TREATING OUR ASH ADDICTION Author Disclaimer: The only field in which I am an expert is my own. Pun intended. Please consult www.prairietrees.ca to see the results of the extensive trial conducted by the WNGG from 2007 to the present, along with a comprehensive list of tree ratings and recommendations compiled by Western Canadian nursery growers. It is my opinion that this list should be THE primary source for recommendations on trees in the Prairie Provinces of Western Canada. We are addicted to Ash (Fraxinus spp). Landscape designs in the Northern Prairie Zone (Zone 1a-3c) have used this Genus as an anchor tree forever and for great reason. It does everything we want it to do and we have a hard time imagining what the world would be like if we didn’t have it. We don’t have a lot of choices in our frigid zone. As with any eco system, the numbers of species that occur and thrive get fewer as the factors that pressure life get more and more extreme. Ash as an anchor of our designs is under threat and we need to figure out how to proceed. We don’t know exactly how this threat will manifest itself in the prairie provinces, and I’m not here to advocate erasing them from our lists. I think every tree has its place. But the question is on everyone’s minds. Emerald Ash Borer (EAB), an invasive beetle from Northern Asia capable of killing all the Fraxinus spp we use, has made its way from Detroit/Windsor in the early 2000s to Winnipeg MB (discovered late 2017). The current state of this infestation in Winnipeg is unclear as this is being written and summer reports show no new adults in traps in Winnipeg, but we await fall counts.
Emerald Ash Borer Regardless, this pest threatens urban forests in the northern Prairie zones to a much more significant degree than its previous path through the Midwest USA and Southern Ontario, due to the progressively diminished diversity of options available for urban forests in the colder zones. Between Ash and
07
Elm (Ulmus spp), these genera make up a majority of urban boulevard, commercial frontage and park plantings in northern prairie zones for multiple reasons. Should EAB fully infest our cities in AB, SK, MB and Northern Ontario, many cities will have a 9 figure bill on their hands for removal costs. Yikes! Elm has already been under threat from Dutch Elm Disease, though this threat is highly mitigated by the high level of preparedness of most Western Canadian cities. And the progress of DED is more of a slow march than the unpredictable and ‘viral’ spread of EAB. Many cities have a plan should DED occur. But the question remains…now what? The answer isn’t simple…Ash are used for many reasons and other trees are NOT used for many reasons. This article will glean over some of the more common trees available and explain their attributes and limitations in the landscape. In short though, there is an answer to overcoming this challenge, but it’s complicated. I believe the answer lies in adjusting our expectations, being creative in our designs and spending more time on the groundwork of landscaping…all the stuff we do BEFORE we plant the tree, mulch it, water it and walk away. The answer DOES NOT lie in simply ‘substituting Ash for something else.’
TREES ARE STILL GREAT! Despite this threat, I predict tree planting will continue to be an ever-increasing degree because the public is becoming more and more aware of the impact urban greenspace makes on the livability of our cities. Greenspaces reduce urban temperatures, absorb and slow the runoff of storm water, attract property buyers and provide space for casual and organized recreation. The Village Square is becoming an integral part of new neighbourhoods. Linear Parks have been designed to be part of larger bicycle and walking path systems that connect neighbourhoods to schools, parks and suburban business centres. And traditional streetscaping continues to be a priority for most cities. Trees are in demand, but future designs will likely not include many, if any, Ash.
WHY WERE WE ADDICTED TO ASH So here’s the meat of the article. Let’s analyse why we use so much Ash. For the rest of this article I’m going to ignore Elms. We still use them. We grind our teeth when we do, wondering if and when DED will ooze like an amoeba across our personal section of the map. But it’s a bit of a magic tree so we keep our faith in the pruning programs of our cities and the geographic distance between them.