There's been a lot written about New Zealand's Predator Free 2050 programme, including my own post from 2016, but while the primary focus has been on fauna, what about the invasive species of flora? Until recently it was easy to think of plants as poor man's animals, with little in the way of the complex behaviour that characterises the life of vertebrates and many invertebrates. However, that's been changing thanks to studies that show the life of plants is actually rather complex - and includes the likes of chemical signalling. Although they might not have the emotional impact of animals, land vegetation alone has about one thousand times the mass of terrestrial fauna. So they're important - and then some!
A few months' ago I was volunteering on the sanctuary island of Motuihe, less than an hour's boat ride from downtown Auckland. Our group was charged with cutting down woolly nightshade, a soil-poisoning plant native to South America. Destroying these evil-smelling shrubs made me wonder how and why they were introduced to New Zealand in the first place, considering they don't look particularly attractive and their berries are poisonous to humans. Like so many exotic plant species, they were apparently deliberately introduced as a decorative garden plant, though frankly I can't see why.
Like many similar stories from around the world, New Zealand has been inundated with large numbers of non-native floral species. Unlike woolly nightshade, some were introduced for practical purposes, such as radiata pine for timber and gorse for hedging, while others were accidentally brought in as seeds in soil. In many cases they are stories of greed and incompetence, for which later generations have paid a heavy price.
Although there were pioneering lone voices who from as early as the late nineteenth century could see the deleterious effects of exotic plant species on native vegetation, it wasn't until the last half century that any serious effort was made to promote their removal. British botanist and presenter David Bellamy was one of the first scientists to popularise this message, starring in a 1989 television advert to explain why Clematis vitalba (AKA Old man's beard) needed eradicating. Bellamy then went on to present the tv series Moa's Ark, which drew attention to the country's unique biota and the dangers it faced from poorly managed development.
Given his botanical background, it's perhaps not surprising that rather than see plants as the background to dramas of the animal kingdom Bellamy made them central to the ecosystem, claiming that we should put nature before culture. Again, although lacking the dynamic aspects of fauna, invasive weeds (by definition, aren't weeds just plants in the wrong place?) such as Old man's beard can gain up to ten metres in a single growing season. You only have to look around a suburban garden - mine included - to see that constant vigilance is required to remove the likes of self-seeded wattle and climbing asparagus before they take hold and smother native species.
It isn't just on land that we face this issue: freshwater systems can easily be choked by the likes of Elodea canadensis, a North American pondweed that has escaped from its ornamental aquarium environment (thanks to highly irresponsible people, of course) and been spread by boats and fishing equipment, clogging and stagnating streams and lakes. What is worrying is that it is far short of being the worst of the fifty or so non-native aquatic plants that threaten New Zealand's waterways. Considering that around three-quarters of all invasive species in this environment have a detrimental effect, it clearly makes the point that introduced flora is just not good.
So what can - and is - being done? Thanks to numerous volunteer groups, sanctuaries for rare native species (principally fauna, but occasionally flora too) are keeping invasive weeds at bay. Outside these protected environments, annual weeding programmes aim to reduce wilding pine, but the issue here is that commercial interest still maintains the upper hand. Whether for timber plantations or carbon sequestration, species such as Douglas fir continue to be planted, allowing the seed to spread to new areas far and wide on the wind. Luckily, there are numerous websites to help the public identify and destroy pest plants; here are just some of the online resources available for New Zealanders:
- https://www.weedbusters.org.nz/weed-information/weed-list/
- http://www.landcareresearch.co.nz/resources/identification/plants/weeds-key
- http://www.nzpcn.org.nz/page.aspx?threats_naturalised_plants
- https://www.doc.govt.nz/nature/pests-and-threats/weeds/common-weeds/
- https://inaturalist.nz/
Clearly, this isn't an issue that will ever go away. With most Government-led efforts focusing on pest animal species, eradicating invasive plants has been given far less support and so they remain comparatively unknown. Perhaps it would be good if schools undertook a compulsory programme, including practical work, in the identification and removal of non-native pest flora? Trapping and poisoning invasive animals can be a complex business, but weeding is comparative child's play. Everyone can help out: in effect, this is a form of citizen science that has a positive practical effect on the environment. Why not start with your garden today?
