Sometimes our beautiful natural spaces are no longer quite as "natural" as they might appear because they have been taken over by invasive species.
Among animals, invasive species include grey squirrels, which are sometimes black, native to eastern Canada and were released in Stanley Park, from which they have spread. The starling is a non-native bird introduced from England in the eastern U.S.A. over a century ago and is now common in urban areas across North America.
The plant world includes a number of species with similarly invasive tendencies. These include Himalayan blackberry, giant hogweed, lamium, knotweed and several others (for more information, see www.invasiveplantcouncilbc.ca).
It's important to note non-native species are not always a problem. Our gardens typically contain many non-native plants that add beauty and often provide some benefit to wildlife as well.
But some non-native plant species are so aggressive in their growth that they crowd out beneficial native species and create an extensive monoculture that truly alters the landscape, displaces native species and diminishes ecological values. Because of their forceful growth habits, invasive plants can be extremely difficult to eradicate.
But due to increasing awareness of this problem, some municipalities and many volunteer groups are now working to eradicate some of the worst of the invasive plants often by hand-weeding or, in some cases, chemical treatments for especially hazardous plants such as giant hogweed.
Of course, the best way to control invasive plants is to work with nature. Wherever the so-called invasive plants grow naturally (and they all have a place on Earth where they have naturally evolved), there will be natural pests or predators that keep their growth under control. To develop a natural control, biologists need to identify these biological enemies and then select one that is so specific in its action that it affects only the invasive plant. Ensuring this natural method of control is completely specific in its action on the host plant is typically the key requirement.
Such an approach has been used successfully many times to control more than 300 invasive weeds. A local successful example is purple loosestrife, a plant that once invaded and dominated wetlands but now appears to be kept in check by a leaf-munching beetle.
Once a host-specific pest is released, it usually takes several years for an ecological balance to be achieved between the plant and pest. Complete eradication, of course, is never achieved but is also not necessary as long as aggressive growth is kept under control.
As one of the many volunteers at DeBoville Slough working to keep what was once a virtual forest of three-metre-high knotweed under control, I was much encouraged to learn that a natural pest for knotweed has now been identified and tested in Britain.
Knotweed is quite a menace in the U.K., where this invasive plant can grow through concrete and damage the structural integrity of buildings. The damage it causes and associated plant removal costs almost $300 million annually.
Through research, scientists have leaned that, in Japan, where knotweed is a native plant, it is kept under control by 168 insect species and 40 fungi. This provided a large number of possible candidates to test in England.
After much research, an insect pest called a psyllid (i.e., a plant-louse) was chosen as a host-specific pest for additional testing. Laboratory tests confirmed this two-millimetre-long psyllid has no impact on 90 other plant species, including a number of important crops and native plant species. Very limited field trials were conducted last year. This year, the British government gave permission for more extensive field testing to begin. Depending on the results of this testing, we might expect testing to begin in North America some time in the near future.
No doubt, all the volunteers working to keep knotweed under control throughout the Lower Mainland will be encouraged to know that help might finally be on the way.
Elaine Golds is a Port Moody environmentalist who is vice-president of Burke Mountain Naturalists, chair of the Colony Farm Park Association and past president of the PoMo Ecological Society.
