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Overview Of Classification Methodology For Determining Land Capability For Forestry

water class 1 class 2 class 3 class 4 class 5 class 6 class 7

The mapping of land capability for forestry is based on a national classification system comparable with the other Canada Land Inventory sectors. Land is rated according to seven classes depending on its capability to grow commercial timber in areas stocked with the optimum number and species of trees. This rating considers the land in its natural state, without improvements such as fertilization, drainage, or amelioration practices. With improved forest management, production may change and limitations may be overcome so that class changes may occur, however, significant changes will only be achieved through costly and continuing practices. The best lands for tree growth are Class 1, and Class 7 land cannot yield timber in commercial quantities, these represent the extremes, because of unsuitable climate, no Class 1 lands will be found in several regions of Canada and in certain regions, Class 2 areas will be too small to show at the chosen scales of mapping.

The capability mapping is accomplished through interpretation of air photographs and field surveys. The assignment of land units to a capability class is made on the basis of all known or inferred information about the unit, including subsoil, soil profile, depth, moisture, fertility, landform, climate, and vegetation. Associated with each capability class is a productivity range based on the mean annual increment of the best species or group of species adapted to the site at or near rotation age. Productivity classes are expressed in gross merchantable cubic foot volume to a minimum diameter of four inches. Thinnings, bark, and branch wood are not included. The productivity as expressed is that of "normal" i.e., fully stocked stands. It may be assumed that only good management would have produced stands of this nature. The following are not considered in the classification: location, access, distance to markets, size of units, ownership, present state, or special crops such as Christmas trees.

As shown in the symbols on the above map, the capability class is indicated by large arabic numerals. The smaller numerals following the capability class give the proportion of that class out of a total of ten. The capability subclass, shown as a capital letter, indicates the environmental limitations to tree growth. The letters under the capability class represent the native tree species that can be expected to yield the volume of timber associated with the capability class. These forestry maps represent the first comprehensive set of forest land capability maps for Canada. The maps are a valuable source of resource information for application in regional planning for the forestry sector as well as for multiple land-use planning and sustainable development strategies for Canada's resource dependent communities.

 

Land Capability Class Descriptions for Forestry.

The classes indicate the degree of limitations for commercial forestry use. The subclasses indicate the kinds of limitations that individually or in combination with others, are affecting commercial use.

ClassDescription
1
Lands having no important limitations to the growth of commercial forests.
2
Lands having very slight limitations to the growth of commercial forests.
3
Lands having slight limitations to the growth of commercial forests.
4
Lands having moderate limitations to the growth of commercial forests.
5
Lands having moderately severe limitations to the growth of commercial forests.
6
Lands having severe limitations to the growth of commercial forests.
7
Lands having severe limitations which preclude the growth of commercial forests.

 

Land Capability Subclasses for Forestry.
There are four major categories of subclasses. The first is climate, where the subclasses denote significant adverse departure from what is considered the median climate of the region, that is, a limitation as a result of local climate; adverse regional climate will be expressed by the class level. The second is soil moisture, which denotes a soil moisture condition less than optimum for the growth of commercial forest but no including inundation. The third is permeability and depth of rooting one, which denotes limitations of soil permeability or physical limitation to rooting depth. The fourth and final is other soil factors which individually or in combination, adversely affect growth. 

a
Drought or arid conditions as a result of climate.
c
A combination of more than one climatic factor or when it is not possible to decide which of two or more features of climate is significant.
h
Low temperatures, that is too cold.
u
Exposure.
m
Soil moisture deficiency.
w
Soil moisture excess.
x
A pattern of "M" and "W" too intimately associate to map separately.
z
A pattern of wet organic soils and bedrock too intimately associated to map separately.
d
Physical restriction to rooting by dense or consolidated layers, other than bedrock.
r
Restriction of rooting zone by bedrock.
y
Intimate pattern of shallowness and compaction or other restricting layers.
e
Actively eroding soils.
f
Low fertility.
i
Soil periodically inundated by streams or lakes.
k
Presence of perennially frozen material.
l
Nutritional problems associated with high levels of carbonates.
n
Excessive levels of toxic elements such as soluble salts.
p
Stoniness which affects forest density or growth.
s
a combination of soil factors, none of which, by themselves would affect the class level but cumulatively lower the capability class.


Jean Thie - Ecoinformatics International Inc.