Part B, Working Papers, February 1974 - Special Collections - US ...

candidates for normal mortality. If the number of trees harvested In this waydoes not greatly exceed the level of mortality in the relevant size classes,and Is not highly specific as to kind of wood sought, the impact upon the naturalforest organization and structure is not great. If the trees are selected as tospecies and the selection process is repeated at short time intervals, this formof harvesting can, in the long run, result In depletion of the preferred speciesin the stand composition. This does not occur rapidly If the species is one thathas a relatively high frequency of occurrence in the stand and is well representedIn the understory. It would, of course, occur much sooner if the preferred specieswas one that was relatively low in frequency of occurrence and if the selectiveharvest extended over a large unbroken area.Many of the areas of lowland forest in Southeast Asia have, in fact, been highgraded over a long period through economic selection in this manner. Over largeareas of the lowlands Lagerstroemia has become the most prevalent of the largetree species because it has been less desirable than the Diptocarpaceae speciesthat are far more durable. Lagerstroemia has become a much more prevalent componentof the upper canopies of the forest in many areas because of this selection process.In discussing the first class dense forests of Cambodia east of the Mekong River,Rollet ^962) notes that Lagerstroemia represents by far the major proportion of thestanding volumes. Gartner and Beuschel (1963) refer to the dominant position ofLagerstroemia In Thailand because of the long history of high grading. They notethat while it represents 26.2 percent of the total exploitable stock It representedonly 3 percent of the annual cut.Study of the lowland forests of South Vietnam from low level aerial photographsindicates that Lagerstroemia, a very distinctive tree, represents at least as largea component of these forests as it does of their counterparts in Cambodia and Thailand.These aerial photographs also indicate that the preponderance of the forestsof South Vietnam having large trees In the upper canopies were very low in large11-9