PRESS RELEASE--from Wildlife Bureau Department of Natural Resources...
The cause and effects of the timing of spring burns on native vegetation, mostly Conservation Reserve Program (CRP) ground, are a hot topic this time of year.
Pun intended.
The dog days of March, before field work gets rolling, is a popular time to take care of that prescribed burn requirement on some CRP acres. The requirements of the contract are met, freeing up time for other projects, but what is the impact on desirable vegetation that doesn’t start growing until the ground is warm? And what is the impact on the undesirable vegetation like Canada thistle and volunteer trees that we are constantly battling? Could an early spring burn actually help the stuff we don’t want?
All sites are different, but we need to consider some generalities when it comes to native prairie vegetation and unwanted species. Canada thistle and invasive brome grass starts growing when soil temperature reaches about 45 degrees. Most warm season prairie vegetation doesn’t kick in until the temperature four inches below the surface reaches 50 degrees. All springs are different and soil temps can rise quickly, can rise slowly, and they can rise and fall. I’ve seen temperatures jump to 50 degrees for a few days and then fall to 45 degrees for weeks before rising again. That was a very bad Canada thistle year.
Monitoring soil temps for trees isn’t as critical because we can see the leaves when they start growing. Burning before leaf out does little to affect an established tree except reduces competition from native vegetation. The tree will resprout with a vengeance, using its energy reserve to create new stems and leaves. However, if a prescribed back burn is conducted after leaf out, usually in early May, that tree is severely stressed because it doesn’t have enough energy below ground to produce more stems and leaves needed to conduct photosynthesis. Just remember that required management for CRP cannot be done after May 14, to minimize impacting the primary nesting season for ground nesting birds.
Burning in late spring will likely benefit native grasses and set back flowers in a prairie stand. And this is true with a grass dominant 30/10 seed mix. The best way to prevent grass dominance is to plant a very diverse 20/20 mix with equal amounts of grass and flower seeds. Pollinator CRP mixes are 10 grass seeds and 30 flower seeds per square foot. It is very hard to make these stands grass dominant just by burning later in the spring.
Using prescribed fire in March or early April might not be right time-wise based on the type of CRP practice and what objective achieved through burning. If trees and weeds are present, a slow early May backburn into the wind is the way to go. If the CRP stand is surrounded by trees, has a history of Canada thistles, or cool season brome encroachment, late April to May 14 is the time to light the match. Burning before the soil temperature is consistently above 50 degrees could open the stand to thistle and tree invasion. Resulting in more work and expense to rid your acres of those undesirables in the future.
