Tom's Blog

Monday, January 1, 2018

Controlled burns: Increase efficiency by doing two burns at once

I am reviewing the 20-year history of burns at Pleasant Valley Conservancy. Every year I have kept careful notes of each burn, and have written a narrative afterward, with a map showing burn coverage. We have always tried to do large burns, especially for the oak savannas. However, the topography of PVC is complicated, and we have two savanna areas that are only connected in the middle (by what we call the Side Road). There is a Ridge-top Savanna, consisting of units 8, 10, and 19A,B,C,D  (about 13 acres). And a Basin Savanna, consisting of three units that form a basin surrounding the Pocket Prairie (Units 11, 12, and 18), about 24 acres. See map

When we first started burning these savannas, we often did them on different days. However, good burn weather doesn’t come along every day. My philosophy has always been: “When the weather is right, and the crew is available, burn, burn, burn!

The first time we did two burns at the same time was November 14, 2003. Because it was a fall burn, there were lots of people available (we had 15) and all were experienced. When we met at the cabin, I realized that we did not need so many people for a single burn, and suggested to the two most experienced people that we run two separate burns simultaneously. They agreed, and each chose his crew members.

The wind was out of the south west, about 5-7 mph gusting to 11-12 mph. We liked the wind speed and direction, since it helped carry the fire up through the units. Getting the fire to carry well was often difficult in those early years of restoration, since the warm-season grass was just getting started, so we used head fires a lot. The temperature was 50 F and the R.H. in the upper 30s.

We had everything set the day before: fire breaks, water jugs spotted near the burn units, drip torches full, etc. We took the whole crew and all the equipment to the top of the hill in trucks, dropping the Basin Savanna crew off on the way to the farther Ridge-top Savanna.

Backburning from the Service Road

The crew doing the Ridge-top Savanna burned Unit 19 first, thus establishing a solid black line at the downwind side of the unit. They had two drip torches, one went along the north side of Unit 19 and the other went along the service road. Once Unit 19 had been burned (about 1:30 PM), this crew used a head fire by lighting along the fire break at the south side of Units 8 and 10. The SW wind carried the fire up through the units, getting an almost 100% coverage. This was the best these two units had burned. In past years we had needed a lot of interior lighting to get good coverage of these units, but not this year.

Simultaneously, the Basin Savanna crew started at the top (NE) corner of Unit 12A, near the steep ravine. One drip torch went west. The main problem here was because of the SW wind, they had to ensure that Toby’s Prairie did not ignite. Spotters were placed inside Toby’s Prairie, but fortunately spotting was not a problem. Once the drip torch reached the west end of Unit 12A there was less problem. This drip torch continued lighting the savanna south of the service road (shown in red on the map), backburning Units 12B and 11B. It was 1:30 PM when the drip torch reached the top of the hill where the unit 19 burn had begun. This drip torch continued west along the service road to the side road, lighting Unit 11A.

The other drip torch of the Basin Savanna burn went south down the edge of the steep ravine. Although there was little fuel in the ravine, this line made sure fire did not burn down into the ravine. Once this line reached the bottom of the ravine (adjacent to the Pocket Prairie) the drip torch moved along the south edge of Unit 12A, 11D, and 18. The southerly wind carried the fire uphill, so there was little problem with the Pocket Prairie burning. By the time the bottom crew reached Pleasant Valley Road the Ridge-top crew was finished and one of its drip torches and two waters burned the line separating Units 7 and 18.

Two drip torches were used for interior lighting in Unit 11, starting below the crest of the hill. There was a good leaf pack at the west end of Unit 12 and the east end of Unit 11, and these areas burned very well. The lower part of these units had less leaf pack (fewer trees) and did not burn as well so extensive interior lighting was done.

We finished interior lighting at 3 PM, at which time the wind had mostly died down and a bit of rain started to fall. Great timing!

There was very little mop-up. We had cleared around snags and some special trees the day before. One large snag burned and fell, but well inside the burn unit. Also, there were a few piles of cut logs or brush piles scattered here and there. Most of these burned, a few for quite a while, but since none of these were near the edges, we let them burn out (our standard practice).

In all, a great burn!

There are several advantages to this two-burn approach. All crew members were used extensively. Once there was a black line around the perimeter, novices could be used for interior lighting. And with changeable weather, more fire on-the-ground can be obtained before conditions worsen.

Typical forest floor in the early years of a savanna restoration
A head fire is often the only way to get the fire to carry

One of the problems in savanna burns is getting the fire to
carry through downed timber and coarse woody debris


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