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3.3 Ecosystem Map Units
Ecosystem map units are either simple, containing one ecosystem unit, or
compound, containing up to three ecosystem units (for which one or all of
the three attributes: site series, site modifier, and structural stage differ
one from the other) (see Figure 3.8). The proportion of ecosystem units
is indicated with "deciles." Ecosystem map units may also
have minor inclusions that are too small to map at the scale of the
survey.
| Figure 3.8 | Compound
map units |
An ecosystem map unit should have a limited range of characteristics, so
that it can be interpreted and treated uniformly (e.g., it should not contain
highly contrasting ecosystem units unless one is of minor extent and cannot
be feasibly mapped as a separate simple unit). The objectives of the survey
will often determine which characteristics are important.
Only ecosystem units that occupy 20% or more of a polygon are typically
indicated in the map label. Those that occupy less than 20% of the polygon
(e.g., a small wetland) can be indicated in the map label if they are particularly
significant for an interpretation. Another option is to indicate these ecosystem
units in the database comments field or as an on-site symbol. The
intent of this guideline is to minimize compound map units and encourage
delineation of new polygons where there is considerable complexity.
The inclusion of three ecosystem units in a compound map unit should be
done sparingly. Nevertheless, it is recognized that in some study areas
with a complex distribution of ecosystems, ecosystem units are difficult
to separate and compound map units cannot be avoided.
Minimum Polygon Size
A minimum polygon size of 0.5 cm2(e.g., 0.7 x 0.7 cm ) is recommended.
This polygon size corresponds to a land area of: 0.5 ha, at a scale of 1:10
000; 2.0 ha, at 1:20 000; and 12.5 ha, at 1:50 000.
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