Science Prevails when Managing Woody Invasions
You can more effectively manage woody invasions and mitigate their impact on ecosystems by leveraging scientific research and the biology of resprouting. It wasn’t until after 2000 that understanding resprouting behavior and biology research became a growing interest (Bond and Midgley 2003). As the field evolves with new discoveries, it’s essential for land managers to integrate the latest research to ensure their practices are based on the most current evidence rather than outdated assumptions. Keeping current and understanding the biology improves the effectiveness of restoration efforts and allows for adjustments when new insights emerge. In our dynamic ecosystems, where the introduction or invasion of woody species can have significant impacts, staying informed and applying recent research is key to successful long-term management.
Restoring and managing native ecosystems in the Driftless Area can be a challenge. On any given 50 acres the topography, soil type, and plant species can vary dramatically. Within a short distance, soil can fluctuate from dry and rocky to wet mesic, with oak savannas and oak-hickory woods vying for space with invasives like the multiflora rose, bush honeysuckle, autumn olive, and brambles.
Overgrown oak savannas, woods, and prairies are not necessarily or solely caused by fire exclusion (mesophication); it could be the loss of grazing, increased CO2, and more contemporarily, a reduction in mowing (Miller et al. 2017, Bond 2008, Heisler et al. 2003). Nor can the return of fire prevent invasion or remove the invaders; it isn’t that simple (Milbauer & Leach 2007, Rooney and Leach 2010). The introduction of non-native, invasive woody plants has altered our ecosystems. They displace native plants and need removing to restore a healthy balance. Disturbances, such as fire, haven’t proven effective (Bellingham and Sparrow 2000), but understanding their biology and applying a targeted method is effective.
Before and after photos of one oak savanna we are restoring. Once cleared of the big stuff, it has taken 2 additional years of follow up to get the resprouting woodies (and herbaceous invasives) under control and into maintenance mode.
Long entrenched beliefs in single factor explanations are no longer tenable. (2008)
What is Resprouting?
The difficulty in removing unwanted, woody plants is their resprouting growth. This growth is dominated by a central growing stem, this process is called apical dominance. When the central growing stem is intact, it inhibits other stem growth. Once that central stem is damaged, the plant faces a fight-or-flight response but without the ability of flight it fights by producing multiple stems. These resprouting stems develop their own apical dominance and the pattern repeats with each disturbance. Resprouting after disturbance is very common in woody species (Heisler et al. 2003, Bond and van Wilgen 1996). This is what makes non-native, invasive plants particularly troublesome.
Click the button below for a detailed explanation of the biology.
The above photo shows the green stems that are resprouting from the damaged base. What was originally a 4-stemmed multiflora rose is now more than 7 stems after a burn.
The Search for Answers
Tackling these unwanted resprouting woodies within our limited resources (time and money) required some research. I consulted research papers and talked with other restoration practitioners. Anecdotal accounts have some educational value but what worked on one parcel of land at one particular time might not work on another – a universal truth of nature! One landowner burned annually then trudged through the leg-cutting canes of the top killed brambles herbiciding the resprouts. Year after year after year the intense emotions of charring the land and laying out copious amounts of herbicide were felt. Why weren’t these resprouting woodies decreasing?
The complexities of fire as a management tool underline the importance of considering the broader ecological impacts and potential biases in promoting such practices (Brancatelli et al. 2024). The idea of frequent burns to topkill or “set back” woody vegetation might seem effective at first glance, but the benefits are often temporary and come with significant trade-offs such as harming soil health, erosion, an increase in woody vegetation due to resprouting, and/or negatively impacting biodiversity (Miller et al. 2017, Heisler et al. 2003, Bond 2008, Bellingham and Sparrow 2000). It’s a reminder that ecological management strategies should be carefully evaluated and tailored to the specific goals and conditions of the ecosystem in question. Furthermore, the removal of thatch through fire creates an environment conducive to native plant germination but that same environment also encourages the growth of undesired species (Loydi et al. 2013).
Annual burns or frequent burns to control resprouting woodies is like painting over the spot on the ceiling when the roof leaks. Each time it rains, the spot returns. Why not fix the roof and not concern yourself with the leak for the next 15-20 years?
In another oak savanna, managers mowed several times a year as the sole management activity. Cool season grasses became dense and lush. Once the mowing stopped, the resprouting woody growth was profuse and luxuriant, especially multiflora rose. Over ten years of mowing and there was no evidence the roots were weakened. Over ten years of wasted resources with the ecosystem in no better condition to support our native wildlife.
