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Moving into a  new subdivision? Here’s why it is so vital you plant native trees

Picture yourself as a bird. A chickadee. Proud parent of half a dozen nestlings. You have a territory - an area with a radius of about 50 metres that you defend from others of your species to get first dibs on resources. You have a job - to work with your mate to get food to your chicks. It’s a challenge.

Many may think of you as a seed and  berry eater. But for chickadee nestlings, seeds are of no interest. These youngsters need protein! And that comes from insects. Ninety-six per cent of terrestrial birds rear their young on insects. The best source of protein is  caterpillars - the larvae of moths, butterflies and sawflies.

Back and forth, back and forth. You and your mate work from dawn to dusk to satisfy the chicks’ voracious appetite. How much do they eat? Doug Tallamy, professor of Entomology and Wildlife Ecology at the University of Delaware, parked himself by a chickadee nest and counted.

He found the pair delivered food every three minutes. Once, they delivered 30 caterpillars in 27 minutes. They foraged from 6 am to 8 pm. He figured they delivered 390-570 caterpillars a day. The chicks spent 16-18 days in the nest. Just getting the young to a point where they can leave the nest takes 6,240-9,120 caterpillars!


Can you believe one chickadee pair would be able to find 9,000 caterpillars in your yard? And all the other breeding birds that are sharing the space, can they find this much protein for their progeny? Fortunately they know where the caterpillars are hiding and are onto them before you’ve even noticed any bite taken out of the foliage. 

Desiree Narango, one of Tallamy’s graduate students, followed up on his observations with a research project monitoring chickadee nests in Washington D.C. from 2013-2016. She wanted to study how the modern home-owner's preference for non-native species impacts reproductive success in chickadee populations. 

 The results were dramatic: in the  neighbourhoods where non-native trees predominated, the nestlings did poorly or died. Not enough insects. A poignant detail: under some dead nestlings, researchers found sunflower seeds that the desperate parents, having been unable to find suitable food, had attempted to feed their young. The chicks were unable to consume these emergency rations.

What’s going on here? Why are there more insects on native trees? It’s because native trees are part of a food web that includes the kind of insects the chickadees want to eat, and these insects consume the foliage of the trees in the same food web. Ninety per cent of insects that eat plants can develop and reproduce only on the plants with which they share an evolutionary history. This is because plants develop toxins to prevent themselves from being eaten - but the insects that evolve with these plants over millennia develop digestive strategies to overcome the toxins.

An example of this is the Monarch butterfly: its larvae (caterpillars) have evolved defences against the toxins in North American species of milkweed. There’s a European species of milkweed known as Dog-strangling Vine that is invading the forests of southern Ontario (and has arrived here in Huronia in a few locations). The Monarch recognizes it as a milkweed and lays its eggs on the leaves. But when the caterpillars hatch, they lack the evolutionary defences against the alien milkweed’s toxins, they are unable to consume the foliage, so they starve and die. The North American species of milkweed are host plants for the Monarch, the European one is quite the reverse. 

Narango quantified the proportion of native to non-native plants in a territory that will allow a chickadee family to fledge into healthy maturity: she found that 70 per cent of the plant biomass needs to be native. Less than that, the insect prey is insufficient and the chickadee population is not sustainable despite the best efforts of diligent parents.

As land is cleared to make way for subdivisions, new homeowners can rise to the challenge of restoring native vegetation as they decide how to landscape their yards. When you do that, picture yourself as a bird. You’re going to need 9,000 caterpillars for the kids. These caterpillars will not adversely affect the plantings that you, the homeowner, are putting in because you, the bird, will scoop them up and fly them to the nest as fast as possible. The native trees will be the keystone of your yard as a living ecosystem, helping to restore biodiversity.

The good news for the home-owner anxious to enhance property values with aesthetically pleasing planting schemes is that the native flora of the North Eastern seaboard are exceptionally beautiful. Here are five of my favourite large trees to plant either in numbers as a grove, or as a single specimen. 

  • Northern Catalpa (Catalpa speciosa) A few years ago, I wrote a blog about the wonderful, glorious, stunning Catalpa. In July, it is covered with huge white frilly orchid-like blooms, their centres delicately highlighted with purple stripes and splashes of orange. With its large leaves and long pods, it’s a real statement of a tree. 
  • Red Maple (Acer rubrum) This is one of the stars of the changing of the colours, turning an eye-popping red in fall. The North American autumnal display is more vivid and striking than anywhere else in the world, we should showcase it in our gardens. Don’t be confused by the tree more commonly referred to as a red maple, which has foliage of a deep burgundy colour in spring and summer as well as fall and is actually an alien invasive Norway Maple (Acer platanoides).
  • Red Oak (Quercus rubra) The oak, any kind of oak, is Tallamy’s champion when it comes to the number of species of butterfly and moth caterpillars it hosts. Tallamy sets the number at 557. The handsome Red Oak (also a stellar performer in fall) is one of the most common forest trees in our region.  Restoring it to the landscape through plantings in new subdivisions has particular value for our native wildlife.
  • White Pine (Pinus strobus) Make space for the king of the forest, one of the trees that inspired the Group of Seven, its bold silhouette cutting into the sky. Granted, it will take more a few years before the silhouette of the tree you plant cuts into the sky, but even in its early years this is a graceful and elegant species. And it’s surprising how time flies when you measure it in tree height. 
  • Paper Birch (Betula papyrifera) This is a tree of moist woodlands but is also found on sand dunes, where the sand is damp below a dry surface. A decorative and fast-growing tree, often planted in a clump of several stems. Do not confuse with the Eurasian white Birch (Betula pendula), favoured by the horticultural industry because it turns white at a younger age.

Finding a good selection of native trees isn’t always easy but availability is improving. The five species I have listed here are carried by the large wholesale growers - so ask your local garden centre to source them for you. You might also want to talk to whoever is making the decisions about landscaping in the shared and public areas around your new home. 

Every spring, conservation authorities sell bareroot native plants - bareroot means freshly dug, unpotted, needing to be planted right away while still dormant, and inexpensive.  In my area of Huronia, the local source is the Severn Sound Environmental Association. Be sure to watch for their ad early in the new year and get your order in. 

A final note: it’s not just the trees that support the ecosystem. You need to look at everything - annuals, perennials, shrubs, vines and groundcover to provide a full range of habitat and host plants.  

A few years ago someone came to me with a proposal for a “pollinator kit” to market to owners of newly built homes.  I thought it was a brilliant idea and developed a plan for a $20 pollination station with five good-looking plants that also support beneficial insect (and hummingbird) populations:  Oswego Tea Beebalm (Monarda didyma), Dense Blazing Star (Liatris spicata), Anise Hyssop (Agastache foeniculum), Obedient Plant (Physostegia virginiana), and Spotted Joe Pye Weed (Eutrochium maculatum). I even planted a specimen bed to show how it would look. 

But the lady with the brilliant idea did not return and my customers tend to come with their own ideas. They aren’t interested in a starter kit. Still, hold on to the idea that in your new space, at least 70 per cent of planting at at all levels will be native - for beauty and the birds.

Links:

Non-native plants reduce the population of an insectivorous bird

Wonderful, glorious, stunning Catalpa

Note: Return of the Native is closed Saturday June 22 for the Tiny Marsh BioBlitz.

 

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