Vegetation Inventory Project: Boston Harbor Islands National Recreation Area, Massachusetts

Largay, Ery; Sneddon, Lesley

Vegetation classification and mapping of Boston Harbor Islands National Recreation Area (BOHA) follows established National Park Service (NPS) protocols under an umbrella agreement with NatureServe and its component network of Natural Heritage programs. NatureServe developed an initial vegetation classification for the park based on the U.S. National Vegetation Classification (USNVC), Elliman’s (2005) natural community classification, and the Bell et al. (2002) marine intertidal habitat classification. Forty-seven vegetation classification plots were sampled in the summer of 2006. Associations were mapped onto an orthorectified composite aerial photo background from the Commonwealth of Massachusetts Office of Geographic and Environmental Information (MassGIS) using on-screen digitizing. One hundred seventy-two accuracy assessment points were collected to verify the accuracy of the vegetation map in 2008. The final accuracy of the vegetation map is 82% at the level of USNVC association and alliance, 86% at the level of USNVC group and macrogroup and 89% at the level of USNVC division, formation, subclass, and class. The final vegetation map is composed of 42 map classes. Thirty (30) classes are of vegetation classified to a USNVC association; three classes are of vegetation classes equivalent to a phase of a USNVC association (“sub-associations”), and one class is comprised of a single USNVC association mixed with a land use-land cover class that is equivalent to an Anderson Level II class. The remaining eight classes are land use - land cover classes equivalent to Anderson Level II classes. Altogether, 766 ha (1,894 ac) were mapped. The vegetation associations and land uses are mapped to the shoreline edges of all 34 islands and peninsulas as shown in the 2005 MassGIS orthophotography. In total, 587 ha (1,451 ac) of terrestrial and intertidal vegetation communities including un-vegetated beaches are mapped. Of this total, 179 ha (443 ac) are mapped as solely land use - land cover categories. Thirty 32 (32) USNVC associations were classified and described, with one association comprised of three distinct phases (34 vegetation types total). BOHA supports habitat for three globally rare (G1-G3) and five (S1-S3) state-ranked natural vegetation associations. The coastal setting and centuries of past land use on each of the islands and peninsulas have influenced the present-day vegetation. Successional forests, woodlands, shrublands, and old fields are the most abundant terrestrial vegetation throughout the park, comprising 251 ha (620 ac). The most abundant native, natural, terrestrial vegetation in BOHA is shrublands dominated by staghorn sumac (Rhus typhina). Three variants of staghorn sumac shrubland have become established on 52 ha (128.3 ac) of the park. Beaches, with inclusions of the Beach Strand vegetation association, comprise 123.4 ha (305 ac) of BOHA. Maritime Red-cedar Woodland, a globally rare vegetation association, occurs on the rocky headlands on World's End, Langlee, and Ragged islands in Hingham Harbor. Two other unique vegetation associations are Maritime Rock Cliffs and Outcrops and Maritime Erosional Bluffs and Cliffs. The park provides habitat for diverse vegetation associations including native upland forests, shrub swamp, (fresh, brackish, and salt) marshes, and intertidal rock and mudflat vegetation. Non-native vegetation associations including Norway Maple Forest, Black Pine Forest, Common Wormwood Gravel Field, Eastern Reed Marsh, and Reed-grass Tidal Marsh also occur throughout BOHA, covering a total of 67 ha (164 ac). Descriptions of the local and global expressions of each vegetation association and a photo-interpretation key, field key, plant species list, metadata for the vegetation plot data, and an index to photographic documentation are included as appendices.

Vegetation Inventory Project: Boston Harbor Islands National Recreation Area, Massachusetts

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