SAMPLE PLOTS IX SILVICULTURAL RESEARCH 83 



51. All plots should be normal rather than empirical. By strict definition 

 a normal stand is that producing the maximum volume in cubic feet for a given 

 age and site (thinnings usually being disregarded) ; practically, however, this 

 definition must be applied with sufficient flexibility to permit finding plots at 

 a reasonable expense. Obviously, then, the leeway necessary will depend on 

 the character of the species and the region studied. 



52. Understocked stands may be identified by such criteria as presence of 

 holes in the crown cover (except for intolerant species), presence of excessive 

 undergrowth or reproduction, abnormally low number of trees per acre, and 

 abnormally high diameters for the age class in question. 



53. Overdense stands are uncommon and often hard to identify. They 

 should usually be measured whenever encountered unless there is no uncertainty 

 as to their identification. They may have such characteristics as an abnormally 

 high percentage of suppressed trees or very slow diameter and height growth 

 even on dominants. 



54. Stands with pronounced variations in stem density should be avoided 

 where possible. 



(a) Age will usually be determined by means of increment borings, approxi- 

 mately average dominants being chosen. Abnormally large trees should be 

 tested to see if they are older than the main stand and occasional small trees 

 bored to ascertain whether the stand is essentially even aged. 



(&) Increment cores should be numbered to permit identification and 

 preserved for later detailed analysis. 



55. The length of time required for seedlings to reach the point at which 

 the age was determined must be ascertained by measurements of seedlings on 

 similar sites. Open-grown seedlings should be selected which will obviously 

 develop into average dominants at the ages of greatest importance in the yield 

 study. 



56. The d.b.h. of each tree on the plot should be measured with diameter 

 tape or calipers, depending on which instrument was employed in preparing 

 the corresponding volume table; if a different instrument is used average 

 discrepancies should be determined. 



57. These measurements should be to the nearest inch. 



58. All living trees over one-half inch d.b.h. should be tallied. 



59. The diameter-class limit should be from 0.6 to the following 0.5 inch, as 

 from 9.6 to 10.5 inches. 



60. Measurements should be taken at 4 a /4 feet from the average ground level. 



61. All measurements should be tallied by species and by crown classes. 



62. The use of three crown classes is sufficient unless perhaps work in the 

 same or adjacent similar regions has been based on four classes. 



63. All species, even those of subordinate importance, whether softwood or 

 hardwood, should be recorded, the word " miscellaneous " being avoided. There 

 is, however, no objection to grouping in a miscellaneous column a number of 

 subordinate species, providing that the tally identifies the species of each tree 

 for which record is made. 



64. The height and d.b.h. of a sufficient number of sample trees should be 

 measured to permit the drawing of a curve of height over diameter for each 

 plot. 



65. The complete range of d.b.h. ? s present should be covered by these samples. 



66. The number of sample trees required is not a fixed percentage of the 

 total number on the plot but is determined by the number needed to yield a 

 satisfactory height curve. 



67. Height should be measured with any standard instrument, such as the 

 Forest Service or Faustman hypsometer or the Abney, distances being taped. 



68. Trees measured should be sufficiently normal to be acceptable for volume- 

 table work, forked and broken tops, for example, being avoided. 



69. Separate curves are needed for any subordinate species present unless 

 so unimportant proportionately as to make it practicable to use the height 

 curve of the principal species. 



70. The height of 5 to 10 mature dominant trees adjacent to the plot should 

 be measured where possible as an aid to site classification. 



71. The height of 10 to 15 dominants growing in obviously open or over- 

 dense stands adjacent to the plot, on similar sites and of the same age, should 

 be measured wherever such stands are found to permit a study of the effect of 

 density on height, 



_ 72. The plot description should include the following headings : Crown den- 

 sity ; Normality ; Percentage of boundary in open ; Type ; Distribution ; Slope 



