weather

It's been a strange weather year in much of the U.S. I'm currently working on Hine's emerald dragonfly monitoring near Chicago, and have seen several examples already this summer of natural stochasm in action.

Through June, rainfall was well above normal. One site, on a river, flooded at least twice. Others, away from major watercourses, were wet but less extremely so. One storm in late June included high winds, severe enough to break tree branches, and probably to damage the fragile wings of dragonflies caught away from shelter.

Then the the rain just stopped for a couple of weeks, and water levels fell to what would be expected for mid-summer.

This morning another storm moved through. There were more fallen branches, more power outages, more heavy rain. Weather is expected to improve for the rest of the week, so we'll be right back out there to see what effect it's had.

Early in my dragonfly studies, I watched female Hine's emerald dragonflies oviposit in a range of locations from cool spring runs to warmer lower channels. Under normal conditions, the middle streamlet reaches are usually optimal habitat; the spring runs are too cool and slow development, and the lower resches are too warm and too prone to fish and other predation on larvae, as well as increased competition from other odonates.

Using the full length of the streamlet hedges bets, and ensures survival of some animals through drought, or flood, or "normal" conditions. In a stochastic floodplain environment, it's a logical strategy.

Too often when planning restoration projects we fail to account for stochasm. We target "normal" conditions, even though "normal" will not happen in some years. By designing restoration sites without allowing for stochasm, we could potentially doom some populations.