Tag Archives: wildflowers

Trying to Figure Out What We Did Right

Posted on by
30

When converting crop land to restored prairie, it’s always hard to predict what you’re going to get.  Numerous examples prove that even when you control as many variables as possible – including soil conditions and the rate, timing, and technique of planting – no two seedings turn out alike.  Sometimes, you can use hindsight to explain what happened (weather conditions, herbicide carryover, etc.) but most of the time it’s clear that we just don’t understand much of what’s happening out there.

I’ve been analyzing some data from one particular restored prairie lately, and trying to puzzle out what’s going on.  In this case, the results are good – which is nice.  It’d be nicer, of course, if I could explain WHY things worked so well and then replicate whatever happened…

The Dahms 2000 prairie restoration has turned into one of the most aesthetically pleasing prairies we manage along the Platte. It has tremendous diversity and abundance of wildflowers. Most importantly, its plant diversity is still increasing fairly rapidly after twelve field seasons.

The prairie in question was seeded with a mixture of about 200 plant species onto 69 acres of disked cropland that had been in corn the previous season.  The seed was planted sporadically between December 1999 and April 2000.  Wetlands were added to the site by excavating down close to groundwater and recreating the kind of swale/ridge topography that is typical of nearby Platte River meadows.  Those wetlands and sandy spoil piles (ridges) were seeded with appropriate seed as well. 

All of the seed was broadcast onto the site – some by fertilizer spreader and some by hand (I was experimenting) and no harrowing or packing of the soil was done.  Unfortunately, this was the last year BEFORE I started keeping good records of the amount of seed from each plant species I included in the mixture, so I only have a list of the species we harvested seed from that year.  What I know is that my seeding rate per acre was about 15 gallons of grass seed (mostly big warm-season natives) that was harvested by combine from nearby prairies, and about 1/2 gallon of hand-harvested forbs, grasses, and sedges.  That’s roughly 12 bulk pounds of grass seed and 1/2 pound of forb (wildflower) seed per acre.  I have no idea what germination rates were that year, but it was a pretty light seeding rate compared to what many others around the country use.  Today, our typical mix is a little lighter on grass and includes about twice the forbs.

To cut to the results, this prairie has turned into our most diverse and showy restoration we’ve ever done.  You’d never know we’d used such a light seeding rate of forbs by looking at the site now – its appearance is dominated by big showy wildflowers.  By every measure I use to look at the plant communities of our restored prairies, it comes out high.  I’ve found 178 plant species in the site so far, which is excellent.  The mean Floristic Quality (combination of species number and “conservatism values”) is high, and still climbing rapidly.  It averages twelve plant species per square meter, which is higher than most other restored or remnant prairies in the area.  (Yes, I know that seems like a very low number to you eastern tallgrass prairie folks, but it’s good for out here.  Don’t rain on my parade, ok?)  Twelve years after it was planted, tall warm-season grass species are still not very dominant.  The species found at the highest frequency is big bluestem, and it was only in about 80% of 1m2  plots stratified across the site last June.  In short, it’s a beautiful prairie.  And I don’t know why.

I know most of you are ITCHING to see the actual data tables and graphs, but because there are a few who aren’t, I’m including them as a PDF file, which you see by clicking here.  The PDF also includes a cumulative list of plant species found in the restored prairie.

Flower species such as black-eyed Susan (foreground) and bee balm (pink flowers in the background) are still dominating the plant community in this photo from 2009 (the 10th growing season of this seeding). The lasting abundance of those species is, I think, tied to the lack of dominance by major grass species.

It’s particularly impressive that this seeding turned out so well, because the odds seemed stacked against it early on.  It was seeded right at the beginning of a 7 year drought.  The first several years were dominated (as usual) by weedy species and a few colonizing native species such as Canada wild rye and common evening primrose, but in this prairie those species remained dominant for several more years than is typical.  Once other plant species started breaking through, there were few legumes present – and we don’t typically have problems establishing legumes in our prairies.  Those legumes are still more scarce than in other nearby sites, but they’re increasing over time.  Finally, in about its eighth season, the site stopped looking like a weed patch and matured into something that most people would recognize as a prairie.

