I learned of the following article from a Jan. 10, 2018 Heritage Toronto email.
The Dec. 21, 2018 Guardian article, that I learned about, is entitled: “‘There’s no major city like it’: Toronto’s unique ravine system under threat: Without urgent action against environmental degradation, the forest ravines covering 20% of the city could be reduced to sterile valleys within decades.”
An excerpt reads:
The thickly forested valleys of Toronto’s ravine system are peerless: no major urban centre in the world comes close to its steep, voluminous corridors of woodlands. In total, the dramatic formations measure more than 30 times New York’s Central Park, earning Toronto the nickname “the city within a park”.
But the valleys and forests – which cover nearly 20% of the city – are disappearing with worrying speed, according to a study released earlier this year by the University of Toronto. Invasive species are making short work of the ecosystem. Without dramatic action, the ravines could be reduced to sterile valleys in the coming decades, the authors warn.