The dry conditions in many regions in Canada have resulted in a higher incidence of forest fires. For those of us not in the fire areas themselves, we have been seeing the signs with smoky conditions for extended periods of time.
Fire ecology is the processes linking fire in an ecosystem as well as the ecological effects of the fire. It is important that even though fire is devastating, that same fire is a necessary contributor to habitat vitality and renewal. Many plant species in a naturally fire-affected environment require fire to germinate, establish or to reproduce. Fire is the mechanism by which the forest is regenerated. The fire consumes dead and decaying vegetation that accumulates on the forest floor, clearing the way to new growth. Therefore fire is an integral component in the function and biodiversity of natural habitats.
The response of trees and shrubs to fire varies significantly between and within species. These effects are also tempered by what has been happening in the ecosystem both before and after the fire. It is considered to be reasonable that temperatures of around 60 C are lethal to kill shoot tissues in most cases. This is dependent on the amount of heat received as well as the duration of exposure and the moisture content of bark, leaves and twigs.
Generally early in the growing season, during active leaf formation, there is a higher level of moisture present within the plant that decreases over the growing season and will continue to decline during dormancy. Therefore it would take a greater amount of heat to ignite a fire in spring and early summer than later in the growing season. However, if a fire hits an ecosystem in the spring and early summer, the plant material has used the majority of their energy reserves so there may be inadequate energy reserves to promote new growth.
If fire strikes just following dormancy, it is more likely (depending on the fire damage) for plant materials to sprout the following spring.
How a fire impacts the stem of a shrub is dependent on the protective quality of bark, thickness, composition and moisture content that have an influence on the ability of the bark tissue to absorb and transmit heat. Depending on the severity of the fire, it can also cause root mortality.
During intense fires, tree and shrub mortality may be instantaneous. This affects the ecosystem by opening entire areas to new growth and rejuvenation. For example germination adaptations include hard-coated seeds and serotinous cones that lie dormant until a fire passes. Under less severe fire situations, death may not occur or be delayed several years. Post-fire sprouting for trees, forbs and grasses are dependent on a number of factors including the severity of the fire, the interval between fires, weather conditions, land use, seasonality and more.
In saying all of this, please be careful when you are outdoors with cooking and recreational fires. Ensure when you leave the fire it is truly extinguished.
— Hanbidge is a horticulturist with the Saskatoon School of Horticulture and can be reached at 306-931-GROW(4769); by email at growyourfuture@gmail.com or check out our website at saskhort.com
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