LTREB: Rapid Ecotonal Shifts, Pest Outbreaks, and Mortality of a Dominant Tree Species in Response to Record Drought

这项LTREB研究将检验四个关键预测。首先，植物对草食的抗性影响群落和生态系统水平的过程。从1982年开始，鉴定出具有遗传抗性和易感的树木，每年在1/2的易感树木上去除2种常见昆虫。研究包括树木对慢性草食的适应性反应、菌根群落的反应、隐型keystone草食动物的群落后果，以及在重建过去气候中使用抗性和易感树木。正在进行的关于土壤细菌、养分循环和抗性成本的研究使得这些长期实验非常重要。其次，干旱导致快速的生态转移，改变了群落结构和生态系统动态。1996年发生了一场创纪录的干旱，导致60个地点的树木死亡率达到30%至70%，估计有75,000棵成熟树木死亡。这些样地经历了从矮松林到杜松林或草地的快速生态转变。其中11个地点与邻近的低死亡率地点相结合，代表了一种宝贵的资源，因为它们是气候变化事件的直接结果。这些地点对于研究气候变化对菌根共生菌、微生物分解者、节肢动物和脊椎动物群落的原因和后果，以及环境胁迫对生物多样性和生态系统功能的差异影响至关重要。第三，重复干旱事件与单一干旱事件的影响不同。今年，2002年，已经被确定为有记录以来最干旱的一年。继1996年干旱之后，这次新的干旱使我们能够确定同一地点是否遭受了重复的死亡和选择，这可能会产生与单一死亡事件截然不同的长期后果。草食动物与环境相互作用影响昆虫爆发，改变群落结构和生态系统过程。自1982年以来，我们一直在监测局限于慢性应激地点的蛾类和介壳类昆虫的分布。然而，为了应对1996年创纪录的干旱，规模已经从这些震中扩大到西南地区最大的爆发。我们绘制了它们的扩张地图，并正在研究抗旱性和易感性树木如何受到干旱的影响。更广泛的影响：美国西南部正处于干旱之中，类似于许多气候变化模型预测的美国大部分地区会增加的干旱。通过研究小松及其相关群落学到的原则可以用来对这些预测的气候变化的后果做出明智的决定。此外，由于NAU位于一个人口多样化的地区，包括42个美洲原住民部落，我们建议培训和指导来自不同代表性不足群体的学生。我们这样做的能力将通过现有的项目得到加强，包括nsf赞助的针对代表性不足群体的环境生物学大学指导项目和NAU资助的促进本科生研究的项目。

This LTREB research will examine four key predictions. First, plant resistance to herbivory affects community and ecosystem-level processes. Beginning in 1982 genetically resistant and susceptible trees were identified, and on 1/2 of the susceptible trees, 2 species of common insect have been removed each year. Studies involve tree fitness responses to chronic herbivory, mycorrhizal community responses, the community consequences of a cryptic keystone herbivore, and the use of resistant and susceptible trees in reconstructing past climates. Ongoing studies of soil bacteria, nutrient cycling, and costs of resistance make these long-term experiments very important tocontinue. Second, drought results in rapid ecotonal shifts, which alter community structure and ecosystem dynamics. In 1996 a record drought occurred that resulted in 60 sites that suffered 30-70% tree mortality and killed an estimated 75,000 mature trees. These sites underwent a rapid ecotonal shift from pinyon-juniper woodland to juniper woodland or grassland. Eleven of thesesites, paired with adjacent low mortality sites, represent a valuable resource because they are the direct result of a climate change event. These sites are crucial for studying the causes and consequences of climate change on mycorrhizal mutualists, microbial decomposers, arthropod and vertebrate communities, and how environmental stress differentially affects biodiversity andecosystem function. Third, repeated drought events have different effects than single drought events. This year, 2002, is already identified as the driest year in recorded history. This new drought following the 1996 drought allows us to determine if the same sites suffer repeated mortality and selection, which is likely to have very different long-term consequences than a single mortality event. Four, herbivore x environmental interactions affect insect outbreaks to alter community structure and ecosystem processes. Since 1982 we have been monitoring the distribution of moth and scale insects that were restricted to sites of chronic stress. However, in response to the record drought of 1996, scales have expanded from these epicenters to become the largest outbreak in the southwest. We have mapped their expansion and are studying how resistant and susceptible trees are affected by drought. Broader Impacts: The southwestern US is in the midst of a drought similar to those predicted to increase throughout much of the US by many climate change models. The principles learned by studying pinyon pine and its associated community can be used to make informed decisions regarding the consequences of these predicted climate changes. In addition, because NAU is located in an area with a diverse population including 42 Native American tribes, we propose totrain and mentor students drawn from a diversity of under-represented groups. Our ability to do so will be enhanced by programs already in place, including an NSF-sponsored University Mentoring in Environmental Biology grant targeting under-represented groups and an NAU grants program that promotes undergraduate research.