A unit of Lasting Forests evolving since March 30, 1999
A Total Forest Management Plan and Wildland Management Decision Support System
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Slope and Elevation Classes and Their Diversity

The following tables analyze the proportion of the area in various slope and elevation classes. The emphasis is upon general decisions which often emphasize percentages (or proportions) of areas steeper than....some specified amount. Decisions often include risk expressed as ".... a high proportion of land in class VI and VII. "

The Shannon Index reported with each is an index of evenness or how evenly distributed the land is in all classes. If there are equal proportions in all classes the index will be at its maximum.

The index will be strongly correlated with indices of surface roughness. It is likely that it will relate to other watershed characteristics but enough studies (e.g., simple plots of suspected relations in different watersheds) have not been done.

The table is simple: Where there were 20 classes of slopes in a table, 4 percent per class (e.g., 0.0 to 3.99, 4.00 - 7.99, ... with the last class being 76.0- 99.99) then the proportions of the area in each class can be presented and the Shannon index shown as a summary statistic (in one case for a large watershed, 1.629).

A table can be created slopes (by degree or class, acres, percent; then aspects can be sprarated and the same table presented.

Where slope classes are used, cumulative acres can be presented, first in ascending order, then descending order. These columns can be used to evaluate the percent of the area that is within certain slope constraints. (Constraints are steepness limits beyond which present technology and land protection needs make certain actions inappropriate (e.g., timber harvests and road cuts.)

A picture of the distribution of slopes can be useful in comparing areas, the cost to an animal population of moving within an area, runoff potentials, etc. Here frequency is the percent of cells within each degree slope class. Other classes can be used.

Capability Classes

Fairly well recognized land capability classes are used. These are mostly percent-slope classes. (Gross ranges are published but assigning a map pixel to a class requires a precise criterion as shown in the following table.) The classes are of different size, making analyses very difficult. Information on Class V is currently unavailable. A table is created showing the acres (and hectares) in each class with a percentage or proportion of the total area in each class. Perhaps a diversity index computed using these proportions may have meaning for some people.

I	0.0 - 2.0
II	2.1 - 7
III	7.1 - 15
IV	15.1-25
V
VI	25.1 - 35.0
VII	35.1 - 99.9

Equipment Operability Slope Classes

Logging equipment and others are designed to operate on steep slopes, but there are limits. Typical logging equipment has the following operability classes. A table presenting the acres and proportions of an area in each class suggests "land unsuitable for conventional forestry " and productive potential of areas. Potential for trails, hunting, or other recreational use may be suggested (or the needs suggested for other classes and analyses.) See these classes within the section on Aspect.

I	0.0 - 20.0
II	20.1 - 40.0
III	40.1 - 99.9

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This Web site is maintained by R. H. Giles, Jr.
Last revision July 13, 2001.