Patterns of soil and vegetation change associated with grassland-shrubland transitions: a case study

TitlePatterns of soil and vegetation change associated with grassland-shrubland transitions: a case study
Publication TypeThesis
Year of Publication2008
AuthorsHansen NKay
Number of Pages152
Date Published2008
UniversityNew Mexico State University
CityLas Cruces, New Mexico
Thesis Typepp
Accession NumberJRN00506
Call Number00945
Keywordsdissertation, 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
AbstractThe 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); and 4) the formation of coppice dunes has led to the loss of landscape integrity.