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The UNESCO Classification System

The UNESCO classification system (Table 3.3) is a comprehensive classification based on vegetation structure and environmental variables that reflect both stress and function (climate, soils, topography, successional state). However, the vegetation formations determined with this system are too large to be useful in predicting management requirements for a particular stand. Where good forest community maps are available, they can be incorporated into the UNESCO system to serve as a guide to forest management.

The map of forest communities in the Luquillo Experimental Forest of Puerto Rico (Fig. 3.6) was developed using the UNESCO system. The Tabonu-co forest dominated by Dacryodes excelsa corresponds to the submontane to montane forest in the physiographic climax formation of UNESCO. Tabonuco is a valuable timber species that has good form and its response to management is well known (USDA 1990). Above Tabonuco on the mountain slope is the Colorado community, dominated by Cyrilla racemiflora. This community, which corresponds to UNESCO's alto-montane forest (moist) category, is much less valuable for timber production but has been used for charcoal in the past. It is valuable as a habitat for wildlife, most notably the endangered Puerto Rican parrot. On steeper slopes and wetter soils, the forest is dominated by the sierra palm, Prestoea montana, which has little commercial value. On the highest peaks of the mountain the dwarf forest occurs, composed of dense stands of short, small-diameter, twisted trees and shrubs heavily covered with mosses and epiphytes. This would correspond to UNESCO's alto-montane moss forest (wet, misty).

A major problem with the UNESCO system is that it must be used in conjunction with accurate maps of forest communities. Due to the time and expense of preparing them over large areas such maps often are not available.

Table 3.3. The UNESCO classification system of tropical vegetation formations. The table presents a climatic gradient from the climatic equator towards higher latitudes, and the corresponding gradients of plant habitus and of the main plant formations. Habitus is expressed as the type of climatic adaptation and corresponding morphological adaptation. Formation refers to formation group and formation levels of ecological-structural classification. Climatic data refer to tropical lowlands below 300 m altitude. (UNESCO 1978)

Table 3.3. The UNESCO classification system of tropical vegetation formations. The table presents a climatic gradient from the climatic equator towards higher latitudes, and the corresponding gradients of plant habitus and of the main plant formations. Habitus is expressed as the type of climatic adaptation and corresponding morphological adaptation. Formation refers to formation group and formation levels of ecological-structural classification. Climatic data refer to tropical lowlands below 300 m altitude. (UNESCO 1978)

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