Forest Definition
General observations
In large area forest inventories, estimation of forest area is one of the most important results. Forest area is a concept that is easily understood and extremely important in the context of discussion sustainability of the forest development in a region or country. Of course, a forest definition is not necessary for an inventory of forest stands for which up-to-date and accurate maps are available. Of course, the definition of forest is crucial when deforestation is discussed. Deforestation refers to lands where forest has formerly been. Then it becomes extremely important to use exactly the same unambiguous definitions of forest at both points in time – otherwise, the stated deforestation can not be properly understood.
The definition of forest varies with the context; there are differences in forest definitions from a silviculture, ecology or legal point of view. However, for large area forest inventory, the definition of forest needs to comply with two – some times slightly contradicting – requirements:
- it should be close to the definition used in the National Forest Act viz. in national forest policy processes; and
- it must be operational so that the decision can be made without major complications whether at a defined point there is forest or not. This refers to both data sources: field observations and observations in remote sensing imagery.
The issue of forest definition has been discussed in the forestry, forest policy and forest inventory community for decades and the discussions are likely to continue. A very comprehensive compilation of forest definitions from all parts of the world has been published by Gyde Lund: [[1]].
Components of a forest definition
When we look at forest definitions, we can clearly distinguish two different classes of criteria: quantitative and qualitative criteria.
Quantitative criteria include measurable thresholds such as minimum area of a “tree cluster” to be called “forest”, minimum width, minimum height of the tree vegetation, minimum crown coverage, and in some countries also minimum productivity (\(m3/ha\)). Qualitative criteria include the definition of “tree”, statements how to deal with roads, buildings, timber storage sites and other infrastructure within a forested area, and how to deal with creeks or lakes, with temporary clear-cuts etc.. Usually, roads and creeks are included as forest land up to defined maximum width. In many regions it may also be necessary to explicitly exclude some land use systems ‑ such as agroforestry systems ‑ which fulfill many of the “biophysical” criteria of sufficient tree cover, but are obviously not a forest because used for agriculture.
