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How will climate change and latitude interact to affect tree species in the Great Lakes Region?
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Climate change has historically had a profound impact on plant species, inducing adaptation (Cheddadi et al. 2016), long-distance migration (Davis and Shaw 2001), and even extinction (Jackson and Weng 1999), however, climate change does not affect communities uniformly, nor are its effects uniform across species ranges. Mixed responses among species can cause communities to break apart and new associations to form, and mixed responses within a species range can cause some populations to decline, and others to thrive (Davis 1983). Modern climate change may produce effects similar to those of prior climate change, or, because modern change is proceeding more rapidly than historic change, more severe effects. Indeed, plant phenology (Willis et al. 2008), distribution (Harsch et al. 2009), and growth (Liu et al. 2013, Silva et al. 2016) have already been affected, particularly at the edges of species ranges. Populations at the warm edges tend to be in decline, while those at cold edges are on the ascent, portending potential changes in species distribution and community composition (Parmesan 2006). Climate-change responses will not only differ among species and populations, but they will likely differ around the earth. The Great Lakes Region is a region with a unique climate and a high concentration of forests, which are ecologically and economically important. How will climate change affect these communities? Who will be the winning and losing species, and how will this vary with latitude, a factor thought to influence range limits? Further, the region contains long-lived tree species, the tree rings of which have been used for reconstructing climate of times preceding the instrumental record (Ford 2014), however, the ability to reconstruct climate depends on a temporally consistent relationship between tree growth and climate. This relationship may be breaking down in some regions (D’Arrigo et al. 2008). Is that the case in the Great Lakes Region? Below I discuss plans to address the above questions, by studying the tree rings of nine species of the Great Lakes Region along a gradient of latitude. Tree rings can tell us how the growth of a species responds to seasonal climate, such as temperature, precipitation, moisture indices, and Great-Lakes ice cover. I will use principal-component regression to quantify growth responses to climate, and compare responses among species at a given site and within species along a latitudinal gradient. Quantifying responses to current and historic climate will help me predict how a species or population will fare under ongoing climate change. A model will be established, based on the climate variables that most strongly influence growth, and used, along with projections of future climate, to predict future growth. Growth is indicative of vigor, and if a population will lack vigorous growth under its future climate, then it may lack enough vigor to reproduce at rates necessary for long-term persistence. On the other hand, if a population on the edge of its species’ distribution will exhibit accelerated growth under its future climate, then it will likely be vigorous enough to persist at the site, and potentially even expand its range. Tree rings can also tell us how consistent the relationship between growth and climate is over time. I will assess this by using a historic segment of the growth models that I establish to predict recently observed climate. If the model successfully predicts recent climate, then the growth-climate relationship is temporally stable, but if the model is unsuccessful, then tree-ring-based climate reconstructions in the Great Lakes Region will be viewed with more skepticism. Regarding the above questions, I hypothesize (1) that growth-temperature responses will be more negative at southern and more positive at northern limits, (2) that growth-precipitation responses will be more positive at southern limits, (3) that growth will increase at northern and decrease at southern limits over the rest of the century, and (4) that the growth-climate relationship is not temporally stable—growth-climate models based on older data will inadequately predict recent climate. Finally, I discuss below the importance to my study of the Colonial Point Hardwoods, the trees of which are mature enough to provide a growth record long enough to test the temporal stability of the growth-climate relationship. I am taking a novel approach with this project, using tree rings from species with both northern and southern limits to make predictions about community responses to climate change. I will study a larger latitudinal gradient and include more species than other, similar studies. Understanding how responses to climate change differ across species ranges and within communities will aid predictions about species migrations and the resultant changes in biotic interactions, which can greatly alter communities. This work will help guide decisions about planting location and conservation priorities in the Great Lakes Region, but it has implications for ecology and conservation science at-large. If differential growth-climate responses are found among species within mesic forest communities of the Great Lakes Region, then differential responses likely exist in other community types and regions, too.
Colonial Point Hardwoods
Researcher Profile: Scott Warner
Years research project active: