Monthly Archives: August 2011

Lessons from a Fenceline

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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?

Photo of the Week – August 26, 2011

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I photographed these butterflies (numerous photos below) last weekend at our family prairie.  Besides being very pretty, they and the flowers they’re feeding provide an interesting insight into the way biologists sometimes see the world.

Painted lady butterfly near Stockham, Nebraska.

Painted lady butterflies are very common and ubiquitous species found on several continents.  They’re found equally often in prairies and urban gardens, so they’re considered to be habitat generalists.  There’s nothing wrong with painted lady butterflies, but they’re not as exciting for a biologist to see as, say, a Ottoe skipper, which is a rare butterfly that is restricted to native prairies.  There’s an extra thrill in seeing a species like that because of their rarity, but also because the presence of specialist species like the Ottoe skipper can be an indication that a prairie has sufficient size and ecological function to maintain even the most sensitive of species.  Painted ladies are very pretty, but don’t provide that extra little adrenaline rush for biologists.

The butterflies in these photos are feeding on Baldwin’s Ironweed (Vernonia baldwinii) which is similar to the painted lady butterfly in terms of its abundance and generalist habits.  Ironweed is rarely grazed by cattle and so is common in prairies that have been chronically overgrazed to the point where most other wildflowers have disappeared.  It also moves across the landscape easily, so it is often found in old fields (crop land left idle) and other “weedy” habitats.  Many people, in fact, consider ironweed to be a weed, which isn’t really fair since it’s not aggressive at all – it’s just good at filling open space left by intensive grazing, tillage, drought, and other events that reduce the vigor of dominant prairie plants.  While ironweed can exist in prairies that are full of much more specialist and rare plant species, its ability to grow almost anywhere else as well means that its presence is not a good indicator that a prairie is in “good shape” ecologically.

While neither painted lady butterflies nor ironweed are great indicators of whether or not prairies have a full complement of species and ecological processes, both are important components of prairies.  Ironweed can provide nectar and pollen, for example, in prairies that are missing most other wildflower species.  Similarly, painted lady butterflies can provide some pollination services in prairies that might be missing many other pollinator species.  In addition, both species are aesthetically pleasing!  Sometimes it can be hard for biologists to remember how valuable generalist species are – and to step back and enjoy their presence, rather than dismissing them as somehow less important or exciting to see than other species.  There’s clearly much to be admired about generalists.  They’re successful in a world that makes it difficult for many other species to survive.  What’s not to like about that?

Some people probably have a hard time understanding why biologists would have this almost dismissive view of generalist species.  Here’s my best explanation.  Few people would pay to go to a zoo full of species such as squirrels and robins.  Those species can be seen almost anywhere.  Zoos make money because they can show people species like polar bears, pandas, and crocodiles that can’t easily be found elsewhere.  That’s kind of what it’s like for biologists when we see generalist species.  It’s not that we don’t appreciate them (I like watching squirrels in my yard – except when they’re stealing apples from my tree) but we see them all the time.

One of the great things about being a photographer, as well as a scientist, is that I get the opportunity to see the natural world from two different perspectives.  Each helps balance and inform the other and, I think, makes me better as both a scientist and photographer.

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