Prairie Response to Grazing and Drought

Fire, grazing, and drought are the three dominant forces that shape(d) our prairies over time.  Because of the drought we experienced last year, many of our prairies experienced all three of those forces in the same season.  We manage most of our sites with variations of patch-burn grazing.  After we burn a portion (patch) of prairie, cattle concentrate their time within that burned patch, grazing it much more intensively than other portions of the same prairie until a new patch is burned.  As a result, the dominant grasses are much weakened by the end of the season, temporarily opening space for opportunistic plants of many species.

Showy evening primrose is prominent among a number of profusely blooming plants in this restored prairie that was burned and intensively grazed during last year's drought.  The Nature Conservancy's Platte River Prairies, Nebraska.

Showy evening primrose is prominent among a number of profusely blooming plants in this restored prairie that was burned and intensively grazed during last year’s drought. The Nature Conservancy’s Platte River Prairies, Nebraska.

The patch of prairie in the above photo is not being grazed this year, which will allow the dominant grasses – still present, but much reduced in size and vigor – to recover.  In the meantime, butterflies, bees, and other pollinators are enjoying an abundance of “weedy” flowers such as hoary vervain (Verbena stricta), showy evening primrose (Oenothera rhombipetala), yarrow (Achillea millefolium), upright prairie coneflower (Ratibida columnifera), black-eyed susan (Rudbeckia hirta), and many others.  At the same time those pollinators can still find their regular fare of more “conservative” long-lived perennial forbs (prairie clovers and other legumes, perennial sunflowers and silphiums, etc.) – they are just visually obscured by the species responding positively to last year’s grazing and drought.  If you’re interested, you can see some plant data from this site from a couple years ago that shows some trends in species frequency and floristic quality over time.

Here’s another photo of the same patch prairie, showing the diversity and abundance of opportunistic wildflower species and a thin, weakened (temporarily) stand of grass.

Another shot from the same prairie as above.

Another photo from the same prairie.

One of the aspects of fire/grazing management I enjoy most – and one that can make some people uncomfortable – is the variability in prairie response between years and between sites.  Every time we burn/graze a prairie, we see somewhat different responses from the plant community, even if we’re using very similar timing and stocking rates each time.  I think that’s great, and that it adds to the kind of messy, dynamic diversity I think is important in natural systems.  That messiness helps prevent any species or group of species from becoming too dominant, but also helps ensure that each species has the opportunity to thrive and reproduce now and then.

Griffith Prairie (owned and managed by Prairie Plains Resource Institute of Aurora, Nebraska).  The area shown in this photo was burned and grazed during the drought of 2012 in a way very similar to the prairies shown earlier.  However, the plant community response at Griffith was very different - including a big flush of deer vetch (Lotus unifoliatus) and abundant reproduction of leadplant (Amorpha canescens).

Griffith Prairie (owned and managed by Prairie Plains Resource Institute of Aurora, Nebraska). The area shown in this photo was burned and grazed during the drought of 2012 in a way very similar to the Platte River Prairie shown earlier. However, the plant community response at Griffith was very different – including a big flush of deer vetch (Lotus unifoliolatus) and abundant reproduction of leadplant (Amorpha canescens), among other things.  Visually, the prairie is very flowery this year because the vigor of the dominant grasses is suppressed from last year’s drought/grazing.

These days, I spend quite a bit of time thinking about the scale and arrangement of our management treatments across the landscape.  For example, I’m not sure how big each of our within-prairie habitat patches should be.  I don’t think it matters much to plants, but habitat patches have to be large enough for animals to live in, yet small enough that wildlife and insects don’t have to travel unreasonable distances to find appropriate habitat when conditions change from year to year.  For example, voles living in a thatchy patch of unburned prairie will have to relocate when that patch gets burned.  How far can they travel to find another patch of unburned prairie?  What kinds of habitat do they need as they make that trip?

