Background-
The Herrontown Woods
was given to Mercer County by Elizabeth and Oswald Velben on July 22, 1957.
The Velben’s turned over 81.3 acres to be maintained as a wildlife
and plant sanctuary with nature trails. Subsequently, other parcels
were added to bring Herrontown to its present size of 128.5 acres.
The woods are located
in northeastern Mercer County, New Jersey, in the center of the area bounded
by Kingston, Rocky Hill, Princeton, State Highway 27 and U.S. Highway 206.
On the topographical map of the U.S. Geological Survey, Herrontown Woods
appears partly on the Princeton and partly on the Rocky Hill quadrangles.
Herrontown Woods is
a forested tract, which, for its size, is quite diverse. Basically,
it is an oak forest with a mixture of other
trees, some of which may be dominant over the oaks in specific
locations. Most of the woods were not cleared for farming.
Firewood cutting, and a clear-cut harvest of timber occurred several times,
with the last clear-cut in the mid-1920’s. Selective cutting occurred
as late as the 1940’s. A major disturbance occurred in 1950, when
a 40 to 50 foot wide strip of forest was cleared, a trench dug and
a major gas transmission line laid across the property. The strip
was widened in 1968, opening even more land where the natural revegetation
has been forced to start from bare ground. The strip today is occupied
principally by herbs and shrubs of open sunny places.
Rationale-
The Herrontown Woods
provided an almost perfect site for our research project.
Most of the area has been undisturbed for several decades, but the
pipeline cut, running in a southwesterly direction across the tract, provided
us with a clearly defined "edge". Beginning
at the north edge of the pipeline cut, we were able to go into the forest
200 meters, with very little variation in elevation, soil changes, drainage
patterns, or other variables which could affect the number and diversity
of species.
Procedure-
1)
From point A on the map a 100 m west line was laid
out. From that point a 200 m line perpendicular to the pipeline was
established and seven 10 x 10 quadrants were flagged every 30 m.
In addition, quadrants adjacent to the 200 m line were flagged to provide
a "continuous" view of the forest for at least 80 m.. A compass and
tape measure were used for establishing the quadrants.
2) Each 10 m quadrant was represented by a 10 cm X 10 cm grid. All trees with a DBH (diameter at breast height) at least 1 cm were identified, given a number code, and their exact location in the plot marked. The circumference of each tree was measured with an inexpensive cloth tape measure. The conversion to diameter, d = C/ pi, a mathematics connection, could be done in the field or back in the classroom.
3) Numerical data representing species and diameter were entered into spreadsheets, and saved as a text matrix file. Data was analyzed, and visuals were created using scientific visualization programs, Spyglass Transform and Spyglass Plot.
Conclusions-
1)
The edge effect was definitely evident to a depth of about 10 m.
Species diversity was greatest, and the total population highest in these
quadrants.
2) After the first 10 m, the forest became remarkably consistent; diversity of species and total population decreased. The dominant species did change; oak-sweetgum canopy with dogwood understory near the edge to beech-maple canopy with ironwood-hornbeam understory near the center. Kramer (3) hypothesizes that the upland woods that we sampled will return to a beech-maple climax forest. Perhaps the dominant species present is also a function of the edge effect.
3)
Qualitative observations-
a. There was a marked increase in the number of herbaceous
plants present
in the first several quadrants.
b. There were numerous tree seedlings growing in quadrants
near the edge,
especially those of tulip tree.
c. The first two quadrants were "thick"- the total
amount of ground cover-
herbaceous plants, shrubs, vines, seedlings and saplings made walking
difficult. This thickness, however, would provide the most cover,
food, and
niches for animals and birds. A logical extension of this project
would be a
study of the faunal diversity and population along an edge.