Vegetation Classification and Mapping at Weir Farm National Historic Site, Connecticut

Metzler, Kenneth; Barrett, Juliana; Nosal, Thomas; Millinor, William; Sneddon, Lesley

Vegetation classification and mapping was conducted at Weir Farm National Historic Site during the fall of 2003 and the summers of 2004 and 2005, creating a current digital geospatial vegetation database for the park. There are nine natural vegetation types that occur in the park; four upland forest types, one upland non-vascular type, two forested wetland types, and two wetland shrub thicket types that reflected the soil moisture conditions of the site. In addition, four anthropogenic vegetation types occurred; one successional forest and three non-forested types (two in mowed upland fields, and one herbaceous wetland seep). Each of these is described in detail in this report. The vegetation reflects the land use history, ongoing management, and varied environmental settings of the park. Deciduous forest is the primary vegetation, with non-forested vegetation occurring only in areas too wet to support trees and in man-made fields maintained by mowing. A man-made pond adds to the diversity of the site. The Northeastern Dry Oak - Hickory Forest covers the largest acreage of the park, intergrading with the Lower New England Slope Chestnut Oak Forest on areas with shallow soils. In many areas, the floristic difference between these two types is subtle, with few indicator species present to distinguish between types. The natural vegetation structure throughout the site has been heavily altered by over-browse of white-tailed deer (Odocoileus virginianus), with a near elimination of the shrub layer and a low diversity of herbaceous plants. This lack of both structural and floristic diversity made the recognition and classification (using TWINSPAN) of the vegetation difficult. In this regard, familiarity with the vegetation types within this region and the presence of representative species in the herbaceous layer were the only clues to distinguish between the types. Nonnative invasive plants occur throughout, albeit in small numbers, with the control of their spread due to the diligence of NPS staff. No Federal Endangered or Threatened species occur within Weir Farm; but a single small population of blackhaw (Viburnum prunifolium, State Special Concern) occurs on the eastern edge of the site. A map showing the locations of the vegetation associations within the park was created following the USGS/NPS Vegetation Mapping Program protocols (TNC and ESRI 1994a, b, c). Each association was cross-walked to the US National Vegetation Classification (USNVC) in order to provide a regional and global context for the park’s vegetation. A dichotomous field key to the vegetation types was also developed to assist with field recognition and classification. This project documents the vegetation associations of Weir Farm National Historic Site based on previous work, supplemented by 2004/2005 field sampling and mapping on both 2001 black and white photography and 2004 false-color infrared aerial photography. This inventory completes one of 12 basic inventory data sets for the park.

Vegetation Classification and Mapping at Weir Farm National Historic Site, Connecticut

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