Global Warming

IN TORONTO ? After an incredibly warm autumn, we’re now having record snowfalls in these parts. When I see snow, I put away all my worries about how plants will survive. After all, a good blanket of snow is the best mulch there is. Everything underneath is kept in a consistent state: no freeze/thaws to ravage the plants.

But what are all these confused weather patterns doing to our plants? I called Diana Beresford-Kroeger, a botanist who lives in Merrickville, just outside Ottawa. Last year’s ice storm badly damaged all of her trees (one of her specialties), with the exception of a few native Carolinian species such as Catalpa speciosa and Liriodendron.

The full extent of the storm’s damage won’t be known for at least another 10 years, she says. Millions of hectares of trees were affected, and the canopy from Ottawa to Montreal was almost removed. This reduces the trees’ ability to survive, and the forest has to start over again. The canopy’s absence, in turn, affects global warming. Just as our toes are about to freeze, we don’t want to hear about global warming. But, as gardeners, we must pay attention. These are the points that Ms. Beresford-Kroeger makes:

  1. With global warming, there is an increase in soil temperature that changes the delicate balance between bacteria and fungi. One overwhelming the other increases plant diseases of all kinds. This could extend to the presence of mites in birds’ nests, for example. If mites proliferate with higher temperatures and humidity, the next generation’s young birds may die. Birds and bugs (good and bad) emerge at the same time. We need those birds to pick off the pests.
  2. Swings from very cold to very warm weather mean an increase in fungal diseases such as downy mildew. Such swings increase the wasp and other insect populations such as sawflies and thrips that love heat. A rapid rise in temperature also can shatter bark in a straight line; more ice in the bark will create a long open wound.
  3. There is also an increase in sunburn across North America. It fries green-coloured soft plants such as tomatoes and petunias that have no waxy cuticles to protect them from the sun’s rays. Those most affected are in the Solanum family. This includes potatoes and tomatoes; they are becoming more difficult to grow in southern regions because they get burnt up in summer. Plants such as petunias and calla lilies also are suffering, though most of the herbs aren’t.
  4. Across North America, monocotyledons (grains, grasses and sedges) and some trees grown in the garden are being affected by increased ultraviolet A and B irradiation. When fertilization takes place, the pollen goes on the plant’s female part, which is in a vulnerable position. The pollen tube is injured when it is exposed to ultraviolet light. Fertilization is affected and all seed production is lowered.
  5. Anyone who uses pesticides should be extremely careful. Increased heat, especially around houses, makes all pesticides more toxic to people. They are more volatile, and affect small children and animals more quickly. Signs announcing pesticide use should go up well in advance and stay in place for at least five days, especially in parks and public areas.
  6. The use of organic and inorganic fertilizers should be cut back as the heat goes up. The higher the temperature, the greater the stress for plants. This coming summer, which is expected to be hotter than usual, use at least 20 per cent less fertilizer; that includes organic gardeners who use only compost. Step up the amount of watering.
  7. Another indirect effect of global warming is the lack of ozone, leading to more ultraviolet A and B. That disables plants’ immune systems so they can’t fight off diseases. We see it in onions, carrots and potatoes. This is the first year that Phythoptera infestans (potato blight, of Irish famine fame) has raised its ugly head.
  8. Crazy weather patterns are leading to more and more lightning strikes, thus adding nitrogen to the air. This means the potential for germination increases with an increased nitrogen load in summer rains. And so we get more weeds.
  9. Last autumn, trees did not all go dormant. If you were to prune now, you’d see they are still bleeding. The abscission layers (or bud scars) are also bleeding, again affecting the trees’ health.
  10. It’s not all bad news. Many North American native species — native orchids, agrostemma, club mosses and ferns — are on the rise. There are more butterflies that thrive with the heat and drink the sap spilled from broken trees.