Tag Archives: conservation

Prairie Restoration (Reconstruction) as a Landscape-Scale Prairie Conservation Tool

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As promised, here is a summary of the presentation I gave last weekend to the Winter Meeting of the Iowa Prairie Network.  I advocated using prairie restoration to increase the size and connectivity of fragmented remnant prairies and improve our chances of conservation success.

INTRODUCTION

Of all the threats to prairie conservation, habitat fragmentation is by far the most serious.  Encroachment by invasive species and woody plants, chronic overgrazing, and broadcast herbicide/pesticide spraying are big threats to prairie species and communities too, but the fragmentation of grasslands into small isolated pieces makes all of those other threats even more dangerous and difficult to counteract.

When a large contiguous prairie landscape (left) is broken up into small isolated fragments of prairie surrounded by cropland, roads, and other human developments, prairie conservation becomes very difficult.

For example, pressure from both predation and invasive weeds and trees is usually most severe near the boundaries of a prairie.  Because of their size, small prairies have very little area that is not exposed to these “edge effects”, so resident prairie species have no refuge from high predation rates and invasive species.  In addition, the intensity of invasive species pressure in prairies with a lot of edge exposure increases the need for control efforts and makes excessive responses like broadcast application of herbicides more likely.  Small prairies can also be more likely to be overgrazed because they’re not large enough to make up a significant part of an agricultural landowner’s income – and thus don’t get the careful management that larger grasslands would.

Most importantly, small prairies simply aren’t large enough to provide the physical space and population sizes needed to sustain many species of plants, insects, and animals.  Small populations, whether of birds, butterflies, or wildflowers, are much more vulnerable to local extinction because a disease, weather event, management treatment, or other stressor can easily affect the entire population.  If one of those small populations is wiped out by a particular event (or series of events), the only chance of that species reappearing is through recolonization from nearby prairies – but in a small AND isolated prairie, that’s unlikely to occur.

The fragile nature of small populations in tiny isolated prairies makes those prairies extremely difficult to manage for biological diversity.  Every management decision is going to favor some species at the expense of others.  Because small populations aren’t very resilient, it’s easy for them to be much more strongly affected by individual management decisions than they would be in a larger prairie where populations are larger and management treatments are less likely to spread across the entire site (leaving refuges for species to recolonize from, if necessary).

Here’s a goofy but perhaps useful analogy.  Imagine that prairie conservation is like trying to catch hundreds of pieces of popcorn falling from the sky.  In order to save a species (a piece of popcorn), you have to catch it as it falls.  Managing small prairies is like trying to catch all of that falling popcorn in a coffee cup.  Because the cup is small, the task is impossible.  If you move one way to catch some popcorn pieces, you’ll miss others.  And even if you’re really agile, your cup isn’t big enough to hold all the popcorn anyway – so you’re doomed to failure before you start.

Conserving prairie species in tiny prairies is like trying to catch falling popcorn in a coffee cup. (sort of)

The difficulty of maintaining a prairie ecosystem in small isolated fragments leads to feelings of frustration and helplessness among prairie managers.  It also leads to conflicts between managers and advocates of various prairie species/groups.  For example, some rare prairie butterfly experts advocate managing prairies without the use of prescribed fire because fires can destroy larvae, and a fire that burns an entire small prairie can completely wipe out the whole population of some rare butterfly species.  Avoiding the use of fire may make sense for those few butterfly species, but what about all the other species that would suffer from a lack of fire?  Do we manage some prairies exclusively for butterflies – and whatever other species can survive with that management?  I don’t think we have enough prairies left to start managing each of them for individual species or groups of species.  And yet, the threat of losing butterfly species is real – and important.   Unfortunately, the underlying issue is not whether or not fire should be used to manage small prairies, the issue is that rare butterfly populations are small because the prairies they rely on are small and isolated.

Ok, so small isolated prairies create all kinds of problems for conservation, but they’re all we have in many places, particularly in North America’s tallgrass prairie region.  What do we do about it?  One choice is to continue trying to catch popcorn in our coffee cups, knowing that we will eventually fail to save many species.  The second choice is to make more prairie – and enlarge and reconnect some of the existing remnant (pre-existing and unplowed) prairies to give ourselves a better chance of conservation success.  In other words, we can turn our prairies into something more like a wading pool – instead of a coffee cup – so that it becomes easier to catch the falling popcorn.

