IX, A, 6 Bi'own and Mathews: Dipterocarp Forests 539 



The effect of regulation by a diameter limit in a forest less 

 overmature and where logging is more selective than intensive 

 is very different from that just described. In the forest of 

 northern Laguna logging to a diameter limit of 40 centimeters 

 has been carried on, in a desultory manner, for the last fifty 

 or sixty years. The result is very clearly shown by our volume 

 table for this forest, which is presented on page 438. The men 

 who have been logging this region have not been able to use 

 every tree or even every species. They have gone through the 

 forest selecting the medium-sized straight-boled trees of the most 

 desirable species, especially those of Shorea polysperma (tan- 

 guile) , Dipterocarpus sp. (apitong) , Hopea pierrei (dalindingan 

 isak) , and a few of the understory trees, such as Machilus phil- 

 ippinensis (baticulin) and Eugenia spp. (macaasim). They 

 have rarely returned to the same spot in two successive years. 

 The result of their operations has been to change the composition 

 of the forest by a slight reduction in the volume of the species 

 which they have most desired and to change the volume composi- 

 tion of the forest by the removal of the medium-sized and larger- 

 sized trees. The result in regard to volume composition is very 

 clearly shown by our table, and from the forester's standpoint 

 a proper and elastic diameter limit would probably work very 

 successfully. The past success of this limit system for this 

 forest is in part due to the better distribution of age classes 

 and in part to the fact that the logging has not been intensive. 



We have now considered a situation where the diameter limit 

 system of regulation has proved an entire failure, and one in 

 which it would probably prove a noticeable success. Between 

 these two extremes we have all gradations. If the diameter 

 limit has been correctly determined, its successful use will depend 

 upon the distribution of the volume throughout the various 

 diameter classes and upon the intensity of the logging. Wher- 

 ever the volume is grouped in the larger diameter classes, the 

 system will fail, even though the logging is selective. Where 

 there is a uniform distribution of volume in all size classes, 

 it will prove a success if logging is not intensive. Where large 

 investment calls for heavy utilization, an arbitrary limit which 

 permits of the utilization called for by the size of the investment 

 will usually fail over large areas. It will succeed on any large 

 area for that portion of the forest where very small amounts of 

 the larger sizes of trees exist, but will fail in all parts of the 

 forest where a heavy stand of large-sized trees is encountered. 



The reason for the failure of the diameter limit in overmature 

 forests over large areas is that the limit approximates clear cut- 



