1902. 



FORESTRY AND IRRIGATION. 



163 



damage to the value of the timber in the 

 tree. When frost is leaving a tree on 

 account of rapidly rising temperature, 

 the outside layer is again the first to re- 

 ceive the effects of the sudden change, 

 and first commences to relax its contrac- 

 tion and expand under the influence of 

 the rising temperature. If the change 

 from a low temperature to a higher one 

 is very sudden, the outside rim expands 

 so much more rapidly than the inside 

 growth of timber that the sudden ex- 

 pansion causes the outer layer to break 

 or tear away from the colder and more 

 slowl}' expanding layers of wood inside. 

 The report of the check or separation 

 gives out a mufSed or deadened sound, 

 instead of the clear-cut, wdiip-like crack 

 of the contraction check. 



Frost checks of this description occur 

 chiefly in the trunks of trees, in that 

 portion near the roots where they are 

 least protected by foliage or branches 

 from the action of the sun. Frost 

 checks from expansion are most fre- 

 quentl}' found on the south side of trees 

 where they receive the unobstructed 

 rays of the sun, after having been sub- 

 jected to a very low temperature for a 

 sufficient length of time to contract 

 them to their smallest diameter. 



Expansion checks nearly always ex- 

 tend in a circular direction, following 

 and opening up along the annular rings. 

 They often connect with some contrac- 

 tion, since an open check caused by 

 contraction is naturally the weakest 

 portion of the tree from which a circular 

 or ring check could start, and the timber 

 would give way there first. 



Expansion checks do not necessarily 

 show on the surface of a tree, however, 

 as I have found at different times by 

 examining a tree after hearing it emit a 

 muffled snap when the frost was leaving 

 the timber. Not being able to find any 

 perceptible check showing on the sur- 

 face, I have had the tree cut for the 

 purpose of ascertaining the effect on the 

 timber, and in such instances have 

 found an open ring check extending in 

 a semicircle around the tree with no 

 opening to the surface of the tree, as 

 shown in Fig. 3. Such checks, how- 

 ever, are usually split open to the out- 

 side surface of the tree bv the next 



sudden contraction, as, on account of 

 this ring checking, that portion of the 

 tree is weakened and thus becomes the 

 more susceptible to the strain of con- 

 traction (Fig. 4). 



The movement of the tree, caused b}^ 

 the action of the wind and repeated 

 contraction and expansion afterward, 

 keeps these checks opening and clo.sing, 

 and causes the inner portion of the tree, 

 where the checks exist, to become ex- 



FIG. 5. THE EFFECT OF A CONTRACTION 

 FROST CHECK UPON BIRCH. 



posed to the air and the action of the 

 elements. As a natural result, deca}^ 

 sets in, after which there is no possi- 

 bility of those affected portions of the 

 checks ever growing together solidly. 

 It is in this manner that much of the 

 so-called wind shake and ring rot is 

 started. These phenomena are partic- 

 ularh' noticeable in coniferous species, 

 which are the ones chiefly affected bj^ 

 frost check, as all people experienced in 

 cutting timber are aw^are. Frost checks 

 are noticeable in the broad-leaf trees, 



