Talk to students next to you or around you and discuss the Figure or Table. Remember to follow the step one- step two approach we have practiced in class.
Sprugel (1976) studied balsam fir communities, the uppermost tree zone in the northeast U.S. It was well known that in these high-altitude fir forests "waves" of crescent-shaped bands of dead trees about 50 m in size were found in systematic patterns. The waves are areas of standing dead trees with mature and healthy forest surrounding them, and they can easily be seen from a distance.
Sprugel's main site was Whiteface Mountain in New York; Whiteface is the most northerly peak in the Adirondacks and in his study locale 99% of trees are balsam fir. He also worked in New Hampshire and Maine. Sprugel measured direction of tree die off by taking transects through the waves; here he also determined tree ages by coring them. For another part of the study he marked trees for several years and classified them into improved or deteriorated categories by examining browning of tips and overall browning.
From left to right the cross section in Figure 4A shows a mature forest, an adjacent area of dead and dying trees, an area where dead trees are being replaced by fir samplings of successive age, and a second area of dead trees.