Sampling For Forest Inventories

Abstract

The objective of forest inventories is to obtain qualitative and quantitative infor-mation about forest resources and their physical environment, at a specified point in time and at reasonable cost. Its main goal is to report on the status quo of the forest: areas, volume, and volume distribution in terms of size classes, but also on the expected changes (growth, vitality, mortality). Because of the increasing multiple use of forest resources during recent years, its scope has been enlarged and may include information about the potential of the forest for wildlife, recreation, and other uses. Forest inventories may therefore be classi-fied as follows: • National and regional forest inventories, which form the basis for forest policy decisions and long-term planning of the forest industry in its entirety • Management inventories which are required for management decisions and more particularly for the construction of working plans • Inventories for the appraisal of stumpage value • Surveys required for planning logging operations • Multiresource inventories, for example, those required for land-use manage-ment, wildlife and recreation • Inventories to assess and estimate the impact of pollution on vitality and growth of trees and forests Each of these categories requires specific information and prescribes a spec-ified accuracy. A stand inventory to assess the timber value requires accurate estimates of the growing stock and, to a lesser extent, this applies also to a stand inventory for planning logging or thinning operations. For a survey undertaken to estimate the forestry potential of a region, however, it may be more important to estimate site productivity than stand volume per unit area. National forest surveys are carried out to provide a basis for forest policy decisions. 229 230 Sampling for Forest Inventories The reasons for sampling in forest inventories are: 1. A total enumeration of large forest tracts is not feasible and prohibitively expensive 2. Complete tree measurement implies destructive sampling which, for example, is implemented in stem analysis, but cannot be carried out on a large scale 3. Sampling is advantageous for updating forest inventories at reasonable cost 4. Sampling makes it possible to obtain more accurate information for selected sampling units The sample consists of n sampling units on which tree, stand, or site character-istics are counted, estimated, or measured. It is drawn from the population and represents the aggregate of sampling units for which information is required.