|Fire in Camp Johnson; photograph courtesy of Peter Hope|
Sandplain forests grew in much of Chittenden County Vermont before the area that is now the Saint Michael's College campus was cleared for farming by European settlers. The sandplains formed when rivers including the Winooski deposited sand and built deltas in Lake Vermont, and then the Champlain Sea. As glaciers receded they dropped materials to the south forming a terminal morain that functioned like a dam containing the meltwaters from the glaciers forming what geologists call Lake Vermont. A layer of finely ground 'rock flour' that settled from the melt water can still be found beneath what is now Lake Champlain. The weight of glacial ice that was literally miles in thickness depressed the earth's crust in Vermont below sea level. When the glaciers melted back as far as where the Saint Lawrence River mouth is today, sea water flowed in forming the Champlain Sea. Eventually post-glacial rebound brought the Champlain Valley above sea level and the deltas were lifted above the water level. Modern-day Lake Champlain is roughly 100 feet above sea level.
Because of the very sandy soil in these old deltas, the forests tend to be adapted to well-drained dry soils and would be expected to periodically burn following lightening strikes. The pitch pine is a tree species example that is one step beyond fire tolerant and is actually fire dependent. Pitch pine cones open only after fire and the seed can only grow when the organic matter layer on top of the soil is burned back to bare sand. In the Gil Brook Natural area where fire is suppressed, we can see that the pitch pines are gradually dying out and being replaced by white pines. Coincidentally, a patch of Gil Brook accidentally burned this week and it will indeed be interesting to see how this affects the vegetation there.
The planned burn in the sandplain forest in Camp Johnson this week was designed to burn off most of the organic layer and facilitate growth of the natural vegetation including pitch pines. The 2013 burns are just the latest in a series of burns implemented to preserve the sandplain forest and perpetuate the heath-like vegetation that would have dominated this region before European settlement.
For a number of years, Saint Michael's College students enrolled in General Biology have sampled insects, trees, and plants in both Gil Brook and Camp Johnson. These efforts were complimented by intensive sampling by students under the direction of Valerie Banschbach and Peter Hope last summer in the areas slated to be burned. Post burn sampling will happen this summer and the Fall General Biology class will be the first set of students to sample from recently burned forest plots. It's a lot of fun to work with students on real research questions during the course of regular classes!