Now You See Them, Now You Don’t (But They Might Still Be There!)

Grazing, especially by goats and/or sheep, is often promoted as a control method for weeds or shrubs.  Depending upon the life strategy of the weeds being targeted, grazing can be effective, but it’s important to set realistic objectives.  As you might expect, many perennial grasses, forbs, and shrubs have evolved strategies for surviving repeated defoliation.  In those cases, grazing may appear to effectively control plants while grazers are present, but the plants bounce back right after grazers are removed.

One of my all-time favorite research projects showcases this exact phenomenon at a site in South Dakota owned by The Nature Conservancy.  Back in the early 1990’s, an estimated 75% of the Conservancy’s Altamont Prairie Preserve was covered by leafy spurge (Euphorbia esula).  In 1994, goats and sheep were installed in separate pastures and spurge was treated by using periodic high-intensity grazing sessions during both early summer and early fall.  Both the goats and sheep were very effective at eating the spurge plants, and after five years, managers conducting walk-through inspections the site felt like excellent long-term control of spurge had been achieved.  Inside small exclosures, spurge was still abundant and vigorous, but outside the exclosures, almost no plants could be seen.  As a result, the goats and sheep were removed and everyone was happy.

One of the goats used at Altamont Prairie and an exclosure showing a dramatic difference between abundant and blooming leafy spurge in ungrazed areas and no apparent spurge in grazed areas. Photos courtesy of TNC’s Minnesota, North Dakota and South Dakota Chapter.

…Until the next season when spurge plants popped right back out of the ground and the pasture looked essentially as it had before the grazing treatment had started.  In dismay, the managers looked for another option and decided upon flea beetles (Apthona spp.), which ended up being a much more successful choice, greatly reducing the footprint of leafy spurge over the next several years.

You’d be excused for thinking the use of sheep and goats was a total waste of effort, but additional data collected at Altamont Prairie adds some interesting nuance.  As it happens, mean Floristic Quality (a kind of qualified plant diversity metric) stayed relatively stable within the grazed area during the five years sheep and goats were present.  During the same time period, mean Floristic Quality decreased significantly in exclosures.  In other words, while grazing didn’t eliminate the spurge problem, it may have stabilized some of its negative impacts for a while.

This, to me, is one of the best attributes of many grazing-for-weed-control efforts.  Even if grazing can’t eradicate many weeds/shrubs from a prairie, it might be a strategy that prevents further spread (eliminating flowers and reducing vigor for belowground reproduction) and/or reduces the weed’s ability to compete with desirable plants.  In a large site where more effective long-term strategies (such as selective herbicide application or biocontrol releases) aren’t feasible across the whole area, using grazing as a suppression tactic in some areas of the site while you kill it in others can make a lot of sense.  In other words, grazing might buy you time to work on a problem that would otherwise seem overwhelming in scope.  (However, it’s also important to remember that grazers will also be eating and suppressing the vigor and reproduction of desirable species with similar growth strategies to the invader you’re targeting.  If you do succeed in reducing populations of invaders, you might also reduce populations of those desirable plants.)

Grazing can sometimes provide effective control of short-lived plants if it prevents flowering and seed production and forces plants to die without reproducing.  Just remember that more seeds are likely waiting in the soil, so it will likely take repeated grazing treatments to reach your goal.  Here in Nebraska, we often use short-term intensive grazing as a tool to knock back the competitive ability of perennial cool-season grasses such as smooth brome (Bromus inermis) or Kentucky bluegrass (Poa pratensis).  We don’t expect the grazing to kill those grass plants (and it doesn’t) but we can allow other plants a chance to flourish for a few years until the invasive grasses regain their vigor.  By repeating the treatment periodically, we can maintain a more diverse plant community.

Periodic early-season cattle intensive grazing helps us temporarily suppress cool-season invasive grasses like smooth brome and reduce its ability to outcompete many native grasses and wildflowers.

Personally, I’ve never used goats or sheep to help with a management challenge.  In contrast with cattle, goats and sheep, feed preferentially on forbs, and I’m usually trying to suppress grasses and encourage forb growth.  However, I do think goats, sheep, and cattle can all play important roles in controlling invasives as long as you don’t expect them to do more than they can.  I worry that landowners and land managers can sometimes end up paying an exorbitant price to someone that brings animals in with the promise of weed control.  It’s important to remember that if you do that, you’re providing food for that contractor’s animals, and that should be factored into whatever price one of you pays the other.  When we use cattle for prairie management, the cattle owner always pays us.  That seems not to be the case with many goat grazing operations.  I’m not saying it’s wrong to pay someone to graze their goats on your land, I’m just saying it’s important to fully process what each party is getting from the transaction.  That includes the forage provided to the animals from your land, the time and expenses incurred by the owner of the animals, and  – importantly – the actual effectiveness of the treatment.

