Tree Inventory 2019-2021

The Friends of Petrie Island, in partnership with the Ottawa Stewardship Council (OSC) and Ottawa Field Naturalists’ Club (OFNC), has been working on a 3 year Tree Inventory.

Data collection over the summers of 2019 and 2020 collated information on over 1000 trees on Petrie Island, primarily in areas that have public access.  A focused inventory on all willows on the Island was undertaken in September 2019 as a complementary exercise. These activities were documented on INaturalist.com. 

The objectives of the inventory, which was envisioned as a three year project, were identified as:

  1. establish a baseline against which changes can be measured
  2. identify invasive species and their locations

The work this summer focused on the east side of the Island with particular attention to Cottonwood trees. All 669 observations were completed by one summer staff allowing for consistency of data collection (in part due to COVID-19 limitations). Thanks to Kyra McKenna for her thorough and methodical work.

The data reveals:

1. Significant biodiversity in the tree populations. This is likely related to the Carolinian environment (Petrie Island is at the northern most range) twinned with frequent flooding.  Thirty different species have been documented including black willows, hackberries, butternut, and slippery elm.  An outstanding specimen of peachleaf willow graces the northwest shore of the Island. The cottonwood, hackberry and silver maple populations appear stable.  Butternut canker has been a problem (only one sapling from nursery exercise remains) but butternuts on one of the other islands are being used as a seed source in the RVCA Butternut Program.  

2. The threats to the trees of the island include diseases such as Dutch elm disease which is progressively taking the American elms; infestations such as the emerald ash borer which has nearly wiped out the ash populations, and beavers which have predated many cottonwoods.  Buckthorn, common and glossy, which beavers do not eat, is now found extensively on the Island, crowding out native species.  Dog strangling vine and Japanese knotwood are other invasives recently found at Petrie.  As is typical, invasive species are concentrated in areas with public access.

The effects of climate change are a factor for future management at Petrie Island.  In addition to invasive species, flooding and extreme weather will likely continue to affect the ecosystems at Petrie Island.

In determining next steps it is important to align with The Friends’ mandate to protect flora such as trees and to preserve the Carolinian forest ecosystem.  Philosophically, the Friends use a light touch approach for the western section of the island and the independent islands.  Areas that have public access receive a more active approach with conservation activities such as the tree nursery, wire wrapping and monitoring.  Future actions will require consultation with key stakeholders:City of Ottawa;

-Parks, Recreation and Culture as administrators of the Island;

-City of Ottawa, Forestry, as accountable for community based forest management plans, and

-Rideau Valley Conservation Authority as lead for long term sustainability planning;

-Ottawa Stewardship Council and the Ottawa Field Naturalist Club, as content experts. 

Other contributors are Carleton University Environmental Studies, and the summer staff and volunteers that have contributed to the inventory.

Based on the data and conversations with our expert partners, the key areas for Action:

  1. continue monitoring the tree populations, and expand the inventory to the remote areas.  Enforce no public access in the western section and the island to protect species at risk.  Consider expanding inventories to other species.
  2. preserve at risk, “special” trees such as large cottonwoods in proximity to interior waterways,  large hackberries, bitternut hickory, butternut, slippery elm with wire wrapping
  3. add to the biodiversity with tree planting of native species suitable to Petrie Island conditions; e.g. swamp oak, witch hazel
  4. address invasive species with a focus on public access areas e.g. Japanese knotwood, buckthorn, dog strangling vine
  5. develop erosion control measures in collaboration with RVCA.

The combined (2019-2020) inventory in order of frequency shows: 

Eastern Cottonwood: 298

Silver Maple: 202* (under represented as areas such as along Muskrat Trail are extensively silver maple; individuals trees were not inventoried in homogenous areas.

Common Hackberry: 128

Green Ash: 108 (significantly diseased)

Basswood: 99

American Elm: 91

Butternut: 30

Black Ash: 16

Bitternut Hickory: 12

Eastern Black Walnut: 3

Bur Oak: 3

Paper Birch: 1

Buttonbush: 1

Choke Cherry: 1

Trembling Aspen: 1

Grey Alder: 1

Black Locust (off Sunrise trail): 1


To view the data and maps on INaturalist visit https://inaturalist.ca/projects/petrie-island-tree-inventory-7528cae5-1237-4370-a84c-b6167eea6f0c

Check out iNaturalist for more information

https://inaturalist.ca/taxa/54857-Celtis-occidentalis

https://inaturalist.ca/projects/petrie-island-ottawa

Thank you to our inventory team leaders:

  • Owen Clarkin – OFNC Conservation Committee Chair, well-known for his deep knowledge of trees.
  • Janet Mason – OSC Chair, field naturalist, and tree enthusiast.

If you are interested in future tree inventory activities, please email: inquiries@petrieisland.org