How Small Is Too Small?

What’s the minimum effective size of a prairie?

For example, can a prairie be the size of a kitchen table?  Let’s say someone converted a landscape full of prairie to an immense gravel parking lot, leaving only a round kitchen table-sized parcel of vegetation in the middle.  Is that tiny isolated parcel a prairie?

The question might seem silly, but the question became a useful little thought experiment for me.

That little parcel certainly wouldn’t be big enough to meet the needs of most prairie animals.  Birds, small mammals, snakes, and even smaller creatures like grasshoppers and bees would be unable to find enough food to survive within that small area.  The loss of those animals would affect many of the ecological services and functions that make prairies work.  Those services include pollination, nutrient cycling, herbivory and more.

Even small creatures like grasshoppers would have a hard time surviving in a patch of plants the size of a kitchen table.

Some tiny herbivorous invertebrates might be able to survive in that little parcel of vegetation, but probably not enough of them to support most predators that feed on them.  The lack of predation would allow those invertebrate populations to grow much larger than they otherwise would, leading to significant damage, or even mortality, to the plants they feed on.  Once their food is gone, the invertebrates would starve and die as well.

Plants that manage to survive invertebrate attacks and an absence of pollinators in our little parcel would still face major challenges.  In the long-term, they would probably suffer from a huge genetic bottleneck because they don’t have other individuals of their species to cross breed with.  In the meantime, it would take a lot of intensive and thoughtful management to keep them alive.

Smooth brome and other invaders can quickly dominate small prairie patches without constant vigilance and suppression.

Invasive species management would be a huge problem because it wouldn’t take long for an aggressive invader to quickly dominate that small area.  Quick action would be needed to remove invasive plants as they arrive.  Fire or mowing would also be needed to prevent a smothering thatch from accumulating as plants grow and die back each year.  Unfortunately, every fire would kill most invertebrates aboveground at the time and destroy their food sources.  We could try to burn only a portion of the parcel and save some of the insects, but with such small populations, we’d still probably lose most species eventually.  Mowing and raking might be an alternative, but we’d still end up removing either the invertebrates or their food sources.

Ok, so we’d just have to live without most prairie animals, but we’d still have plants.  Or at least a few of them.  Some of those plants would be more competitive than others, especially in an animal-less environment, so it would take a lot of effort to keep them from pushing the less competitive plants out.  And, of course, we’re assuming the mysterious belowground processes that allow plants to survive would still function in our tiny parcel – microbial relationships that allow plants to access and process water and nutrients, for example.  If those are sufficiently intact, we’d have some plants.

Would that be a prairie?

I’m pretty sure no one would argue that a kitchen table-sized area containing few plants is a prairie.  Even in the first moments after the parking lot was created, I would argue the remaining patch of vegetation had ceased to be a prairie, even though it still contained a reasonable diversity of plants and animals. It wasn’t really a prairie anymore, just a doomed fragment of its former self.

If we can agree that a kitchen tabled-size patch of land is too small, how big would we have to make that patch before we’d be willing to call it a prairie?  What species and/or ecological processes should we use as criteria?

Can we agree a prairie needs to be big enough to support a healthy pollinator community?  Does it need to be able to sustain viable populations of small mammals, snakes, leafhoppers, spiders, and other little creatures?  Is it a prairie if it doesn’t have a full complement of grassland bird species?  Does that requisite bird community include larger birds such prairie chickens or other grouse species?  What about at least moderately-sized predators such as badgers and coyotes (or even bigger ones) or large ruminants like bison or elk?  Which of those components are we willing to live without, and more importantly, which can a prairie live without and still sustain itself as an ecological system?  A prairie without badgers, coyotes or bison is functionally different than one with those animals, but is it a non-prairie or just a different kind of prairie?

Bison herds need very large prairies, but we don’t know as much about the amount of land needed to sustain populations of bees, leafhoppers, jumping mice, or even genetically viable plant populations.

Even if we reach consensus on the key components of a prairie, we’re still hamstrung by our lack of information about how big a prairie needs to be to support each of them.  We have decent data on the prairie size requirements for many grassland bird species, but beyond birds, we’re mostly just guessing.  If we want the full complement of species, including bison and other large ruminants, we’re going to need thousands of acres, but how many thousands?

