SAMPLE PLOTS IN SILVICULTURAL RESEARCH 35 



venience often dictates, however, that the point of measurement be 

 established 4% feet above the ground on the uphill side of the tree. 



In some unusual cases, e.g., a tree growing on a boulder or a log 

 with its base high above the ground, the point of diameter measure- 

 ment may be 4% feet above the root collar. On leaning trees the 

 breast-height measurement should be taken 4% feet from the average 

 ground level as measured along the bole. 



If abnormal swellings or depressions occur at breast height, the 

 diameter measurement should be taken at the nearest point above or 

 below it where the trunk is normal, if such a point exists between the 

 heights of 2% and 6 feet above the ground. If no such point exists 

 within that height range, measurement should be made at breast 

 height regardless of abnormality. In such cases, if the abnormality 

 has materially increased the diameter, it is desirable to estimate 

 what the normal diameter would be and to use this estimated diam- 

 eter in all calculations. At times of remeasurement, the periodic 

 diameter growth of a tree the diameter of which has been thus 

 estimated should be assumed to have matched the plot average for 

 trees of its original estimated diameter and of its crown class. The 

 point at which measurement is taken should always be definitely 

 recorded. Usually the contents of trees measured below or above 

 breast height because of abnormality can be derived from volume 

 tables in the same way as if the diameters had been measured at 

 breast height, without causing serious error in the plot total. A 

 sounder practice for applying volume tables is to measure the diam- 

 eter at two points equidistant from breast height where no abnor- 

 mality is present and average them. Measurement at a single point 

 is believed to be preferable in most cases, because it creates less 

 confusion and less chance of error in computations. If the plot is 

 small and a considerable proportion of the trees cannot be measured 

 at breast height, volume determination may require a special study. 



Under some conditions it is impractical to use breast height as 

 the standard for diameter measurement. Diameter is customarily 

 measured 9 feet above the ground on pines that are to be worked 

 for turpentine, and approximately at the high-water line on hard- 

 woods or cypress subjected to frequent and long-continued inunda- 

 tion. Aside from such special cases, before any departure is taken 

 from the standard practice of measuring diameter at breast height 

 the effect should be considered most carefully; sooner or later, such 

 a departure is likely to cause confusion in comparisons of growth. 



In general, vines and moss should be removed from a tree trunk 

 before the diameter is measured. Some vines, such as species of 

 Rhus, so unite with the bark that they cannot be removed from soft- 

 barked trees without considerable loss of bark or even exposure of 

 the cambium. Under such conditions it is usually preferable not 

 to remove firmly established vines preparatory to diameter measure- 

 ment. In recording diameter measurements no allowance should 

 be made for distortion due to such vines, but their presence and 

 their approximate diameter should be noted. If the vines are very 

 large, it is desirable to remove them, so far as is practical, at the 

 point at which the tree is to be measured, by careful use of a light 

 hand ax, unless the study contemplates their continuance. 



