LTER Cross-Site: Contrasts of Global Change and Ecotonal Shifts: Buffering Effects of Mycorrhizae and Nurse Plants and Increased Sensitivity due to Herbivores and Mistletoe

Northern Arizona University, Flagstaff AZ

Investigators

Abstract

0087017 Gehring Global change models predict an increase in the frequency of intense drought in the continental interior of the US, and recent field studies have shown that semiarid ecosystems can be highly sensitive to this type of abiotic stress. For example, in the 1950's a severe drought in New Mexico resulted in high tree mortality that shifted ecotones by 2 kilometers in less than five years. Rapid, sustained ecotonal shifts depend on to processes: high rates of mortality of one or more of the dominant plant species in the ecosystem, and lack of recruitment of the dominant plant species following the mortality event. This LTER cross-site research will test the hypothesis that the probability that an ecotonal shift will occur depends on the degree of abiotic stress, and on the relative effects of positive and negative biotic associations on the dominant plant species. Positive associations, such as mycorrhizal associations and nurse plants, could buffer communities from major ecotonal shifts while negative associations with herbivores and parasites could increase sensitivity to global change. This study will focus on pinyon pine growing at the southern edge of their distribution in New Mexico and Arizona. Pinyon is an ideal candidate for global change studies because it is a dominant member of the third largest vegetation type in North America. Both paleoecological and recent studies show that pinyon is highly sensitive to environmental change. Much is known about the interactions among pinyon pine and its associated community, including is co-dominant tree associate and the bacteria, fungi, invertebrates and vertebrates that live in close association. This knowledge of broader interactions will allow a more accurate prediction of the effects of pinyon mortality on other members of the community and on ecosystem processes.