SAMPLE PLOTS IN SlLVlCULTUPvAL RESEARCH 41 



In uneven-aged stands or in culled forests, height measurements 

 must be made on practically every tree at each remeasurement. 



Since the limit of " merchantable height " is variable and may 

 be due to either branching, defect, or excessive taper, and since 

 standards of merchantability change with economic conditions and 

 utilization practices, no measurement on a merchantability basis 

 should be made without adequate definition. (For a discussion of 

 the measurement of upper diameters of standing trees, see the sec- 

 tion on " Taper ".) 



" Height to base of crown " (Ht-B C) may be recorded if it is 

 significant and can be determined with reasonable accuracy. The 

 base of the crown is usually defined as the place where the lowest 

 branch leading into the crown proper emerges from the trunk. 

 The definition varies among studies, depending, for instance, on 

 whether the value to be determined is clear length of bole or crown 

 length. 21 In cases in which base of crown is a questionable point, 

 definite notation should be made as to what point is considered the 

 base. 



TAPER 



In studies in which current information on change in tree form is 

 needed, it is necessary to measure the diameters and bark thickness 

 of individual trees at various heights from the ground. This is 

 clone by climbing the tree or by using a dendrometer. 



The climber measures diameter with a tape, and bark thickness 

 with the Swedish bark measurer. If data on age and rate of growth 

 are needed, he also bores the stems at the measuring points. Usually 

 he determines the distance from each measuring point to the ground 

 by means of a tape attached to his belt. This operation is illus- 

 trated in plate 7, B. 



The measurements may be taken at irregular height intervals, 

 because of the difficulty of relocating an exact point of measure- 

 ment. Usually the intervals between measurements made by a 

 climber are very irregular, depending largely as they do upon the 

 availability of resting places. In most studies this makes little 

 difference if the data are plotted to produce a tree diagram. 22 



Since studies of form are based on averages, it is often unnecessary 

 that remeasurement for changes in form be made on the same trees 

 as the former measurements. Where it is desirable to record form 

 changes of individual trees, remeasurements of each tree should be 

 made at the same heights as the original measurements, and for this 

 reason the heights should be definitely marked. Tags may be hung 

 or a band may be painted at each point of height measurement. 



To climb standing trees by sheer muscular effort is often difficult, 

 especially if the trees are large and tall and if they possess few 

 branches or other projections on which the climber may rest. On 

 sample plots it is inadvisable, however, to use climbing irons such 

 as are used by telephone linemen, because the irons wound the 

 trees. Wounds thus made may attract insects or sapsuckers; admit 

 disease or mistletoe infection; result in pitch flow, pitch soaking of 



21 In some foreign studies (6!,), one-half the distance between the lowest branch and 

 the first definite whorl of branches has been taken as the base of the crown. 



tJ2 For tbe purpose of drawing a form curve, all the data for each individual tree 

 can be entered on a graph form, such as Forest Service form 558a, on which the 

 ordinates represent area in square feet and the abscissas represent height in feet (60). 



