Category Archives: Prairie Management

Report from the 2011 Grassland Restoration Network – Part 2: Grassland Birds

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The Grassland Restoration Network’s 2011 annual meeting was at The Nature Conservancy’s Kankakee Sands prairie/wetland restoration site in Indiana.  This year, we focused more than usual on creating habitat for various animal taxa, and I previously reported on the herpetology portion of the meeting.  Here is a summary of the discussions we had regarding grassland birds.

While the diversity of insects in a prairie is strongly tied to plant diversity, grassland birds have no such relationship.  The species richness, abundance, and breeding success of grassland birds are mainly related to variables such as vegetation structure, habitat patch size, and the amount of grassland in the neighborhood around their nesting sites.  At Kankakee Sands, the 6,000 acres of restored prairie/wetland habitat are obviously increasing both the patch size and total amount of grassland in the neighborhood, so our discussions focused on vegetation structure.  The ideal situation, of course, is to have a diversity of vegetation structure scattered across the site so that all grassland bird species can find the habitat they require for nesting.

This kind of tall vegetation is typical of most of the restored prairie at Kankakee Sands (and most other tallgrass prairie restoration sites). While valuable for many species, it's not much good for grasshopper sparrows and other animals that require short or patchy habitat structure.

We talked mainly about two different approaches to creating habitat structure in order to accomodate a rich variety of bird species.  The first approach is to design seed mixes for each desired habitat structure type, and the second is to design seed mixes that promote overall biological diversity, and then manage for structure with fire, grazing, and other tools.  Kankakee Sands is employing both strategies, so we were able to look up close at each.

We first looked at a restored prairie that had been seeded with about 60 species of short and medium-height plant species, and that included bunchgrasses like dropseeds and little bluestem instead of tall and strongly rhizomatous species like big bluestem.  The resulting structure was very favorable for grasshopper sparrows and other species that prefer that short to mid-height structure.  The seeding was nearly a decade old and seemed to be maintaining its structure and species composition with only a couple of prescribed fires as management.  The short patchy vegetation is definitely a contrast to the majority of other seedings at Kankakee Sands (and most other tallgrass prairie restoration sites) which are mainly tall and rank.  Those taller sites provide excellent habitat for Henslow’s sparrows and species with similar habitat preferences, but don’t do much for grasshopper sparrows.

Chip O'Leary (left) describes grassland bird habitat and research results with participants of the 2011 Grassland Restoration Network workshop. This restored prairie was seeded with short and medium-height plant species (including bunchgrasses instead of tall and strongly rhizomatous species).

The second example we visited was one of the first seedings done at Kankakee Sands (in the late 1990’s).  From the beginning, the several hundred acre prairie has been dominated by grasses and has been low on forb species diversity.  For the last several years, the Conservancy has been experimenting with patch-burn grazing as a way to create more heterogenous vegetation structure and to increase forb diversity in this prairie.  To date, forb diversity has neither increased nor decreased, but habitat structure has certainly changed.  The recently burned (and thus currently grazed) portions of the prairie provided excellent grasshopper sparrow habitat, while other portions were more tall and rank.  Though no change has been detected in forb abundance or diversity, the staff has noticed that a few forb species seem to bloom less abundantly than in the past – including compass plant, prairie dock, and Canada milkvetch.  Because of that, we discussed the value of fencing out a significant portion of the prairie each year to ensure that those species were given a complete break from grazing pressure periodically.

The two methods of creating bird habitat (seeding design vs. active management) both seem to be working well so far.  Both the prairie seeded with short/bunchy vegetation and the grazed prairie had significantly different vegetation structure than did the majority of the tall rank prairies around them – and birds are responding to that structure.  However, there are still plenty of questions about the long-term future of both approaches to creating bird habitat. 

In terms of the seeding design approach, one potential downfall is that the site was seeded with considerably fewer plant species than most other tallgrass prairie seedings at Kankakee Sands.  The potential effect of this lower diversity on insects and other species is unknown.  In addition, planting short and medium height plant species in soil/climate conditions that typically favor tall species could result in a relatively unstable prairie community.  In the long term, the fact that those shorter plant species aren’t using all of the available light/soil/moisture resources could lead to encroachment by either tall grasses (defeating the purpose of the design) or invasive species (which create obvious problems).  The planting we looked at was located on dry sandy soils with very low organic matter, so it probably is less at risk for that kind of instability than if it had been located in wetter or heavier soils. 

