METHODS DEPENDENT ON THE USE OF PLOTS 287 



Great care must be taken in the use of circular plots to obtain the 

 width of the plot correctly. An error in this factor is more serious than 

 that on a strip, since it affects the entire boundary. The same principle 

 as to size and number of plots and per cent of area covered applies 

 to these methods as to strip estimating. In dense brush and with small 

 timber, the common size is one-fourth acre, while plots 1 acre in size 

 are required for old and large trees. The amount of timber on each 

 plot is obtained by the use of the same variety of methods as for strips. 



Examples. Spruce in the Northeast on large tracts. 



Size of plot 5 acre 



Number of strips per forty 1 



Distance between plots on strip 20 rods — 5 chains 



Per cent of area covered 2^ 



Measurement of distances By pacing 



Measurement of trees D.B.H., calipered or tallied by eye 



Heights A few sample heights taken on each plot for 



curve of height on diameter 



Types Separated in mapping 



Cull By per cent applied to total estimate 



Correction of estimates to get average . None 



Large Timber on the Pacific Coast. 



Number of strips per forty 1 to 2 



Size of plots 1 acre 



Number of plots per strip 5 



Per cent of area 12^ to 25 



Measurement of distance By pacing 



Measurement of trees on plot Average tree selected for each species. Diam- 

 eter at stump inside bark and at top 

 measured. Average of these diameters 

 taken as diameter of the average log 



Volume Obtained by rule of thumb (§ 214). (Any 



of the three standard methods for obtaining 

 the contents of trees on a plot or area apply 

 to this method.) 



Types Blank areas eliminated and stand obtained for 



average acre 



Cull By a per cent of the total estimate 



Correction factor to the estimate Obtained by general observation and com- 

 parison with stands on the plots 



