When we compare the two samples side by side, we see an interesting situation. Fires have been occurring regularly in the forests of northern Mexico throughout the 20th century. In the sample taken from the Arizona forests, there has been a greater attempt at fire control, causing practically all 20th century fires to be suppressed. Note the large curl of growth on the sample to the right of the image. Changes in tree growth rates as seen in their tree rings also supply clues to forest ecologists about possible disturbances that may have affected the forests.
Growth is from the left to the right.
The abrupt decline in tree growth rates, marked by the narrower rings in the center of the image, suggests some event occurred during the life of the tree that killed or damaged many of the pine needles, reducing its ability to grow. The disturbance event could be related to storm dmage caused by high winds or perhaps some insect defoliator may have attacked the tree as well. Finally, tree rings can also supply forest ecologists with information about wildlife. The cross section on the right is a red oak sampled at the Adrian J. Rogers Memorial Woodlot in Ashland, Wisconsin. The scar at the top of the sample was made by a porcupine that was feeding on the inner cambium, the softer tissue just inside the bark.