Trees Please Hamilton

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A summary of our Invasive Plants workshop

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On May 29th, we held our Invasive Plants workshop.  Our amazing speakers were Nadia Cavallin, Lindsay Barr and Corey Burt of the Royal Botanical Gardens.   They covered a number of topics including: definition of invasive plants, real life examples and tools that can be used.

Invasive species is generally defined as not native and harms the natural environment.  It is one of the biggest threats to biodiversity and costs Canada approximately $13 – 50 billion dollars annually.

Our speakers brought in a number of examples to look at.
Our first plant was the Norway Maple.  Nadia explains that it is moving into natural areas and with its dense roots and canopy, little can grow underneath this tree.  One easy way to identify Norways is when you pluck a leaf and look at the stem, there will be a milky sap.

Photo 1 Norway

Nadia is holding up an example of the Norway Maple 

White Mulberry trees are hybridizing with our native Red Mulberry trees.  Our Red Mulberries are considered a Species at Risk.  Trying to distinguish White Mulberries from Red ones are challenging as most ones we see or have been planted are White Mulberries.  Red Mulberries leaves have fine hairs making it feel soft.  These hairs only appear when the tree matures.  The only real way of telling is by sending a sample to a genetic lab in Guelph for verification.  As well, you can contact Royal Botanical Gardens staff and they might be able to assist.

Privet is a shrub that is commonly found in our local nurseries.  At the RBG, it’s a challenge to get rid of.  It is one the top three invasive shrubs as well as Buckthorn and Honeysuckle.  Speaking of Honeysuckle, it’s berries are high in carbs and not protein.  So birds are unable to sustain long flights without having to stop and feed.

Multiflora Rose is very thorny.  One identifying feature mentioned at the talk was “it will rip your skin apart”.  Another identifying feature is taking a look at the bottom of the stem, the hairy part looks almost like a separate section.  Our native roses are more solid and the stem looks more continuous.
Multiflora Rose leaf
Tools that can be used:


Photo: Extractigator (orange handle – top of the photo), hatchet (middle) and tree girdler (bottom)

Extractor can be used to lift the entire plant out.  We found one local shop with two locations one on Barton and the other on Rymal Road that sells it for approximately $200 +HST.  Click here for store website.
Disposal must be done carefully.  When in a wooded area, invasives can be uprooted and if left, the plant can re-root themselves.  Lindsay often will hang buckthorns upside in trees to prevent the roots from touching the ground.


Lindsey extracts an invasive from the parking lot

A hatchet can be used to girdle a tree.  Go around the tree and cut through the inner bark this way you can slow down nutrients moving up and down the tree.  Lindsey clarifies that we want to be careful not to cut the tree down as that will cause the tree to sprout.  While girdling the tree will cause some sprouting, cutting it down will intensify the trees’ reaction.

A tree girdler is another tool that can be used.

Steps to get rid of invasives.
It basically cooks the plants.
Step 1: Place black tarp (could use thick black plastic garbage bags) to smother and heat up the invasives.  Depending on the invasive, could leave up to one year.  And leave anchored in place.  Can use rocks or garden staples.
Step 2: once the tarp / material is removed, layer at least 6 layers of newspaper down and place mulch or soil on top.  Make sure newspaper is wet to hold it down.
Step 3: create holes in the newspaper and mulch and plant native plants.

Main messages:
1) When at a nursery, ask for native species and keep asking.
2) Corey and Nadia explain the term “sterile”.  When buying a non-native the”sterile” label refers to that particular cultivar.  Examples of cultivars are: Emerald Queen Norway Maple and Crimson King Norway Maple.  So that two sterile Crimson Kings are not able to reproduce.  It can become fertile if two different ‘sterile’ cultivars mix and match.  And if for example, a Crimson King Norway crosses with another Norway of a different cultivar, the deep red leaves characteristic will probably be lost in the hybrid of the two cultivars.
3) When trying to remove Invasive Species, patience is key. Most of the time, it requires going back year after year and working away.
4) The impacts of Climate Change means more flooding and some invasives especially their seeds can travel by water for example, Giant Hogweed.  Shorter winters might mean that invasives are able to survive in our area when previously they couldn’t.

Grow Me instead

1) Grow Me Outside brochure.  A handy list of what to grow and what not to.
2) Early Detection and Distribution Mapping System is now available online to track new emerging invasive areas.  When caught early, it’s easier to manage.  For more information, click here.
3) Doug Tallamy’s book Bringing Nature Home is a great resource for what to plant instead.

A BIG thanks to Nadia, Lindsay and Corey for their insights, information and stories.  We learned so much!  Thanks to everyone who came out to attend our workshop and thanks to you our readers!


Author: treespleasehamilton

A project of the Hamilton Naturalists' Club and Environment Hamilton. Funding by Ontario Trillium Foundation.

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