A final potential disadvantage of the seeding design approach is that the location of the short/medium habitat structure is static.  Grazing and other management tools for manipulating structure can be moved around a site from year to year, creating a shifting mosaic of habitat conditions.  That kind of mobility could help keep predator or pathogen populations from building up under consistently favorable conditions at any one site (this is speculation).  In addition, the staff will have to be careful to avoid repetitive management treatments aimed at maintaining the same structure year after year – that management could consistently favor some plant species over others, further reducing the plant (and insect?) diversity of the prairie.

There are plenty of concerns about the patch-burn grazing strategy as well.  To date, the plant diversity in the grazed prairie we looked at has not gone down, but neither has it increased – though increasing plant diversity in a grass-dominated prairie is very difficult with any strategy.  Because the prairie started with few forbs, it’s hard to know what the impact of patch-burn grazing would be on a more diverse plant community, but that needs investigating.  We discussed the possibility that a higher stocking rate and the addition of a large exclosure that changes location each year could help with both habitat and plant diversity over time. 

The burned patch of the patch-burn grazed prairie at Kankakee Sands. While the compass plant in this photo is blooming under grazing, other individuals (of compass plant, prairie dock, Canada milkvetch, and others) appear to be blooming less frequently than they did prior to the introduction of cattle. While this doesn't kill the plants over the short-term, it is a concern down the road, and the Kankakee Sands staff is considering strategies to mitigate those potential impacts.

A higher stocking rate would lead to more intense grazing of the dominant grasses such as big bluestem that are likely preventing existing forbs from becoming more abundant.  Currently many of the grass plants inside the most-recently burned patch are only being moderately grazed, and that can actually induce those plants to divert extra resources into rhizome production – leading them to expand their footprint (not the objective here).  More intense grazing on those grasses could create better opportunities for seed germination and seedling establishment around those plants, and would create even shorter vegetation structure, which might help attract upland sandpipers and as well as grasshopper sparrows. 

Regardless of stocking rate, the use of a grazing exclosure would help ensure a periodic break from grazing for plant species that otherwise be vulnerable to annual grazing – even in the unburned (and lightly grazed) portions of the prairie.  With a higher stocking rate, the exclosure would become even more important.  In addition to protecting plants from grazing, it would also protect fuel for the next year’s burn.  An exclosure roughly 1/4 or 1/3 of the size of the prairie would probably sufficient for protecting both plants and fuel, and would still leave cattle access to both burned and unburned portions of the prairie – something is important when promoting selective grazing. 

Even with those potential alterations to the current patch-burn grazing system, there are still plenty of unknowns about the long-term impacts of cattle grazing at Kankakee Sands.  It seems clear that grazing can create a shifting mosaic of habitat structure, but whether or not it can maintain the kind of plant diversity (and other diversity) desired by the Conservancy at this site is still an open question.

Discussing those kinds of questions while standing on the ground, however, is the best part of our Grassland Restoration Network workshops.  We don’t all agree on the best strategies, because we are all still experimenting with our own ideas on our own sites – and none of us feel like we have all the answers.  Being able to see for ourselves what various restoration and management treatment results look like helps us better compare those results to what we see on our own sites.  While we don’t have all the answers yet, we’re certainly moving much closer to them as a group than we would be individually.

Report from 2011 Grassland Restoration Network – Part 1: Herpetology

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Last week was the annual workshop of the Grassland Restoration Network.  This year, the host was The Nature Conservancy’s Kankakee Sands Prairie/Wetland Restoration Project in Indiana.    There were more than 80 people – mainly from Illinois and Indiana this year.  As always, the workshop was an opportunity for sharing notes and ideas on prairie restoration, but we also had a particular focus on animal habitat this year.

I felt like the workshop was especially productive and interesting this year, and have several posts worth of information to share from it, but I thought I would start with herpetology.  Kankakee Sands is restoring wetland habitat by plugging/filling ditches and also doing some excavation – and then seeding wetland vegetation.  One of the goals of that work is to create habitat for reptiles and amphibians. 

Dr. Bob Brodman, from nearby St. Joseph’s College, has been sampling amphibians (and reptiles) in the area since before restoration work began, and has observed exponential increases in populations at the restoration site.  It’s not really surprising that he’s found higher numbers of amphibian populations, since the Conservancy has added new wetlands to the site.  More interesting – and gratifying – is that he’s also finding that the number of amphibian species per wetland is also increasing (as is the total number of amphibian species across the site).  In addition, Dr. Brodman has collected data on other amphibians and reptiles that seem to show those species moving in from nearby remnant habitats.  Since the major goal of the Kankakee Sands project is to reconnect those disjunct remnant habitats (for vertebrates, invertebrates, and plants) those data are encouraging.

Dr. Bob Brodman (herpetologist) examines and photographs a toad.

