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| Aggressive tall goldenrod - is it an ecosystem killer? |
They wipe out all else. In both prairie and woodland restoration, irruptions of aggressive (malignant) species can kill off most of the conservative or "high-quality" species.
In the early days of prairie restoration, Dr. Betz's hypothesis was that aggressive prairie species could outcompete aggressive "weeds." Indeed, if you plant plenty of big bluestem and burn regularly, it will drive out farm weeds, tall goldenrod, and most other species in a few years. Unfortunately, the resulting few-species stand of big bluestem and a few others can make it more challenging to restore most other prairie biodiversity (from conservative plants to birds to butterflies).
Ecosystem responses are complex - and different from spot to spot. Thus, diverse quality can replace both tall goldenrod and big bluestem, but it may take decades of burning and seeding. And in other spots, instead of diversity, woodland sunflower took over and killed even the tall goldenrod.
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| Here woodland sunflower - after three decades of "restoration" - replaced tall goldenrod and all else. The previous summer, we had scythed the sunflower one time, and it grew back this strong the next year. We had raked the mowed sunflower into piles and burned it (the area now bare). Underneath the sunflower, little grew. See The Battle of the Aggressive Sunflowers. |
Many other species are aggressive only in the short run. They will be out-competed by diverse quality species (if present or seeded) over the years. In my experience, these include tall boneset, hog peanut, white snakeroot, Japanese hedge parsley, garlic mustard (in prairies though not in woods), oxeye daisy, and wild carrot. They just "go away by themselves."
In both long and short term, controlled burns can actually encourage many aggressive species. If there's been a long period with no fire, a burn will kill many invaders, which then leaves empty space for trouble. Quality species, if seeded or present, may slowly establish in the gaps. But invasives can explode. In many situations, diversity will outcompete the invaders in time with regular burns. Mowing the fast-increasing species a couple of times a year for a couple of years seems often to tip the balance in favor of the good guys.
On the other hand, uncontrolled tall goldenrod often promotes the return of brush. In many situations, tall goldenrod patches won't burn. In those cases buckthorn often slowly replaces the goldenrod.
Many aggressive species are most troublesome in rich soils, rather than a very dry or sandy sites. It's different from place to place. But an observant steward can figure out successful strategies.
Acknowledgements
This post was inspired by a good question on the relationship between fire and aggressive species from Kirk Garanflo on the post restoring-oak-woodlands.
I don't have much experience managing woodland sunflower long term but have been able to observe tall goldenrod over time, in one particular area I can attest that it has subsided and given ground up to more conservative species such as shooting star and wild hyacinth with little management apart from 1 fire in 7 years but this may be only this one particular site. Sedges have gotten thicker and I wonder if this is a factor.
ReplyDeleteThe Prairie of the Illinois Country, Dr. Robert F. Betz, 2011, pp. 229
ReplyDelete“Even worse setbacks occurred in tracts that had been in recent cultivation and had been continually doused with a variety of agricultural herbicides. For years these tracts remained with only a slight scattering of prairie grasses with almost no First Stage Successional forbs. Even after a number of yearly enrichments, they reluctantly advanced into the Successional First Stage.”
The Fermi Lab restoration was started the year after Roundup was introduced. Other herbicides must have been used to control weeds on the agricultural fields prior to the Fermi Lab restoration. Herbicides like Atrazine take a few years to break down (Restoring the Tallgrass Prairie: An Illustrated Manual for Iowa and the Upper Midwest, Shirley Shirley, pp. 39). Some of the initial, and continuing, dominance of tall grasses at the Fermi Lab restorations were likely because tall grasses were the only thing that could grow in soil with residual Atrazine. Although, tall grass dominance has continued to be a long-term phase at many other sites. Perhaps excluding tall grasses from seed mixes during the establishment phase is the best option (like you did at Spring Creek). Seeding more heavily with high-quality species might also be helpful along with including parasitic species (betony). The latter is now being done by many people.
Another thing that could be done is irrigate. High-quality prairie seed is expensive. It is a rare year that there is enough rain for conservative prairie species to establish. Irrigation would help get conservative species established from the beginning (especially this year).
You often say, “In many situations, tall goldenrod patches won't burn. In those cases, buckthorn often slowly replaces the goldenrod.” I have controlled buckthorn seedlings in tall goldenrod patches and agree that more buckthorn seedlings are in these patches than in unburned quality prairie areas. However, the Park District in the village where I live successfully burns areas that are mostly patches of either Symphyotrichum lanceolatum or Solidago altissima. These plantings, taken over by these native weedy species, burned so well recently they killed 4-inch dbh Salix lucida to the ground. Is the reason your tall goldenrod patches are not burning well because Somme Prairie Grove is being burned in the fall? Tall goldenrod may not be dried out enough to burn in fall. The Park District in the village where I live burns mostly in spring (often too late in my opinion). The Park District in the village where I live does not have a problem getting tall goldenrod to burn in spring. Maybe all that needs to be done is after burning off groves with maple leaves in fall, return to burn off the tall goldenrod areas in spring.
It does seem true that areas dominated by coarser forbs burn much better in early spring than fall, because of how late asters and goldenrods cure. I ended up with an over-abundance of woodland asters, goldenrods, and Joe Pye at my place, and I've opted to cut them down a couple of weeks prior to burning in fall. Cutting them down two or three times in summer has allowed more graminoids and lower forbs to to establish. Burning in early spring would be fine, but the window is pretty narrow before bloodroot and prairie trillium are up...but that's what I would probably opt for if the area was so large laying down the vegetation to accelerate drying was not an option. The areas with the better herbaceous structure burn in fall just fine.
DeleteMy favorite tool for cutting coarse stems, either to lay them down for fire or to open things up more in the growing season, is my electric brush cutter with a metal blade (Ryobi expand-it brush cutter attachment).
DeleteOver the last 3-4 years I've been mowing patches dominated tall goldenrod and other aggressive forbs in mesic to dry mesic woodland, savanna, and prairie zones and have observed far more graminoids by the following year. I'm hoping this trend continues long-term.
ReplyDelete