PETAWAWA EXPERIMENT FOREST STATION. 169 



boundaries of the plot at every 30 feet or, if the stand is very 

 dense, at every 15 feet. Strings are then stretched between the 

 opposite stakes, and if the plot is very dense a line is staked 

 across it. In this way the plot is divided into squares with 

 sides of 15 or 30 feet. The mapping is done on cross-section 

 paper to a scale of i/ioo for the permanent or 1/200 for temporary 

 plots. The exact position of the trees which are blazed for 

 removal, as well as of the remaining trees, is shown on the map. 

 The number of trees is noted on the map as well as the 

 diameter at breast-height (D.B.H.), 4-5 feet, and the tree-class of 

 the blazed trees. Then the final map is prepared in the office, 

 the trees being drawn to scale. If the plot is drawn to a scale of 

 1/200 the scale showing the D.B.H. of the trees is i/ioo, and 

 when the scale of the map is i/ioo the scale used for the 

 trees is 1/25. A different colour is used for each species. 

 Circles are used to show the tree, a heavy circle indicating that 

 the trees are to be removed. When the plots have been 

 mapped as described above, the blazed trees are removed and 

 the actual volume obtained by accurate measurements. 



Any of the felled trees which are considered to be good 

 representatives of the remaining stand are recorded as sample 

 trees. In addition a suitable number of sample trees is selected 

 in the stand but outside the sample plot. About 30 to 40 trees 

 are generally required to obtain a satisfactory curve for height, 

 form-factor, or volume. 



The sample plots are laid out in unthinned stands as well as 

 in stands which have been previously thinned. As a rule 

 stands of full density are selected. (Sample plots for experi- 

 menting in young forests should, if possible, be laid out in 

 unthinned stands, but in forests over fifty years of age, it is best 

 to establish the plots in stands from which abnormal trees have 

 been previously removed.) 



Tree-Groups and Grades of Thinning. 



Since the thinning work of the experiment station should be 

 conducted on a plan that will secure uniformity of the thinning 

 and demonstrate the objective purpose thereby, it is advisable 

 that the trees be classified into well-defined classes, especially 

 at an experiment station such as the Petawawa Experiment 

 Station, where the thinning experiments must often be made by 

 different persons. Owing to the extent of the country and its 



