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Updated: Jul 4, 2026
10:19
A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function
Published on: November 21, 2015
Woody plants in grasslands: post-encroachment stand dynamics
Dawn M Browning1, Steven R Archer, Gregory P Asner
1School of Natural Resources, University of Arizona, P.O. Box 210043, Tucson, Arizona 85721, USA. dbrownin@ag.arizona.edu
Summary
Shrub cover in semidesert grasslands stabilizes over time, with soil type affecting dynamics but not the final cover extent. This dynamic equilibrium requires monitoring patch structure for accurate biomass projections.
Area of Science:
- Ecology
- Vegetation Science
- Rangeland Management
Background:
- Woody plant proliferation, particularly shrubs, is a global trend in savannas and grasslands.
- Understanding shrub dynamics is crucial for assessing impacts on biogeochemical cycles and ecosystem function.
- Predicting future vegetation changes requires knowledge of shrub cover relative to maximum potential for specific soil and bioclimatic conditions.
Purpose of the Study:
- To quantify the cover and biomass dynamics of velvet mesquite (Prosopis velutina) in an Arizona semidesert grassland.
- To analyze the rates and extent of shrub proliferation and stabilization phases.
- To determine the influence of soil properties on shrub cover and biomass accumulation over time.
Main Methods:
- Utilized time-series aerial photography from 1936, 1966, and 1996.
- Conducted field studies to quantify shrub cover and biomass.
- Mapped individual shrub distribution and patch dynamics.
Main Results:
- Shrub cover on sandy uplands remained dynamically stable around 35% from 1936-1996.
- Shrub cover on clayey uplands increased from 17% in 1936 to 36% by 1966, then decreased slightly to 28% by 1996.
- Soil type influenced the rate of landscape stabilization but not the equilibrium cover level; however, shrub biomass was higher on clayey soils.
- Declines in cover between 1966-1996 were associated with smaller patch sizes, suggesting density-dependent regulation.
Conclusions:
- Semidesert grassland landscapes can reach a dynamic equilibrium in shrub cover.
- Soil properties mediate the speed of achieving this equilibrium and influence biomass density.
- Future biomass projections necessitate monitoring patch dynamics and stand structure, not just total cover, to account for shifts towards dynamic equilibrium.
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