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.
