Stability Part Three: Promoting Old Growth and Controlling Unwanted Vegetation Should Go Hand in Hand   

Story and Photos by Ecologist Dan Carter
April 2, 2025

Figure 1: Spring view of an area where glossy buckthorn (Frangula alnus) was removed the previous fall and winter. Little herbaceous vegetation remained beneath. What is visible here is a mix of species seeded immediately after brush work and opportunistic natives like burnweed (Erechtites hieraciifolius). Quaking aspen (Populus deltoides) was subsequently girdled. Here seeding, aspen girdling, prescribed fire, and targeted removal of unwanted vegetation (e.g., pulling and flaming of glossy buckthorn seedings, pulling of small Canada thistles, Cirsium arvense) are being combined in close sequence.  

This article is the third in a series on promoting stability—or perhaps doing the least damage to it—as we encourage and sustain old-growth prairie, savanna, and oak woodland sods. Prescribed fire¹ and grazing² were obvious topics that were addressed earlier, but the other management practices we use, particularly those that kill or remove excessive woody vegetation or invasive/aggressive herbaceous species, deserve attention. Removing unwanted species represents much of what we do in defense of fire dependent ecosystems. As with fire and grazing, its effects relate to physical parameters like nutrient availability, light, and microclimate, but those effects also relate to direct impacts to what we’re trying to save. Sometimes it just comes down to not injuring or killing the good stuff by accident.

Woody encroachment and many non-native herbaceous plants can destabilize old growth composition, structure, and ecological process if not addressed. They do this by altering light, water, nutrients, and air movement. Some species produce allelochemicals that cause local changes to vegetation. A good example of a species that alters most or all of those parameters is common buckthorn (Rhamnus cathartica), which casts excessive shade and produces emodin, a likely allelochemical. What I find more sinister is the microbial community associated with buckthorn³, which supports more free-living nitrogen fixing (diazotrophic) bacteria; these ensure that the buckthorn has a continual supply of nitrogen to fertilize the area under its canopy with its fast-decomposing (labile) leaf litter. The increased nutrient cycling and availability from leaf litter inputs of many problem species, woody⁴ and herbaceous⁵, are a big part of why intervention is needed. However, practices that remove unwanted vegetation usually create physical disturbance or leave behind excessive available nutrients in their wake. These wounds require mending, and their healing requires sustained care.

A common mistake is instead to assume that the ecosystem will heal on its own, either by natural dispersal or from the seed bank. Three inconvenient realities work against that hope. Opportunistic species (most herbaceous invasive species, sometimes “weedy natives” like tall goldenrod, Solidago altissima), many of which are problems in the communities we manage, are better at dispersing to open spaces where unwanted species have previously been removed. In many instances the landscape is too fragmented for old-growth-associated species to have any chance to get there, However, disturbed areas overrun with opportunistic species surround the places we care for. Second, physical conditions continue to be altered even after areas are daylit (e.g., nitrogen availability is greater), which further favors re-colonization by opportunistic species. Finally, many long-lived, old-growth-associated species do not persist in seed banks^6,7, which means recovery in the wake of invasive species removal relies on remaining vegetative plants. Often when plants have persisted, they have not flowered and set seed for a long time, so use of heavy-handed management practices should not assume that the seed bank is an insurance policy, but I hear that exact claim or assumption again, and again! It is true that there are native species in the seed bank, including uncommon native species⁸ (especially where seed inputs are still ongoing), but flora that may lead to the restoration of ecological integrity⁹ do not reside where old growth vegetation has been suppressed or absent for any length of time.

Figure 3: Representative late winter / early spring sap flow in a previously treated glossy buckthorn stump.  

Healing the damage caused by unwanted species requires integrating approaches that both control those species and actively promote the establishment and persistence of species associated with old growth. In cases where desirable species have been lost or gaps in desirable vegetation have been created in the wake of removing unwanted species, we should gather and broadcast seed or propagate and plant plugs. We can also ameliorate the excessive nutrient availability by facilitating the early establishment of species that produce relatively slow-decomposing litter (native grasses and sedges especially¹⁰), the decomposition of which requires microbes to draw more nutrients from the surrounding environment. Grassier and sedgier vegetation also allows us to reestablish flammability and volatilize excess nitrogen out of the ecosystem using frequent dormant fire. Finally, establishing grassy vegetation (and probably the vegetation of our restoration target community more generally) may slow re-invasion by providing competition for the seedlings of invasive species (e.g., buckthorn¹¹), though I believe complementing the establishment of desirable vegetation with the use frequent fire is important for suppressing invasive species in the longer term. Removal of unwanted species ought to be combined with restoration of core ecological processes—by facilitating dispersal and using frequent dormant fire to promote and sustain conditions (low litter, low nitrogen availability) that allow species associated with old growth to establish and begin to stitch themselves back into a functioning ecosystem.

