Tom's Blog

Wednesday, November 10, 2010

Big north woods burn Monday Nov 8, 2010

The weather finally cooperated and we were able to do the large burn of the north woods. Fall burns are tricky, because the days are short, the temperatures are lower, and the humidity is often high. The kinds of conditions we look for are what used to be called "Indian summer." These are unusually warm conditions that develop in the late fall after one or more hard freezes. The freezes cause plant senescence and bring the leaves down, and the warm sunny weather is generally accompanied by lower humidities. Fortunately, this week we had almost perfect Indian summer.

We planned to burn about 25 of the 30 acres on our major north woods. However, due to fuel conditions, we could only get about 16 acres to burn well. The map at the bottom shows the area that actually burned.

This is a complicated burn, and requires quite a few personnel. We had 13 people (a few volunteers, but mostly paid). The woods are on a steep hill, and because they are heavily forested, visibility is not good. We had 10 high-quality two-way radios, and needed all of them to keep everyone in communication. We also had 10 drip torches, and needed all of them as well, as well as lots of extra drip torch fuel. (Thanks to the Prairie Enthusiasts for the loan of extra radios and drip torches.)

We spent most of the morning tuning up the fire breaks while waiting for the temperature to warm up and the humidity to drop. We cleared around quite a few standing snags. Also, we used several large-volume Stihl leaf blowers to clear residual leaves from the fire breaks. (See my earlier post for details on making the fire breaks.)

We had a long fire break along the top of the hill, stretching the whole length of the north woods. The plan was to back burn down into the woods. (County F at the bottom of the hill provided an excellent fire break on the north side.) We started lighting at the top of the hill in the middle of this fire break. This area was in the sun, so it burned well, as the photos here show.

Once this whole line was blackened, we started down the hill into the woods itself. The east and west ends of the woods burned least well, because there were fewer trees and hence less oak leaves on the ground. However, the major part of the woods in the middle has lots of large black and red oaks, and a substantial leaf litter. Most of the leaves had come down recently and hence were dry and curled up. Because of this, they carried a fire fairly well.

Every available person with a drip torch worked on the side of the hill. For safety, they kept in touch by radio. It took about 2 hours to complete lighting the whole slope.

The last area to be lighted was the road cut along County F. Because the leaf litter was fairly sparse here, it did not burn as well, although some areas burned quite well. (See Amanda working hard in the photo below).
The whole burn was finished by 3 PM, after which Kathie and I checked the whole fire break for possible problems. Mostly the fire line was clear, but there were two snags on the north fire break that were smoking even though they had been cleared. One of these was well inside the burn unit, but the other one was right on the burn line. Kathie spent about 30 minutes dousing this snag with water, and managed to put it out. Next day, we had someone with a chain saw cut it apart and toss the pieces down the hill (well inside the burn unit).

Kathie and I did a complete circuit of the burn unit the next day. The middle of the burn unit was virtually 100% black, with only occasional small patches of unburned leaves here and there.
I measured the area that had actually burned, using my Garmin GPS which has a separate data card for recording detailed Track data. I started at the top of the hill, where the burn had first started, and walked down the west side along the edge of the burned zone. Except for a small area at the very top, the burned zone followed the west fire break down the hill. Once I reached the road cut, I walked east along the edge of the burned zone until I reached an area that had not burned. I then walked up the hill along the edge of the burned zone, until I reached the east end of the burn unit at the top of the hill. I then moved along the north fire break to the point of beginning. (After this rather vigorous workout, I took a rest!)

Today I loaded the Track data from the Garmin into my computer and converted it in ArcMap into a polygon shape file. The results can be seen in red in the map below, which also includes the similar results in white from the 2008 burn of the same woods.
The area that actually burned, according to ArcMap, was 16 acres, which is about 64% of the whole burn unit. However, in the middle of the burn unit, the burn efficiency was closer to 100%.

The burned area in 2008 was about 14 acres, somewhat less than this year. See my 2008 blog post for details on that burn.


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