Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2011
Publication Date: April 1, 2012
Citation: Browning, D.M., Duniway, M.C., Laliberte, A.S., Rango, A. 2012. Hierarchical analysis of vegetation dynamics over 71 years: Soil-rainfall interactions in a Chihuahuan Desert ecosystem. Ecological Applications. 22:909-926. Interpretive Summary: The shift from grass- to shrub-dominated plant communities is a widely observed phenomenon in the world’s rangeland ecosystems that holds important ramifications for land use, ecosystem services (e.g., clean water, human health, and recreation) and potential vegetation. We enhance existing understanding of vegetation transitions by integrating field survey of soil properties, landscape-scale mapping of shrub and grass cover, and manual interpretation of patch-scale processes over a 71-year period using aerial photography and satellite imagery. By delineating how shrub patches change over time, we bolster the interpretation of changes in percent shrub cover to demonstrate non-linear vegetation dynamics and how soil properties interact with rainfall to result in distinctly different endpoints or states. This study bridges the fields of geographic information technology, remote sensing, and soils to monitor and assess landscape condition from 1937 to 2008 in an arid rangeland with a history of livestock grazing. In this manner, our findings are of benefit and interest to state and federal land managers and decision makers charged with efficient allocation of resources for management activities such as grassland remediation, as well as ecologists and soil scientists involved in ecological state mapping.
Technical Abstract: Proliferation of woody plants in grasslands and savannas (hereafter, “rangelands”) is a persistent problem globally. This widely-observed shift from grass to shrub dominance in rangelands worldwide has been heterogeneous in space and time largely due to cross-scale interactions between soils, climate, and land use history. Our objective was to evaluate the relationship between spatial patterns in soil properties and long-term shrub dynamics in the northern Chihuahuan Desert of southern New Mexico, USA. To meet this objective, shrub patch dynamics from 1937 to 2008 were characterized at patch- and landscape-scales using historical imagery and a recent digital soils map. Effects of annual precipitation on patch dynamics on two soils revealed strong correlations between shrub growth on deep sandy soils and above-average rainfall years (r = 0.671, p = 0.034) and shrub colonization and below-average rainfall years on shallow sandy soils (r = 0.705, p = 0.023). Patch-level analysis of demographic patterns revealed significant differences between patches on deep and shallow sandy soils during periods of above- and below-average rainfall. Both deep and shallow sandy soils exhibited low mean (standard deviation) shrub cover in 1937 [1.0 (2.3)% and 0.3 (1.3)%, respectively] and were characterized by colonization or appearance of new patches until 1960. However, different demographic responses to the cessation of severe drought on the two soils and increased frequency of wet years after 1960 have resulted in very different endpoints. A shrubland occupied the deep sandy soils with mean cover in 2008 at 19.8 (9.1)% while a shrub-dominated grassland occurred on the shallow sandy soils 9.3 (7.2)%. Present-day shrub vegetation constitutes a shifting mosaic marked by the coexistence of patches at different stages of development. Management implications of this long-term multi-scale assessment of vegetation dynamics support the notion that efforts to remediate grasslands on sandy soils should be focused on sites characterized by near-surface water holding capacity as those lacking available water holding capacity in the shallow root-zone pose challenges to grass recovery and survival.