As long as you have clear objectives and a good understanding of the plant(s) you’re targeting, grazing may be a great tool for invasive species control.  Just remember one of the biggest lessons from the South Dakota spurge experiment: just because you can’t see the invasive plant anymore doesn’t mean it’s gone!

Hubbard Fellowship Blog – Stewardship Positivity

The following post was written by Evan Barrientos, of our two Hubbard Fellows for this year.  Evan is a talented writer and photographer, and while you’ll get the chance to see some of his work here during the next year, I also encourage you to check out his personal blog.

Although I’ve been participating in land management since high school, I still find myself learning so much from it, although perhaps not in the way you’d expect. Yes, I’ve learned several management techniques and strategies since starting the fellowship, but the lessons I consider most valuable are the ones that teach me how to think about land stewardship. Let me explain.

If you were a Hubbard Fellow during the second week of June, you would probably find yourself riding an ATV back and forward across one of our restored prairies, searching for the fluffy purple flowers of Musk Thistle. Upon spotting a thistle, you would pluck off all the flowers, thrust your spade through the base of the thistle with a satisfying crunch, pull out the plant, and then knock the dirt off of any uprooted roots. Over the next three weeks you would repeat this process thousands of times until you had covered every inch of all 14 of our Platte River properties and their 4,000+ acres. Then you would check them all again.

We celebrated the end of thistle season by burning the flowerheads in a bonfire.

When we finally finished musk thistles we celebrated by burning the seed heads that we had collected in a bonfire.

This may sound like exhausting and repetitive work, and it can be, but that wasn’t the hard part for me. The hard part was staying positive when it felt like I wasn’t doing enough. I felt this way when I returned to a prairie for its second thistle check and found piles of thistle seed below “zombie thistles” (thistles that flowered and produced seed after I chopped them because I left too much dirt on the roots). Or when I walked through a prairie that I had already checked twice and still found thistle stalks that had already released their seed to the prairie. Most of all, deciding to spend July 2nd chopping thistles before they released more seed instead of spending time with my family forced me to think hard about my role as a land steward.

As a land steward you develop a strong connection to the land you are working on. Seeing a healthy community of native species flourish on your property is extremely gratifying, but it also pains you to see invasive species spreading. Land stewards almost always have more tasks than they can complete and it’s very easy to let this make them feel overwhelmed and stressed, but it doesn’t have to be this way. After reflecting upon the first month of my fellowship, here are three lessons I’ve learned so far about being a happy steward:

  1. I cannot control nature. I am a steward, not a god. Expecting myself to control exactly which species grow on a property will only bring me frustration. The role of a land steward is not to dominate the forces of nature, but to regulate its extremes. Translation: my job isn’t to exterminate musk thistles, but to prevent them from outcompeting other species and lowering overall biodiversity.
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A Regal Fritilary (Speyeria idalia) on Musk Thistle (Carduus nutans). Like it or not, Musk Thistles have become part of the local ecosystem. Being a steward doesn’t mean exterminating thistles, but keeping them under control.

  1. There is no endpoint. A land steward’s work is never “done.” My job isn’t to “fix” a property; it’s to guide the property toward a range of conditions that meet our management goals. Removing thistles from the same property year after year does not mean that we are failing at our job of “restoring” the prairie. On the contrary, it means we are doing our job of actively fostering biodiversity.
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Common Mullein (Verbascum thapsus) is non-native, but also non-invasive. We don’t remove it because it doesn’t lower plant diversity.

  1. Stewardship should be viewed as a positive action, not negative. There are two very different ways to look at land management. From one angle, a day spent chopping thistles could be considered a violent battle against an evil enemy; a task to evict an unworthy invader. From another angle, it could be considered a process of creating beautiful and biodiverse prairies. In my experience, viewing invasives as enemies just leads to exhaustion and bitterness. Only by viewing stewardship as a process of care and creation, in my opinion, can one generate the tremendous amount of energy needed to take on its many tasks.
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Black-eyed Susans (Rudbeckia hirta) in the Platte River Prairies, Nebraska.

Land stewardship is an essential component of conservation and it’s imperative that we do it well. Unfortunately, it also is a very demanding job that can burn you out if you’re not careful. I’m happy to say that the first month of this fellowship taught me some very important lessons about setting realistic expectations and viewing my work as a positive contribution to prairie biodiversity. It’s important to be a happy steward!