What Makes A Heritage Tree? Part 1: Time

Time and the Heritage Value of Trees

The 2008 book, Heritage Tree of Alberta, lists 28 trees within the City of Edmonton. While I believe that this list represents a cross-section of the City’s total number of heritage trees, I think that we can draw a few lessons from its pages. Generally, three things come together to make a heritage tree; time, novelty, and narrative. In the first of three posts, I will explore the relationship between heritage trees and time.

Mature Trees Are Cultural Artifacts

You can’t plant old trees, but you can plant and nurture young ones. Mature urban trees are the result of continuous care at best and benign neglect at worst. Development, overzealous home-owners, changes to drainage patterns, pests, extreme weather, climate change, diseases, or disruption to the root zone can all result in the premature death of an urban tree, so it’s no wonder that mature trees are uncommon. This fact alone makes mature trees rare enough to give heritage status.

Mature trees are the products of our past. Their history is our history. Trees are living cultural artifacts whose stories simultaneously reach into the past and future. A healthy, mature urban canopy is evidence of a culture that values the future.

Trees and Time

While the location of my city has been occupied for many thousands of years, the municipality known as Edmonton is relatively young and started as a trading post in 1795. As a bustling frontier town emerged, trees of notable size and value were likely cut-down for the fuel and lumber needed to support its growth.

While Edmonton’s native Alberta spruce (Picea glauca) are capable of living for hundreds of years, I am unaware of a single individual that predates the founding of Fort Edmonton in 221 years ago. Aspen poplar (Populus tremuloides), a clonal species, which lends its name to Aspen Parkland, the bioregion in which Edmonton is situated, grows relatively short-lived trunks, it can live for tens of thousands of years as a regenerating mass of younger shoots. I was unaware of any urban examples until I was recently tipped off to an aspen stand at the south-end of Magrath Heights Park – hopefully, more on this in the near future.

Trembling clonal-giants aside, the oldest tree in the City of Edmonton’s tree inventory – a list of all publically maintained trees – was a Manitoba Maple (Acer negundo) known as the Garneau Tree and was planted around 1874 by Metis settlers Laurent and Eleanor Garneau. The Garneau tree was the only tree in the City’s Inventory that predated 1900. Sadly, the tree came down in 2017 over safety concerns.

Edmonton’s Garneau Tree

Remembering the History of the Garneau Tree, The Gateway, September 26, 2017

“[The Garneau’s Tree, a Manitoba Maple] was planted by early homesteaders Laurent and Eleanor Garneau at the rear of their home. Laurent was Métis, and well known in the area as an excellent fiddler, as well as for his role in the Red River Rebellion of 1869, where he served as one of Louis Riel’s soldiers. The Garneaus moved to the south side of the North Saskatchewan River in 1874, where Laurent worked for the Hudson’s Bay Company as a charcoal burner and later as a freighter, before moving to St. Paul in 1901.” – Edmonton.ca

Old Age Is Relative (To Ourselves)

How long does a tree need to live before we call it old? If one stops to consider that the lifespan of trees is as diverse as the number of tree species it’s a bit of an odd question. While fifty-years is old for an Amur Cherry (Prunus maackii), a Rockey Mountain Bristlecone Pine tree (Pinus aristata) can live for thousands of years. Due to plant blindness – the inability to recognize plants or distinguish them from each other – we have a tendency to lump all green things together. Lacking perspective and a sense of time much greater than ourselves we measure their age against our own. It is thus our biology – not theirs – that determines heritage.

The turn of the twentieth century saw the planting of Edmonton’s oldest Elm trees (Ulmus americana). While we view them as old, they are roughly one-third of the way through their life expectancy. If Edmonton’s elms were people, they’d be pushing thirty. Like mayflies watching human children, we consider one-hundred-year-old saplings as ancient.

I suspect that we start thinking of trees as old around the time that they reach the average life expectancy of a human; about eighty-years. The Stark Oak (1933), Holowash Horsechectnut (1920), and Margaret Martin Willow (1907) are as old as Edmonton’s eldest residents. At 86 years old, the Stark Oak planted in 1933 is old but its contemporary, the 60-year-old Queen Elizabeth II Oak doesn’t feel that old. Give it another twenty years.

The lens of human-life-expectancy means that short lives species will never achieve heritage status via age alone. While short-lived species are more likely to die from old age, long-lived trees are more likely to die from diseases, climate, and development.

Age and Size are the Products of Time

Could it be that faster or larger growing species are more likely to achieve heritage status than their slower, smaller counterparts? Since a tree’s rate of growth varies between species, the size of a tree is a crude stand-in for age. One Colorado study found that the diameter at breast height (BDH) of local Cottonwood trees (Populus deltoides) grew at roughly twice the rate as Red Maples (Acer rubrum). Forgive the casual observer for thinking that the Cottonwood is twice as old as the Maple. Many long-lived species are known for their slow rates of growth. Their slower speeds of growth may even be a contributing factor to their longevity. The opposite of “play hard die young.” By the way, red oak grows half as fast but can comfortably live twice as long as cottonwood.

Might the slower growth-rate of some species cause us to underestimate their age and thus undervalue them? Do we do the opposite with faster-growing species? If so, we might expect to see a higher percentage of faster-growing trees (ex. Manitoba Maple) and a lower percentage of slower-growing ones (ex Oak) in the tree inventory – assuming similar rates of planting.

Tree Age and Urban Development

Since trees can live longer than the buildings they cohabit the landscape with, the development of a site has an enormous impact on the age of trees. Developers prefer blank-slates so clearing the site of trees is common practice. Bigger buildings fetch bigger profits, and while mature trees also increase property value, they’re susceptible to damage from nearby excavation, soil compaction, and regrading. Since development is a large and important topic, I have dedicated a sperate post to exploring the link between development and life-expectancy of trees.

How To Grow An Old Tree Takeaways

• Choose tree species with a long life expectancies
• Choose tree species that are not prone to pests or diseases
• Consider development setback requirements when choosing planting locations
• Maintain tree health with proper care and pruning done to ISA standards
• Support landscaping standards for new developments. ex. Edmonton Landscaping Standards
• Support protections for plants identified as having heritage value

Not All Heritage Tree Are Old

While time seems to be one of the more important identifiers of heritage, it is not a necessity. Two additional, but interconnected categories also play a role; novelty and narrative. In my next few posts, I will explore the impact of novelty and narrative on the makeup and survivability of heritage trees.