Nearly half the territory of Québec–
an area of more than 750,300 km² - is covered by forest!
Any good storekeeper will tell you that the success
of a business depends on knowing exactly how many goods are in stock,
and how they rate in terms of quality.
However, unlike modern storekeepers who have bar
codes to help them take stock of their goods, it would be impossible
to count and check every single tree in Québec. Not only
that, but the forest is a dynamic and constantly changing environment.
Foresters use forest surveys to obtain information
on the condition of the forest and monitor any changes. Surveys
identify the various tree species, establish their age, height and
growth rate, estimate the volumes of timber available for harvesting
and provide details of surface deposits, disturbances and slope
classifications.
The main steps in a forest survey
Interpretation of aerial photographs
A survey begins with aerial photography.
Approximately 200,000 photographs to a scale of 1:15,000 are
needed to cover the entire forest.
The photographs are taken from an aircraft using a high-precision
camera.
Photo-interpreters then use special devices such as stereoscopes
to examine the photographs individually.
They identify areas that are fairly standard in terms of
species composition, tree density and tree height. These areas
or groupings are known as forest stands. Each stand is assigned
an identification code.
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In cartographical language, a scale
is the ratio of the distance on the map to the actual distance
on the ground. On this photograph, 1 centimetre represents an
actual distance of 15,000 centimetres (150 metres). |
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Mapping
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The contours from the aerial photographs are then drawn
to a cartographical scale of 1:20,000 using a special software
application. The resulting images are used to produce digital
maps known as ecoforest maps.
Because of the limited space available on the maps, the data
are presented in code form.
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This is how the codes for the stand shown in yellow on the above
map would be interpreted:
ErFt
This code means “tolerant hardwood-sugar maple stand”.
Sugar maple is the dominant species, but the stand also contains
other tolerant hardwood species.
C
This letter is an indicator of forest density, and represents the
percentage of cover formed by the ground projection of the canopies
of trees over 7 metres high. The letter “C” means a
cover of between 40% and 60%.
1
The figure following the density code indicates the average height
of the trees. “1” means that most of the trees in the
stand are over 22 metres high.
Vin
This code indicates that the forest is old-growth, with trees varying
in age from 60 to 120 years.
Cp shows that partial cutting has previously been
carried out in the stand.
D represents a slope classification of between
16% and 30%.
R refers to the surface deposit (the layer of
loose material covering the rock). Here, the surface deposit is
very thin, with frequent rocky outcrops.
II refers to the moisture balance (dry in this
case).
1534
Because all the data are computerized, the stand number (1534 in
this case) can be used to search a database containing details of
the codes and the area.
Checking the data
On-site sampling is required to verify the accuracy of the photo-interpretation
data,.
To do this, foresters visit and examine roughly 200,000 special
sites scattered throughout the forest. The sites are known as sample
plots.
Imagine yourself inside a circle with a radius of 11.28 metres.
This circle (400 m²) is a sample plot. Within the plot, the
forester identifies all the trees, counts them, rates them for quality,
measures them and establishes their age. He or she also notes the
features of the area, including its slope, altitude, drainage and
soil type, and takes a soil sample for analysis.
In Québec, 190,000 sample plots are temporary, that is,
they are normally used for only one survey program. The other 10,000
are permanent – in other words, they will be reused for the
next survey. The new measurements are compared with those from the
previous survey, and the results of the comparison provide an indicator
of stand growth.
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These foresters are using a hand-held
computer to enter data on the trees in a sample plot.
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| Here, a forestry technician is measuring
the diameter of a tree. |
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A huge task
A forest survey in any given area takes place over
a period of three years. Forest survey work is carried out every
year on part of the territory, and it takes approximately ten years
to cover the whole of southern Québec. In 2002-2003, all
Québec’s forests will have been surveyed for the third
time.
The forest survey and data analysis process will
be perfected as the discipline of geomatics (computer processing
of geographical data) is developed.
Using the results to prepare forest management
plans
Once the survey has been completed, the forestry
companies have the information they need to move on to the next
step in the forest management process, namely the preparation of
forest management plans.
Each plan covers a given area, and indicates where,
when and how trees will be harvested in that area. Forest survey
data is subjected to statistical methods and mathematical processing,
and the results are used to determine the volume of timber that
can be cut on a regular basis, year after year, in the area in question.
As a result, the forest’s economic assets can be harvested
in the short term without harming their future potential.
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