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Weed = BAD. Native plant = GOOD! Or is that definition way too simplistic in the 21st century? Should we leave some weeds in natural landscapes well alone?
Toby Query, a natural resources ecologist in Portland OR, has found his approach to managing invasive weeds has subtly shifted over the 16 years that he’s been responsible for several hundred acres of wetlands and forests. It seems that native fauna can adapt so well to non-native vegetation that removing it can even endanger vulnerable animal and bird species.
Query describes the case of the rare willow flycatcher, a bird that likes to nest in dense, thorny vegetation like the local hawthorn. After finding an area infested with non-native reed canary grass and blackberry, he and his workers set about removing the blackberry so they could replant the area with hawthorn and indigenous trees.
Blackberries near Wimple Cross. geographe.org.uk
Sadly it turned out that they’d unwittingly timed the job for willow flycatcher nesting season. During the blackberry removal process, many nests were destroyed, as the team were unaware that they were cutting down essential bird habitat.
Query says that any natural environment that’s long been colonised by non-native vegetation needs to be very carefully surveyed before any weed removal starts, explaining:
“It’s not as simple as bad and good. It’s a lot more complex than that.”
Years ago I noticed something similar in Australia, while walking in a National Park in Sydney. Many trees were festooned with invasive ballon vine and morning glory, forming dense thickets that were smothering the local trees. My immediate reaction was “Can’t something be done about this?! We need to get in here and do some bush regeneration and clean this up.”
Then I noticed the huge number of tiny birds, like blue wrens and honey eaters, many of which I hadn’t seen in Sydney since my childhood, that were darting in and out of the protective canopy of the vines, escaping the predatory and territorial larger birds which couldn’t follow them. Removing those vines would have destroyed an essential habitat, albeit a weedy one, to which those birds had adapted, as their natural home of large and densely-foliaged shrubs had all but disappeared from Sydney’s suburbs, replaced with open trees, grasslands, cottage gardens and clipped hedges.
Mark Davis, Professor and Chair of Biology at Macalester College in Minnesota says that words like ‘invasive’ and ‘alien’ are indiscriminate and emotive terms that don’t recognise that a whole new ecosystem might have already developed over decades if not hundreds of years that includes the newer, non-native plants and animals. By indiscriminately removing the non-natives we could lose benefits we haven’t yet recognised, and removal often means the use of herbicides, with far more damaging, long-term environmental consequences.
Spraying weeds in Dunlewey. Geographe.org
Davis says we should stop worrying so much about getting rid of non-native plants and instead focus our limited resources on the things that can cause real harm, such as fungal and viral pathogens, and insects, as these can:
“devastate and threaten society. There is not enough emphasis on that and way too much preoccupation worrying about non-native plants.”
Read more about these most interesting view on non-native plants at The Weeds Network
Interesting. Here in South Australia, blackberry thickets are a smothering pest in creek lines, but they also provide important bandicoot habitat. In my garden, eastern spinebills and honeyeaters visit camellias as well as grevilleas, and a pair of spinebills also frequent my local plant nursery, feeding on a huge range of exotic species.
A highly effective farmland rehabilitation technique whose name and demonstration location I unfortunately have forgotten forget relies – initially, at least – on encouraging naturally adventitious species (predominantly weeds) to flourish, thereby stabilising the soil, providing organic matter, reducing soil temperatures etc. The weeds ameliorate conditions so that secondary, more desirable species can get a toehold.
Bush ecologists or managers would usually take an inventory of not only the local plants remaining in weed infested areas, but other species too, particularly birds.
Despite the presence of unwanted plants in the bush, they are still a part of the ecosystem and removing them too quickly can result in a net loss of biodiversity. It’s a very nuanced rope bush managers walk.
Sadly, the interactions between non-native species and local fauna are often overlooked. The language of ‘alien’ and ‘invasive’ plants tend to illicit panic, and many will rush headlong into clearing out non-natives en masse as their first priority.
A simpler and slower approach is not only money better spent, it will benefit the whole ecosystem in the long term – for both plants and animals.
It’s a complex issue to get your head around – but a great topic!
We own some lantana-infested land and had local bush regens in to start clearing it out. We have quite a few hillsides now with much less cover than before. I suppose that it gives some native vegetation a chance to grow, but things are pretty bare and now I’m worried we’ve destroyed precious habitat for little birds like wrens.
On exactly this topic don’t miss reading Fred Pearce’s book “The New Wild: Why Invasive Species Will Be Nature’s Salvation”, which has just been released (Allen and Unwin $35). Fascinating reading.