Tuesday, April 1, 2014

Natives vs Aliens - Callenging our Ethics

Asclepias tuberosa 'Hello Yellow'

Astrid Muschalla – Etobicoke

When educating people on the value of natives vs aliens, I’m often asked, “Why are we allowing these imports, if they are so dangerous to our natural environments?”

It’s a messy topic but one worth sorting through in our minds as we talk to the public about plant choices, especially in the face of extreme climate variables like this winter. We hear from many scientists, like Dr. Douglas Tallamy (author Bringing Nature Home), that biodiversity is an essential and non-renewable natural resource, yet few are thinking like this. It’s argued that selecting for ornamentals creates fragmented and small populations which are vulnerable and can lead to local extinctions. We are also learning that we can turn this trend around but we need to share our spaces. The trouble with planting an alien though, is that it’s not really ecologically equivalent to a native because aliens are poor at supporting other life forms (aka ecosystems services). In other words, non-natives don’t usually form functional communities, which also include the soil microbiology.

So, a lot of work is being done with natives and the development of new varieties that may please more gardeners. You might say, “more pleasing for whom?”. Can we do varietal testing in a more ecologically responsible way? At the University of Guelph test gardens, I saw new varieties of our native Asclepias tuberosa (butterfly weed) loaded with Monarch butterfly caterpillars - a "Nativar". So, it does seem like we can breed our natives in such a way to preserve ecosystem services integrity. However, the science to prove the debate on Native vs Nativar is not yet developed.

It’s not to say that foreign ornamentals have no place; indeed, nature moves plants around the world all the time via storms, wind, etc. but not at the rate and help we give to these new introductions. Now that we know some of the consequences, like serious disease introductions that have no natural predators, perhaps we can be persuaded to pause and to research choices better, asking “will this choice best support the environment?”, which by the way would also include a homeowner needs, such as choosing a stronger cultivar and thus less replacement cost.

Our choices reverberate up the chain as the increased demand for natives demonstrates. How is the industry responding? It is now estimated that approximately 75% of our native plants for sale comes from Ecuador or Holland and only 6 to 10% are actually from the 100 km mile radius defined as native by the North American Native Plant Society (NANPS). If a native is grown in Ecuador, is it really native (likely propagated on Oregon stock)? Will the so-called native do well in Collingwood, especially in volatile winters?

Current research with MTO on highway plantings demonstrates that plant stock bred in the region fare significantly better than imports of the same variety.  It’s not the natives that are being planted on these disturbed sites though and that’s likely because the aliens that adapt to disturbed soils grow with more vigour – and that’s their job in nature – to quickly cover bare soil. So ethical complexities abound – is it ever right to not plant a native? Perhaps when it’s not the right place, like a challenging city environment or highway?

Ultimately, it comes back to biodiversity and protecting the genetics of our natives and that includes creating more corridors of plants for insects, birds, etc. and that’s where home gardens become really important. There is a growing niche market for growers to propagate local native plants.  As a buyer then, the most important factor for choosing plants has to be that they are locally propagated. What could save us will be biodiversity, but doesn't that include all plants like aliens too? 

Know your native plants at the North American Native Plant Association Database:  http://www.nanps.org/index.php/gardening/plant-catalogue-databse

Astrid teaches a credit Natives course at Humber College starting in May.  Here's the link

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