86 JOURNAL OF FORESTRY 



Mean annual increment. See Increment. 



Mean sample tree. A tree of representative form which in diameter, height, and 



volume is an average of the trees in a group or stand. 

 Medium. See Crown density. 



Merchantable. A term to designate the portion of trees or stands which can be 

 marketed under given economic conditions, usually refers to log material only. 

 Merchantable length refers to the marketable length of log in a tree. 

 Merchantable volume refers to the marketable volume. 

 Merchantable form factor. See Form factor. 

 Middle forest. {Obs.) See Composite forest. 

 Mild humus. See Humus. 



Mixed forest. Forest composed of trees of two or more species. In practice usually 

 a forest in which at least 20 per cent are trees of other than the leading species. 

 G., gemischter Bestand. F., peuplement melange. 

 Model forest. See Normal forest. 

 Mother tree. See Seed tree. 

 Mound planting. See Forest planting. 

 Natural pruning. See Pruning. 

 Natural reproduction. See Reproduction. 

 Net income. See Income. 



Normal. Used as in common parlance in varying sense as conforming to a standard, 

 rule or principle, a model, or as denoting an average of conditions, or the best of 

 conditions. 



G., normal. F., normal. 



Normal age classes. The presence of a complete series of age classes corres- 

 ponding to the rotation {see Age class). 



Normal age class distribution. vSuch distribution of age classes as will permit 

 annual or periodic fellings to be made without damage to adjoining stands. 

 Syn.: normal age class arrangement. 



Normal increment. The best average increment attainable by given species 

 on given sites, as represented in normal yield tables. 



Normal forest. A standard with which to compare an actual forest to bring 

 out its deficiencies for sustained yield management; the conception of an ideally 

 regulated or organized forest; a forest with normal increment, normal age classes 

 in size and distribution, and normal stock. 



Normal growing stock or Normal stock. The amount of material represented' 

 by the stands in a normal forest; practically, the contents of the normal age 

 classes as represented in normal yield tables. 



Normal yield table. An accepted standard yield table with which to compare 

 actual yields. The statements of a normal yield table are derived as an average 

 from the best producing fully stocked areas for given species and sites. If a 

 normal forest were not merely an idea, but actually attainable, the normal yield 

 table would represent its productivity and stock. 



Normal stand. A stand fully stocked and in proper growing conditions, con- 

 forming to the yield table and having normal increment. 

 Normal form factor. See Form factor. 



Nurse tree. A tree which protects or fosters the growth of another in youth. 

 G., Schutzholz. F., essence d'abri. 



