44 CIRCULAR 3 3 3, U.S. DEPARTMENT OF AGRICULTURE 



growth of that tree, but that when one boring per tree is obtained 

 from a large number of trees eccentricities of diameter growth are 

 usually ironed out. In collecting growth data by one boring per 

 tree, special care should be taken to avoid bias. 



Considerable difficulty is sometimes encountered in measuring pre- 

 cisely the growth made during individual years or during groups of 

 years. Various devices have been developed to aid in making such 

 measurements (19, 2 J/.. 59). 



Occasionally data are needed on growth during the last few 

 years. Increment borers are seldom sharp enough, and the hand 

 holding them is seldom steady enough, to make a clean cut without- 

 crushing or distorting the outer 2 or 3 annual growth rings, except 

 in a relatively small number of species. To obtain such data, a chip 

 about three-fourths of an inch square should be cut from the tree 

 with a sharp wood-chisel. The cut should be sufficiently deep not 

 to cause cleavage between annual rings. 



In the case of plantations the period since planting should be 

 recorded as the age of the stand, no matter how old the trees were 

 when planted. Records should be kept, however, of the age of the 

 stock used. 



In even-aged stands, age is considered by 10-year periods the first 

 of which dates from the time of the stand's origin. Thus the 20- 

 year age class is composed of trees aged from 20 to 29 years, in- 

 clusive, and the 30-year age class of trees aged from 30 to 39 years, 

 inclusive. In studies of uneven-aged stands, especially those in- 

 volving old-growth timber, trees beyond the sapling stage may be 

 considered in four major groupings — young, thrifty mature, mature, 

 and overmature. The spread of ages included in any one group is 

 not fixed, but varies with species and site. In long-lived species such 

 as ponderosa pine (Pinus ponderosa) , maturity may be taken as 

 between 150 and 250 years. In shorter-lived species such as short- 

 leaf pine (P. echinata) . maturity may be taken as between 75 and 

 100 years. 



Taking borings at an angle often has the result that small bits of 

 wood break off in the borer and clog it. particularly in pitch-soaked 

 or punky heartwood. Clogging is less likely to occur if the barrel 

 is frequently swabbed with kerosene or, preferably, with high-grade 

 machine oil : this, however, does not entirely prevent clogging or aid 

 greatly in removing the compacted material. Material that cannot 

 be removed with the extractor sometimes can be removed with the 

 aid of a stiff wire. It can be removed quickly with a 3%-i ncn wood 

 and steel drill welded on a T Vinch steel rod the top of which is bent 

 so as to form a handle (-56). 



Growth by 5-year intervals should be measured on the freshly 

 extracted core, before any distortion can have been caused by shrink- 

 age. A growth record of this kind made in the field is particularly 

 valuable, because of the fragility of cores and the unevenness with 

 which they shrink. If lengths representing 5 years' growth each 

 are marked off on the core they can readily be marked off also on a 

 field form that will become a part of the permanent record. If the 

 boring misses the center of the tree, a diagram of the first few years' 

 growth as inferred from the core should be drawn on the form so 

 that future workers will have information as to the interpretation 

 made. 