More importantly, what does this mean for the many remaining patches of prairie vegetation too small to support whatever we decide are the key components of a prairie?  It certainly doesn’t make them worthless, but it might be important to make sure we’re viewing them realistically.  What are the likely ramifications of the missing components?  The absence of prairie chickens or upland sandpipers might be disappointing, but might not have the ripple effect that the absence of pollinators or coyotes might have.  Can we identify and compensate for the absence of key prairie components by managing differently or more intensively?  If not, how do we adjust our vision of the future for that prairie parcel, and how does that adjusted vision affect how much management effort we invest?  (You can read more about the challenges of managing small prairies here.)

For many of today’s small prairie patches, the only chance of preserving their species and ecological functions is to make those small patches larger and/or more connected to others.  Restoring adjacent land back to high-diversity prairie vegetation allows formerly landlocked populations to expand and interact with others, and creates enough habitat for larger animals to survive.  Identifying potential restoration opportunities might be the highest priority conservation strategy for those of us working with small prairies.

Reasonable plant diversity and the presence of larval host plants like this prairie violet have so far allowed our family prairie to support a population of regal fritillary butterflies, but the small size and isolated nature of our prairie means if the butterflies have a bad year, they could easily disappear and never return.

Our family prairie is a little over 100 acres in size, is managed with large ruminants (cattle), and has regal fritillary butterflies, coyotes, badgers, upland sandpipers, and even an occasional prairie chicken.  However, I’m certainly not comfortable that our 100 acre island within a sea of cropland will to sustain a prairie ecosystem indefinitely.  This thought experiment has forced me to think more seriously about prospects for increasing the size of our prairie and building connectivity to other grasslands.  I hope it’s useful to others as well.

Monarch Conservation Strategies

Last week, I attended a conference aimed at creating a statewide conservation plan for monarch butterflies.  The meeting was really informative and thought-provoking.  I learned a great deal about the ecology and conservation needs of monarchs from Chip Taylor of Monarch Watch and others, and was part of some good discussions about potential strategies to help the species recover.  I thought I’d share some of what I learned from those discussions because they helped me better understand the issues surrounding monarch conservation.  Any errors in the following are a result of my misunderstanding what smart and knowledgeable people told me, and I apologize in advance.


Monarch butterflies on a summer morning.  The Nature Conservancy’s Platte River Prairies, Nebraska

Monarch Migration

The monarch butterfly is a migratory species, but it takes multiple generations to make the migration from parts of North America to Mexico and back.  Here in Nebraska, we’re part of the Eastern Population of monarchs, which extends from roughly the east edge of the Rocky Mountains to the east coast.  The butterflies in this population leave their Mexico wintering grounds in late February each year and head north.  They lay eggs in the southern United States and the monarchs produced by those eggs then head north into the northern half of the U.S. and the southern edge of Canada during May and early June.

During the summer, there are a couple generations of monarchs that mature and lay eggs without migrating.  However, in mid-August and September, monarch adults get the urge to migrate and start heading south.  Those that survive the trip usually reach the Sierra Madre Mountains of Mexico by early November.


This migratory monarch is fueling up on a native thistle.  Thistles are among the top food sources for monarchs and other butterflies.  Allowing non-invasive thistles to persist in natural areas is an important part of pollinator conservation efforts.

Threats to Monarchs

There are two categories of threats to Monarchs: 1) Factors we can control, and 2) Factors we can’t.  The big factor we can’t control is weather and the way it interacts with migration timing and butterfly survival.  Weather can have a tremendous impact on butterflies, and many millions of butterflies are killed by hot weather, storms, or other events.  However, since we can’t control the weather, we have to focus on what we can control.

There is a long list of human-induced factors that affect monarch populations.  Those include the conversion of grasslands, roadsides, and field edges to row crops (largely facilitated by government policies) as well as farming practices that have nearly eliminated milkweed from farm fields.  Pesticide use is another factor, including pesticides used for farming and pesticides used for other purposes, including mosquito control.  Logging of forests in the wintering grounds of Mexico is another important issue.

