The Impact of Simulated Climate Change on Sugar Maple at the Hardwood/Boreal Forest Ecotone

森林对气候变化的反应有据可查。对植物群落的研究表明，在最近一次冰河期之后的18000年里，北美的植物物种为了响应自然气候变暖而转移了范围。在该增温期，温度上升速度适中，植物物种迁移困难不大。然而，对未来几百年人类活动引起的气候变化的预测表明，气候变暖的速度可能比树种之前经历的要快得多。这种快速的气候变化可能会严重影响许多物种在目前发现的地区繁殖和生存的能力。最重要的是，许多物种可能最终无法迁移到更适合其环境需求的地方。总的来说，这个问题可能导致森林群落的改变，这些群落主要由具有广泛环境耐受性的物种主导。本研究的重点是评估人类活动引起的气候变化对北美北部地区糖枫幼苗和种子的影响。研究人员将评估糖枫幼苗对空气温度和土壤湿度条件变化的敏感性。作为北美东部森林的优势树种，糖枫可能影响人类活动气候下的生态变化。研究人员将检查哪些气候变量（温度和/或降水）控制生长并导致植物压力或死亡，最终危及糖枫在这些森林中的持续存在，并进一步扩展到北美东部糖枫分布范围的北部。该项目有两个目标：(1)确定未来的气温和降水制度可能对加拿大安大略省中部糖枫目前北部限制的现有糖枫幼苗产生的影响；(2)确定来自两个地区（安大略省和伊利诺伊州）的种子在糖枫当前生长范围内温暖和寒冷气候下的田间条件下发芽和生长的程度。这些问题将以两种方式解决。首先，将采用红外热灯和防雨结构来改变安大略省中部天然糖枫幼苗的温度和降水制度，以模拟20世纪60年代研究区域预测的气候条件。其次，研究人员将从两个地点收集并相互分散糖枫种子，这些地点代表了糖枫当前范围内的极端温度条件。糖枫的未来具有重要的生态和经济意义。对于那些远距离种子传播能力有限的物种，如糖枫，人类可能有必要作为种子传播者进行干预。该项目将开始确定在需要人类辅助种子传播时可能作为种子来源的种群。因此，该项目将增加生物地理学和森林生态学的知识基础，研究气候变化对自然生态系统的影响，最终目标是在植物无法适应（或无法长距离分散）快速变化的条件时，人类做好干预准备。该项目的结果将提供关于生态阈值是否存在的信息，超过这个阈值糖枫可能无法生存，以便森林管理者、建模者和政策制定者可以开始考虑环境变化何时可能变得不可挽回地有害，并监测这些变化即将发生的迹象。

Forest response to climate change is well documented. Studies of plant communities demonstrate that plant species in North America shifted range in response to natural climate warming over the past 18,000 years following the most recent ice age. During that warming period, rates of temperature increases were moderate and plant species migrated with little difficulty. Projections of human-induced climate change over the next several hundred years suggest, however, that warming may be much faster than tree species experienced previously. This rapid rate of climate change may severely impact the ability of many species to reproduce and persist in regions where they are currently found. Most significantly, numerous species may ultimately be unable to migrate to locations more suited to their environmental needs. Collectively, this problem may result in altered forest communities dominated largely of species with broad environmental tolerances. The focus of this research project is to evaluate the impact of human-induced climate change on sugar maple seedlings and seeds at the species' northern limit in North America. The investigators will assess the sensitivity of sugar maple seedlings to alterations in air temperature and soil moisture conditions. As a dominant species in forests throughout eastern North America, sugar maple may influence much of the ecological change under human-modified climates. The investigators will examine which climate variables (temperature and/or precipitation) control growth and lead to plant stress or death, ultimately jeopardizing the continued presence of sugar maple in these forests and, by extension, across the northern portion of sugar maple's range in eastern North America. This project has two objectives: (1) To determine the impact that future air temperature and precipitation regimes may have on existing sugar maple seedlings at sugar maple's current northern limit in central Ontario, Canada; and (2) To determine the degree to which seeds from two regions (Ontario and Illinois) germinate and grow under field conditions in warmer and cooler climates within sugar maple's current range. These questions will be addressed in two ways. First, infrared heat lamps and rain-exclusion structures will be employed to alter the temperature and precipitation regimes of naturally occurring sugar maple seedlings in central Ontario to mimic modeled climate conditions projected for the study area in the 2060s. Second, the investigators will collect and reciprocally disperse sugar maple seeds from two sites representing extreme temperature conditions within sugar maple's current range.The future of sugar maple is of great ecological and economic importance. It may be necessary for humans to intervene as seed dispersers for those species with limited long-range seed dispersal, like sugar maple. This project will begin the process of identifying populations that may act as seed sources in the event that human-aided seed dispersal becomes necessary. This project therefore will add to the small but growing knowledge base in biogeography and forest ecology that investigates the impact of climate change on natural ecosystems with the eventual goal of preparing humans to intervene in the event that plants fail to adapt (or are unable to disperse long-distances) to the rapidly changing conditions. The project results will provide information regarding whether ecological thresholds exist beyond which sugar maple may not survive so that forest managers, modelers, and policy makers can begin to consider when environmental changes may become irreparably detrimental and monitor for indications that those changes are imminent.