Forest Inventory and Analysis - Forest Health Monitoring

Forest health monitoring (FHM) has been a component of Wisconsin's Forest Inventory and Analysis (FIA) program since 1990. In 2000, the FIA and FHM were further integrated by merging their field plots under a single system. FHM plots, which occur in the landscape at a density of approximately one plot every 96,000 acres, can now be thought of as a subset of the FIA plots.

To access the latest report on forest health conditions in Wisconsin, visit the Department of Natural Resources Division of Forestry Forest Health Protection program.

Measurements

FHM sampling, also known as phase 3 sampling, takes place during the growing season in June, July and August. The suite of ecological data collected at each plot is described below.

Leaf Damage From Air Pollutants

Air pollution, particularly from ozone, has been shown to reduce tree growth, alter species composition, and leave trees vulnerable to attack by insects and disease. Tree species showing leaf damage typical of ozone serve as important biological indicators of air pollution problems.

Tree Crown Characteristics

Crown characteristics such as crown ratios, crown dieback and leaf density reflect the health of trees. For example, large, dense crowns imply vigorous growth rates, while small, sparse crowns suggest unfavorable conditions, such as competition from other trees, lack of moisture, or defoliation due to insects. Tree crowns are also important because they directly influence the vigor of other plants and animals in the forest.

Soil Quality

Because they provide nutrients, water, oxygen, heat, and mechanical support to trees and other vegetation, soils play a critical role in forests. Thus, any change in soil function has the potential to influence the productivity, health and species composition of forest systems.

Lichen Frequency and Diversity

Lichens are fungi that live in association with microscopic, photosynthetic organisms known as algae. Lichen communities growing on trees and shrubs are extremely sensitive to nitrogen and sulfur-based air pollution and thus provide an early indicator of improving or deteriorating air quality in forests.

Down Woody Material

Measurements of down woody material, such as coarse woody debris, duff, litter and slash piles, not only serve as a general indicator of forest health, but also give scientists insights into forest fire risks, the availability and structure of critical habitat for wildlife, and the amount of carbon stored in forests nationwide.

Vegetation

FIA measurements focus on trees, while FHM sampling encompasses all the vegetation present within field plots, including shrubs, herbs, grasses and ferns. Inventories of understory vegetation allow scientists both to detect the presence of invasive plants and assess their potential to invade. In addition, forest community types based on both overstory and understory plant species are highly correlated with ecosystem properties, such as productivity, response to disturbance, and use by wildlife.

Damage-causing Agents

FHM monitoring also includes surveys for cankers, fungi, open wounds, broken limbs, dead tops, brooms and other signs of damage-causing agents.