Forest ecosystems of Canada

Glossary

Autotroph
An organism capable of synthesizing the organic nutrients it needs from the mineral compounds present in nature. Plants and many bacteria are autotrophs or producers. Autotrophs do not need to obtain their nutrients from other living organisms. By contrast, heterotrophs cannot make their own food and so they feed on the tissues of other organisms.

Avifauna
Birds, in particular, all the birds of a given site: the avifauna of a marsh, a prairie, etc.

Biomass
The organic matter (cellulose and lignin) produced by plants. The term forest biomass generally refers to all of the material contained in the trees of a forest, including all their components (roots, branches, leaves, etc.).

Carbon budget
Comparative evaluation of the amount of carbon stored in natural forests (sinks) and the amount emitted by them (sources), which is undertaken to determine whether the forests are sequestering more carbon than they are emitting to the atmosphere. Carbon budgets can be drawn up on various scales, including global.

Carbon sink
A carbon reservoir that absorbs and stores carbon from another part of the carbon cycle. A sink stores more carbon than it emits to the atmosphere. This store of carbon can also be termed a reservoir or pool. Although a growing forest can be considered a carbon sink, when the forest stops growing and its trees die and start decomposing, it becomes a carbon source, because it emits more carbon than it stores.

Competitive exclusion
In ecology, the competitive exclusion principle (also known as Gause’s principle) states that no two species can occupy exactly the same fundamental niche indefinitely in a habitat where they are competing for the same essential resource, and that one species will crowd out the other.

Deciduous species
Trees that lose their leaves in the fall, such as birch, maple and basswood, are deciduous species. “Deciduous” means falling off or shed seasonally.

Decomposers
Micro-organisms that break down, digest and metabolize organic wastes, such as dead leaves, dropped fruits, wood and dead animals.

Decline
Disease that is characterized by a progressive decline in a tree’s health and in its growth and that may kill it. While the causes of this phenomenon are not known, it is generally believed that a combination of factors is to blame: pollution, soil acidification, drought, freeze-thaw action, etc.

Digital model
Computer-based representation of a mathematical model describing natural phenomena. These models use complex equations to perform essentially mathematical simulations of natural phenomena. They are used to study and test hypotheses about tides, climate change, the changes in an insect population or a forest, and so on.

Fire weather index
The fire weather index (FWI) is part of an approach that Canadian meteorologists use to estimate the wildfire risk in forest regions. Calculation of the index components is based on consecutive daily observations of temperature, relative humidity, wind speed and 24-hour rainfall.

Fungicides
Products that can inhibit the growth of fungi or kill them. Fungicides are used in agriculture and industrial plantation forestry to protect plants and trees from certain fungal diseases.

Granite bedrock
Geological formation that dates back more than 450 million years and is characterized by vast expanses of granite of volcanic origin. The Canadian Shield is made up largely of granite bedrock. Since granite has little capacity to neutralize acid rain, the forest ecosystems in these regions are fairly vulnerable to the effects of acid deposition.

Industrial plantation forestry
Tree cultivation using methods of intensive silviculture: plantations made up of genetically improved stock, fertilization, drainage, phytosanitary treatments, release of higher quality stems, etc.

Lichen
Organism consisting of a fungus (mycellium) and an alga (green alga cells) living in association. Lichens have a high tolerance for cold, drought and heat. They should not be confused with mosses, which are chlorophyll-containing plants.

Litter
Upper layer of organic debris on a forest floor, essentially the freshly fallen or only slightly decomposed material (leaves, branches, bark fragments, twigs, etc).

Microfauna
Soil-dwelling micro-organisms (animals) that cannot be seen with the naked eye. Synonym: soil fauna.

Micro-organisms
Living organisms (bacteria, microbes, yeasts) that can be seen only with a microscope. Micro-organisms that are likely to cause disease in other living organisms are called pathogens.

Nutrients
Mineral or organic substances (elements or chemical compounds) that plants and animals require for normal growth and activity. Plants and trees obtain nutrients primarily from the soil by absorbing them through their roots.

Parasitoid
An organism that lives at the expense of another (its host), impedes its growth and eventually kills it. Insect parasitoids, which are often very tiny, attack a single organism (plant or animal), from which they derive everything they need for their own growth and reproduction. One way a parasitoid does this is by laying its eggs in the body of the host insect. Parasitoids are being used more and more for biological control of insect pests, thus reducing the need for chemical insecticides. Predators, unlike parasitoids, prey on more than one organism and kill and consume their tissues.

Permafrost
Permanently frozen ground comprised of an active layer of soil overlying a layer of ice that varies in thickness. Permafrost is completely impervious to water because it does not thaw, although the active layer does thaw seasonally.

Phloem
The part of the tree that is produced through the growth of cambium cells in an outward direction. It may also be called secondary phloem. The sap produced by the leaves travels through the phloem tissue downwards in the tree. Compared with the xylem (wood), the phloem occupies a very small part of the tree.

Piedmont
The area of foothills at the edge of a range of mountains, which represents the transition between mountain and plain. The Foothills of Alberta are an example of a piedmont.

Pioneer species
Species that are the first to colonize a new site or a new ecosystem. They are generally shade intolerant and need a lot of sunlight in order to grow. Poplars and birches are pioneer species.

Precommercial thinning
Silvicultural treatment that consists in freeing trees that have good growth potential from competition by cutting the lower quality stems that are competing with them.

Rainforest
Forest that occurs in an area of high rainfall. Rainforests are usually found near the sea or in mountainous regions that receive a great deal of rain. Tropical forests are generally rainforests.

Secondary succession
Process whereby one stand or plant community supplants another; it is triggered by a major disturbance in a forest ecosystem.

Sedge
Herbaceous plants that have narrow leaves with sharp edges, flowers that are grouped into spikes and fruit (achenes) enclosed in small sacs. Sedges grow in tufts at the water’s edge and in wetlands.

Last Modified: 2007-10-09