For now, we’re just doing what seems reasonable, but I’ll feel better if we can get some data to help us better evaluate the travel abilities of insects, snakes, small mammals, and others.  Anybody looking for a career’s worth of research projects?

The Role of County Weed Officials in Prairie Conservation

This week, I’m giving a presentation on the impacts of drought to the 2013 Nebraska Weed Control Association’s Annual Conference – a statewide training session for county weed superintendents.  In some parts of the country, weed control agents and prairie ecologists don’t always see eye to eye.  One man’s weed is another’s wildflower, after all.  However, in Nebraska, I think county weed superintendents are truly on the front lines of prairie conservation.  

Wildflowers or weeds?

Wildflowers or weeds?  It’s important that weed control officials and prairie ecologists see the world in similar ways.

Many people in Nebraska have a fairly cynical view of weed superintendents.  The stereotypical “county weed guy” drives around in his spray truck, indiscriminately spraying roadsides and other wildflower habitat – or, alternatively, just sits around all day and ignores the hordes of musk thistles growing along the road he travels between home and office.  However, apart from the fact that many “county weed guys” are actually female these days, I’ve found those broad stereotypes to be far from accurate.  In fact, my interactions with weed superintendents have been very positive, especially over the last five years or so, and I’ve been impressed with their knowledge of and interest in ecology and conservation.  (Though there are a few exceptions who may somewhat resemble the aforementioned stereotypes.)

I think weed superintendents are on the front lines of conservation for two reasons.  First, they are increasingly collaborating with each other through multi-county Weed Management Areas to develop and implement large-scale and effectve strategies for controlling invasive plants.  Second, they are often the first person a landowner calls when he or she has a concern about some plant “taking over the pasture”.  One of my priorities over the last several years has been to help ensure that when that call comes in, the superintendent can identify the “aggressive” plant species, understand why it is becoming abundant, and prescribe an appropriate response.   

Many times, the problem weed turns out to be a native plant responding to a grazing strategy, rainfall pattern, or something else that has temporarily altered the competitive balance of the plant community.  A slight tweak to the management of the pasture or hay meadow can often reduce the abundance of the “weed”.  Other times, the abundance of the plant species will diminish on its own, especially as rainfall patterns change. 

A confident and well-informed weed superintendent can help a landowner become comfortable with the role and importance of “opportunistic plants” on their land.  When that kind of common sense advice is not available, native prairies tend to get broadcast sprayed for non-problematic plant species such as ragweed, annual sunflower, or hoary vervain.  A weed superintendent’s ability to help prevent that kind of catastrophic overreaction is a critical component of prairie conservation work in Nebraska.

The current drought conditions are surely going to increase the number of calls coming in to weed superintendents this year.  Perennial grasses were severely weakened last year, and that is going to open abundant space for lots of opportunistic plants.  Many landowners will assume their pastures and hay meadows are being taken over by a cast of aggressive weeds.  Weed superintendents can help landowners keep things in perspective and let those opportunistic plants do their job. 

During the droughts of the 1930's, heath aster exploded in abundance across many prairies.  Sudden drastic changes in plant composition can be downright scary for landowners, making it crucial to have weed superintendents and others who can explain what's going on and offer good advice.

During the droughts of the 1930’s, heath aster exploded in abundance across many prairies. Sudden drastic changes in plant composition can be downright scary for landowners, making it crucial to have weed superintendents and others who can explain what’s going on and offer good advice.

County weed superintendents in Nebraska tend to be underappreciated, underpaid, and overworked.  Despite that, many go the extra mile to be thoughtful, strategic, and proactive in their approach to invasive species control.  Saving prairies isn’t part of the official job description of a weed superintendent, but it may be their most important contribution.

I’ve spent a fair amount of time over the last several years helping to train weed superintendents in plant identification and ecology, and have found them to be enthusiastic listeners and strong partners.  If you are a prairie manager or ecologist and haven’t engaged with your local weed control official, I strongly encourage you to do so.  You might be surprised at the result.