Viewpoint: Atmospheric CO2, soil water and shrub/grass ratios on rangelands
|Title||Viewpoint: Atmospheric CO2, soil water and shrub/grass ratios on rangelands|
|Publication Type||Journal Article|
|Year of Publication||1997|
|Authors||Polley H, Mayeux H, Johnson H, Tischler C|
|Journal||Journal of Range Management|
The abundance of woody plants on grasslands and savannas often is controlled by the availability of water and its location in soil. Water availability to plants is limited by precipitation, but the distribution of soil water and period over which it is available in these ecosystems are influenced by the transpiration rates of grasses. We discuss implications of recent and projected increas- es in atmospheric CO2 concentration for transpiration, soil water availability, and the balance of grasses and shrubs. An increase in C02 concentration often reduces potential transpiration/leaf area by reducing stomatal conductance. On grasslands where effects of stomatal closure on transpiration are not negated by an increase in leaf temperature and leaf area, rising C02 concentra- tion should slow the depletion of soil water by grasses and poten- tially favor shrubs and other species that might otherwise suc- cumb to water stress. Predicted effects of C02 are supported by results from C02-enrichment studies in the field and are compat- ible with recent models of interactions between resource levels and vegetation pattern and structure.