<oding in Northfield last weekend was bad for Froggies, but good for the Arboretum’s floodplain forest. In the lower Arb, river and forest ecology depend upon periodic flooding events. Some of Carleton’s floodplain tree species include: cottonwoods (Populus deltoides), silver maple (Acer saccharinum), and willows (Salix spp.). Flooding is also an important disturbance event, leveling trees or other vegetation leaving bare soil for new seeds to colonize. In this way, it works much the same as the Arboretums burning of the tall grass prairie. Floodplain forests rely on the soil that flood waters transport, and vice versa, terrestrial material carried into the river by floods serves as an important energy source for aquatic organisms and the trees both support the river bank and shade its waters, helping keep the water cool and oxygen rich in summer. Additionally, the trees and plants found in the flood plain forest as well as soil bacteria help take up nutrients, such as those used for fertilizers, decreasing their impact on the water system. Too many nutrients (which are highly concentrated in agricultural fertilizers) can cause eutrophication of water systems, especially lakes. Typically eutrophication results in phytoplankton blooms which use up the dissolved oxygen in the lake. If the lake becomes hypoxic many fish and bottom dwellers are killed off. The very flood that soaked West Field is just another part of the complex ecology of Carleton’s Arboretum.
-Adrienne Wilber, ’11, on behalf of Arb naturalists.