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

[0087017] gehring全球变化模型预测，美国大陆内陆发生强烈干旱的频率将增加，最近的实地研究表明，半干旱生态系统对这种非生物胁迫可能高度敏感。例如，在20世纪50年代，新墨西哥州的严重干旱导致树木死亡率很高，在不到五年的时间里，过渡带移动了2公里。快速、持续的生态转移取决于以下几个过程：生态系统中一种或多种优势植物物种的高死亡率，以及在死亡事件发生后优势植物物种缺乏补充。这项LTER跨站点研究将检验生态转移发生的概率取决于非生物胁迫的程度，以及积极和消极生物关联对优势植物物种的相对影响的假设。积极的联系，如菌根联系和护理植物，可以缓冲群落免受主要生态转移的影响，而与食草动物和寄生虫的消极联系可以增加对全球变化的敏感性。这项研究将重点关注生长在新墨西哥州和亚利桑那州分布的南部边缘的小松。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。古生态学和最近的研究表明，松树对环境变化非常敏感。人们对小松及其相关群落之间的相互作用了解甚多，包括其共同优势的树同伴和密切生活在一起的细菌、真菌、无脊椎动物和脊椎动物。这种更广泛的相互作用的知识将使我们能够更准确地预测小松死亡率对群落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.