It's much easier to catch falling popcorn (conserve prairie species) with a wading pool (large prairie) than with a coffee cup (small prairie).

Our ability to restore (reconstruct) prairies by harvesting seeds and converting cropland to diverse plant communities has come a long way since its early days.  Numerous local pioneers have worked out successful methods of seed harvest, site preparation, planting, and weed control, and know how to establish hundreds of acres of restored high-diversity prairie each year.  Those prairies can contain hundreds of plant species, and can support many of the insects and animals found in remnant prairies.  However, there’s still much to learn about the extent to which restoring prairie around and between remnants increases population viability for those species, and we still need to identify those species that can’t make the jump between remnants and restorations – and find out why.  That said, we know enough to start using restoration to make prairies larger and more connected (and we don’t really have a lot of other options.)

It's not feasible to restore entire landscapes to prairie, but if we can strategically restore parcels of land around and between remnant prairie fragments (right), we can greatly increase our chances of conserving prairie species.

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GETTING IT DONE

If we’re going to use prairie restoration to make a real difference in conservation, the first step is to get better at strategically targeting our restoration efforts around and between existing small and isolated prairies.  This is being done at a few sites, but the vast majority of prairie restoration work is scattered piecemeal across the landscape.  Because restored prairie doesn’t compete economically with rowcrop agriculture, prairie restoration on privately-owned land generally happens when an individual landowner makes it a high priority and/or when Farm Bill programs like the Conservation Reserve Program (CRP) or other similar cost-share programs can help close the financial gap.  The agencies that administer those cost-share programs typically have little capacity to go out in the field and sell the programs to strategically-located landowners.  Instead, they usually sign up the people who come to them (and there are usually enough of those to use up the available money).  As a result, the location of prairie restoration depends more upon which landowners express an interest than where their property is located.

Another issue we need to address is the way in which these cost-share program funded restorations are designed.  For the most part, agency guidelines allow only enough funding per project to pay for a low-diversity seed mixture.  This is largely because the continued funding of these programs by Congress depends heavily on the total number of acres enrolled each year – making it necessary to spread the available money broadly instead of focusing it on a few high-quality projects.  While low-diversity seed mixtures can help species like grassland birds, many other species (including pollinators) rely on a high diversity of plant species, and the overall ecological function of a high-diversity prairie is much higher than that with only a few plant species.

Improving the strategic location and quality of prairie restoration will mean taking several approaches.  In some cases, conservation groups can simply attempt to purchase tracts of land around and between remnant prairies and restore them.  While effective, this can be difficult and expensive.  However, if fundraising efforts are targeted toward our highest priority remnant prairies and situations in which the potential for success is high, even small parcels of conservation ownership can be helpful.

In order to bolster the viability of more than a few high priority prairies, however, private lands are going to have to be a large part of the strategy as well.  Because agencies like NRCS (Natural Resources Conservation Service) don’t usually have the ability to direct market their programs to landowners, other conservation groups can help by approaching owners of key land parcels and discussing the potential for conservation program enrollment with them.  Finding a few interested landowners and helping them enroll can pay big dividends because one successful project often leads to other enrollments by neighbors who see the aesthetic and conservation benefits from across the fence.

Influencing the design of restoration projects funded by NRCS and other agencies is often possible as well.  For example, the biggest obstacle to using higher-diversity seed mixes is the cost.  If conservation groups can help find additional funds to increase the number of plant species in seed mixes – and if the landowner helps push for it – restoration quality can improve dramatically.  In addition, those conservation groups can help by building and maintaining long-term relationships with enrolled landowners.  Helping landowners understand the benefits of their restored land, and how it fits into a larger conservation strategy, will improve the chances that the restored prairie will be carefully managed (and even retained as prairie) as the years go by.

Prairie conservation is difficult.  In highly fragmented landscapes it can sometimes seem nearly impossible.  However, we have the ability to greatly improve our chances of success by converting isolated prairies from coffee cups to wading pools, so to speak.  Success will depend upon a concerted and collaborative effort between conservation groups, government agencies, and private landowners, but it is possible.  Surely we can agree that prairies are worth the effort?

Epilogue: How do we measure the success of prairie restoration?

