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Changes to US forests are double-edged sword for environment

Climate change, nitrogen deposition and fire suppression are leading to shifts in the types of trees that dominate American forests. These changes will have environmental consequences, potentially positive and negative, according to a National Science Foundation-funded study. The researchers developed a mycorrhizal tree map of the contiguous United States. The map, developed based on more than 3 million trees, shows the abundance of trees associated with mycorrhizal fungi, which have symbiotic relationships with tree roots. Arbuscular mycorrhizal fungi grow inside the tissues of roots and are more common on trees such as maple, ash and yellow poplar. Ectomycorrhizal fungi live on the outside of a plant's roots and are often found on pine, oak, hickory and beech trees. The fungi act as extensions to a tree's root system, allowing them to reach more water and nutrients. In return, the trees provide needed carbon for fungi survival. Over the last three decades, the authors find, forests dominated by ectomycorrhizal trees have given way to those dominated by arbuscular mycorrhizal species. That's in large part because arbuscular mycorrhizal trees are better suited for the conditions associated with climate change.

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