Burning time

We took a couple of youngsters to Indian Lake Park this afternoon. They liked the trail and the views, and discovering new things. One of the signs explained that in Indian times the whole area was prairie, preserved as such by fires. When German settlers started living there they suppressed (or did not set) fires, and trees began to take over the hill--they dominate today.

We've been through a few years of drought, and though there were sporadic fires they weren't widespread. Assuming the climate was the same 200 years ago as now (not always a safe assumption), I estimate that fires would have been more than 20 years apart, which would be plenty of time to get some trees started. (Googling suggests that's a good estimate) So I'm WAG'ing that fires would have been set.

So what was their cue to toss the coals into the brush and take to the lake? Given that some of the plants could grow over 2m tall in a year, maybe it was when the grass got too high; which might be every year or every other year. It seems a drastic way to mow the lawn, but in the event it seemed to work.