We often make faulty assumptions about how safe certain applications of herbicide are for ecosystems, but we can also do damage even when we follow herbicide labels to the letter. In old growth the use of herbicide should be very judicious. Where necessary, it should utilize only the most targeted applications of the chemicals that pose the lowest risk, either because they are the most selective or they can be applied in very targeted ways and do not tend to persist in or migrate through the soil. Do not assume that overspray from herbicide treatments in winter will not affect native vegetation, many old-growth-associated species maintain green tissues above ground that can be impacted. Assessment of that risk is where most mistakes happen. We need to start paying closer attention to and sharing accounts the collateral impacts treatments have.  I’ll describe and share photographs of a couple examples from my experience.

The first involves a degraded area where I oversaw the cutting and stump treatment of glossy buckthorn (Frangula alnus), common buckthorn and several other unwanted woody species in a dense thicket between late autumn and late winter. I applied 20% triclopyr ester, either in mineral oil with basal dye or basal oil with dye, to cut stumps using a hand-held pump sprayer on low pressure. This allowed me to carefully drip herbicide onto the cut stumps. Herbaceous vegetation was very sparse in the wake of clearing, so the area was seeded heavily with wild ryes (Elymus spp.) to quickly establish grassy cover. I also seeded conservative, old-growth-associated species appropriate for the site. In late February and very early March when the ground began to thaw and warm, I noticed that glossy buckthorn stumps, most treated weeks or months before, began oozing sap. None of the other treated species oozed sap in the same way. By midsummer it was obvious that treatment had effectively killed the buckthorn and other unwanted species. Nearly all treated stumps were dead, but around each glossy buckthorn stump was a dead zone where no herbaceous vegetation (including seedlings—even those of wild ryes) grew. While the extent of these dead areas and their impact was minor in this instance, the experience has made me wary of treating cut stumps with triclopyr ester in areas with high quality vegetation, especially where the density of treated stumps would be high. It will be worth investigating whether herbicides that are mixed with water (vs. oil) or applications made in summer that potentially have more time to kill stumps ahead of the following spring could produce fewer negative effects.

Figure 5: Representative late July view of a treated glossy buckthorn stump with surrounding bare area inferred to be result of spring sap flow. Away from stumps seeded species as well as seed bank species like burnweed and biennial evening primrose (Oenothera biennis) grow. In this setting this collateral effect is probably acceptable, but in cases with remnant old growth-associated vegetation, it would not have been.  

Recently, I visited a site where several months prior 20% triclopyr ester in basal oil had been used to treat mostly common buckthorn cut stumps with a wick-type applicator. That treatment had been performed in the winter when there was a shallow layer of snow. Still, there was obvious damage to the herbaceous woodland and savanna vegetation, presumably from herbicide that had come in contact with the snow or moist soil and spread out, and probably also leached into the sandy soil without being immobilized or broken down by soil organic matter or microbial activity. Triclopyr has a relatively short half-life, but that half-life depends on temperature, moisture, and sun exposure. In summer we worry about volatilization of triclopyr ester and some other herbicides due to heat, but in winter reduced microbial activity and solar irradiance might allow herbicides more time to migrate to where they can cause damage, even if they are being applied in targeted ways.

