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

Gehring全球变化模型预测美国大陆内陆强烈干旱的频率将增加，最近的实地研究表明，半干旱生态系统可能对这种类型的非生物胁迫高度敏感。例如，在20世纪50年代，S在新墨西哥州的一次严重干旱导致了树木的高死亡率，在不到5年的时间里，交错带移动了2公里。快速、持续的生态转变取决于生态系统的变化过程：生态系统中一个或多个优势植物物种的高死亡率，以及死亡事件发生后优势植物物种缺乏补充。这项LTER跨地点研究将检验这样一种假设，即生态转变发生的可能性取决于非生物胁迫的程度，以及正负生物联合对优势植物物种的相对影响。积极的联合，如菌根联合和保育植物，可以缓冲群落免受重大生态转变的影响，而与草食动物和寄生虫的消极联合可能增加对全球变化的敏感性。这项研究将重点关注松树分布在新墨西哥州和亚利桑那州南部边缘的松树。Pinyon是全球变化研究的理想候选者，因为它是北美第三大植被类型的主要成员。古生态和最近的研究都表明，Pinyon对环境变化高度敏感。人们对松树及其相关群落之间的相互作用知之甚少，包括共同优势的乔木群落和生活在一起的细菌、真菌、无脊椎动物和脊椎动物。对更广泛的相互作用的了解将使人们能够更准确地预测松树死亡对社区其他成员和生态系统过程的影响。

0087017Gehring 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.