An Assessment of Forest Health and Soil Nutrient Status to Determine the Effects of Logging Practices on Water Quality in New York City's West-of-Hudson Watersheds

Figure 1 - Map of the study area located in the upper Neversink River watershed of the Catskill Mountains.

Figure 2 - Areial view of the harvested forest of the Dry Creek watershed shown in figure 1.

The growth of temperate forests is typically limited by the availability of nitrogen. Elevated concentrations of nitrate in some Catskill Mountain streams, which are tributary to New York City's water-supply reservoirs west of the Hudson River, indicate that the forests of this region are at the early stages of nitrogen saturation. That is, nitrogen is available in excess of the amount utilized by vegetation and soil microorganisms in the forests. Nitrogen saturation is a concern because the mobile nitrate that moves through soil is accompanied by other nutrients such as the base cations calcium and magnesium that are necessary for forest growth but are present in short supply in some Catskill soils. And, nutrient cycling and forest health are directly related to water quality. For example, increased nitrogen concentrations in streams may, in combination with phosphorus, increase eutrophication to a greater extent than phosphorus alone in reservoirs.

Forest harvesting may provide a management tool for improving the retention of nitrogen and associated nutrients because a young forest grows faster and has a higher nitrogen demand than the 75-100 year-old forests typical of the Catskills. A preliminary assessment of Neversink soils indicates that calcium and magnesium availability is similar to that measured in dying sugar maple stands in Pennsylvania. If depletion of these base cations is limiting growth in the Catskill region, harvesting may not increase growth rates to a level sufficient to increase the retention of nitrogen. Furthermore, harvesting may worsen base cation depletion by removing the large supply stored in trees. Understanding the balance between nitrogen and base cation availability is therefore essential to the effective implementation of harvesting strategies.

The soil nutrient concerns mentioned above indicate that developing best management practices for forested watersheds should include harvesting practices that are designed with regard to soil nutrient status. To develop such practices, the nutrient cycling processes that control water quality in forested watersheds must be understood through scientific studies.

To develop such practices, the nutrient cycling processes that control water quality in forested watersheds must be understood through scientific studies. This study will involve the following work elements:

1. Continued monitoring of nutrient release from watersheds logged during a previous USGS study.
2. Monitoring of nutrient release from six treatment areas (duplicates of three treatments) that will be logged to remove about 30%, 50%, and 70% of forest biomass.
3. Experiments in which nitrogen and calcium will be added to plots to determine how the availability of these nutrients affects growth, health, and nutrient release from declining sugar maple stands.
4. A forest nutrient model will be developed, and will be used to predict the long-term (50-100 yr) consequences on forest growth of the interactions of nitrogen deposition and forest harvest.
5. A survey will be conducted of the condition and chemistry of forests, soils, and water throughout the NYC water-supply watersheds in the West-of-Hudson region. A map will then be developed of the sensitivity of northern hardwood forests in Catskill watersheds to harvesting intensity with regard to the potential for soil-nutrient depletion and water-quality degradation.
6. The research sites will be part of an environmental education program that will be coordinated by an educator who will be in frequent contact with the research scientists participating in the study.

Study participants include the U.S. Geological Survey, the U.S. Forest Service, State University of New York College of Environmental Science and Forestry, the Institute of Ecosystem Studies, and the Frost Valley YMCA.