The challenges faced by ravines

Our ravines define Toronto and make it unique. They're our equivalent to the canals of Venice, the hills of San Francisco, and the grand avenues of Paris. As our largest natural refuge, they contain the last remnants of the forest that once graced the entire region. They help filter and cool our air, and though they weren't a result of an international design competition, they bring immense beauty to our city.

Unfortunately, the kilometres of waterfront that line our rivers don't enjoy the same attention as those bordering Toronto's oft-talked-about harbour. If we don't start paying attention, the ravines that so many of us enjoy will succumb to a host of pressures. Here is a list of some that we should all be aware of.

1. Erosion It used to take a week to drain the Don Valley watershed; now it takes less than three days. Water flowing from the city's ever-expanding impermeable paved surfaces moves quickly through the ravines. Its speed washes away soil, which is then gone for good and hampers the growth of plants. It tears trees from their banks, wrapping them around bridges downstream, and wears away at riverbanks and the habitats they provide for plants and wildlife. "Toronto is at the receiving end of the water course," says the City's supervisor of ravine protection, Norman DeFraeye. "As the outlying areas become more urbanized, we get more uncontrolled run off coming through and causing more damage." But development isn't the only culprit. Non-native trees hogging the sunlight so that smaller plants, which also hold together the soil, can't grow, and pressures from recreational activities are also to blame.

2. Development Toronto's ravine system is dying from a thousand cuts. The City adopted a harmonized ravine protection bylaw in 2002 to safeguard all trees and prevent changes to a slope's grade. But with 18,000 acres of ravines to manage, enforcing the bylaw doesn't come easy. Hydro lines, bridges, roadways, new buildings, additions, and landscaping — each chip away at our forested valleys, enabling the introduction of non-native plant species and increasing water run-off, which leads to erosion. "People think ravines look after themselves," says Beth McEwen, manager of the City's Forestry and Natural Environment Management. "When people [who own ravine property] get a home inspection, they should get a ravine inspection, too. We need to change the mentality so that people pay attention to the ravines."

3. Water Pollution Whenever there's a heavy rainfall, our ravines take on a lot of shit. An overabundance of water causes our old combined sewers to overflow, dumping untreated sewage directly into our rivers. But even the water that runs into storm sewers from a moderate rainfall, or from a hose used to wash a car, carries a variety of pollutants, including fuel, oil, brake and transmission fluid, animal feces, and, in the winter, a high concentration of road salt. These pollutants threaten the entire food chain, including fish, insects, and plants.

4. Recreation With their mature trees, quiet paths, and bubbling streams, ravines offer a welcome escape from the noise and bluster of the city. Urbanites, used to being cooped up in condos and office towers, descend into these green getaways for leisure, be it cycling, jogging, or going for a walk. Like gentrification, as the number of people who use the ravines increases, the desirable features they were initially coming to enjoy begin to disappear. Adventurous mountain bikers and hikers create new paths that cut through natural areas, packing down the soil and crushing tender understory plants. Owners let their dogs run free, damaging flora, disturbing animals, and tracking in the seeds of non-native plants.

5. Invasive Species Ecosystems consist of a wide diversity of plants, animals, and insects that have evolved in relationship to each other over the course of thousands of years. Human disturbance, such as cutting down trees for power lines, disrupts these ecosystems and allows invasive plants and insects to move in. Often arriving from other parts of the world, they may have few natural predators. Norway maples, the trees that line many of our residential streets, are among the worst offenders. Wind carries their abundant seeds into the ravines. The resulting trees grow quickly and have extensive root systems that soak up water and large leaves that shade the ground below. Starved of water and light, native plants die, increasing the rate of erosion. Birds, animals, and insects that once relied on the diversity of plants move on in search of new sources of food and shelter. A separate but equally pressing problem is the invasion of exotic pests such as the Asian Longhorned beetle, which would decimate trees if it were to enter our ravines.

6. Climate Change Climate change will compound the litany of problems facing our ravines. As the summers get longer and hotter, additional people will seek refuge in the forested valleys, further damaging plants and contributing to erosion. Prolonged droughts will put stress on trees, killing some and making others more susceptible to insect damage. Warmer, shorter winters will enable insects that would normally be killed off by the cold to survive until the following spring to munch on more leaves. Summer storms are expected to increase in frequency and severity leading to greater erosion and further degradation of rivers and streams. Fluctuating winter weather will result in more ice storms and, in turn, greater use of salt, which already plagues our waterways

There is a lot that can be done to save and protect our ravines from further damage. Toronto's urban forestry department recognizes that there is a problem. Unfortunately, it doesn't have adequate resources to deal with it. Over 500 volunteer groups, large and small, are working to improve the ravines in various ways, but it's not enough. The city needs a management plan for its ravines. Its ravine protection bylaw needs to be more strictly enforced. Nurseries should no longer grow and sell invasive species of plants and trees and tax breaks should be given to homeowners who restore portions of ravines on their property. Individuals who use our ravines should be educated to keep their dogs on leashes and stay on groomed paths. Recognizing the gravity of the problem, however, is an important first step.