The cause, says Thomas Hutchinson, a biologist and professor of ecology at Trent University, is a slow poisoning of the ecosystem, mainly by air pollution.

The poisoning has made it impossible for lichens to live. It has seriously hampered the ability of sensitive wildflowers to survive. And it has driven sugar maples and white pines out of the city’s central areas.

In addition to trilliums, the trout lilies, bloodroot, doll’s eyes, wild ginger, and hepatica ``are largely gone from Toronto,’’ Hutchinson says. ``And although we don’t know for sure, I suspect that there are more flowers on their way out that we consider part of the Canadian heritage, such as blue bead lily, wild sarsaparilla, and the Canadian mayflower.’’

Hutchinson’s observations are buttressed by the work of one of his graduate students, Diane Smith. Her Ph.D thesis was based on a study of plant life in urban and rural sites.

There were 20 sites in the study, stretching from Toronto through Peterborough to Eganville, 40 kilometres west of Renfrew. The sites were all on flat land, and contained trilliums and mature maples that were at least 100 years old.

The sites in Toronto were on the grounds of Sunnybrook Hospital, Glendon College, the Toronto Brickworks (west of Bayview Avenue in the Don Valley), and at the Federation of Ontario Naturalists property at Leslie St. and Highway 401.

Within the Toronto sites, the absence of lichens is particularly troubling. They are not essential to the food chain, Hutchinson explains, but they are an extremely reliable indicator of the the extent to which land can support life. ``Their absence is giving us a serious warning signal,’’ he adds.
                     
Air pollution causes multiple assaults. It produces acid rain which can change the acidity on the stigma of blossoms and prevent pollination. The stigma is the sticky spot on which pollen is received. It’s at the end of a slender stalk that descends to the plant’s ovary.

Smog, also known as ground-level ozone, drives insect pollinators away, especially bees. When plants breathe it in, the ozone burns leaf tissues, creating yellow spots and inhibiting photosynthesis, the process by which plants convert sunlight into energy.       

Air pollution also deposits metals, such as lead, nickel, cadmium, chromium, zinc, and vanadium, that slow the rotting of dead leaves, and deprive plants of nutrients.  According to Hutchinson, a leaf may have only 30 parts per million (ppm) of metals while hanging on a branch of a tree. But when it falls, it may absorb metals from the ground to a level of several hundred ppm. High metal content can slow down microbes working to decompose the leaves by up to 20 per cent.

Potentially most damaging, however, is the decline of fungi below ground level. Called mycorrhizae (root-fungi), they extract nutrients from the soil -- such as minerals, phosphorous, and even moisture -- and make them available to plants. They also screen out toxic chemicals.

In the fall or late summer, the mycorrhizae branch to the surface where they develop and release spores. It appears, says Hutchinson, that air pollution is inhibiting the development of spores, and therefore the ability of mycorrhizae to propagate.

``We haven’t yet got specific figures (that quantify the reduction in mycorrhizae), but we know there is a strong decrease,’’ he says. Ninety per cent of all families of plants depend on mycorrhizae to flourish.

Now, step back for a moment, and look at what air pollution is doing in Toronto. It’s driving out pollinators; it’s reducing the ability of plants to receive pollen; it’s weakening photosynthesis, their main life support system; it’s killing off root-fungi that helps them feed; and it’s depleting their food supply.

Isn’t it time to get serious about reducing air pollution, instead of reducing the number of people who enforce pollution laws?