Colonization Potential of Oaks under Climate Change

by Elizabeth Medford

While the impact of climate change on a variety of animal populations and their ranges has been studies extensively in the past, the study of the impact of warming on tree species also provides useful information for policymaking. A variety of different modeling systems apply different variables and make predictions about tree species distribution in the future as temperatures rise. In this study however, Prasad et al. (2013) combine two different commonly used technologies to overcome the constraint of computation time and allow assessment of colonization potential for oak species. Four oak species were chosen to focus on because they are strongly climate-driven species: black oak, post oak, chestnut oak, and white oak. Using the DISTRIB and SHIFT models together the authors were able to determine the future dominant forest types in the northeastern United States. This study determined that even under optimistic conditions ignoring some influential factors, only a small fraction of suitable oak habitat is likely to be occupied by oaks within 100 years. The authors urge that the information garnered in this study be used to inform assisted migration practices for vulnerable tree species. They additionally call for further studies focusing on how each individual species will adapt to increases in temperature.

Trees have three different options for responding to climate change; they can adapt, migrate, or go extinct. Luckily the high genetic variability in many tree species allows for rapid adaptation to environmental changes. This adaptation ability can be traced to phenotypic plasticity and abundant fecundity, both of which help to explain their ecological success. It is important to understand the effects of climate change on tree species because of their exposure to changing environments and interspecific interactions. However, genetic constraints on adaptation and impediment to both gene flow and dispersal by landscape fragmentation could threaten tree species in the era of climate change. To evaluate the effects of climate change on four different oak species the authors used SHIFT modeling technology along with DISTRIB technology. SHIFT models use historical tree migration rates to estimate future colonization with light parameters applied to the model. The DISTRIB model is used to predict and map current and future-climate tree habitats for 134 tree species via changes in relative importance values. Combining these two modeling systems the authors were able to use historical information on rates of past migration events to predict future potential migration. This new approach accounts for the structure of the landscape using information regarding fragmentation of habitat quality, information that many models ignore. The conclusions obtained from the combination of these models can be used for protecting vulnerable species in the future.

The results of these studies imply that minimal amounts of the potentially colonizable habitat would actually be colonized, highlighting the dangers of relying on models that provide information about the potential colonization by tree species. Specifically, Prasad et al. found that only 5% of suitable habitat would be colonized and that only 2% of habitats have a 50% chance of being colonized. Moreover, the authors ignored additional factors that could play a role in limiting colonization by trees such as insects, disease, and competition from maple species. Studies that included these other factors would likely produce even lower rates of predicted colonization by oak species. However, the authors also ignored the characteristics of the oak trees that could potentially benefit them in a warming climate, such as their drought tolerance. The findings of this study can be used to initiate new populations, and to facilitate migration, and these populations do not need to be large. Specifically, these studies can be used for specialist species that have narrow niches, which will likely be more negatively affected by climate change. Additionally, the DISTRIB and SHIFT models provide information about suitable corridors and patches for facilitating migration of tree species. For example, one migration corridor for the black oak is in Wisconsin. In the future this information can be used for facilitated migration of black oak trees.

This study is significant because of the way that the authors applied different models to overcome the computational barrier and tackle many species efficiently. Moreover, Prasad et al. were able to account for multiple scenarios for each species, which will be essential for understanding the affects of global warming on the distributions of different tree species.

Prasad, A., Gardiner, J., Iverson, L., 2013. Exploring Tree Species Colonization Potentials Using a Spatially Explicit Simulation Model: Implications for Four Oaks Under Climate Change. Global Change Biology 19, 2196–2208.


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