In each forest, plots are established around the throughfall collectors and the abundance of each herbaceous plant is determined in the plot. With the establishment of permanent plots, long-term changes in plant diversity and in the times of flowering can be recorded to measure changes in ecosystem health. Trees Two of the symptoms of an unhealthy tree are the loss of leaves and the presence of dead branches at the crown. This condition is referred to as tree die-back or as forest decline when it occurs throughout an entire forest. Causes of forest decline include climate change, natural pests, poor forest management, and air pollution.
Acid rain contributes to forest decline by removing essential nutrients from forest soils.
Students identify tree species, measure tree diameter at breast height, measure leaf chemistry, and estimate tree height using home-made clinometers. They also visually estimate the overall health of trees with a tree-rating system which encompasses all aspects of a tree in one index that represents the overall health of the tree. This rating system, the North American Maple Program, was developed for sugar maples by Forestry Canada and the United States Department of Forestry, and it provides a quick and easy assessment of forest health that can be repeated annually. Soil Long-term monitoring of soil pH and chemistry is required to determine whether soil acidification is continuing. In addition, the physical characteristics of soil must be examined to allow researchers to describe the type of soil and estimate the potential availability of the nutrients and trace elements.