I’d heard that the loss of milkweed from crop fields was a big deal for monarch butterflies, but hadn’t really understood why.  At the conference, we heard that research has shown that about four times as many eggs/plant are laid on milkweed plants in crop fields as on milkweed plants in other habitats.  (I’m not sure anyone understands why.)  In addition, while the eastern population is spread across a huge area of North America, about 50% of the butterflies that reach Mexico are born in the cornbelt of the U.S. – the intensively farmed Midwestern states.  Prior to the widespread use of glyphosate-resistant crops, milkweed was a pretty common inhabitant in crop fields throughout this prime breeding area for monarchs.  Now that farmers are so much more efficient at weed control, we’ve lost the most productive egg-laying habitat in the country’s most important breeding area for monarchs.

Conservation Strategies

Because monarchs can only be raised on milkweed, getting more milkweed plants in the landscape, especially within the cornbelt states, is a key part of increasing the monarch population.  It’s likely that more than a billion additional milkweed plants will be required to stabilize the monarch population.  Increasing milkweed populations to that extent will require a wide range of strategies.  In addition, protecting and restoring the wildflower-rich grasslands and other natural areas that provide food for adult monarchs, as well as for thousands of bee and other pollinator species, is also vitally important.

Swamp milkweed

It is critically important to increase the number of swamp milkweed (Asclepias incarnata) and other milkweed species available for monarch egg-laying.

One clear strategy is to plant more of monarchs’ favorite milkweed species in gardens, parks, roadsides, nature centers, and many other sites.  In the north-central U.S., milkweed species such as common (Asclepias syriaca), showy (A. speciosa), and swamp milkweed (A. incarnata), are known to be favorites, while green antelope horn (A. asperula) is important in more southern states.  You can find sources of seeds and plants at Monarch Watch or from the Xerces Society’s Project Milkweed website.  Sites like can help with garden and landscape design ideas.

More milkweed in gardens and landscaping can make a big difference, but an even bigger part of monarch recovery needs to come from a change in the way milkweeds – and the weedy, edge habitats they thrive in – are perceived by the public.  Elimination of milkweed from roadsides, field edges, and odd corners and margins of our landscapes happens because we are uncomfortable with the “messiness” of those areas if they aren’t frequently mowed and/or sprayed with herbicides to make them look uniform in height and composition.  Allowing milkweed and other wildflowers to thrive in those odds-and-ends habitat areas can have a huge impact on monarchs and other pollinators, along with pheasants, song birds, and many other wildlife species.  Reducing mowing frequency and spot-spraying truly invasive plants – instead of broadcast spraying to kill anything that’s not grass – in these habitats saves both money and time as well.


“Sanitized” monoculture roadsides like this offer no benefit to monarch butterflies or other pollinators.  We need to change our cultural aesthetic and acknowledge the value and beauty of roadsides that actually offer habitat values to monarch butterflies, pollinators, pheasants, and other wildlife and invertebrate species.

The Role of Prairies?

Last week’s meeting also encouraged me to focus even harder on an additional aspect conservation I’ve already been working on – improving the contributions of native prairies and rangeland to pollinators.  The experts at our meeting, along with other sources of information on monarchs, seem to be focused largely on milkweed and the kinds of farm fields, edge habitats and landscaping mentioned above.  While all those are very important, I can’t help but think about the value of native prairies – especially in places like Nebraska where we still have millions of acres of grassland.

Milkweed in prairies

Many of our restored Platte River Prairies maintain milkweed populations for many years after establishment, even under fire and grazing management.  Figuring out what management strategies facilitate survival of milkweed may be a very important part of successful monarch conservation.

A healthy prairie with a diverse wildflower community is invaluable to bees and other pollinators, and also provides nectar resources needed by monarch butterfly adults.  If that prairie contains vibrant populations of milkweed species that provide egg-laying habitat to monarchs, that’s even better.  Many prairies don’t currently have strong milkweed populations.  Some milkweed species are not strong competitors in a tight-knit plant community, and certain grazing and other management practices tend to further discourage milkweeds.  Over the next several years, I am hoping to learn more about how to make prairies support stronger milkweed/monarch populations.  Hopefully, we and others can help make North American prairies even better contributors to the survival of monarch butterflies.