In both cases I was surprised by the collateral effects. My own calculation of risk versus reward for my actions and the advice I offer changed. I urge readers to take a second look at practices that are often taken for granted. Don’t just track the efficacy of treatments against unwanted species; also monitor surrounding vegetation before and after treatment. Do areas that receive treatment continue to be problem areas? Perhaps there were collateral impacts to native vegetation that further destabilized the community, or perhaps additional types of care (e.g., seeding, monitoring for re-invasion, more fire) are needed to address underlying problems and get things on the right track. Last year on his Strategies for Stewards blog¹² Stephen Packard offered the following wisdom:

“Is killing invasives our goal? Or restoring integrity and health to the ecosystem? Herbicides are needed. But herbicide treatments may solve one problem while ultimately not helping, or even making things worse. Restoration requires a wise overall plan with appropriate sequencing. The work then needs close oversight by someone who has a good working knowledge of the site’s ecology and the long-range impact of possible treatments.”

Figure 7: Pointed-leaved tick-trefoil in the same area that was presumably impacted by herbicide dripped on snow during a winter, 2023 cut stump treatment.  

References

¹ Carter, D. (2024). Stability part one: Why I recommend frequent dormant season burning. Prairie Promoter, Spring: 14-19. https://theprairieenthusiasts.org/stability-part-one/

² Carter, D. (2024). Stability part two: Stability Part Two: Why I Seldom Recommend Grazing. Prairie Promoter, Summer: 12-17.  https://theprairieenthusiasts.org/blog_dan-carter/

³ Rodrigues, R. R., Pineda, R. P., Barney, J. N., Nilsen, E. T., Barrett, J. E., & Williams, M. A. (2015). Plant invasions associated with change in root-zone microbial community structure and diversity. PLoS One, 10(10), e0141424. (Shown in Rhamnus davurica, which is nearly identical to R. carthartica, similar ecologically, and also occurs in the Upper Midwest where it may often be mistaken for R. cathartica).

⁴ Ashton, Isabel W., et al. “Invasive species accelerate decomposition and litter nitrogen loss in a mixed deciduous forest.” Ecological Applications 15.4 (2005): 1263-1272.

⁵ Edwards, J. D., Cook, A. M., Yannarell, A. C., & Yang, W. H. (2022). Accelerated gross nitrogen cycling following garlic mustard invasion is linked with abiotic and biotic changes to soils. Frontiers in Forests and Global Change, 5, 1050542.

6 Schott, G. W., & Hamburg, S. P. (1997). The seed rain and seed bank of an adjacent native tallgrass prairie and old field. Canadian Journal of Botany, 75(1), 1-7.

⁷ Lamb, N., Havens, K., Holloway, J., Steffen, J. F., Zeldin, J., & Kramer, A. T. (2022). Low passive restoration potential following invasive woody species removal in oak woodlands. Restoration ecology, 30(4), e13568.

⁸ Abella, S. R., Hodel, J. L., & Schetter, T. A. (2020). Unusually high‐quality soil seed banks in a Midwestern US oak savanna region: variation with land use history, habitat restoration, and soil properties. Restoration Ecology, 28(5), 1100-1112.

⁹ Ecological integrity is the condition of an ecosystem where composition, structure, and function operate within the natural range of variation for that region.

¹⁰ These are an important element for restoring ecological processes like fire and nutrient dynamics, but so are some forbs and forbs should not be neglected, because they support much of the biodiversity.

¹¹ Schuster, M. J., Wragg, P. D., Roth, A. M., Bockenstedt, P., Frelich, L., & Reich, P. B. (2025). Revegetation of Elymus grasses suppresses invasive Rhamnus cathartica in deciduous forest understories. Ecological Engineering, 210, 107438.

¹²Packard, Stephen. (2024) Destructive herbicide in the ecosystem. Strategies for Stewards blog. https://woodsandprairie.blogspot.com/2024/01/destructive-herbicide-in-ecosystem.html

This article appeared in the Spring 2025 edition of The Prairie Promoter, a publication of news, art and writing from The Prairie Enthusiasts community. Explore the full collection and learn how to submit your work here. 

Read the rest of Dan Carter’s Stability Series:

Stability Part One: Why I Recommend Frequent Dormant Season Burning

Stability Part Two: Why I Seldom Recommend Grazing

About The Prairie Enthusiasts 

The Prairie Enthusiasts is an accredited land trust that seeks to ensure the perpetuation and recovery of prairie, oak savanna, and other fire-dependent ecosystems of the Upper Midwest through protection, management, restoration, and education. In doing so, they strive to work openly and cooperatively with private landowners and other private and public conservation groups. Their management and stewardship centers on high-quality remnants, which contain nearly all the components of endangered prairie communities.