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Plant Responses to Climate Change and an Elevational Gradient in Mont Mégantic National Park, Québec, Canada

Abstract With steep climatic gradients over short distances, montane ecosystems provide exceptional opportunities to study ecological responses to climate and other environmental changes. Here we present a summary and synthesis of 10 years of research on this theme in a protected area in southern Québec, Canada (Parc National du Mont Mégantic), with ecological conditions closely similar to the northern Appalachians. During the ∼150 years since European settlement, anthropogenic disturbance has reduced the abundance of certain taxa (e.g., Picea [spruce]), while favoring other taxa that thrive during succession (e.g., Betula [birch], Acer [maple]). In more recent decades, climate warming (∼0.21 °C per decade) appears to have prompted upward elevational range shifts for many plant species, although such responses lag behind changes in climate itself. Experimental studies with seeds and seedlings of Acer saccharum (Sugar Maple) suggest that upward range expansion might be constrained by non-climatic factors such as belowground properties and seed predators, while escape from insect herbivores might actually accelerate range expansion. Similar studies with understory plants have not revealed clear evidence of non-climatic constraints on range limits, although some preliminary data presented here suggest a possible role of a lack of microsites with rich, moist soil at high elevation. Current studies focus on the lower elevational range limits of species restricted to mountaintops, such as certain lichens. Vegetation and flowering phenology are also sensitive to climate, and we have found that earlier springs are associated with decreased potential gene flow across populations at different elevations; ongoing studies will determine how differential sensitivity of herbs vs. trees might influence the duration of a high light period in spring in the understory. Overall, we have found clear signals of plant responses to long-term anthropogenic disturbances and recent climatic warming, but considerable uncertainty remains about how climatic and non-climatic factors will interact to determine the future of this montane ecosystem.