Monthly Archives: November 2010

Goldenrod – Pretty Flower or Evil Invader?

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Recent update.  If you are looking for information on how to reduce the abundance or dominance of tall goldenrod, here’s a great post from the Grassland Restoration Network you might find useful.

When did goldenrod become such a bad plant?  It’s really quite attractive, I think.  It’s a signature plant of the late summer/early fall prairie.  Yes, some species can form fairly dense patches and can take advantage of a weakened grass stand to get a quick foothold.  But would we complain if compass plant did the same thing?

Canada goldenrod and big bluestem at Griffith Prairie (a preserve of Prairie Plains Resource Institute).

Some people mistakenly blame goldenrods for hay fever. That, at least, is an easy illusion to dispel.  The bright colorful flowers and the abundance of pollinating insects crawling all over them clearly indicate that goldenrods are insect pollinated, not wind pollinated like ragweeds and other hay fever-causing species.  So spread the word… goldenrod doesn’t make you sneeze.

Apart from the hay fever myth, though, there are some prairie ecologists who are struggling with how to categorize and treat goldenrod in a prairie plant community.  There are, of course, many species of goldenrod – including some very rare prairie and savanna species.  Most people are fine with categorizing those as species in need of conservation.  I’m talking about some of the taller and more prolific/common species like Canada goldenrod and stiff goldenrod.  Even Missouri goldenrod (which, ironically, is the state flower of Nebraska) gets occasionally thrown into the “down with goldenrod” conversation.

One issue with these goldenrods is that they are very effective colonizers.  Their windblown seeds can disperse widely and can quickly establish in bare soil and/or in places where competition from other plants is light.  And, unlike many other colonizers (ragweeds, hoary vervain, black-eyed susans, and many annual plants) goldenrods don’t typically fade away in the face of competition from perennial grasses.  These characteristics make them a staple plant of old fields – cropfields that are allowed to stand idle and be colonized by whatever species can do so.  That’s an ideal situation for goldenrods, and they can quickly become one of the dominant species in an old field.  Many prairie restoration (reconstruction) projects that attempt to convert those old fields to prairie vegetation have found that simply tilling those old fields and seeding into them doesn’t work well because of overwhelming competition from goldenrods and other old field species that have built up populations and seed banks.  However, that’s not a knock on goldenrod, it’s a failure to properly prepare the seed bed for the restoration project.  When seeding into a site that’s been repeatedly cropped and doesn’t have a history of goldenrod populations, goldenrod is usually much less of an issue.

The colonizing ability of goldenrods gets them in bad with ranchers as well because if cattle grazing continually weakens the dominant grasses in a pasture, space opens up for the establishment of other plants.  Species like goldenrod that are not very palatable to cattle do particularly well in those circumstances.  And, again, once they establish, their ability to survive even when the grass regains its vigor sets them apart from other species like hoary vervain and ragweed, which tend to fade quickly.  Once they’re abundant they look like some kind of noxious weed, and it’s not uncommon for prairies to be sprayed to control goldenrod – a native wildflower.

So, which is it?  Are these goldenrods showy wildflowers that provide valuable resources to pollinators in the fall?  Or are they plants gone bad and in need of suppression?  Maybe both – depending upon the situation.  What I’ve seen in Nebraska prairies is that these goldenrods can look very abundant when they’re blooming, but the prairie community around them maintains its diversity pretty well, and the goldenrod tends to plateau at a certain density and not get to the point where it forms large monocultures.  But I’ve seen restored prairies in places like Illinois where it sure looks like goldenrod is dominating the plant community to the detriment of other species.

Goldenrod… pretty fall flower or aggressive invader of prairies?

If goldenrod needs control in some situations, what’s the best technique?  It doesn’t seem to be suppressed by dormant season fire.  Broadcast herbicide spraying is almost certain to be counterproductive both because it destroys the much of the larger plant community and because goldenrod will almost certainly benefit more than other species from that suppression of competing plants.  The fact that goldenrod is not palatable to cattle might mean that it’s susceptible to repeated defoliation (mowing, etc.) or prescribed fire during the growing season.  Has anyone had luck with that?

I’d like to hear about examples of goldenrod gone bad, successful or failed attempts to suppress it, or passionate defenses of these pretty flowers…  Just leave a comment below.

Measuring Success in Prairie Conservation – Species Composition vs. Structure and Process

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Stick with me – this isn’t as complicated as the title might lead you to believe…

I was involved in an interesting discussion a couple weeks ago among some fellow prairie ecologists about what makes a “good prairie”.  The discussion brought into sharper focus something I had thought a lot about but only in general terms.  Here is the discussion – with some over-simplification of the respective positions:

Position A – Species Composition:

A high quality prairie (tallgrass prairie, in this case) can be judged largely by its plant species composition.  A “good” prairie might have 20 or 30 plant species per square meter, for example, and more than 100 species per acre – including a mixture of both common and rare species.   Besides the value for the direct conservation of species, that kind of plant diversity provides multiple ecological benefits.  More plant species means more choices for animal species that rely on them as food and/or habitat resources, as well as a more consistent supply of those resources through the season – because some plants will always be emerging/blooming as others go dormant.  Because of that, prairies with lots of plant species tend to have lots of insect and other small animal species as well.  In addition, prairies gain resilience from plant species diversity, because if multiple species fill similar ecological roles the prairie community can better withstand the temporary decline of some species due to drought or pest outbreak.   A prairie that is missing many of its species, or that is dominated by a few species with only scattered small populations of others, can’t be considered to be of high quality or to be “conserved.”

A diverse prairie at the Madison Arboretum – Madison, Wisconsin.

