There has been a lot of talk in the last few years about using ‘native’ plants in the cultivated landscape. The reasons for this, as I see it, are several:
1) Native plants are horticultural underdogs
They were here before us, they are threatened due to competing introduced or exotic species, loss of natural habitat (development, etc.) and they are, perhaps unfairly, considered less ‘garden-worthy’ because of their plain-jane looks;
2) Native plants are important and vital key elements in our eco-systems
They provide habitat, food and often a valuable host plant to animals, insects and microscopic organisms; moreover, their health reflects the overall health of our natural environment;
3) Native plants have or may have unique characteristics (aesthetic, medicinal, edible, etc.) that are valuable to us and our future on this planet
But what are these plants? How do we determine what is ‘native’ (= it was here before European colonization?) and if it is native, is it intrinsically valuable because it is? Plants that have adapted to thrive in specific environments are often no longer present in those same places after our intensive infringement, nor would they necessarily survive if they were re-introduced. This is perhaps due to their inability to adapt or compete within these new conditions, or because we have simply renounced them for more desirable plants. Plants that may have been considered valuable by indigenous peoples, whatever their contribution (i.e. medicine, food, dye, tools, decorative, etc.), were not necessarily seen in the same light by European settlers.
Conversely, seeds of plants from oversees were lovingly transported by pioneers as symbols of home and security. Many of these plants became garden staples and others became a scourge of our natural landscapes.
I thought I would take a bit of an inventory of the plants I came across on my walks with Skye-dog through the woods in non-residential areas within Ottawa. I’ll see if they can be considered ‘native’ and if they are, what their contribution to us might be and what their future holds. Or if they’re not, how they might have gotten here and what their value might be to us as gardeners and backyard ecologists.
Perhaps the plant we most commonly encounter is buckthorn; both the common (also known as European) and glossy species (Rhamnus cathartica and R. frangula). Both of these are imports that travelled here with European immigrants; apparently they thought buckthorn was garden-worthy!
R. cathartica was also known as Purging buckthorn for its use as a medicinal purgative but has now been found to be a host for the soybean aphid (a serious pest to soybean crops), while R. frangula was prized because the charcoal from its wood was used for gunpowder. They are proficient seeders and have reproduced quickly throughout North America. Often found forming thickets which are almost impenetrable due to their dense branching and sharp thorns (found only on R. cathartica), both these plants choke out native species of shrubs and small trees and are considered highly invasive.
Volunteers at the Fletcher Wildlife Garden have been on a program to eradicate buckthorn from the Central Experimental Farm for about the last ten years. They have been sounding the call against it as an invasive plant and talk about it here.
There is a buckthorn that is, in fact, native to this area called Alder-leaved Buckthorn (Rhamnus alnifolia). This species is usually found near water and grows only to about 3′ in height. It has similar foliage to the two species above and the same inedible black berries.
Another plant we encountered on our walk is known as the Trembling or Quaking Aspen:
Populus tremuloides is a native tree and is often found in stands or clusters that are favoured by beavers for creating dams. It is actually the most commonly found tree in North America. It reproduces most actively by suckering and the invading roots can become a hazard in the home landscape (they are a member of the Willow family, after all). So despite its attractive grey trunk and striking golden fall colour (not to mention the evocative sound and sight of its leaves quaking), this tree is not usually available to the home gardener and no cultivated varieties exist.
Poplars are well known for being short-lived trees; they grow at a fast rate leading to easy breakage and the resultant high susceptibility to pest and disease damage. They are also responsible for the white ‘fluff’ that takes to the air when the trees catkins explode and release their seed, carried by the wind and covering much in their wake.
In natural stands, however, poplars are very useful trees because they provide habitat for a wide variety of animals including hare, black bear, deer, elk, ruffled grouse, woodcock as well as many smaller birds and animals. They also provide a host for numerous insects, bacteria and fungi: borers, leafminers, caterpillars, beetles, aphids, leafhoppers, weevils — the list goes on and on. A comprehensive description of this tree is available here.
In industry, P. tremuloides is primarily used for the creation of pulp and composite wood products (i.e. particleboard and MDF); they are also desirable when a splinter-free wood is required.
This native white birch, pictured above, called Betula papyrifera is found throughout Canada (except the far north, Nunavut) and the United States, as far south as New Mexico and North Carolina. The paper birch and trembling aspen are two of the most common deciduous trees populating the Boreal Forest in North America.
I digress, but did you know that:
“The Canadian boreal region contains the largest area of wetlands of any ecosystem of the world, serving as breeding ground for over 12 million water fowl and millions of land birds, the latter including species as diverse as vultures, hawks, grouse, doves, cuckoos, owls, nighthawks, swifts, hummingbirds, kingfishers, woodpeckers and passerines (or perching birds, often referred to as songbirds). It is estimated that the avian population of the boreal represents 60% of the landbirds in all of Canada and almost 30% of all landbirds in the United States and Canada combined.”
According to: “Birds in Canada’s Boreal Forest: New paradigms for paradise found”, State of Canada’s Forests (Cdn. Forest Service) 2005-2006, p 72 ; and Peter Blancher, “Importance of Canada’s Boreal Forest to Landbirds”, Canadian Boreal Initiative and Boreal Songbird Initiative, May 2003, p. ii, http://www.bsc-eoc.org/borealbirdsprpt.html
The Paper birch, to me, represents Canadian heritage and history, but it is also a tree that you can no longer find in many local nurseries. This is due, almost exclusively, to the voracious bronze birch borer which attacks the tree, usually at a pre-existing wound, and kills it from the inside out. According to the Pest Diagnostic Clinic at the University of Guelph, the best control against this native pest is cultural: that is, ensure the tree is planted in the appropriate place and is kept healthy.
This birch is an important source of food for many woodland creatures including moose, deer, hare, porcupine and beaver. A variety of birds also nest and feed from the tree including sapsuckers, woodpeckers and vireos. The tree is also the larval host for the Eastern Tiger Swallowtail butterfly and the Luna Moth. The bark was used by First Nation people for canoes, baskets, cradles, wrapping and storing food, roofing pit houses and they also constructed small tools with it. The sap was taken medicinally to counteract colds.
There was more to see on our walk but I was distracted by the sound of water. It was a stream emanating from a storm drain and its surprisingly clear water was gently flowing down toward the river.
I’ll have more for you in Part II.