PARENT SESSION
Oral Session #75: Plant Communities: Vegetation Analysis. Presiding: J. Fralish.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Hall of Ideas F.
The relationships of the savanna herbaceous layer to gradients in gap size, canopy cover, and soil conditions.
PAVLOVIC, NOEL1, GRUNDEL, RALPH1, SLUIS, BILL2, 1 2
ABSTRACT- The herbaceous composition of Midwest oak savannas is determined by light and soil gradients, fire regime, and grazing history. However, the dynamics of the tree canopy is important because, when tree fall occurs, the newly created gaps have altered light levels and soil conditions. We examined the relationships among plant community composition, environmental variables, and gap size across five sites in northwest Indiana. Three gap habitats were selected for sampling: gap interior, gap edge, and under the adjacent tree canopy. Herbaceous composition varied among sites and was related to gradients in pH, cation exchange capacity, and elevation above ground water. Within sites, vegetation at gaps was correlated with topographic, moisture, soil, and light gradients. These correlations were strongest where canopy cover has been stable over time. Within sites there was no consistent pattern in the vegetation by habitat. However, within any particular gap, vegetation differences did occur among habitats. Vegetation composition at gap, gap edge, and gap canopy became less similar to each other as gap size increased. This pattern was strongest at the site with the most stable canopy over time. These patterns in vegetation variation indicate that the savanna is truly a mosaic and that vegetation at any particular location is determined by position on the topographic, moisture, and light gradients, by how long the gap has existed, and by the composition of the local species pool.
KEY WORDS: sand savanna, herbaceous vegetation, gap size, restoration