Category Archives: Introduced diseases

Butternut Bridges Over the Don

Lady Simcoe 1794 Winchester Street bridge over Don (Playter's bridge)

Watercolour by Lady Simcoe, 1796. Retrieved from:

Winchester Street, bridge over Don R. (Playter’s bridge)

In the diary that describes her travels through Upper Canada between 1792-6, Lady Simcoe provides the first settler account of a bridge over the Don River. What, in 1796, she calls Playter’s “picturesque” bridge is actually a modified, fallen butternut tree. Rooted and alive, the branches – which still grew the distinctive long, compound leaves – were spry enough to support the installation of a pole to be used as a handle (as depicted in Lady Simcoe’s watercolour).

 

The bridge – located at the foot of what is now Winchester Street – would not have been far from the green pedestrian bridge that currently links east and west Riverdale Park and also serves as an access point to the Lower Don Trail. In 2013 the City of Toronto commissioned a master plan for this area, which includes scheduled changes in its environmental protection. We believe that environmental protection should mean incorporating ecological integrity as a target. Scientific research into the ecological integrity of our ravine system – like our proposed surveys – is greatly aided by descriptions that we find in texts like Lady Simcoe’s diary.
Though a highly suitable habitat, you are unlikely to find butternut (Juglans cinerea) growing in Toronto’s ravines today. Butternut is a species exemplifying many of the challenges that exist for the ecological integrity of our ravine system. Though a member of the walnut family, butternut is a relatively short lived tree that is under duress from butternut canker and the introduction of non-native walnut species, with which it easily hybridizes. Butternut canker (Ophiognomonia clavigignenti-juglandacearum) is a usually fatal fungal infection that appeared in North America during the last century and has contributed to the butternut’s listing as a species at risk in Ontario.

Introduced Diseases and the Transformation of Our Ravines

Below and to the south of the dwelling [Castle Frank] was a deep ravine down which between hog-back formations ran a stream named Castle Frank brook, which flowed into the Don, just above a small island on the west side. The marshes gave way on the right at this point to good land covered with elm, butternut and basswood trees (From Robertson’s Landmarks of Toronto, Vol. 1).

Texts like Robertson’s and Lady Simcoe’s diary provide us with important glimpses of what the Toronto ravine system looked like when it was ecologically integral.

The above passage lists three tree species: American elm (Ulmus americana), butternut (Juglans cinerea), and basswood (Tilia americana). Two of these species, butternut (see our entry “Butternut bridges over the Don”) and elm, have had their populations decimated by diseases introduced in the last century: butternut canker and dutch elm.

This story is too familiar. From American chestnut to American elm and continuing with butternut and all our species of ash, a huge part of the transformation that has occurred in our ravine system and other natural areas is due to the widespread loss of native tree species to recently introduced diseases.

There is important work to be done finding and developing resistant strains of these species, but for those species that cannot at the moment be regained, the question becomes what has their loss meant for the ecological functioning of the environment? To what extent are these services provided by the species that have moved in? How has the change impacted other flora and fauna, and is it possible to increase the presence of other species to mitigate these effects? Some of this work has already been done (including by Eric Davies, a member of our team), but we still lack clear data on the scope of the transformation in Toronto’s ravines. It is useful then to have some quantitative measurement of these changes to couple with our historical vignettes. In addition, a survey of the ravine system is an excellent way to locate resistant trees. This is what our project, beginning by revisiting of the Taylor and Scrivener 1975 Park Drive ravine survey, strives to achieve for the city.