Dastardly Duo Destroy Habitat, Imperil Homes
Jan 29, 2004
Once again it is the season when the hedgerows and roadsides begin to bloom with the bright yellow, pea-like flowers of gorse and broom. Like after dinner guests who just won’t leave, many people are finding these harbingers of spring have outstayed their welcome. Unfortunately, after we invited them to our shores and even carefully tended to their initial shaky start, they have flourished and exhibited their “no holds barred” strategies for survival.
These highly adaptable and successful invasive plants have many tactics to ensure their continuation. Like those people fortunate enough to have a healthy bank account that can take them through retirement, broom and gorse ensure their long term existence with a sizable seedbank. They produce copious quantities of seeds that remain viable in the soil for many, many years (some accounts have broom seeds still able to germinate after 80 years!). The determined work of homeowners and volunteers to remove these plants is made more challenging by the continued germination or “withdrawals” from the seedbank. One of the challenges of removing broom and gorse plants is that the light that now reaches the ground will often stimulate the seedbank to sprout.
Another weapon in their arsenal of survival strategies is the ability to resprout. In my experience, the two species are not created equal. Broom is much more likely to die if cut to the ground, while gorse usually surges back, virtually none the worse for its pruning. This makes gorse, in particular, very difficult to control. For all that many of us think of broom as a terrible pest, gorse is its nasty, brutish cousin. Infested with long sharp spines, it seems determined to inflict as much damage as possible on anyone who attempts to control its spread. One publication states that “a single (gorse) plant can be 10 m in diameter”. So first you must whack you way through 5 m of fierce spiny branches to get to the main trunk and then you cut it back, only to have it resprout soon after!
Both gorse and broom belong to the pea family, plants that change soil chemistry by adding nitrogen through their root structures. While enhancing the soil with nitrogen is something we all think is a great thing for our flower and vegetable gardens, it can have a very negative effect on our native plants. Also, the litter they drop, in the form of leaves and branches, changes the soil by making it more acid.
In all natural plant communities, there are plants, who, like the kids at school who were smart, athletic and popular, have it all. They can survive and flourish in diverse situations, while others, sort of like the kids in the computer club, are able to find their niche in places too dry, too wet or too poor for the more generalist species. When introduced, invasive plants; such as broom and gorse, arrive and enrich and acidify the soil, they change the soil dynamics and the more sensitive, specialized plants are crowded out (goodbye computer club). As you can see from this analogy, it is important to help retain our native species and the ecosystems they inhabit. It’s more than possible they have something valuable to contribute, just as the archtypical computer nerd, Bill Gates, contributes substantial benefits to our communities.
Besides the loss of native species and biodiversity that broom and gorse engender, they are extremely dangerous fire hazards. Both species are full of volatile oils that produce hotter than normal fires. Gorse in particular, is a fire waiting to happen. It contains more oils than broom and as it grows, the inner branches die off and become dense, highly flammable dead material just waiting for a cigarette, carelessly thrown from a passing car window, to ignite it. Remember how nervous we all were last summer throughout fire season? I would wager that cigarette buts being tossed into stands of gorse and broom is high on the list of our fire chief's nightmare scenarios. Even if you don’t understand all the fuss about protecting the native environment, you should be worried about the proliferation of broom and gorse and their destructive potential to your home and family from their extreme flammability.
Methods to Control Broom and Gorse
In the best of all possible worlds, there is the most advantageous time to do things. However, real life often interferes with those schedules and best intentions. It is better to tackle invasive species when you can, rather than wait for the “right” time and miss it because you are busy or distracted by something else. I have had a lot of success cutting broom in the wet season, provided it is cut to or just below soil level. A stub, however, especially on young plants, will often regrow, although “old growth” broom is less prone to resrouting. If you are removing plants from roadsides with ditches during the wet season, take care not to let any dirt fall into the water. We don’t want to remove the invasive plants only to endanger aquatic habitat!
Always start with areas which have the fewest invasive plants and work towards areas with the highest densities. If you have an area with only a couple of broom or gorse plants, take them out first, to remove their ability to flower and build up the seedbank. Face it, in densely invaded areas the seedbank is already well endowed! Aside from roadways; work from areas of greatest sensitivity to areas of most disturbance. For example; work first from areas with the highest density of native and rare plants, to areas of stripped hillsides. That said:
➢ Cut plants to the ground just after flowering when much of the plant's energy has been depleted but before seed set, or during the summer, when the plant will already be stressed from our summer droughts.
➢ Small plants can be easily pulled in the winter, when the soil is thoroughly wet, although this can cause soil disturbance, which can encourage seed germination. It can also dislodge any native bulbs that might still be surviving. I generally place my boots against the plant as I pull, to minimize disturbance. This is particularly important on rocky moss balds, with their shallow soils.
➢ To deal with the more problematic gorse, I have read articles that endorse the “cut and paint” method. This entails cutting the gorse to ground level and then “painting” the stump and any remaining bark with a systemic herbicide such as Round-up™ at one part Round-up ™to 5 parts water (200ml Round-up™/litre water). There is conflicting advice on the amount of time that you have, (from 20 seconds to 20 minutes) from making the cut to applying the solution. It is more likely to be successful if done either in late spring or in the fall when roots are regrowing. You can apply with a squeeze bottle, using protective gear. Before applying, speak to a certified pesticide specialist and use all precautions recommended.
➢ Herbicides have apparently been successful with younger plants but must be used with extreme caution. Contact an certified pesticide expert.
➢ Repeated burning has been recommended as a way to kill off small plants that germinate once the seedbank has been stimulated. To reduce risk of forest fires, try a tiger torch in the wet season, but be careful not to damage native plants and the mosses and lichens that protect the soil. This is experimental only and expert advice should be obtained first.
➢ There has been some success with covering the newly broom and gorse free soil with back plastic to kill off the seedlings, however this will substantially damage any native vegetation. Replant with appropriate native plants.
➢ The Bradley Method entails removing invasive species from areas around native plants and slowly, as the natives gain strength and dominance, venture further into the infestation. This is a long term tactic that has been successfully used in New Zealand.
➢ Treating pastures with lime, to raise the pH, has been partly successful, either by weakening the gorse and broom or by increased competition from other plants more adapted to increased pH levels.
All of these methods are only effective if there is a commitment to continue removing broom and gorse for a very long time. There is no easy panacea for the problems they pose. Although gorse is becoming prevelent in Metchosin, East Sooke and Langford, as yet it has only a toehold on Southern Vancouver Island. If we work now to eradicate it, we might prevent the type of severe infestation that has destroyed great swaths of New Zealand, Hawaii and other countries.
Garry Oak Ecosystems Recovery Team, 2003. Invasive Species in Garry Oak and Associated Ecosystems in British Columbia. Garry Oak Ecosystems Recovery Team, Victoria, BC. Website: http://www.goert.ca/reference/invspecies.htm
Hoshovsky, M., 2001. Element Stewardship Abstract for Ulex Europaeus. The Nature Conservancy, Arlington, Virginia. From the website: http://www.conserveonline.org/2001/05/d/en/ulexeur.PDF
Mallinson, R, 1998. Pest Plant Control, Gorse Fact Sheet PP05/98, Whakatane, New Zealand. From the website: http://www.ebop.govt.nz/Land/Plants/Fact-Sheets.asp