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

LTREB的这项研究将检验四个关键预测。首先，植物对草食的抗性会影响群落和生态系统层面的进程。从1982年开始，鉴定出了遗传抗性和感病树，在1/2的感病树上，每年有2种常见昆虫被移除。研究涉及树木对慢性草食的适应性反应，菌根群落反应，一种神秘的Keystone草食动物的群落后果，以及利用抗性和敏感树木重建过去的气候。正在进行的对土壤细菌、养分循环和抗药性成本的研究使这些长期实验继续下去非常重要。其次，干旱导致快速的生态过渡，从而改变群落结构和生态系统动态。1996年发生了一次创纪录的干旱，导致60个地点的树木死亡30%-70%，估计有75000棵成熟的树木死亡。这些样地经历了从松柏林地向刺柏林地或草地的快速过渡。其中11个地点与邻近的低死亡率地点配对，是一种宝贵的资源，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互助者、微生物分解者、节肢动物和脊椎动物群落的原因和后果，以及环境压力如何以不同方式影响生物多样性和生态系统功能至关重要。第三，重复干旱事件的影响不同于单一干旱事件。今年，2002年，已经被认为是有记录以来最干旱的一年。1996年干旱之后的这次新的干旱使我们能够确定相同的地点是否遭受重复的死亡和选择，这可能会产生与单一死亡事件非常不同的长期后果。第四，食草动物与环境的相互作用影响昆虫的暴发，从而改变群落结构和生态系统过程。自1982年以来，我们一直在监测仅限于慢性应激场所的蛾类和介壳虫的分布。然而，为了应对1996年创纪录的干旱，规模已从这些震中扩大到西南部最大的疫情。我们已经绘制了它们的扩展图，并正在研究耐干旱和易受干旱影响的树木。更广泛的影响：美国西南部正处于干旱之中，与许多气候变化模型预测的美国大部分地区的干旱程度相似。通过研究松树及其相关群落学到的原理可以用来就这些预测的气候变化的后果做出明智的决定。此外，由于北卡罗来纳大学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已经到位的项目来增强，包括由NSF赞助的针对代表性不足群体的环境生物学大学导师资助项目，以及促进本科生研究的NAU资助项目。

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.