HEIGHT GROWTH AS KEY TO SITE 759 



The second objection — that the mere determination of site by height 

 growth tells nothing about the physical factors — is unessential, since it 

 applies equally to all site indicators. The physical environment should 

 always be described in all possible detail ; otherwise the classification 

 becomes a mere catalogue of heights with little practicable value. The 

 omission of such data from many of our published yield tables was 

 unfortunate. It is generally recognized that differences in the physical 

 factors of site are often hard to describe and exceedingly hard to for- 

 mulate as bases for a site classification. This is for the forest experi- 

 ment stations to work out. In the meantime and for many years to 

 come we must be content with less refined determinations. 



The third objection — that a given species may show the same height 

 growth on diff'erent sites — is undoubtedly valid as a fact, and it appears 

 to necessitate a modification of the numeral classification of sites based 

 on height growth. A great number of our species recede from optimum 

 growth conditions in the direction of poor soil drainage on the one 

 hand and excessive drainage on the other. In either direction points 

 mav be found where the height growth is the same, yet the site condi- 

 tions, the yield, and the indicated management are totally different. 

 Here it seems that the height-growth basis must point to its other vir- 

 tues and acknowledge its inability to cope logically with the situation. 

 A simple mechanical way out of the difficulty is to supplement the site 

 class number with a word designating the physical cause for less than 

 maximum height, or "spruce, site I\" (swamp)." It would be unneces- 

 sary to qualify both directions of deviation from the maximum. It 

 should be noted that just such a procedure is essential in species studies, 

 whether or not a standard classification of sites based on height growth 

 is adopted. 



Professor Roth's "blanket" schedule of "standards" subdivided into 

 "sifes" and inclusive of all important North American species is ex- 

 ceedingly restful to the eye. it may l)e that it has cut the Gordian knot 

 which Mr. Zon insists should be untied. Undoubtedly there are yet 

 difficulties to be overcome before its full object can be attained. For 

 exam])le, it is doubtful whether we can resist the temptation to deflect 

 it from its true purpose by impressing the height growth of certain 

 index species — like chestiuit in the East — to determine a large class of 

 forest sites irrespective of, or at least superior to, other sjiecies present. 

 Then there is the possibility that the total height attained at maturity 

 will i)rove a better basis at first than that at lOO years or any other 

 designated age. In \iew of the great difference between species in the 

 jirogress of heiglit grcnxth, the age-height curve would seem the most 



