Forest Vegetation

A fern-lined forest stream in summer. — A rich lowland forest in Prince William Forest Park. Photo: NPS/Paradis

Forests are the dominant vegetation of national parks in the National Capital Region Network (NCRN) and the surrounding area. Approximately two-thirds of this park land is forested. These forests are part of the Eastern Deciduous Forest that stretches from Florida to New England and southern Canada, and extends as far west as Louisiana and Minnesota. These forests are dominated by broad-leafed deciduous trees, but conifers, such as pines and hemlocks, are common in some areas as well.

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Most of the land in eastern US has been logged or cultivated at some point in the recent past. America's Eastern Deciduous Forest once occupied about a million square miles most of which is now human dominated. The remaining lands have some disturbance (logging concessions, secondary forests on abandoned farm fields, etc.) and are often found in smaller fragments. In the NCRN, forests are typically surrounded by urban or agricultural areas.

Monitoring

Forest vegetation monitoring includes many individual measures. Within each plot trees, shrubs, vines, and specific herbaceous plants are identified to species. Individual trees and shrubs are tagged and recorded and trees are assessed for canopy class and their diameter measured at breast height. Any evidence of deer browse on trees or shrubs is noted. Seedlings are counted and cover of herbaceous plants is recorded in 12 small quadrats. Presence of targeted invasive exotic plants and targeted insect pests and pathogens is recorded. Coarse woody debris is measured along three transects.

Forest vegetation monitoring has occurred every year since 2006 in all NCRN parks. Sampling is conducted from approximately May through September at more than 400 sites spread across the NCRN. Each year 100 of the plots are monitored. After four years the cycle is repeated.

Objectives

The NCRN will document status and long term trends in:

Tree and shrub distribution, composition and richness: Deer browse, exotic plants, and pathogens all have the potential to impact some plant species more than others. Monitoring species composition will allow the NCRN to identify individual species which have a changing geographic range throughout the region. This will be an effective means of monitoring species which tend not to be very abundant in individual plots, but are present in many plots. Locations or forest types which are particularly species rich or contain rare species can also be identified and may merit special management consideration. All tree and shrub species will be monitored.
Tree and shrub basal area and abundance: Basal area is a measure related to the total woody biomass of a forest stand. Large declines in basal area are indicative of a major disturbance in the forest ecosystem. If these declines were widespread and not part of natural disturbance processes they could have a significant negative impact on all other forest species. Abundance and basal area of individual tree and shrub species will allow the NCRN to determine if individual species are declining or increasing region-wide. This will be particularly useful for species which are found in many plots and tend to be abundant in those plots.
Amount of coarse woody debris per plot: Coarse woody debris is an important habitat for many animal and microbial species. Declines in the amount of coarse woody debris could negatively impact a wide variety of other species.
Distribution, abundance and basal area of exotic trees and shrubs: This will allow the NCRN to determine if exotic trees and shrubs are becoming more common and to determine what changes in forest vegetation condition are associated with these exotic species.
Exotic understory plant distribution and cover: Exotic plants may be able to out-compete native understory plants. By monitoring the distribution of understory plants the NCRN will be able to determine which plants are spreading throughout the region. The NCRN will monitor the cover of exotic plants to determine how large of an impact they are having in the plots where they occur. The NCRN will work with the regional Exotic Plant Management Team and the Invasive Species Coordinator to determine which plants should be monitored. The list is updated annually as new plant species invade network parks.
Vines on trees: The NCRN will identify all vine species growing on each tree, including exotic vines, and determine which trees have vines growing in the crown. This will allow us to determine if invasive vines are spreading and if trees that have vines have a higher mortality rate that those without vines.
Presence of select forest pests and diseases: The NCRN will record the presence of select forest pests and diseases on trees. The NCRN will work with the regional Integrated Pest Management Coordinator to determine which pests and diseases should be monitored. We will focus on those which are particularly destructive. By tracking the survival of infected trees, the NCRN will determine if these pests and diseases are causing significant tree mortality in network parks.