Prairie burns in the fall?

Why is it so hard to get a good prairie burn in the fall?

Update 11-1-2016 See bottom of this post
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It would be nice if prairies could be burned in the fall. Not many people are burning so it is easier to get a burn crew together. In our area, no DNR permit is needed, which simplifies scheduling. 

Unfortunately, fall prairie burns are difficult to accomplish effectively, primarily because the principal fuel, warm-season grass, is often not cured.

What is curing? Most tallgrass prairie species go through a life cycle that involves growth and seed production, after which the above-ground plant matter undergoes senescence followed by death. (In perennial grasses, the roots remain alive and carry the plant through to the next growing season.) During senescence the leaves start to lose their chlorophyll and brown patches or spots appear. At about 50% cured, whole sections of the leaves become brown and gradually the whole leaf becomes brown. At this point, the grass is 100% cured. From then on, the moisture content of the plant will no longer depend on the plant itself, but on past rainfall and relative humidity.

The curing process will vary with the year, and with the site. The progression of curing will be different in different prairies, and will be affected by rainfall and temperature. Even in a single prairie, curing can be patchy.

Most of the research on curing has been done in Australia, and involves completely different species and different habitats. But the general principals are the same. Here’s a link the the Australian work.

If the prairie is not burned annually, some of the fuel will be dry residues from previous seasons. This material is of course fully cured but will not carry a fire as well as fully cured prairie grass from the present growing season.

There is also a U.S. curing guide focusing on the Great Plains, provided by the U.S. National Weather Service. In addition to the data in tabular form (see below), there is also a photographic guide, which can be found at this link.

In our climate in the southern part of the Upper Midwest, curing is a rather slow process, and may often not be completed before the snow flies. This explains why fall prairie burns are often unsatisfactory.

However, not all is lost. We have actually had a quite successful prairie burn in early December in a year when snow was late in coming. The grass then was fully cured. We wanted to burn then so that we could get all the thatch out of the way so we could spray smooth brome as soon as it came up in the early spring.

A December burn just takes luck and an ability to move immediately when conditions are right. Periodic monitoring of the site is essential.

Also, I have seen years when prairie burns could easily be accomplished on the odd day in either January or February. Obviously these are not fall burns, but the grass then is fully cured.

Update 11-1-2016

This just in from the 11-1-2016 survey.
The warm season grasses at Pleasant Valley Conservancy are now fully cured. (See photos below) This is earlier than usual.

In fact, a good burn could have been done. Here was the situation:

In the morning the humidity was fairly high and there was dew on the grass everywhere. But by noon the humidity had dropped and the temperature was rising. By 3 PM the humidity was about 40% and the temperature was 72 F. A great time for a small prairie burn. Just a light wind.

This emphasizes one of the demands of doing controlled burns: the ability to jump when the conditions are right.

And you obviously can't wait until tomorrow, because tomorrow (now today) it is raining!

Fully cured  Indian grass in the Barn Prairie. Ignore the green, which is an adjacent mowed lawn.

Fully cured prairie grass, ready to burn.
By 3 PM the RH was 40% and the temperature was 70 F. Light wind out of the NE.

Hill's oaks and fall color at Pleasant Valley Conservancy

This has not been one of our better years for fall color. The last half of September was cold and rainy, and it has only been in middle of October that we really had any color, and it went fast.

I had a post in 2010 which gives some detail about Hill's oaks at PVC. Here are two pictures showing fall color. According to some sources, Hill's oak is sometimes planted in urban areas because of its nice fall color.

Both of these photos were taken around the edge of Toby's Prairie, which is the area with the most Hill's oaks.

This species is found primarily in sandy areas. Those specimens around Toby's are mostly still fairly small, but there is an area with larger Hill's in Unit 19B, as shown on the distribution photo below.

Wikipedia has a map showing the U.S. distribution of Hill's oak.

Mullein control: to dig or spray?

Mullein (Verbascum thapsus) is a common invader in the early stages of prairie or savanna restoration. It can't compete in well established native areas, but comes in quickly on bare ground, which is common in the early stages of a restoration. Since it is a biennial, it is important to prevent seed formation.

We used to dig the rosettes with a shovel (a Parsnip Predator is ideal). However, in the early stages of the East Basin restoration we had hundreds of mullein plants, making digging a formidable job. Since there wasn't much else green, we sprayed them all with glyphosate, since that has no residual soil activity.

Once mullein is under control, one still finds the occasional plant cropping up. Yesterday I found one at the edge of the rock outcrop at the East Overlook. Since I had my shovel with me, the first thought was to dig it up. However, it is virtually impossible to get all the roots when digging in a rocky place.

I also had my Garlon 4 spray bottle with me, and it was much easier just to spray the center of the rosette, which is enough to kill the whole plant.

I can't emphasize the usefulness of a spray bottle containing Garlon 4 at 15-20% in bark oil. I always carry one with me. I use it for basal barking any small shrub that may have been missed (buckthorn, honeysuckle, sumac, etc.). And it also works for herbaceous plants such as mullein, burdock, sweet clover, parsnip, bird's foot trefoil, etc.

With these herbaceous plants, with a high concentration-low volume herbicide mix, you don't need a complete foliar spray. Just the center of the rosette is enough to kill the plant.

Mullein plant growing out of the rocks. Digging is almost impossible here,
but a brief spritz in the center of the rosette will do the trick.