Position B – Structure and Process:

What really defines successful grassland conservation is the presence of large-scale and intense disturbances (e.g. fire and grazing).  The combination of fire and grazing shaped historic prairies and that combination is needed today to maintain them.  Without fire, prairies lose integrity in several ways – the most obvious being the encroachment of trees that fire otherwise suppresses.   Fire also helps drive the cycling of nutrients and regulates the amount of standing dead vegetation and thatch in prairies.  Furthermore, the high-quality of the fresh vegetative regrowth following a fire attracts intense grazing by herbivores large and small.  Historically, there would have been few cases where a prairie would burn and not be intensively grazed right afterwards.  That intense grazing suppresses dominant prairie grasses, opening up space for the abundant growth of weedy vegetation once the grazers move on.  As the prairie recovers, the dominant grasses reassert themselves and the vegetation becomes tall and dense enough to carry fire once more.  A landscape consisting of a heterogeneous mixture of recently burned patches and patches that haven’t burned for several years provides the full range of habitat structure – from very short to very tall – and thus supports the full range of prairie wildlife species.  Perhaps most valuable in that range of habitat structure is the post-fire/grazing recovery phase that provides simultaneously provides a wealth of stemmy vegetation cover and abundant seeds for wildlife food.

An expansive prairie landscape in the Nebraska sandhills.

So is Position A or Position  B correct?  Well, yes.  It’s like owning a sports car.  You need to keep all the sparkplugs, tires, and other parts – and keep them in good condition.  On the other hand, a sports car is no good if you can’t drive a standard transmission and/or don’t have good roads to drive on.  Aldo Leopold said, “To keep every cog and wheel is the first rule of intelligent tinkering” – but those important components include both species and the processes that maintain them.

Interestingly, the two positions seem to be strongly correlated with geography.  People who work with the fragmented tallgrass prairies in Midwestern States like Illinois, Wisconsin, and Indiana tend to fall more heavily in the first camp – emphasizing species composition.  In contrast, people who work in the large expanses of grassland in Oklahoma, Kansas, western Nebraska, and the Dakotas, tend to hold Position B – emphasizing process and structure.  In both cases, the positions are reasonable based on the local situation.  In the eastern tallgrass prairie, most of the prairie is gone, so any remaining grassland is precious and there is great concern about the loss of prairie plant and insect species.  Further west, where grasslands still dominate the landscape, there is much less concern about the loss of plant and insect species and more focus on larger wildlife like prairie chickens that require a range of habitat conditions not always found in those ranching-dominated landscapes.

As usually happens in a discussion among reasonable people, a partial consensus emerged in ours, and there was general agreement that neither Position A or B was sufficient by itself.  Proponents of species composition as the measure of prairie conservation success would surely not be fully satisfied with a flowery prairie that was missing species like prairie chickens, upland sandpipers, and bison.  They just don’t often have the opportunity to work with grasslands large enough to support all of those species.  Likewise, proponents of structure and process wouldn’t be happy with 20,000 acres of switchgrass just because it had a heterogeneous mix of fire and bison grazing and lots of prairie chickens.

The point here is not that we need to subscribe fully to either Position A or Position B, but that we can’t afford to ignore either one.  Those working in the fragmented eastern tallgrass prairie need to be sure to emphasize strategies like prairie restoration that can strategically convert crop fields back to prairie vegetation and enlarge remnant prairies to the point where they have a chance of supporting prairie chickens and upland sandpipers, if not bison.  And even at smaller scales, finding creative ways to reintroduce the combination of fire and grazing, where possible, may help provide better wildlife habitat – and might even pay dividends for plant species conservation (more discussion on this in posts to come.)

Meanwhile, ecologists with the luxury of large unplowed expanses of native grassland need not to forget the importance of restoring and/or maintaining both large-scale and small-scale plant diversity.  While adequate habitat structure for species like prairie chickens can be created in a landscape dominated by grasses and weedy forbs, pollinators and many other insects may have a much more difficult time surviving there.  In addition, whether the intervening landscape is dominated by grass or corn, small isolated populations of prairie forbs (and the insects that rely on them) aren’t likely to survive forever if they’re not able to cross pollinate or otherwise interact with each other.  Native bees that have to find consistent sources of nectar within a small radius from their nest rely on small-scale plant diversity to provide abundant blooms every day of the growing season – and pollination by those bees is critically important for the survival of many plant species.  Finally, proponents of process should recognize and appreciate the potential (but understudied) values associated with a diverse plant community – including a diverse and vigorous soil fauna, and the overall resilience offered by a mix of species that provides redundancy of ecological function.

The danger for all of us is that we tend to look at prairie conservation through a cultural lens – and we sometimes don’t see what our prairies, and our strategies, are missing.  It would be great if we could facilitate some cultural exchanges, in which we sent Texas cowboys to the Illinois black soil prairies and Wisconsin prairie restoration experts to the flint hills of Kansas.  Imagine the discussions that would ensue – not to mention the neighborhood coffee shop gossip.

Participants in the Grassland Restoration Network discussing prairie conservation at The Nature Conservancy’s Nachusa Grasslands, Illinois.

I feel fortunate to be involved in two groups that do a great job of stimulating interaction and discussion – the Grassland Restoration Network and the Patch-Burn Grazing Working Group.  The former is a loose affiliation of ecologists working to use prairie restoration as a tool for grassland conservation in fragmented landscapes.  The latter is a network of scientists, land managers, and ranchers trying to find better ways to combine fire and grazing and create heterogenous prairie landscapes.  (I’ll provide more information on both of those groups in future blog posts.)  Now if I can just figure out how to convince the two groups to hold a joint meeting…