@article {JRN55132, title = {Small mammal herbivory and grassland recovery potential in the Chihuahuan Desert}, journal = {Journal of Arid Environments}, volume = {166}, year = {2019}, month = {07/2019}, pages = {11-16}, chapter = {11}, abstract = {

In many arid ecosystems, shrub encroachment is associated with the loss of valuable perennial grasses. Increased native rodent and lagomorph abundance associated with shrub encroachment can have negative effects on grass persistence and restoration. In the Chihuahuan Desert, herbivore abundance can be up to two times greater in degraded Prosopis glandulosa (honey mesquite) shrublands than in intact Bouteloua eriopoda\ (black grama) grasslands. We tested the\ recovery potential of B. eriopoda\ patches in shrub-dominated, grass-dominated and ecotone (grass and shrub co-dominated) states that were exposed to or protected from native rodent and lagomorph herbivores. Herbivore exclosures and control quadrats\ were established in a replicated blocked\ design.\ A disturbance of 40cm x 40cm was created in the center of a B. eriopoda grass patch\ in each treatment quadrat\ in 2001, whereby all above ground biomass was removed in order to examine the ability of\ B. eriopoda to recolonize disturbed areas. The disturbed areas were measured for recruitment and re-establishment of\ B. eriopoda\ in 2002, 2005 and 2008.\ Although herbivore abundance was greater in shrub-dominated states than the other states for the given time periods, there was little difference in recruitment and re-establishment\ of\ B. eriopoda among\ states and in response to rodent exclusion. Because increased herbivore abundance in shrub-dominated states\ did\ not constrain grass recovery potential, other factors are likely to be more important constraints on perennial grasses recovery in the Chihuahuan Desert.

}, keywords = {Bouteloua eriopoda, Chihuahan Desert, herbivory, perennial grass regeneration, prosopis glandulosa, rodents}, doi = {doi.org/10.1016/j.jaridenv.2019.04.001}, url = {files/bibliography/19-013.pdf}, author = {L.N. Svejcar and Brandon T Bestelmeyer and D. K. James and Debra C. Peters} } @article {JRN54917, title = {Effect of climeodaphic heterogeneity on woody plant dominance in the Argentine Caldenal region}, journal = {Rangeland Ecology and Management}, volume = {71:409-416}, year = {2018}, month = {06/2018}, abstract = {

Woody plant encroachment is widespread throughout drylands of the world, but rates and patterns of encroachment at the regional scale can be mediated by soil and climate. Climoedaphic properties may therefore help to explain patterns of woody plant dominance. In the Caldenal region of central Argentina, which is experiencing widespread woody plant encroachment, we used stratified and targeted inventory of vegetation and soils alongside climate data to classify ecological states and then identify factors suggesting resistance to woody plant encroachment. We found that three climoedaphic contexts differ in the degree of woody plant dominance. Sandsheet landforms had the lowest likelihood of a woody plant thicket state. Within loamy soils, sites with deep soil carbonates in warmer and wetter climates were less likely to feature a shrub thicket state than sites with shallow carbonates in cooler and drier climates. These contexts serve as a basis for recognizing different ecological sites to assist mapping and prioritization of management interventions in the Caldenal region. Simple inventory-based approaches can be helpful for designing land management recommendations in other ecosystems.

}, doi = {10.1016/j.rama.2018.03.001}, url = {files/bibliography/18-011.pdf}, author = {L.N. Svejcar and H. Raul Peinetti and Brandon T Bestelmeyer} } @article {JRN54151, title = {Scale-dependent feedbacks between patch size and plant reproduction in desert grassland}, journal = {Ecosystems}, volume = {18}, year = {2015}, month = {01/2015}, pages = {146-153}, chapter = {146}, abstract = {

Theoretical models suggest that scale-dependent feedbacks between plant reproductive success and plant patch size govern transitions from highly to sparsely vegetated states in drylands, yet there is scant empirical evidence for these mechanisms. Scale-dependent feedback models suggest that an optimal patch size exists for growth and reproduction of plants and that a threshold patch organization exists below which positive feedbacks between vegetation and resources can break down, leading to critical transitions. We examined the relationship between patch size and plant reproduction using an experiment in a Chihuahuan Desert grassland. We tested the hypothesis that reproductive effort and success of a dominant grass (Bouteloua eriopoda) would vary predictably with patch size. We found that focal plants in medium-sized patches featured higher rates of grass reproductive success than when plants occupied either large patch interiors or small patches. These patterns support the existence of scale-dependent feedbacks in Chihuahuan Desert grasslands and indicate an optimal patch size for reproductive effort and success in B. eriopoda. We discuss the implications of these results for detecting ecological thresholds in desert grasslands.

}, keywords = {Bouteloua eriopoda, Chihuahuan Desert, critical threshold, desertification, dryland, feedbacks, patch size, resilience, state transition}, doi = {10.1007/s10021-014-9818-9}, url = {/files/bibliography/15-008.pdf}, author = {L.N. Svejcar and Brandon T Bestelmeyer and Danielle Duni and D. K. James} } @conference {JRN53993, title = {Ecological site concepts for the Caldenal ecoregion}, booktitle = {Los Pastizales y el Hombre, producir y conservar}, year = {2013}, month = {03/2013}, address = {Santa Rosa, La Pampa, Argentina}, abstract = {

Ecological site (ES) concepts describe potential vegetation and ecological mechanisms of plant community change within specific soil, geomorphic and climate conditions.\  In this study, a preliminary definition of ES concepts for the caldenal ecoregion was developed by exploring the relationship between landform, soil and vegetation based on 42 sample sites. Woody plant dominance was characterized by plant density (Open, Closed and Fachinal [thicket]), and height (Tall and Short). Herbaceous species composition was grouped in five functional groups: the palatable summer and thin-leaved winter grasses, and the unpalatable winter bunch grasses, forbs, and annuals.\  Ward{\textquoteright}s cluster analysis was used to group sampling sites based on their soil properties along with vegetation characteristics.\  Cluster analysis indicated six distinct plant communities that were easily interpreted.\  Open Calden states were found in dunes and sandy plateaus, while thicketized states (Closed and Fachinal) occurred on soils with greater silt-clay content on hillsides, valleys and plains.\  A short fachinal state was associated with shallow caliche layer (\<0.5 m) and high carbonate levels.\  Open and Closed types were dominated by Prosopis caldenia while the Fachinal was dominated by Condalia microphyla.\  Palatable grasses were more highly associated with Open sites; however all sites showed a large proportion of unpalatable herbaceous species. The ecological sites derived from this analysis can serve as a basis for recognizing different levels of vulnerability to encroachment and change in grass species composition. This study provides a framework for future data collection to further refine ES concepts in the Caldenal.

}, author = {L.N. Svejcar and Brandon T Bestelmeyer and H. Raul Peinetti and Edgardo Adema and Sosa, A.A.} }