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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Lady’s Tresses Orchids in Prairie Seedings

I love mysteries. 

I don’t know much about orchids, but my understanding is that they can be difficult to establish in restored (reconstructed) prairie, largely because they rely on mycorrhizal fungi that are unlikely to be present in soils after years of row crop agriculture.  Regardless of that information, or maybe because of it, (I can be somewhat obstinate) we keep harvesting seed from nodding lady’s tresses orchids (Spiranthes cernua) whenever we can find the plants after they’ve gone to seed in the fall. 

…and darned if they’re not showing up in our prairie seedings!  To date, I’ve found Spiranthes in at least four separate prairie seedings in our Platte River Prairies.  When I saw the first plant, I came up with all kinds of explanations for how it might have occurred, none of which included our seed (there was some bulldozer activity near where the plant was, so surely some plant material and soil came in with the dozer…).  By the third and fourth sites, though, I finally came around to the idea that the plants had to be a result of our seed.  I’m still not sure of that, but it’s pretty hard to think of other reasonable explanations.

We've found nodding lady's tresses plants like this one in at least four prairie seedings now. Those seedings were planted in 1995, 1995, 1997, and 1999, respectively.

So – what’s going on?  Is there something special about the sandy loam soils that allowed myccorhizal fungi to survive many decades of row crop agriculture?  Are those fungi somehow making their way into the soils once prairie vegetation establishes?  Are orchids less reliant on those fungi than we thought – or maybe just able to use a wider variety of fungi species than we thought?

I don’t have any answers, just lots of questions.  I’m hoping to hear from some of you about your experiences with Spiranthes species in prairie seedings.  I’m also hoping that some of you know more about myccorhizal fungi than I do (I still have to check the spelling every time I type it…) and can explain what I’m seeing.

Help?