As I’ve discussed in other blog posts, I’m still struggling to define success in our overall prairie restoration efforts, but at the scale of individual seedings, there are a couple things I look for.  First, I want to see a good diversity of plant species, and I want to see that diversity sustain itself over time.  Second, I don’t want to see invasive species increasing at the expense of that overall plant diversity, even as the prairie is exposed to disturbances such as drought, fire, and grazing.  So far, this restored prairie passes those tests with flying colors.  We’re moving toward implementing some measures of invertebrate use as well, but aren’t there yet.  Initial data and observations, however, show higher butterfly abundance and diversity in this site than in other nearby restored prairies – for whatever that’s worth.

The prairie has been managed with some periodic fire and grazing, which should be helping to suppress dominant grasses. However, this site has gotten much less of that kind of management than nearby restored prairies, and those other prairies have stronger populations of major grasses, so management can't explain the whole phenomenon. In this photo, cattle are grazing in the burned portion of this site - within a patch-burn grazing system. The grasses are primarily grazed short, helping to showcase the abundance of the forbs.

So why did this restoration turn out so well?  I really have no idea.  It caught a couple nice rains during its first spring, but the rest of the summer was awfully dry.  The overall seeding rate for forbs was considerably lower than we use now, but I don’t know how much seed we had of individual species.  I wish I understood why it has taken the big grasses so long to fill in, but I don’t.  I think the delayed grass dominance probably plays a role in encouraging the abundance and diversity of wildflowers at the site, but I don’t know how to replicate it.  The soils at the site are a little sandier than some of our other sites, but we’ve worked on sandier soils and had very quick grass establishment, so it seems unlikely that the sand is the key.

Besides its aesthetic appeal, the prairie is also a great seed harvest site because of its wildflower abundance. Nanette Whitten (left) and Mardell Jasnowski (right) are harvesting seeds in this photo.

The vast majority of our prairie restorations turn out pretty well, but this one is extraordinary, and I can’t explain it.  Was it something about our technique?  Something about the weather or soil conditions?  I know I should probably just be happy with the results, but I want to know WHY! 

Success is sure frustrating.

Lessons from a Fenceline

Posted on by
13

Last week, I spent some time collecting data and thinking about next year’s plans for managing our Platte River Prairies.  While I was out, I made an interesting observation along the boundary of one of our properties and that of the neighbor.

About two years ago, we replaced a section of fence that separated our prairie from the prairie to the west.  The fenceline had become overgrown with shrubs – something that is great for some species of birds but really hard on a barbed-wire fence.  We ended up treating the shrubs with herbicide, pulling out the fence, and shredding the remains of the shrubs before re-building the fence.

This fenceline was cleared of shrubs two years ago so we could re-build the fence. The photo shows the vegetation that came in after the shrubs were removed (left side of the fence). Note the lack of flowering plants in our property to the right.

The above photo shows that fenceline as it looks now.  In place of the shrubs, there is now a stand of thick prairie vegetation, including grasses, sedges, and forbs.  Ok, there’s also some smooth brome and even the beginnings of a stand of Phragmites (the thick-leaved grass in the photo).  But the interesting thing to me is the species that are blooming right now.  If you look at our prairie – which is shown on the right side of the photo – you don’t see any flowers blooming.  That’s not a photography trick.  There really are very few plants blooming right now in that prairie.  Yet in the fence row, Maximilian sunflower and Canada goldenrod are abundant and showy, and there are a few other flower species blooming as well.

