Tom's Blog

Wednesday, March 19, 2014

Tallgrass savanna burn on a steep slope

Burn weather will eventually come and we have to be ready. The south-facing slope is always our first burn because it dries out early. This year requires some careful planning because the grass is very long, meaning a potentially hot fire. Quite a contrast to last year when the grass was so short we had difficulty getting it to burn.

Why the difference between these two years?

As you may recall, the year 2012 was the year of the summer drought. There was no rain in June, which is the main part of the growing season for grasses. By August, when we finally got rain, it was too late to save the grasses. Very short leaf bunches and practically no flowering. The first photo, taken in early 2013 (just before the spring burn), shows what the grass looked like. We mostly used a head fire to burn; even so, the fire moved slowly up the slope.

On the other hand, the summer of 2013 was very favorable for grasses. Lots of lush green which has now cured to a golden brown. The second photo  shows what we will have to contend with in our upcoming (2014) burn.

The short prairie grass on the south-facing slope after the year of the 2012 drought
The lush grass on the same south-facing slope after the good summer of 2013 
The other photo is a closeup, which emphasizes how tall the grass is. With this much grass, a very hot fire is possible.

This closeup photo of the south slope was taken yesterday.
Our main task is to burn the grass without torching the trees. Although the bur oaks are notoriously fire-resistant, we still have to worry about fire in the canopy. The upper branches, especially of the large open-grown oaks at the top of the hill. are very difficult to put out once they get going.

One solution would be to burn the whole slope as a backburn. However, that would take a long time, and because backburns move slowly, the heat stays around the base of each tree for a longer time, which, with the heavy fuel, would lead to lots of burn scars.

Instead of a backburn, we will use the strip headfire technique, and keep the strips close together so that the flame heights remain low. The rule is that the farther apart the strips are, the hotter the burn. Why? Figure it out.

We start at the top, of course, and backburn a wide blackline first. Once that is well established, then the strip fires can begin.

A strip headfire will take more personnel than a backburn, but will be quicker and lots easier to control. The burn boss will have to be on his or her toes, but everyone on the burn will have a radio, and there will be a monitor in a UTV on Pleasant Valley Road moving back and forth and keeping track of the strippers.

Normally, it takes about 2 hours to burn the south-facing slope (about 20 acres). 


Post a Comment

Subscribe to Post Comments [Atom]

<< Home