White (American) Elms – The Choices
It is interesting how an article evolves. For months, I have had research done on 3 topics – the articles sat 90% done – Waiting. The elm article jumped to the forefront because of facts that I found while researching another topic. The clincher came from Rick, my husband, when he more or less said,’Haven’t you already written about elm? Do you think people will want to read anymore about elm?’
Ever since the 30’s when Dutch Elm disease swept through North America and devastated millions of trees, everyone has been hesitant to replant them. Well, now there are choices and, hopefully, this will clarify those choices.
Choice 1 – The Supers
Back in the 80’s, the University of Guelph asked the public’s help to find the last of these giants. The survivors, in order to become part of the recovery program, had to have a girth of 7 feet. With this considerable width, it indicated resistance to Dutch Elm Disease (DED) since these trees would be about 100 years old. From the 1600 trees found, progeny were then grown and inoculated with DED to slowly start the process of selecting the ‘supers’ – the super resistant DED trees. There is no release date published but it will be soon??
Choice 2 – The Naturals
Nurseries, like ours at B Sweet Honey Nature Company, offer progeny from these surviving giants. These trees have natural resistance, like their parents. They are not the SUPERS, but are far superior to the majority of wild elms that grow to about age 20 and then succumb to the disease.
Choice 3 – The Liberty Elm
Developed in the States, the Liberty Elm variety is from second generation crosses of most resistant parents. Their resistance to DED is still inferior to resistant cultivars derived from Asian and European sources.
Choice 4 – The Hybrids
I found out about their existence through websites of various cities on their street tree programs. I came across listings for Hybrid Elm – the hybrid cross were not even mentioned – just blank space. So what were these hybrids? Time to find out.
Hybridizing the American Elm has proved to be extremely difficult. Thousand of attempts have been made to cross the American Elm with the Siberian Elm – all failed. The difficulty is because of chromosome numbers. Our elm has twice as many chromosomes compared to all others (56 vs 28). So, I can only imagine how much, if any, American Elm is in these hybrids.
This is where we venture into troubled waters. This is what sources like Canadian Forest Service and Parks Canada have to say. ‘If hybridization is the only way to save a gene pool, then it may be justified. We shouldn’t plant hybrids without a lot of genetic back crossing so it is mostly native. If there is good evidence of natural resistance, there is no reason to go exotic.’
‘Exotics are one big experiment. People need to understand that when they planting a tree it will live for decades and should fit into the whole landscape and contribute to a healthy, green environment. Introducing exotics into areas may be risky since we don’t know the full impact especially with a changing climate.’
So there are your choices. Personally, I can’t wait for the SUPERS to be released to the public. It would be my dream come true if we could continue to plant the NATURALS alongside the SUPERS. But you know, the experts are already shaking their heads at my statement and saying, ‘Why would you muddy up or dilute the SUPERS with the less resistant NATURALS?’
Yes, the SUPERS are obviously superior over the NATURALS for DED but the NATURALS have a different, untouched genetic base. Who knows what the future will hold – especially with climate change and even more air pollution? We need a huge, varied genetic base for this unknown future. Maybe by limiting the genetic base to just the SUPERS we dooming the species?