Plant Community Sampling Method:

Wetland plant community structure and composition around each light trap was measured using a modified line-intercept method. Four 30 m long line transects were established along cardinal directions with the light trap as the center. At two meter intervals along each transect, we recorded the species and height (cm) of each plant part which touched a PVC pole. In all wetlands the sampling pole was held firm to the substrate, thus in inundated wetlands we measured water depth and vegetation heights. In forested areas we also recorded the species which appeared to be above the sampling point at 500 and 1000 cm above the ground, if present. We also noted the horizontal position (distance from the trap) and height of coarse woody debris (> 3 cm diameter) which intercepted the transect line. We calculated a "canopy roughness" as the ratio of the 120 m (total of the four adjacent 30 m transects) transect length to the canopy surface (the length of a line formed by the maximum height recorded at each 2 m segment). In plant communities with a flat upper surface, as might be found in a wetland with a large open water component, the coefficient approaches 1. As the upper surface becomes more complex, the value of the coefficient decreases.

Jim taking plant data in Kent Bog

Results

from Old Woman Creek

The data we gathered at the River site, the Island site and the Upland site show vast differences in the structure of these three areas. The graphs to the left have been generated using the North and South transects for each site and only include the vertical and horizontal location of the hits, not the species of plants the were encountered. At the River there is a change in the structure of the vegetation as the tall species taper off into floating-leaved and emergent vegetation and open water. At the Island the entire transect is dominated by the floating-leaved and emergent vegetation and the water level is clearly visible around 65 cm. The vegetation at this site is only found between 65 cm and 150 cm. So, what we see is a distinct structure at the Island that is also found in the River site at the right part of the graph where the water level is visible. If you were to make comparisons between the vegetation at the River and the Island what would you need to do first? The Upland site, however, is structurally much different from either of the other two. The plants are shorter and the hits are closer together than the other sites.

The canopy of the plants is the uppermost hit at each 2 m interval. In our calculations we include a value for "canopy roughness" which is the length of the line connecting those hits divided by the length of the transect (60 m). The closer this value is to one the "flatter" the canopy. We use the canopy roughness in site-to-site comparisons.