My research program focuses on the plant ecology of North American savanna. Plant ecology in savannas is poorly understood, which is somewhat surprising for three reasons: (1) about a third of the world's vegetation is savanna; (2) considerable evidence suggests that hominids evolved in savannas; and (3) historically, humans have attempted to create savannas when settling in other vegetation (i.e., we remove trees from forests, and plant trees in grasslands and deserts). Thus, an understanding of savanna genesis and maintenance is important for satisfying human desires. Nonetheless, savannas (especially temperate savannas) are among the least-studied ecosystems in the world.

Plant competition theory suggests that the coexistence of woody plants and herbs is tenuous in savannas, and small changes in the environment may abruptly produce large shifts in the relative abundance of either group. Although major shifts from savanna to woodland and grassland to savanna have been reported throughout the world in the last 300 years, rates and patterns of these shifts are poorly understood. For example, increased woody plant abundance in North American savannas has been attributed to altered climate, reduced fire frequency, increased grazing pressure, increased seed dispersal, and various combinations of these factors, yet few of these factors have been explicitly tested. Furthermore, studies of multiple disturbances have not been conducted in savannas or other temperate ecosystems. Published studies documenting additivity, antagonism, or synergism of multiple disturbances in terrestrial ecosystems simply do not exist.

Current research involves experiments encompassing multiple levels of study in field, laboratory, and greenhouse settings. In field studies, disturbance regimes and microclimate are experimentally manipulated to determine the role and possible synergism or antagonism of these factors in regulating community structure. Autoecological and physiological characteristics of important woody species are investigated in controlled environment experiments.

These data are being used to develop a conceptual model of ecosystem processes in savannas. From such a model, we should be able to predict how the system will respond (structurally and functionally) to disturbance, manipulation, or a changing physical environment.. Results will be directly applicable to research in restoration ecology, ecosystem succession and stability, disturbance ecology, and impacts of global climate change on ecosystem properties.

McPherson, G.R. 1993. Effects of herb interference and herbivory on oak establishment in a semi-arid savanna. Journal of Vegetation Science 4:687-692.

Haworth, K. and G.R. McPherson. 1994. Effects of Quercus emoryi on herbaceous vegetation in a semi-arid savanna. Vegetatio 112:153-159.

McClaran, M.P. and G.R. McPherson. 1995. Can soil organic carbon isotopes be used to describe grass-tree dynamics within a savanna and at the savanna-grassland ecotone? Journal of Vegetation Science 6:857-862.

Hubbard, J.A. and G.R. McPherson. 1997. Acorn selection by Mexican jays: a test of a tri-trophic symbiotic relationship hypothesis. Oecologia: 110:143-146.

McPherson, G.R. 1997. Absence of interactions between perennial bunchgrasses in a semi-arid temperate savanna: a 5-year field experiment. Journal of Arid Environments: 36:565-570.

Weltzin, J.F. and G.R. McPherson. 1997. Spatial and temporal soil moisture resource partitioning by trees and grasses in a temperate savanna, Arizona, USA. Oecologia: 112 in press.

McPherson, G.R. 1997. Ecology and Management of North American Savannas. University of Arizona Press, Tucson.