Canada's Forest Inventory 2001 - Publications du gouvernement du ...

3.4 Site Index
The ability of a particular location to grow trees depends on many factors, including soil nutrients and
texture, drainage and climate. Because soil and climate factors are not easily measured or estimated from
aerial photography, whereas tree height and age are, forest inventories use tree height at a certain age to
predict future performance. CanFI2001 uses an index age of 50 years (100 years in the Yukon).
Site index is not available for all data sources in CanFI2001; of the 310 million ha of forest land in
Canada, 38% (just under 120 million ha) has no site index information. Where information is available,
Canada’s forests have an average site index of 11.8 m at age 50 (Table 11; Appendix I: Table I-4). Volume
per hectare and biomass per hectare tend to increase as site quality increases (Figure 16; Appendix I:
tables I-5 and I-6).
The forests with higher site indices (27.5 m or taller at 50 years) are not extensive, they amount to
about 1 142 000 ha (Figure 17; Table 11). The higher site-index forests contain 369.5 million m 3 of 29
383 million m 3 , or 1.3% of the total volume (Table 11; Figure 18). Similarly, just 1.6% of the biomass is
found in forests of higher site indices. Appendix I: tables I-7 and I-8 show total volume and biomass by
site index and province and territory.
Figure 19 shows the predominant site index, based on the site index with the greatest area within a
mapping unit. The highest site indices are found on the west coast, and a few higher site index areas exist
in Ontario and New Brunswick. Most forests in Canada reach between 5.0 m and 19.9 m at 50 years.
900
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0
Volume (m 3 /ha)
Biomass (t/ha)
7.5 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5 52.5 57.5
Site index (tree height (m) at 50 years)
Figure 16. Average volume and average biomass by site index class.
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