We scratched our heads. These generally accepted methods weren’t working. The science – the biological science of apical dominance — had been ignored.
What Works
By coupling biological science with field research, an effective method for “fixing the roof” has been found – Cut and Treat (Medley and Mohrman no date, Charton and Damschen 2024). This method uses chainsaws and loppers to “cut” the stem(s) at the base of the target plant, then “treat” the cut end with a spritz or dab of herbicide. We use a 20% mixture of Garlon 4® (or Element 4) herbicide in bark oil. This herbicide is effective on the cut stumps and uses less herbicide than similar chemicals mixed with water for foliar spray. We did not need to retreat the original cut plant but if the infestation is dense, a second year of spraying resprouts can be expected because stems were missed. By the end of the 2nd year, we will burn the treated area to encourage resprouting; then we follow up with the Cut & Treat method.
Our experience is the land requires about 2 years of follow-up (after the initial cut and treat) before it becomes a maintenance regime for resprouting woodies. The time spent in the beginning by cutting and treating has decreased expenses and time in subsequent years. There was no risk of biodiversity losses associated with annual and frequent burns, no risk of increasing cool season grass growth with mowing during the growing season, and a very low risk of the wholesale return of the invasive resprouting woodies if management were to stop.
By understanding the biology of apical dominance, we knew any disturbance can cause the unwanted woody to resprout, sometimes profusely. That information allows us to plan our time and manage our expectations. Field research demonstrated that fire was ineffective, but we were able to creatively use it to our advantage. Using an integrated management strategy (aka combining herbicide treatments with fire and/or mowing) has shown we can get our woodies under control within 3 years. After that, it’s a simple management routine of cutting and treating when the birds gift us new seedlings. Additionally, we know that any time a disturbance occurs (e.g. prescribed burn, mowing, storm damage) we need to set aside time for follow up.
Science prevails! Unless the biology of resprouting changes, the science cannot be discounted.
This bush honeysuckle was burned in fall and not treated with herbicide. This is the resprout the following April.
The burnt multiflora rose canes appear to be all that’s left after a fall burn and the native vegetation is growing around it in spring.
This is a close-up photo of the spring resprouting from the multiflora rose that appeared to be only blackened canes.
References
Bellingham, Peter J. and Ashley D. Sparrow. 2000. Resprouting as a life history strategy in woody plant communities. Oikos 89: 409-416.
Bond, William J. 2008. What limits trees in C4 grasslands and savannas?. Annual Review of Ecology, Evolution, and Systematics 39(1): 641-659.
Bond, William J. and Brian W. van Wilgen. 1996. Fire and Plants. London: Chapman & Hall.
Brancatelli, Gabriela I.E., Alejandra L. Yezzi, and Sergio M. Zalba. 2024. Fire as a management tool for invasive woody plants in natural environments: a systemic review. Biological Conservation 293: 1-12.
Charton, Katherine T. and Ellen I. Damschen. 2024. Grassland woody plant management rapidly changes woody vegetation persistence and abiotic habitat conditions but not herbaceous community composition. Journal of Applied Ecology: 1-13.
Heisler, Jana L., John M. Briggs, and Alan K. Knapp. 2003. Long‐term patterns of shrub expansion in a C4‐dominated grassland: fire frequency and the dynamics of shrub cover and abundance. American Journal of Botany 90(3): 423-428.
Loydi, Alejandro, R. Lutz Eckstein, Annette Otte, and Tobias W. Donath. 2013. Effects of litter on seedling establishment in natural and semi‐natural grasslands: a meta‐analysis. Journal of Ecology 101(2): 454-464.
Medley, Kim A., & Mohrman, P. Travis. No date. Invasive bush honeysuckles: ecology, spread, and mitigation.
Milbauer, Michelle L. and Mark K. Leach. 2007. Influence of species pool, fire history, and woody canopy on plant species density and composition in tallgrass prairie. Journal of the Torrey Botanical Society 134(1): 53-62.
Miller, Jesse ED, Ellen I. Damschen, Zak Ratajczak, and Mutlu Özdoğan. 2017. Holding the line: three decades of prescribed fires halt but do not reverse woody encroachment in grasslands. Landscape Ecology 32: 2297-2310.
Rooney, Thomas P and Mark K. Leach. 2010. Replacing hay-mowing with prescribed fire restores species diversity and conservation value in a tallgrass prairie sampled thrice: a 59-year study, Am Midl Nat. 164:311-321.