I’ll deal with this more extensively in an upcoming post, but a brief mention is important here.  When using restoration as a strategy to expand and re-connect remnant prairies, the objective is not to copy the existing remnants (or some historical version of them) but to complement them with restored plant communities that allow the plants, insects and animals within the remnants to have larger and more interconnected populations.  Because of this, evaluating differences between remnant and restored communities should not be the primary measure of success.

There are a number of research papers that have shown differences between the relative abundance of individual plant species, levels of soil organic matter, composition of the insect and soil fauna communities, etc., between remnant and restored prairies.  These papers often interpret those differences as indicators that we’ve not yet restored “real” prairie.  I think that kind of research is interesting, but largely misses the point.  If our objective is to replicate existing or historic prairie we will surely fail – but why would we expect otherwise?  Trying to recreate exact copies of ecological communities that formed over thousands of years – and doing so on degraded soils, in different climatic conditions, and under pressure from vastly different invasive species and other threats – is not a recipe for success.

However, when we look at restoration as a tool for improving the viability of existing remnants, the most important measures are those that evaluate whether or not prairie populations and communities are larger, more interconnected, and more resilient.  Those are difficult things to evaluate, unfortunately, and we need develop better measures than we currently use.  That means we’ll need to shift our current research focus from identifying differences between remnants and restorations to investigating how well they interact with each other.

The Importance of Weedy Flowers for Butterflies

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In our Platte River Prairies, regal fritillaries and other butterflies appear to depend heavily on a few weedy wildflower species as nectar plants.

I was in graduate school when I first started learning to identify butterflies.  I participated in several July 4th butterfly counts around Nebraska, and got to know some people who could help me with the tougher-to-identify species.  I was a good birder at the time, and quickly found many parallels between bird and butterfly identification.  One of those was that skippers were just like sparrows – lots of small drab-colored species that were really difficult to tell apart.  The difference, of course, was that I could catch skippers with my net to see them up close.

One species that wasn’t difficult to identify was the regal fritillary.  Once I figured out how to tell the difference between regals and monarchs I started seeing regals everywhere.  In fact, when I helped with July 4th counts, regal fritillaries were usually one of the most abundant species we saw.  I didn’t realize until later how rare regals are in eastern prairie states, and how fortunate I am to live in Nebraska where their populations are still strong.

Regal fritillary butterflies are still common in many western tallgrass prairies and mixed grass prairies, but have largely disappeared from most eastern prairies.

As I learned more about the species and its conservation status, I saw some inconsistencies between what regals were thought to need for survival in eastern prairies and what our Platte River Prairies were providing.  For example, many people I talked to from the east told me that regal fritillary larvae needed prairie violets for a food source.  However, our Platte River Prairies – which are full of regal fritillaries – only have the heart-shaped-leaf blue violet (Viola pratincola), and no prairie violets.  In addition, plant species like purple coneflowers (Echinacea spp) that are heavily used as nectar plants by regal fritillaries aren’t present in the floodplain of the Central Platte River.  In 2010, with the help of Dr. Ray Moranz of Iowa State University, we started a research project to learn more about how regal fritillaries survive and thrive in our prairies.

Through the project, we’re investigating multiple aspects of regal fritillary habitat use – including nectar plant use, the use of remnant vs. reconstructed prairies, and the way in which regals interact with a landscape managed with a combination of fire and grazing.  We’ve only completed one field season so far, and will need more time to answer those questions, but we have already seen some very striking results in terms of nectar plant use.

To collect our data, we regularly walked transects through our prairies and counted butterflies – noting nectaring behavior when we saw it, and recording the species of flowers the butterflies were nectaring on.  I’m only referring to the nectaring data in this post because we’ve got more work to do to analyze the other data we collected.  It’s also important to remember that these are just pilot-year data, although they match what I and others have observed for many years.

Though we saw many hundreds of regal fritillaries on our transects, relatively few were actually nectaring.  Early in the season when numbers were highest, we saw mainly males – patrolling for newly emerging females.  When those females finally arrived on the scene we started to see nectaring behavior from both males and females, but observations of nectaring were still relatively rare.  Multiple years of data collection will be important to confirm the patterns we saw this first year.

