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What is a Forest?

Written by Dr. Roy Strang PhD,RPF,[ret'd]

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A forest is any tract of land where trees are the dominant vegetation along with associated shrubs, ground vegetation, fungi  and lichens plus an assemblage of animals, birds and insects. It can be of  any size, from a few hectares to many hundreds of square kilometres. It can contain one main species or a  mixture of both deciduous trees  and conifers. Forests can be of any age, from youngest stands to old mature ones.

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Geographically and on the broadest scale, four forest types are  recognized: tropical, made up of  several  scattered broad-lived and deciduous  species; temperate, predominantly  broad-leaved but with an admixture of conifers; boreal, with mostly conifers; and plantations, usually of a single species.

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Forests are classed by age only for management purposes. They can be  undisturbed but few if any remain and, in North America, only the extreme northern boreal forests qualify as pristine; young or immature stands are called ‘second growth’ following disturbance even when old and mature; and truly old growth forests have long recovered from disturbance and are characterized by  a mixture of healthy and diseased, decrepit or moribund stems.

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Soil type, hydrologic regime and local environment  strongly influence  the composition of a forest. For example the coast redwoods of California [Sequoia sempervirens] flourish only because their foliage takes up significant volumes of moisture from mists blowing inland from the Pacific Ocean during the summer dry period.

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Sunnyside Acres Urban Forest is a second growth stand following logging around the turn of the 19th and 20th centuries so that the oldest trees are now approaching 100 years. The drier portion  [one third of the area] is dominated by Douglas-fir {Pseudotsuga menziesii] with some western red cedar [Thuya plicata]  and hemlock [Tsuga heterophylla]. Since Douglas-fir seedlings require light and mineral soil to become established this stand will, over a long period of time, be dominated predominantly by cedar and hemlock stand. The other,  moister two thirds now support a mixed stand of cottonwood [Populus balsamifera] alder, [Alnus rubra] cedar, hemlock and Douglas-fir. Providing there is no disturbance we can postulate that the conifers  will become increasingly dominant as the shorter-lived  alder and poplar die off.

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These slow but inevitable changes illustrate the dynamic nature of forests. They are constantly changing; old growth will succumb to disease or fire or windthrow to be succeeded by an immature young stand. The rate of change is slow and change is gradual so that, from year to year, little difference can be seen but decade by decade the process becomes evident.