Tom's Blog

Tuesday, January 15, 2019

Prairie burns: how complete should they be?

The completeness of a prairie burn is often determined by the continuity of the fuel. If the fuel is patchy, the burn may also end up being patchy. Some people think burn patchiness is a good thing.

I have never agreed with this. Perhaps it was because we were trying to restore sites that had become heavily wooded (due to years without fire). If good prairie was to be brought back to these sites, as soon as the woody vegetation was removed it was essential to get prairie established again. In order to do a proper prairie burn, the fuel had to be continuous. If it wasn’t, then the patches that did not burn had probably been wooded and without fire would quickly become wooded again.

In fact, it is so difficult to get conditions “right” to do a burn, that when you have the weather and the crew, you should work hard to do a complete burn. Don’t say “heterogeneity is OK” and go home. The secret, of course, is “interior lighting” (stripping). In the early years of a restoration, it may be necessary to “force” the burn. (See photo)

I’ve seen a burn crew leave a site which had unburned patches because they ran out of drip torch fuel. Always have lots more drip torch fuel than you think you will need.

Perhaps it’s the microbiologist in me, but if I see small patches of sumac, or brambles, or scattered honeysuckles, I get really nervous. The burn did not pass through these areas for a reason (no fuel). Next year they would likely be worse.

Heterogeneity of a burn is not a good thing if it is due to woody vegetation. It is also not good if it is due to smooth brome or quack grass or Kentucky bluegrass.

Note that heterogeneity and diversity are two different things!

The above refers to real prairie habitats. If the site has areas of wet meadow or shaded ravine, obviously those were not “meant” to be prairie. Heterogeneity then means something different.

Forcing a recently cleared prairie area to burn.
After frequent seeding and lots of burns, it turned into a tallgrass prairie (see below).

The green patches are smooth brome, an exotic grass that develops in the shade.

The same area as in the above photo, some years (and many burns) later


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