There were really only two kinds of wildflowers that attracted the vast majority of nectaring regal fritillaries through the 2010 season, and both are usually called weeds.  The first was hoary vervain (Verbena stricta) and the second was a small group of thistle species – primarily Flodman’s thistle (Cirsium flodmanii) and tall thistle (Cirsium altissimum).  Hoary vervain is a native wildflower that is largely considered to be a pasture weed by many people because it thrives in overgrazed situations.  Cattle don’t like to eat it and it can spread quickly when the surrounding grasses are weakened.  (However, it also decreases in abundance very quickly when the grasses regain their vigor.)  Flodman’s and tall thistle are two native thistles that are also considered to be weedy plants, and that do well in overgrazed pastures.  The third favorite plant was actually several species of milkweeds lumped together (primarily weedy species like Asclepias syriaca and A. speciosa).

During the early part of the summer, the majority of regal fritillaries nectaring on flowers chose hoary vervain.

In late summer and early fall, vervain largely stopped blooming and other species became more important for nectaring, particularly native thistle species.

Most of our data collection centered on regal fritillaries, but we also collected data on other butterfly species.  So far, there doesn’t appear to be much difference in the nectaring preferences of regals and the larger butterfly community.  During the early part of the season, hoary vervain was the primary choice for most butterflies and a variety of other species got only infrequent visits.  Later in the season when hoary vervain was largely done blooming, thistles and a few other species, including wild bergamot – aka monarda or Monarda fistulosa and rosinweed (Silphium integrifolium), shared the load.

Observations of early summer nectaring across all butterfly species showed that hoary vervain was the dominant selection for nectaring.

Later in the season, other flower species split the nectaring observations fairly evenly.

One of the most interesting aspects of doing this research on butterflies has been that I’ve been able to look at our prairies through the eyes of butterflies – and that’s given me some surprising insights.  Our remnant prairies are largely degraded by years of overgrazing and broadcast herbicide use, and we’ve been working to slowly bring them back to higher floristic quality.  I’ve assumed that increasing floristic quality would also be good for many other species, including butterflies.  In addition, we’ve worked very hard at getting the highest plant diversity we can into our restored (reconstructed) prairies.  While we’re not restoring those prairies for butterflies, specifically, I’ve always assumed that butterflies would benefit from high plant diversity.  From our very preliminary data on butterflies, it appears that while our restored prairies have many more flower species, including many showy species, they may not be providing any better nectaring opportunities than our remnants!  The flower species most used by regal fritillaries and other butterflies are hoary vervain and thistles, which are at least as common in our remnants as in our restorations.

Regal fritillaries, and other butterflies, seem to rely heavily on hoary vervain for nectar in our Platte River Prairies.

I’m confident that there many other benefits of the plant diversity in our restorations, of course, including the availability of a variety of larval host plants for butterflies.  But it’s a little humbling – and intriguing – to see butterflies relying on plant species that do well in beat-up pastures rather than flocking to our showy restored prairies!  It’s important, of course, not to extrapolate these results to other parts of the country.  I’m not saying that regal fritillaries can survive in beat-up pastures in eastern states.  If that was so, we’d have many places in the east with lots of regal fritillaries.  Nebraska and other western states with high numbers of regal fritillaries also have landscapes with relatively high amounts of native prairie – and that may be the most important factor for regal fritillary survival.

The other lesson from our early data seems to be that the value of “weedy” species shouldn’t be discounted just because they thrive in conditions many flower species can’t take.  Vervain and thistles could be the primary plant species supporting our butterfly populations along the Platte River right now.  That’s a pretty good argument for being valuable.  In addition, the violet species that the regals must be using as a larval food plant along the Platte is considered to be relatively weedy because it does well in degraded pastures.  I’m sure glad we have a lot of it – and so are regal fritillaries!  Other weedy plant species have value as well – apart from their obvious role in filling space when “good” plants are weakened by fire, grazing, or drought.  The seeds of native ragweed and annual sunflower species, for example, seem to be excellent food sources for many small mammals and birds (judging from the density of tracks around the plants when it snows).

I’m really looking forward to next season’s butterfly transects.  I enjoyed reacquainting myself with butterflies last summer, and it was good for me to look at our prairie work through a different lens.  I’m sure we’ll learn more as we collect and analyze more data.  In the meantime, we (and our butterflies) will continue to enjoy and appreciate our weeds.

A big thank you to Dr. Ray Moranz for his assistance setting up this project.  Also, Mardell Jasnowski directed most of the data collection in 2010, with help from Nanette Whitten, Nelson Winkel, and Natalie Goergen.