17 



dimensions of the trees it contains, in other word*, make an tun- 

 meration survey. In an enumeration survey of a mixed crop, the 

 number and dimensions of the trees belonging 1 to each species or 

 group of species of similar habit should be ascertained and recorded 

 separately ; all important or extensively distributed species should 

 be registered separately, the rest being classed into groups, each 

 group comprising species that resemble each other ill height and 

 shape. 



As regards the dimensions of the trees, their girth is always 

 measured, the height, if that also has to be recorded, being 

 estimated with the eye. Since in every enumeration survey an 

 enormous number of trees has to be measured, it is not practicable 

 to register the exact girth of each tree, but to group the trees into 

 girth-gradations. The range of girth included in each gradation 

 will vary with the size of the trees forming the crop and with the 

 degree of accuracy sought. For the most accurate valuation, 

 survey, the following ranges are narrow enough : 



( large trees . . 3 to 6 inches-. 

 For a crop of < small trees . , 2 



(^ very small trees . 1 inch. 



Supposing 1 inch has been fixed as the range, then every tree 

 above 5 inches, but not more than 6$ inches in girth, will be 

 classed as being 6 inches in girth; every tree above 6 inches, 

 but not more than 7 3 inches in girth, will be classed as being 7 

 inches in girth; and so on that is to say, all fractions not 

 exceeding one-half will not be taken into account at all, and all 

 fractions exceeding one-half will be considered as 1. And so on 

 with any other girth range. Here, in India, a girth range of as 

 much as 18 inches, established by Sir Dietrich Brandis in Burma in 

 1859, has been made use of in most of our working-plans, and 

 has been found to give sufficiently accurate data for the classes 

 of forest we have to work, and for the rough methods of working 

 them we are obliged to adopt. 



As in extensive surveys it is generally found aiore convenient to 

 use diameter callipers than to measure girths with a tape, the cal- 

 liper should be marked in gradations of T 7 T of an inch, or a foot, or 

 other selected unit, so that the girth corresponding to measured 

 diameter may be read on the calliper; the following precautions 

 should however be observed. In crops consisting of fairly regular- 



B 



