UNIFORMITY OF STAND AS AFFECTING METHODS 265 



problem of timber cruising upon whose solution depends the attain- 

 ment of the desired standard of efficiency secured by properly relating 

 costs to accuracy of results. 



212. Degree of Uniformity of Stand as Affecting Methods Employed. 

 The second factor affecting the probability of accuracy in obtaining 

 the average stand per acre is the character of the stand as affecting its 

 uniformity. Uniformity depends, first, upon the range of sizes both 

 as to diameter and height of the trees which compose the stand; second, 

 on the regularity or evenness of their distribution or the variation in 

 the density of the stand over the area. The greater the extremes, 

 both in sizes and density, the more difficult the attainment of a correct 

 average stand by a measurement of a part of the area, and the greater 

 the necessity of increasing either the number of strips or the per cent 

 of area covered in each strip to get a larger total per cent of area in 

 obtaining the average. 



Age of timber increases both the range of sizes and the variation 

 in density. Old timber is never as evenly distributed as a young stand, 

 owing to the progressive losses from natural causes. Mixed forests, 

 composed of several species, are more difficult to average than pure 

 forests of a single or of two or three similar species. There is greater 

 irregularity both in size and distribution in the mixed forest. The 

 greatest irregularities for a given tract are caused by differences in 

 topography and soil, or site conditions, which are reflected in the char- 

 acter of the stand. In mountainous topography, the entire forest 

 changes from bottom to lower slope and from lower slope to upper slope. 

 In more level topography, the type changes as abruptly and completely 

 on the basis of the moisture content of the soil from swamp to drained 

 bottom, from drained bottom to dry upland. Any system of timber 

 estimating must be planned to secure: 



1. The separation of areas which differ radically from each other, 

 but which within themselves are fairly uniform. These areas conform 

 with the types of forest cover. 



2. An arrangement of the strips such as to secure the greatest pos- 

 sible accuracy in sampling, which is done by crossing these variations 

 of density, type and form, at right angles with their longest dimen- 

 sions of area, as far as possible (§§ 219 and 228) 



The degree of detail and cost of the work as reflected either in an 

 increased per cent of area or number of strips or an increased per cent 

 of trees tallied for dimensions, either diameter or height, will thus be 

 increased in proportion as 



The size of the unit diminishes. 

 The size of the timber increases. 



