Like most natural wetlands, the vegetation in Millbrook Marsh is varied and responds to hydrological and soil characteristics. The vegetation types found in the marsh include palustrine emergent, calcareous fen, palustrine scrub-shrub, and upland vegetation, as well as several species of invasive non-native plants. The palustrine emergent and scrub-shrub vegetation is all found within the boundaries of the 100-year floodplain.
Existing information on the plant species in Millbrook Marsh originate from various independent studies and informal inventories. The earliest one found was a Pennsylvania State University thesis (Pursell 1954), and the last include formal and informal inventories of 1997 (Brooks et al. 1998).
Studies of Millbrook Marsh and areas nearby were done for the Environmental Impact Statement for the Mt. Nittany Expressway (PennDOT 1981). They resulted in a list of more than 50 species. "In comparison to other types of wetland, the marsh (fen) at Millbrook is very diverse floristically… Moreover, the various plant communities that are found in such a relatively small area contrast with much less diverse wetlands found in many places in Pennsylvania." (PennDOT, 1980, p. III-12.) This species richness is due to the various hydrological factors affecting different parts of the site, the geology, soils and topography. In 1980, the PennDOT study identified two shrub communities in the vegetation of Millbrook Marsh, one of which was an alder, red willow, skunk cabbage association. The fen was considered the second shrub community despite the short height, due to the presence of gooseberry. It was characterized as a gooseberry, sedge, skunk cabbage, moss and horsetail association, and was found as a patch, and an edge community on the southern forested boundary. In 1980, shrubs were reported as having covered only a small portion of Millbrook Marsh. Presently a much larger area is covered by shrubs, though it is two non-native species, Tartarian Honeysuckle, (Lonicera tatarica), and Multiflora Rose (Rosa multiflora), both broadleaf deciduous shrubs that are dominant in some areas.
A study of calcareous fens in Pennsylvania was conducted in 1994 (Western Pennsylvania Conservancy 1995). The Western Pennsylvania Conservancy (WPC) plant collection occurred on 3 visits during the 1994 growing season, and resulted in the identification of species other than those already known from the 1954 Pursell and 1980 PennDOT data, including species of special concern in Pennsylvania. Part of the Millbrook Marsh fen was considered to be "open" and part considered to be "shrub" fen. According to The Nature Conservancy Eastern Regional Classification System, the fen at Millbrook is a "Carex stricta - Carex prairea Herbaceous Alliance", a new fen classification as of 1995.
In February, 1995, Clearwater Conservancy (CWC) members and members from the Site Assessment for Stewardship and Resources Committee met at Millbrook Marsh for a walk along the banks of Slab Cabin Run and Thompson Run. They reported that in the area covered, grey dogwood thickets were the dominant shrubs with scattered hawthorns present.
Another vegetation list was compiled by the Pennsylvania State University Cooperative Wetland Center (PSU CWC) for three reference wetland sites (Map 7 in Chapter 3) within Millbrook Marsh. One site is a 0.7 ha portion of Millbrook Marsh labeled as Reference Wetland #28 (Brooks et al. 1996). The plant inventory took place in 1994, and again resulted in species not previously identified. The 0.7 ha reference site is located adjacent to the lower reach of Slab Cabin Run, and was identified as a Riverine Mainstem Floodplain, Palustrine Scrub-Shrub/Emergent that is severely disturbed, primarily due to the surrounding urban landscape and high sedimentation rates, including an overhead utility line. The second, site #56 - "Farm 12", is located adjacent to Bathgate Spring Run (Figure 5-1). It was identified as a Riparian Depression, Palustrine Emergent wetland, also severely disturbed because of the prior use as a pasture on the Farm 12 acreage. Site #57 - "Thompson Run" is located on the east bank of Thompson Run, opposite it’s confluence with Bathgate Spring Run, and was identified as a severely disturbed Riverine Headwater Floodplain, Palustrine Emergent wetland (Figure 5-2). This portion, too, is affected by the surrounding urbanized landscape and relatively high sedimentation rate. Site # 56 and # 57 were inventoried in 1997. There are 155 plant species identified in Millbrook Marsh through 1997 (Table 5-1).
Figure 5-1 Reference Wetland Site #56 Severely disturbed riparian depression, to the right of Bathgate Spring Run, in photo midground July 1998.
Figure 5-2 Reference Wetland Site #57. Severely disturbed headwater floodplain, east side of Thompson Run, opposite Bathgate Spring Run confluence, just right of center in the photograph July 1998. (Photo by R. Brooks.)
On to Vegetation Inventory