Watershed Research Relating Ecosystem Structure and Function
to Human Values and Socioeconomic Behaviors
During
the summer of 1998, a team of three graduate students from the Yale School
of Forestry and Environmental Studies conducted an extensive inventory
of riparian corridor vegetation communities within the Quinnipiac
River Watershed. The purpose of this study
was to determine how anthropogenic disturbances effect the character of
plant communities and subsequently impact upon water quality. The data
collected by the vegetation team will be analyzed in conjunction with
data collected by water chemistry, hydrology, macroinvertebrate,
social survey, and environmental economics teams.
Methods:
Within each of the eighteen subwatersheds which comprise the Quinnipiac basin, between 6 and 10 transects were placed along the stream channel based upon GIS land use classification guidelines. These transects were placed perpendicular to the stream running a distance of 200m. At predetermined locations along the transect (5m, 25m, 50m, 100m, and 200m) fixed radius sampling plots were established for overstory(dbh>5cm), understory(dbh<5cm), and groundstory plots. Data was recorded for dbh, LAI, percent cover, dominant species, and various other ecological indicators. In addition to this data, 15cm X 15cm X 10cm soil excavations were performed where possible.
Results:
The
results of this inventory have allowed for the characterization of all
18 subwatersheds along the urban-rural continuum.
Trends in overstory cover include:
1. Basal Area increases from agriculture to urban to suburban to forest.
2. Stem density increased from urban to agriculture to suburban to forest.
3. The proportion of non-native invasive species in terms of basal area is highest in urban areas(>25%), mostly shade trees) but in terms of number of species the proportion of non-natives is highest in agricultural sites(>78%, orchards).
Trends in groundstory cover include:
1. Number of species recorded increases from agriculture to urban to suburban to forest.
2.
The trend of increasing species richness across cover types is comprised
largely of trees and shrubs (woody perennials); whereas herbaceous species
richness varied relatively little between cover types.
2003
Update:
The vegetation analysis of the New Haven Watershed Project includes an inventory of herbaceous and woody vegetation found in riparian zones along the project's eighteen streams. Riparian corridor vegetation and soils were characterized along 200 m long transects on either side of the length of main subwatershed streams. Cover type classification, canopy and understory vegetation, stand composition and structure, soils, and erosion rates were evaluated. With 560 sampling sites and roughly 350 species, this inventory is significantly larger and more comprehensive than most vegetation surveys accompanying projects of this scope. Detailed analysis of the data is presently being carried out as the basis for a doctoral dissertation. The predictor variables are surrogate measures of anthropogenic disturbance within a fixed radius around each sampling site: proportion of impervious surface, indices of landscape fragmentation, and population density.
Additionally, vegetation composition is expected to vary in relation to distance from the site to the stream bank. The response variables are measures of forest community health: stand maturity, soil chemistry characteristics (carbon, nitrogen, and percent base saturation), proportion of invasive species, and species richness, evenness and composition. One of the goals is to present quantitative proof of the hypothesis that health of the vegetation component of urban ecosystems in inversely related to the degree of anthropogenic disturbance. Additionally, it is expected that certain surrogate measures, such as impervious surface as calculated from satellite data, will be revealed as convenient and economical shortcuts for assessing anthropogenic disturbance. Likewise, it is expected that conveniently observed indicator species or soil characteristics will be revealed as signs of ecosystem health.