Timber Sales in Selection Forests 93 



not aggregate at least 5 per cent of the total area. Between 5 

 and 10 per cent is the usual safe percentage chosen. If the area 

 is nearly uniformly covered by trees the former percentage is 

 sufficient; if the forest is irregular, the latter is preferable. If 

 one- fourth acre plots are taken at 330 foot intervals along paral- 

 lel lines that are 660 feet apart, the usual percentage of the 

 whole area taken in the plots will be about 7 per cent, depending 

 upon the shape of the tract and upon large blanks. With half 

 acre plots the intervals between them may be 660 feet, or at alter- 

 nate map stations, to obtain about the same percentage as in the 

 previous case. As large a percentage of sample plot area as 

 time will permit, however, is desirable; but only under excep- 

 tional circumstances should one feel safe in less than 5 per cent. 

 With more intensive methods in the future the percentage in sam- 

 ple plots will increase. 



Laying off the Plot. Prominent principles in this method 

 are : ( 1 ) to take plots always of the same size, the size being 

 chosen before the work begins; (2) to take these plots at reg- 

 ular intervals, in order that one may not be tempted to involun- 

 tarily choose areas better than the average. If one wanders 

 aimlessly through the stand occasionally laying off a sample plot 

 that seems representative, he not only does not know about what 

 percentage of the area he is including in his sample plots, but, 

 worse still, he is almost sure to choose, quite unintentionally, 

 plots that are better than average ones. 



The average stock data will be adversely affected if plots of 

 various sizes are taken, since stock conditions are usually differ- 

 ent on every plot. If a plot larger than the others should be 

 taken on an area better than the average, the total estimate will 

 be too large; if on an area poorer than the average the total 

 estimate will be too small, since that particular area is given 

 undue weight in the' calculations. 



The best way, then, is to locate your sample plots at regular 

 mapping stations. Having paced along the line to a station, set 

 up the compass and fill in the map features. Next, from *he 

 compass as the center, pace to the circumference of the circle 

 and mark the point in some way such as tying a rag to a limb 

 or stick; repeat the operation until there are enough points to 

 make you sure of your enclosure. Frequently four of such points 

 dividing an area into quadrants are found sufficient, since then 

 each quadrant can be treated separately in enumerating the 

 stock. With practice, in the one-fourth acre plots, the distance 



