Lessons From a Project to Improve Prairie Quality – Part 2: Overseeding and Seedling Plugs

Last week, I posted a summary of some findings from a long project to enhance prairie habitat.  I focused that post on the lessons we learned from the fire/grazing management portion of the project, including impacts on regal fritillary butterflies.  This week, I’m looking at the other half of that project – overseeding and adding seedling plugs to our degraded prairies in order to increase plant diversity.  As with last week, you can find all the gritty details, including graphs, tables, and more, by looking at our full final report.

Maximilian sunflower is one of the species we've found easiest to establish in degraded prairies.
Maximilian sunflower is one of the species we’ve found easiest to establish in degraded prairies.  (These particular sunflowers are for illustration only – not from an overseeded site.)

During the five years of the project, we overseeded approximately 500 acres of prairie – focusing mostly on degraded remnant (unplowed) prairies that were missing many characteristic prairie wildflower species.  We harvested our own seed from nearby sites, and broadcast it on degraded prairies right after burning them.  The prairies were managed with patch-burn grazing, so cattle grazed those burned areas intensively for the remainder of the first growing season and then focused their grazing elsewhere in subsequent years.  To measure success of the seedings, I used replicated plots to count the number of new plants that established from seed.  Most of the seedings included multiple seeding rates, so I was able to look at the effect of seeding rate on establishment.

In addition to overseeding, we raised and transplanted more than 800 prairie and wetland seedlings into seven different sites, and added several hundred more seedlings to our nursery beds for seed production.  Most transplanting was done in the late spring, and plants were watered on the day of transplanting but afterward.  We marked (GPS and flags)and attempted to re-locate seedling plugs to evaluate survival, but that didn’t work out very well, and we didn’t find a lot of the plants we’d plugged in.  Some of those plants surely died (which prevented us from finding them), but for others, flags disappeared and GPS points weren’t accurate enough to lead us to the small plants we thought were probably there.  We did find some, but our estimates of success are pretty fuzzy.

We learned two major lessons from this portion of the project:

1.  Overseeding after a burn in a patch-burn grazed prairie can re-establish at least some missing plant species, but the use of a high seeding rate is important.

2.  Overseeding seems to be more cost effective than seedlings, assuming abundant seed can be obtained relatively cheaply.

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Overseeding Prairies

What do you do with a prairie that’s missing most of its plant species?  In some cases, good management can allow some plants to seemingly return from the dead.  In others, though, the species are gone and – especially if the prairie is isolated from others – they’re not coming back.

When the species are gone, the only remedy is to bring them back.  Seedlings are one way to do that, but can be expensive if the area to be restored is very big.  Harvesting seeds from nearby prairies and throwing them out is probably the most cost effective strategy. 

An overseeded prairie north of Lincoln, Nebraska.

However, most people who have done prairie overseeding share a similar tale of the results.  It usually goes something like this.  “I threw the seeds out and nothing happened.  For several years, I looked every year and never saw any new species come up.  So I gave up.  Then, 5 years later, I happened to go by the site and there were new plants everywhere!”

Exploring why and how overseeding works (or doesn’t) is something I’ve been spending a lot of time on lately.  I’ve got several research projects underway that, I hope, will help shed some light on this topic.  There are some things I think I’ve learned that I’ll share in a later post.  In the meantime, I’ll add my own story to the raft of others.

The above photo was taken this fall at a site we manage north of Lincoln, Nebraska.  It was a brome-dominated hill prairie – if prairie is the right word – that had few species other than smooth brome.  Some goldenrod, heath aster, yarrow, and a few other scattered plants that are good colonizers and/or resistant to overgrazing and herbicides.  We burned the site in about 2001, sprayed it with Glyphosate in April when the brome came up, and then seeded it with a diverse mixture of prairie species.  The next year, the brome was back in full force and it looked like nothing had changed.  Over the next several years, it looked exactly the same, except that every once in a while I’d stumble onto an isolated plant of prairie cinquefoil or Canada milkvetch that had obviously come from our seed.

In the last couple of years, I started noticing more of those prairie species, and warm-season native grasses started becoming more abundant as well.  Then, last season, we brought in a bunch of cows and grazed the site for the entire year – down to the proverbial “golf course” height.  And this year, the prairie looks marvelous.  It still has some brome, but it’s not dominant.  I’d love to see some of the species like compass plant and Canada milkvetch be more abundant, but they’re there.  And it looks like a prairie.  Was it the grazing that released everything?  I’m sure it helped, but the prairie was headed in the right direction already.  Why did it take so long?  What finally triggered the species to show up? 

Stay tuned.  I hope to have more ideas on this soon.  And please share your own!