The Delay Between Species Composition Change in Response to Climate Change in Lowland Forests in France

In response to climate change, species redistribute themselves to find more suitable habitats. However, some species exhibit a gap between climate change and their redistribution response. Bertrand et al. (2011) studied this lag in species response to climate change in lowland and highland forests in France between 1965 and 2008. The researchers tested to see if the delay was greatest in the lowland species where climate change is most rapid. By comparing the temperature increases over time and the species composition, they found that the lowland species responded to only 0.02ºC of the 1.11ºC increase, while highland species responded to 0.54ºC of the 1.07ºC increase. Possible explanations for this variation include: higher proportion of resilient species in lowland areas, the availability of short distance escapes for highland species, and increased habitat fragmentation for lowland species. The authors conclude that although highland species are greatly threatened by climate change, the gap in response by lowland species is important and needs to be researched further to avoid a decrease in species in the lowland area.—Isabelle Heilman
Bertrand, R., Lenoir, J., Piedallu, C., Riofrío-Dillon, G., de Ruffray, P., Vidal, C., Pierrat, J.C., Gégout, J.C., 2011. Change in plant community composition lag behind climate warming in lowland forests. Nature, 479 517–520.

           
            Global climate change has caused species to change their distribution patterns, usually resulting in a shift toward higher altitudes and latitudes. In some cases however, there is a delay between the changes in climate and the species redistribution response. Theoretically the gap between climate change and species response should be larger at lowland forest levels than at the highland forest levels because climate change is faster at lower levels. Bertrand et al. (2011) studied this gap with respect to both lowland and highland forests in France, where the effects of climate change have been seen at a greater scale than the world average. To measure the gap, the authors compared “floristically reconstructed” temperatures and “climatically reconstructed” temperatures over the years 1965 to 2008. This method demonstrated a larger gap between the floristically reconstructed temperatures and climatically reconstructed temperatures in the lowland species than in the highland species.
 The climatically reconstructed temperatures were found using instrumental records and climate models. The floristically reconstructed temperatures were found using surveys of flora composition. Surveys from 1975 to 1985 (before the recent warming began) provided the data to create a transfer function using both weighted averaging partial least squares and Breiman’s random forest to estimate temperature from the plant compositions. These two temperature values were paired according to year and location and then compared to find the gap in response.
            The 44 year time period was then divided into two sections, 1965–1985 (before recent climate change) and 1987–2008 (after recent climate change). No significant difference between the temperatures was found for either highland or lowland species during the first time period. During the second time period, both lowland and highland species showed a significant difference between the two temperatures, however, the magnitude of difference was greatest in lowland species. This difference between highland and lowland species responses demonstrated that lowland species did have a greater gap between climate change and their redistribution response than highland species. The authors cited other surveys in different French mountains and a Mediterranean forest where lowland forests were also a relatively unreactive ecosystem with respect to climate change.
            To explain the different reactions of highland and lowland species to climate change, the authors turned to three distinctions between the two ecosystems. First, they considered that lowland areas contain more warmth seeking species, which could explain why species found in this area are more resistant to rising temperatures. Second, species in highland areas have to migrate shorter distances to find suitable climate, while species in lowland areas must migrate longer distances to find suitable temperatures for survival. The researchers called this a short distance escape opportunity in highland areas. Third, lowland species are subject to much more habitat fragmentation than highland species. This fragmentation affects the plants dispersal and migration abilities. These three factors probably act together to make lowland forests less reactive to climate change.
            Although the qualities of the lowland forest have lessened the effects of climate change on species distribution, this habitat will not experience stability forever. As temperatures continue to rise in the lowland forest, its inability to provide suitable climates for its species will change the species composition in the habitat. In the absence of short distance escapes, many plants that currently inhabit the lowland forest will die from being unable to find new suitable habitats once temperatures are too high. The authors recommend more research on the effects of climate change on lowland forests to better protect these valuable ecosystems.

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