@conference {50213, title = {Incorporating invasive species and degraded landscapes into ecological site descriptions}, booktitle = {Society for Range Management Annual Meeting}, series = {Building Bridges: Grasslands to Rangelands}, year = {2008}, month = {January 26-31, 2}, pages = {2100}, address = {Louisville, KY}, abstract = {Ecological Site Descriptions (ESDs) and State-and-Transition Models (STMs) have been developed as means of evaluating the condition of rangelands based on Historic Climax Plant Communities (HCPCs) and for creating land management plans with an understanding of the dynamics of vegetation change. However, with the overall increase of invasive species, either native or exotic, along with natural or man-made land degradation, it is difficult to find sites not influenced by invasive species or changes in site-defining soil properties. In some areas, all available sites may be dominated by invasive species and/or extensively degraded. Although STMs have been developed to include potential states caused by simple disturbances such as long-term overgrazing and increased fire frequency, it is often difficult to create STMs that integrate processes that permanently change an area to a new or modified ecological site. In addition, it is difficult to define reference conditions in extensively altered ecological sites in a way that incorporates the former HCPC and the new ecological site properties. This poster will explore possible solutions for writing ESDs and STMs for sites influenced by invasive species and severely degraded landscapes, along with the strengths and weaknesses of these solutions.}, keywords = {degraded, ecological site descriptions, invasive}, author = {N.K. Hansen and Brandon T Bestelmeyer and Joel R. Brown and A.J. Tugel} } @mastersthesis {50214, title = {Patterns of soil and vegetation change associated with grassland-shrubland transitions: a case study}, year = {2008}, note = {//USDA//LTER V//entered 7/23/2008; PDF availableProCite field[12]: In File, partial (7/23/2008)}, month = {2008}, pages = {152}, school = {New Mexico State University}, type = {pp}, address = {Las Cruces, New Mexico}, abstract = {The conversion of grasslands to shrublands has been a common feature of desertification in the northern Chihuahuan Desert and other arid and semi-arid regions of the world. This study examined the encroachment of mesquite (Prosopis glandulosa) onto grasslands dominated by tobosa (Pleuraphis mutica) and black grama (Bouteloua eriopoda) around Red Lake, a playa in the northwest corner of the USDA-ARS Jornada Experimental Range. To identify factors influencing mesquite encroachment, the influences of sand deposition onto the clay soils of the tobosa grasslands and soil properties (e.g., texture, gypsum content) were intensely studied. In addition, the influences of vegetation and erosion type (wind or water) on size and orientation of intercanopy gaps were assessed for all vegetation communities. Field vegetation assessments indicated that mesquite now dominates 55\% of the study area. GIS-based analyses of imagery from 1942 to 2003 found that mesquite dunelands replaced 37\% of the grasslands in the study area between 1942 and 1973, and dunelands subsequently increased only 3.7\% between 1973 and 2003. Mesquite encroachment was associated with increased size and decreased number of intercanopy gaps. Soil profile characterization revealed that mesquite encroachment may have been limited by high electrical conductivity and/or gypsum content of clay soils, but sand deposition on the surface did not appear to be a factor in the rate and extent of mesquite encroachment onto tobosa grasslands. In addition, cesium-137 analyses provided evidence for net erosion across the study area, with net deposition found only under grass canopies in the ecotones between the tobosa grasslands and the sand sheets dominated by mesquite dunelands. This research indicates that 1) sand deposition on fine-textured soils does not significantly facilitate mesquite encroachment; 2) the texture, electrical conductivity, and gypsum content of soils may affect the rate of mesquite encroachment but not the extent of colonization; 3) intercanopy gaps are influenced more by vegetation type (p < 0.05) than by wind or water vectors (p > 0.05); and 4) the formation of coppice dunes has led to the loss of landscape integrity.}, keywords = {dissertation, grassland-shrubland transition, soil change, soil function, soil characteristics, spatial variability, soil chemistry, soil erosion, soil patterns, soil properties, changes, soil, classification, soil, description, soil, drought, soil, methods, soil, vegetation changes, soil, vegetation on gypsum, soil,dune development, thesis, vegetation change, vegetation change, desertification, vegetation change, grass, vegetation change, wind erosion, vegetation change,mesquite influence, vegetation mapping, methods, vegetation mapping, photointerpretation, vegetation, history, vegetation, management, vegetation, patterns, vegetation, wind erosion, vegetation,gypsum soils, vegetation,shrub encroachment, vegetative succession, Prosopis dunes}, author = {N.K. Hansen} } @conference {50334, title = {Using the GIS to study the past and present of a northern Chihuahuan Desert playa}, booktitle = {60th Annual Meeting and Trade Show, Society for Range Management}, year = {2007}, month = {02/09/2007}, pages = {Paper No. 179}, address = {Sparks/Reno, NV}, abstract = {The encroachment of mesquite (Prosopis glandulosa Torr.) and other desert shrubs into the desert grasslands of the northern Chihuahuan Desert is commonly associated with increased rates of soil erosion. The processes associated with vegetation shifts are still poorly understood. One such example of vegetation shift is the replacement of tobosa (Pleuraphis mutica Buckely) grasslands by mesquite dunelands on the Red Lake playa, an ephemeral lake on the USDA-ARS Jornada Experimental Range in south central New Mexico, USA. The objective of this project was to describe grass-shrubland transitions for vegetation patches based on soil characteristics and spatial context. We used aerial photos from 1942 and 1973 and a digital orthophoto quarter quadrangle from 1996 to define changes in the mesquite-dominated area since 1942. We used the 1996 photos to compare GIS-based mesquite canopy intercept measurements with line-point and canopy intercept measurements completed in 2005. We then used a QuickBird satellite image from 2004 to identify current vegetation community patches based on vegetation type, soil reflectance, and the spatial distribution of plants and bare ground within each patch. Plots were then established in the field within these patches to characterize the soils and vegetation of the site and create highly-detailed soil and vegetation maps of the site. After the initial characterization, the field data and 2004 satellite image were compared against the older imagery and past vegetation and soil maps to identify areas requiring more intensive soil and vegetation measurements. We plan to use these data to identify relationships between various soil properties and vegetation community composition and structure. This information will be used on patterns and processes to propose changes to state-and-trainsition models correlated with soils in this area.}, keywords = {Chihuahuan Desert, GIS, mesquite, soil erosion}, author = {N.K. Hansen and Jeffrey E. Herrick and Laurie Abbott and Debra C. Peters and D. Parker} }