NOTES 



The Requiremknts of Certain Forest Trees ^ 



Hutchinson has brought together much valuable material. His aim 

 has been to give the limiting factors (temperature, water, soil, etc.) in 

 the specific requirements" of certain forest trees with regard to each of 

 these factors, and thereby to account for the respective distributions 

 of some of the trees dominating the forests of Ontario. 



The most interesting part of the paper is its five diagrams. Each 

 diagram, gives the range of the requirements of a number of forest 

 trees for a single important factor. For example, the first diagram 

 gives the relative requirements of fifteen forest trees in temperature. 

 The diagrams are relative rather than quantitative, because quantita- 

 tive data are lacking. It is, however, of no little interest to have the 

 relative requirements of these forest trees assembled in one place. 



The method of constructing the diagrams appears to be compara- 

 tively simple and the diagrams can be understood without undue ex- 

 penditure of time. The range of requirements for any given species 

 and factor is represented by a semicircle. The radius of the semicircle 

 represents the magnitude of the range of the species for the given 

 factor. For example, in the diagram of water requirement, Acer 

 saccharum comes higher up on the scale than Pinus strobus, and has 

 a considerably shorter radius, and therefore smaller semicircle, than 

 Pinus strobus. The Pinus strobus semicircle includes in its upper part 

 almost the entire area of the Acer saccharum semicircle and extends 

 away below the latter. This means that white pine can stand almost as 

 much water as sugar maple and can grow with far less. 



There is a diagram of specific requirements (called "specific toler- 

 ance") for each of the four following factors: temperature, water, 

 soil development (see discussion of soil diagram below), and intensity 

 of light. The fifth diagram combines in one the temperature, water, 

 soil, and light requirements of two competing species, Abies balsamea 

 and Acer saccharum. In this diagram the competition of the two trees 



* A. H. Hutchinson: "Limiting factors in relation to specific ranges of tolerance 

 of forest trees." Bot. Gaz., Vol. 66. No. 6, pp. 465-493, 2 maps, 5 diagrams. De- 

 cember. TQ18. 



■ Hutchinson uses the word "tolerance" instead of recjuirement. This appears 

 to the reviewer confusing, especially in the paragraph on light, where he uses 

 tlie terms "light tolerant" and "shade tolerant" in tlie same sentence. 

 884 



