Wanted: 10,000 Dragonflies, Hungry

I went for a walk in Olivers Woods Friday 22 May 2009 at 1:30. What a remarkable change! I entered the Woods from the SW gate off Chautauqua and set off up the trail that I and scores of ecology students had taken dozens of times from January through April. But I got only about 50 feet along the way before encountering shallow standing water.. and not just a puddle. I was at the edge of acres and acres of 6 inch deep water. Everywhere I looked, shallow water covered 85 % of the forest floor. The water was a light golden color from dissolved organics – leached from the decaying wood and leaves it had recently covered; but mostly clear enough to see the details of the submerged forest floor.

 In places, there was a floating sheen of oil from the new growth of diatoms. As I walked or waded along in my water boots I initially saw little life in the water.. no water striders, diving beetles, whirligig beetles etc. But I did start to see more and more of the little black dots or “wrigglers” of mosquito pupae and larvae.

 A small cloud of mosquitoes gathered around me but kept a respectful distance, repelled by the DEET I had just applied. They were not a problem. But in about a week or two there will be huge numbers of adults emerging. Where are the predators?  the dragonflies, damselflies, aquatic bugs and beetles that should be here gorging themselves and keeping the exponential population explosion in check?

 The mosquitoes (adults and the wriggler larvae) seemed especially prevalent in small sun breaks, gaps in the canopy where direct sunlight illuminated a square meter or more of the watery forest floor.

 As I walked further into the forest wetland, I saw some very large tadpoles (of bullfrogs?) and smaller darting mosquito fish?. I also found a 13 inch or 30 cm snapping turtle partially submerged in water not deep enough to cover it.

 I kept on the familiar route.. although all now was changed by the shallow flooding.. and eventually came to the path up over the crest of the sand dune. It was dry and sunny and a jungle of green, although the trail was still open and clear.

 The south side of the sand dune was dry. Clearly water had been there in some of the heavier rains of the past few weeks.. but it had drained away, probably the day it fell.

 I came back to the flooded forest and began to consider the ecological impact the flooding would be having on the forest. Many of the trees’ roots will be drowning, slowly dying from lack of oxygen. Any forest understory of herbaceous annuals and vines of the sort that were so abundant up on the dry dune, these would be excluded, drowned by the inundation. Small raised hummocks of a few square meters, perhaps an overturned “root wad” would become an island of dry ground where understory plants could survive.

 In the area of abundant bottlebrush sedges, Carex hystericina, the limits of their patches, it was now clear to me, were not topographic low points retaining more soil moisture; but instead were open areas where the canopy cover was gone.. likely from the drowning of the dominant oaks, elms, hackberries etc.. that previously have shaded those areas. If anything, the topography seemed to be somewhat higher where the sedges were growing most luxuriantly.

 The effect on the community of soil organisms must be especially profound.. to the extent that I would imagine earthworms are likely excluded from large areas of the forest by the recurring flooding. They, along with hundreds or thousands of species of soil microarthropods, decomposers, springtails, minute beetles, mites, pseudoscorpions.. anything that cannot or does not fly.. will be excluded, absent from this soil, forced out or excluded by the flooding.

 Same story, I imagine, would apply to most wood rotting fungi and many mycorrhizal fungi. Many of these would likely find it very difficult to colonize and survive the areas of forest that are flooded each year. Interesting consequences for decay half lives of leaf litter and woody debris.

 North and East of the path up over the sand dune, the water had largely drained away and the forest floor was clear. It was obvious that rafts of sticks and organic debris (including soda pop bottles and cans) had been washed there.. and these rafts of debris (at least the natural debris) would provide a distinctive kind of ecological structure, niche or shelter where moisture retention would be longer and soil micro-arthropods could be sustained.

 Walking North along the old Oliver fence line in the center of the Woods the scene looked much more normal. No standing water. It has in fact been a week since our last rain in Norman May 15-16 (~ .75 inches).

 I found a three-toed box turtle on the outskirts of a stand of half meter tall herbs; but no sign of the small group of deer that have been staying in the Woods until recently.

 Making my way back towards the South West gate I encountered a pair of mallards in a section of the shallow flooded forest.

 Emerging from the Woods I was pleased and surprised to find no ticks.. quite a contrast to the 10 ticks I found on my brief walk in the Woods two days previous.

 On that Wednesday I had taken a thirty minute walk on the pond trail into the Woods at the base of the ridge that begins across from Canadian Trails Drive and Chautauqua. I slabbed along the slope near the base of the hill on the well trodden path, clearing the trail here and there with loppers and waving away the abundant mosquitoes. (I had not applied any DEET.) I made it as far as the forested East pond and then returned, amazed with the profusion of vegetation all along the path that had been so clear and open all winter and spring. I am looking forward to help from botanists in learning the names of more of the dominant understory herbs in the Woods.