Restoration ecologist Ted Anchor led field trips for this year’s network participants to show the immediate colonization of newly-created wetlands.  We looked at two wetlands – one with muck soils and one with almost pure sandy soils.  At both wetlands, we saw numerous frogs and toads, though they were much easier to see (and catch) at the more sparsely-vegetated sandy site.  Additionally, we were finding both Fowler’s toads and American toads, as well as many that appeared to be hybrids between the two species.  Dr. Brodman hypothesized that the temperature and moisture conditions this spring had led to the two populations breeding simultaneously in ponds where they would normally show up a couple of weeks apart.

Ted Anchor showing off the muck soils at one of the wetlands on the field trip. The muck had prevented the immediate area from being farmed, and also created a quick establishment of plants from the seed bank - and from seeding - after excavation was complete.

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One of many toads that had physical characteristics of both Fowler's and American toads.

Ted and Dr. Brodman both discussed some of the important factors to consider when restoring wetland habitat for frogs and toads.  In general, they said that most amphibians utilize a buffer zone of upland habitat (about 200 meters wide) around the actual wetland habitat itself.  While that habitat is very important, the most critical factor for annual breeding success tends to be the length of time water is present in wetlands each spring/summer because that determines whether breeding occurs and whether tadpoles can successfully mature before their ponds dry up.  Water depth and organic matter in the wetlands soils can both affect the length of time that water stays around. 

Creating wetlands with varying depths, including at least a few places where it is nearly permanent can help ensure breeding success (though fish and bullfrog populations can be counter-productive, so that can be a tricky line to walk).  Most wetland restorations at Kankakee Sands have very sandy bottoms – as do the ones we’ve done along the Platte River in Nebraska.  Those sites tend to hold water for shorter times than do sites with more organic matter (or clay).  That organic matter will accumulate over time, gradually helping to increase breeding success over time, but again, creating some deeper pools can help in the meantime. 

In addition to helping hold water, organic matter may have two other benefits.  First, the darker colored soil may improve the effectiveness of the dark-colored tadpoles’ camouflage – and could increase survival (logical speculation from Dr. Brodman).   Second, the organic matter increases the density of vegetation, which may help amphibians better thermoregulate and conserve moisture under the shade of those plants.  Those plants probably provide more and better hiding places too…

Ted Anchor and network participants at the sandier of the two wetlands visited on the herpetology field trip. You can see the sparse vegetation in the sandy soils.

At our Platte River Prairies, we’ve experimented with trying to supplement organic matter levels in our restored wetlands by “top-dressing” excavated wetland bottoms (spreading top soil on them).  While it likely increases organic matter, the main impact we’ve seen so far is an increase in invasive plants – and/or lower plant diversity.  It may be that waiting for those wetlands to accumulate organic matter slowly will allow a more diverse plant community to take hold – but may mean lower breeding success for amphibians and other species in the meantime. 

A final discussion topic during our wetland field trips centered on habitat structure for shorebirds – as well as amphibians and other species – as restored wetlands mature over time.  Obviously, the bare sand (or sparse vegetation) conditions immediately after wetland construction provide great habitat for shorebirds.  As that plant community develops over time, a few dominant plant species often end up covering much of the area, reducing bare ground, decreasing plant diversity and somewhat simplifying habitat structure.  We had an interesting set up discussions about whether (or how often) it was valuable to periodically “reset” those early conditions through intensive disturbances such as grazing or disking – and there was no consensus among the group. 

We’ve experimented with periodic intensive grazing at our Platte River sites to create bare ground in and around the deeper portions of our restored wetlands.  Within a year or two after the cattle have moved to another location, those wetland plant communities recover their former plant composition and habitat structure.  We’ve found that kind of grazing to be useful in preventing species like cattails from choking out open water habitat – and in creating temporary habitat for shorebirds and other species that like bare ground.  On the other hand, there are certainly impacts from the cattle in terms of nutrient inputs and sedimentation.  I don’t have the answers about how to balance those tradeoffs.  At this point, we’re banking on the ability of our sites to absorb the potential negative impacts – on a short term periodic basis – and we appreciate the apparent benefits.

It was great to have the opportunity to see what the Conservancy’s 6,000 acres of restored grassland/wetland habitat is doing for reptiles and amphibians in Indiana last week.  As I’ve mentioned before, I find it valuable to think about my own restoration work through the eyes of various animal and plant species.  I admit that toads aren’t one of the species I consider very frequently, so it was helpful to be reminded of the importance of those species and the types of conditions they require.  As I walk our sites this week, I’ll be looking at our wetlands with a different perspective than I would have last week.