Forest land use activities and fragmentation as a threat to Northeastern forest cover and water quality

Phosphorus loading in the Lake Champlain Basin is a contributing cause of algal blooms in Lake Champlain during the late summer months. All land cover types contribute to the phosphorus loading, but less attention has been given to phosphorus exported from forested areas because the amount of phosphorus exported per unit area is small and is not measured directly (Lake Champlain Basin Program, 2018). Forests, however, comprise 78% of the landcover in Vermont and are used for timber harvesting, maple sugaring, and recreation, which could each contribute to phosphorus beyond additional background levels being released into streams that lead to the lake. Earlier in Vermont's history, the land was denuded of most of its trees to provide room for agriculture, and though it does not seem reasonable that the land might be converted to agricultural fields on such a large scale again, there is a definite threat of deforestation due to the development of forested lands into commercial and residential lots. With the subdivision and parcellation of land comes fragmentation of forests, which has been shown to decrease the ability of the forest to provide ecosystem services, such as appropriate wildlife habitat, climate regulation, and water quality control (VTFPR, 2015). The variety of land uses in forested areas and the threat of increased development in the future present good reasons to understand how these changes to the forests of Vermont could possibly lead to decreased forest cover and greater damage to water quality.

Some 80% of forested land in Vermont is privately held, and of these, 62% are held by individuals and families, which represent a heterogeneous group of decision-making land holders (Butler and Butler, 2016). The goal of this project was to create an agent-based model that can simulate land use decisions made by private family forest landowners, with the distinct purpose of investigating how land use decisions in forested areas affect downstream water quality and how forest land cover might change over time. The decisions that the forest landowner agents can make in the model ultimately lead to a total phosphorus output for the watersheds of interest, specifically the Mississquoi Bay. By investigating how landowners make decisions and what their priorities are for their land, we can better understand what activities are leading to phosphorus exports from forested areas and make suggestions for mitigating water quality damage.

Results obtained from multiple scenarios tested demonstrate the potential fluxes in phosphorus output from forested land that might occur if UVA enrollment increases or if Vermont forest landowners begin to harvest timber more frequently and at a larger scale. The results indicate that it is timber harvesting that contributes most heavily to phosphorus output from forested land, which is consistent with findings from the literature and conversations with forestry professionals.