Henry Kock had a vision to save, recover, and restore the white American elm tree.
The former Guelph Arboretum interpretive horticulturalist's curiosity was piqued when observing large elm trees across Ontario that appeared to have survived infection by Dutch elm disease (DED).
In 1998, seeing the devastating effects of the disease on the provincial elm population, Kock, known as 'Mr. Arboretum', created the Elm Recovery Project, collecting samples from survivors, developing a breeding program, and raising young trees for eventual restoration of DED-tolerant elms.
“Elm trees were dying. But some were survivors. It’s still an open research question as to why those survivors existed,” said Justine Richardson, director at the Guelph Arboretum.
“Were they just not exposed to the disease, or did they have something special that made them resilient?”
The long-term project is celebrating 25 years this year.
"We are excited to build towards that long term restoration impact that was always Henry’s vision and something that he always dreamed of," said Sean Fox, senior research associate at the Guelph Arboretum
Fox had a history working alongside Kock.
“I started working at the Arboretum in 2001 and worked with Henry on the project. Not too long after I started, he was diagnosed with a brain tumour and wasn’t able to continue with his work,” Fox said.
Kock passed away in 2005 at the age of 53.
“I and some others, stepped in where we could to keep the project going. We travelled the province and visited over 600 trees. We took genetic sample from these trees,” Fox said.
Since then, Arboretum staff have collected material from more than 600 surviving elms in Ontario, tested responses to the disease-causing fungus and planted resistant specimens in the gene bank.
“In some cases, this would be visiting a farm way out in the countryside. The landowner would say this his property used to be lined with them and there was only one left. So, clearly the disease had been there," Fox said.
"But to truly test that, we would have to make clones of each mother tree, bring them to the Arboretum, and then actually 'try' to kill them, so we would give them Dutch elm disease.”
The arrival of DED in North America in the 1930s resulted in the loss of untold numbers of white American elm trees in Ontario. In addition to losses from the disease itself, thousands of healthy elms were cut down as to stop the spread of the disease.
From the start, Kock was looking at something much bigger and much longer term.
The goal was find mature survivors.
“The elms are so iconic. There was a lot of effort at that time focused on finding a replacement tree, a super tree, something that we could confidently plant on our streets that was going to tolerate Dutch elm disease,” Fox said.
“The focus is on how American elms are going to be able to continue to be part of the landscape, beyond our life span and for many generations to come.”
Some elms possess immune system responses that allow them to tolerate infection without succumbing to the disease.
“However, DED tolerant trees are currently located so far apart that they are rarely able to cross-pollinate,” Fox said.
The advantage, Fox says, is that elms can start to flower and produce seed at a fairly young age for trees, sometimes 10 to 12 years old.
“And they are usually able to put their seeds out and put off offspring before the elm bark beetles which spread Dutch elm disease before they come and feed on the trees,” Fox said.
"And how is it that some elms have survived the disease?”
“All trees have this ability to become infected and fight something off, but with Dutch elm disease, it was a foreign pathogen from Asia when it came to North America, and the trees just weren’t ready for it.”
But a small percentage of American elms had the genetic ability that allowed them to have an immune response that could prevent the spread of the disease, and they continued to grow.
Today, through years and years of testing and surveying, the Arboretum is left with over 100 clones from different mother trees across the province.
“And these are trees that are basically genetic archives at the Arboretum which was always Henry’s goal, to make sure that we are protecting this valuable genetic diversity across the province before they are lost,” Fox said.
“We've tested them, and they are surviving. We tried our darnedest to kill some of them, but are enduring.”
Fox says as the elms mature, the second stage will be to allow them to breed with each other, to share pollen, and to eventually make those seeds available for restoration work across the province.
“The importance of this, is not relying on just one set of genes, because what if something else comes along? It could be the disease mutating, it could be climate change stresses, or invasive insects. And then being a clone, each of these trees is equally susceptible to a future problem.”
Fox says instead of putting all of the eggs in one basket, you can almost look at genetic diversity as a toolbox.
“Each tree has a slightly different set of tools and protecting them and making sure that diversity exists is a real buffer against future issues for that species. So, it's not not just about the nice tree in our back yard, but nature as a whole, and allowing that resilience to disturbances such as climate change and environmental stresses,” Fox said.
The Arboretum is excited to see a second generation of elm trees.
"We have an early grove and then we have a younger grove. Part of the idea is that we have brought these survivor elms closer together so that the trees can cross pollinate, create seed and hopefully some of those seeds will have traits of resilience,” Richardson said.
“We are still in the second phase of a really long-term project. We have taken some seedlings and we have been working with the city and they have been planting some of the seedlings in some of their naturalization projects. Our hope is that some of them will have those tolerant traits."
The operations of the Elm Recovery Project are funded by the Henry Kock Tree Recovery Endowment, which supports the recovery of many rare and endangered woody plants at The Arboretum. For more information or how to contribute, visit the donor page.
