Trees grow a layer of new wood every year. Dendrochronology is the study of these annual growth bands in trees (tree rings). These activities help students understand how patterns of tree ring growth tell us the age of a tree and the history of changes in the tree’s environment during that tree’s life. Students make and evaluate tree cores cylinders of wood, the thickness of a pencil, that are cut from the bark (the youngest wood) through to the center (the oldest wood) of the tree. Tree cores can be taken without hurting the tree.
Lake Cores and Pollen
The San Joaquin Valley was once (until about 100 years ago) covered by shallow lakes and swamps. Sand, mud and other debris fall to the bottom of calm lakes and accumulate in layers referred to as sediment. By cutting a vertical column (core) through the lake sediment we can see how the sediment changed with time. The oldest sediment will be on the bottom of the core and the youngest on the top. Pollen found in each layer indicate the type of plants that lived near the lake at the time that layer formed. These activities help students understand how studying the pollen in each layer will tell us how the plants, and thus the environment, around the lake have changed with time.