Succession – the arboreal kind


By Jennifer Humphries

Whether or not you are a fan of the Succession series, there is a kind of succession that matters to our neighbourhood – the kind that keeps our streets and backyards leafy green.

Over the past few months, the Environment Committee of the Glebe Community Association (GCA) has been encouraging residents to plant new trees and protect the ones they have. The eco-role of trees is well known, and there is increasing awareness of their positive contribution to mental and physical health.

We’ve created a map showing tree canopy gaps, and we’ll soon be canvassing blocks where more than 40 per cent of front yards lack a tree. Take a look at the map, and if your block is in the red or yellow, please consider getting in touch with us at Glebe Annex and Dow’s Lake Area are not yet on our map; we hope to add them in the coming months.

Succession tree map for the Glebe

Succession planning

We estimate that more than half of the trees in the Glebe are 80-plus years old. The lifespan of a tree can reach well over 100 years, but our trees face the usual city challenges of salt and dog urine as well as an increasing number of massive weather events – think ice storms, derechos and the flood-and-drought seesaw. Many of the elders will be gone within a decade or two. Successor tree planting ensures that we will still have canopy when that happens.

Andrew Boyd, a professional forester and consultant for The IFS Group, answered my questions about successor planting. I hope you find this information as useful as I do. And for more tree selection information, Boyd recommends going to a reputable source such as the Morton Arboretum (

Succession Planting Q and A

with Andrew Boyd

I want to plant a new tree in my yard while my mature tree is still healthy, so that when the mature tree dies or is removed, I will have a younger successor tree ready to take its place.

  1. How far from the older tree should I plant?

There’s no hard and fast rule about distance. Every tree has a shade tolerance, so if your big tree has a thick canopy, look for a tree such as a red maple that can tolerate shade. And even though trees are used to sharing below-ground space, make sure the new tree has a reasonable amount of room for roots. Also, since the older tree will eventually have to be removed, consider how a company could access it without impacting the successor tree.

  1. How big a concern are pipes? Won’t a tree’s roots work around them? Can the roots really puncture a pipe?

Tree roots won’t puncture a pipe. If a pipe is leaking water, though, roots will grow towards the water. The City of Ottawa uses copper for its water mains and pipes; these are designed not to break or leak. If you have old lead pipes, there is a city program that can advise and offers a loan to make the switch to copper.

  1. How big a concern are wires? I understand that communications wires are not as big an issue as electrical wires. Why is that?

Communications wires such as those of Bell Canada are less of a concern, though it is a good idea to prune if branches seem likely to bring a wire down (communications companies do not prune). On the contrary, Hydro Ottawa prunes and often in such a way to disfigure a tree and, by making it asymmetrical and moving its centre of gravity, weaken it. If there are electrical wires overhead it’s best to choose a smaller tree, or to plant as far as possible away from them.

  1. Is the species a consideration?

All species are possible, bearing in mind shade tolerance. Another consideration: there are a few species that produce substances that are toxic to other plants and trees. This includes the highly valuable black walnut – good to plant but possibly not alongside your mature tree of another species.

  1. With extreme weather events increasing in frequency, are there trees that are more likely to withstand drought, windstorms, etc.?

A recent article from the International Society of Arboriculture recommends the oak as the tree least impacted by extreme weather events. Its wood is dense, making its branches less likely to break. It is slow growing compared to other species, but its strength makes it worth the wait. The native bur, red and white oaks all exhibit this quality. Oaks are also suited to our local clay soil.

  1. What else should I do to ensure the new tree thrives? Soil, nutrients?

You can improve the hole by adding new soil, but keep in mind that the new tree will have to adapt to the surrounding conditions. Foresters go by the saying, “The right tree in the right place.” In our area, don’t plant a tree known not to thrive in clay.

  1. How close can I plant other plants to the new tree, e.g. bushes, flowering plants?

A garden around the base of a tree is a great benefit. The soil you use for the garden will also be good for the tree. This is much better than lawn up to the base: tree trunks are frequently damaged by lawn mowers and snippers. If you are not creating a garden, consider mulch or other treatment, but be sure not to cover the trunk.

  1. When my elder tree has to go, what should I do to protect the young tree?

From partial shade, the new tree may be exposed to full light when the elder is removed. Removal in midsummer could burn the young tree and send it into shock – best to take down the old tree during the dormant season.

  1. I want to keep my beautiful old tree for a long time yet. How can I minimize damage to it from extreme weather events, such as the ice storm and derecho this past year?

For deciduous trees, reduction pruning is helpful. This means not fully removing branches but taking out 10 to 20 feet (3 to 6 metres) of a group of smaller branches, leaving less surface area to attract wind. For conifers such as spruce, which can be pulled out by the roots in a windstorm, placing (not digging in) limestone blocks around the base of the tree (not up against it) can provide a counterweight and reduce the chances of the tree toppling.

Jennifer Humphries is chair of the Glebe Report Association and a former co-chair of the Environment Committee of the Glebe Community Association as well as the committee’s lead on trees. Contact the Environment Committee at

Map: Della Wilkinson



Explore, hike and get your tree at the Ferguson Forest Centre

Ferguson Forest Centre is a non-profit, community-supported treasure, a half-hour’s drive from the Glebe, in Kemptville. A place to explore trees, hike, walk the dog and select a special tree for your own garden at the Ferguson Tree Nursery. I’ve been intrigued by this place since reading an article in Ottawa Magazine in 2021 (full disclosure, I have yet to visit, but it’s on my agenda for this spring).

The Tree Nursery primarily sells wholesale but will be hosting nine days of sales for the general public this spring: May 18 to 20, 25 to 27 and June 1 to 3.

Check out the Arboretum where signs tell you about each tree species and then, if you like, head to the outlet store to purchase one or more of their native saplings, shrubs and perennials. A range of tree species are available including spruce, maple, willow and oak. Andrew Boyd points out that Ferguson cultivates uniquely native stock, so you can be sure that the genetics of your sapling will be suited to our local conditions. All profits are used to maintain and manage the Forest Centre and its activities.

Details on the eight hiking trails, open to the public year-round, are at Note that they are maintained but, unlike the Arboretum, are not groomed. The Kinderwood Trail, a short hike designed to acquaint children with forest animals and their habitat, is flat and good for all skill levels.

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