So what’s the deal?  Here’s what I think is happening.  Our prairie had a long history of annual summer haying – as far as we can tell.  I don’t think it’s been sprayed with 2,4-D, though I’m not 100% sure, because it has a pretty good abundance of spring and early summer flowers, including pale poppymallow, blue-eyed grass, violets, prairie clovers, Illinois bundleflower, and others.  However, I think many years of annual haying likely eliminated late-blooming flowers from our prairie.  If perennial plants aren’t allowed to bloom and complete their annual life cycle they don’t produce seeds.  Perhaps more importantly, annual defoliation while the plants are still actively growing removes the plants’ ability to produce food for their root systems that were, until they were defoliated, gathering enough resources to support tall vigorous plants.  If wildflowers are like grasses (don’t know if there is research that has tested this) that sudden loss of aboveground vegetation causes an abandonment of large segments of roots – because there is no food coming in to maintain them.  If those plants are defoliated at the same growing stage every year without a break, it’s easy to see how they would eventually die without replacing themselves.

The Maximilian sunflower and Canada goldenrod plants growing in the fenceline are not rare plants, or even plants that are particularly difficult to maintain in most prairies.  But they’re almost non-existent in our prairie.  We’ve begun to overseed some late-season-flowering plants into the prairie, and species such as Maximilian sunflower, stiff sunflower, wild bergamot,  and a few others are slowly establishing – and seem to be surviving well under our patch-burn grazing management.  I hope we can bring them back so that late-summer pollinators (for example) can have something to eat other than what they can find in the fenceline!

A closer view of some of the plant species growing in the unhayed/ungrazed portion of the prairie along the fenceline. The prairie to the left in this photo is our neighbor's prairie - which is annually hayed.

So, if the wildflower species that are missing from our historically-hayed prairie are common in the fenceline where they weren’t being mowed, burned, or grazed, does that mean we should manage (or not manage) our prairie by perennially idling it?  No, I don’t think so.  First, remember that although those flowers are blooming in the fenceline now, they weren’t two years ago because they were covered up by tall vigorous shrubs.  Prairies managed without fire – or something that sets back trees and shrubs – tend to grow quickly to woody vegetation, changing their very nature pretty dramatically.  In addition, though I haven’t looked carefully, I would guess that the fenceline “prairie” is missing many of the early season plants that are so abundant in our prairie because there is nothing that removes each successive year’s thatch along the fence to allow those small plants to get sunshine.  I think one lesson of these plants along the fenceline is that it’s important to provide a periodic rest period for plant species – especially when a site is being managed with the same treatment every year.

One could, I suppose, make the argument that we should manage some portions of the prairie for late-season plants and other portions for early-season plants, and everything will be fine.   Unfortunately, by doing that, we would be reducing the plant diversity – and ecological resilience – of those individual portions by not facilitating the full range of biological diversity and ecological function.  As a result, the entire prairie would be weakened.  This is, by the way, why I disagree with biologists who promote leaving portions of prairies permanently unburned in order to protect insect species that are vulnerable to prescribed fire.  I completely agree that small isolated prairies should not be completely burned (or hayed) in any one year, helping to ensure that refuges are left behind for those species that might be harmed by the management treatment.  Shifting the location of management treatments from year to year should allow species to find appropriate habitat, especially if (as in small isolated prairies) the distance between one management treatment and another is short.  If that’s insufficient, it might be that the real issue is not management, but size and isolation of the prairie – something that can only be solved by strategic prairie restoration of surrounding land parcels.  Reducing the ecological resilience of small prairies by managing them for a small suite of species is certainly not a good long-term solution for those species or the larger community.  (Baby with the bathwater…)

There is one more observation that’s too important not to mention.  The plants that are blooming in these photos somehow survived being covered by dense shrubs for at least a couple decades, and also survived the foliar herbicide application that removed those shrubs.  Plants are tough.  Granted, the wildflower species we’re talking about are species that have a reputation for toughness anyway, but I still think their survival is worthy of note.

I’m not completely sure I’m right about why those flowers are in the fenceline and not my prairie, but even if I’m wrong, just going through the thought process is valuable!  If nothing else, it gives me a hypothesis I can test (and sufficient fodder for an entire blog post).  Isn’t it amazing what we can learn just by looking around us?