GOLD COAST REPORT ON FORESTS. 151 



sufficient to indicate whether the age gradations depart greatly 

 from the normal type or not. 



If the number of plants in the youngest and middle-aged 

 classes is found to be less than that in the mature class, then 

 the forest, so far as the particular species of plant under investi- 

 gation is concerned, is certainly over-mature, and great care 

 will have to be taken in its exploitation ; if, on the other hand, 

 the number of plants found in the youngest class is very greatly 

 in excess of that in the middle-aged class, and the number in 

 the latter in its turn in excess of that in the mature class, then 

 the age gradations approximate to the normal type and a larger 

 number of the mature trees will be available for exploitation 

 without any risk being run of encroaching on the wood-produc- 

 ing capital. 



The method of counting the number of plants in each class 

 that has proved to be the best and cheapest in the tropical forests 

 of Burma for rough approximations of this kind is that known 

 as the system of " Linear valuation surveys." It is quite accurate 

 enough for the purpose of framing preparatory working plans 

 and is the most suitable, under existing conditions at all events, 

 for the dense forests of the West Coast of Africa. They are 

 carried out in the following manner. 



The person making the enumeration of the trees walks through 

 the forest in a definite direction, say south-west, and in addition 

 to measuring the distance walked over counts all the plants of 

 the particular species that it is intended to enumerate that he 

 finds within one chain of either side of his line of march. He 

 enters in his notebook all those that belong to the lowest girth 

 class in the appropriate column for that class by means of a dot 

 or a dash of his pencil and so on for the other girth classes. At 

 the end of the survey he counts up the number of dots or dashes 

 made and thus ascertains the number of plants enumerated for 

 cad i class. After a little practice the girth class that a tree 

 belongs to can easily be ascertained by the eye alone without 

 measurement ; similarly, the distance of one chain on either side 

 of the line can be estimated by the eye, any small errors made 

 in this respect counterbalancing each other. 



"When making the linear valuation surveys, care should be 

 taken in hilly country to carry them out along lines that are 

 roughly more or less at right angles to the ridges forming the 

 water-partings so as to include the trees growing at the various 

 elevations above the levels of the valleys, and thus obtain a 

 fairer average than could be got by keeping the survey at a 

 uniform level above the streams. 



At the same time that the countings are made the actual 

 distance or length of line marched over should be measured in 

 chains by means of a rope. The total distance travelled over 

 (in chains) multiplied by the width of the survey (2 chains when 

 a distance of 1 chain on cncli \/<7e of the line of march is adopted 

 or only one chain when, as in very dense forest, only half a chain 

 on either side is included in the survey), and divided by ten, 

 will give the acreage of the area on which the trees were 

 enumerated. 



