224 



phloem). Hence, if there are no leaf -bearing branches on the 

 stem below the point of ringing, starvation of the roots ensues. 

 This may be slow, seeing that there is a store of food in the bark 

 of the roots and of the base of the trunk to draw upon, but the 

 growth and absorptive powers of the. roots will eventually be 

 checked, and in some cases the functional failure of the roots may 

 be the final cause of the death of the tree. 



The exposure of the wood, where the bark has been removed, 

 introduces other factors endangering the life of the tree. The 

 supply of water for the upper part of the tree has all to pass 

 through the wood at the level of the ring-gap, and from several 

 causes the conducting power of this wood tends to become more and 

 more curtailed until the requisite amount of water can no longer 

 pass through it. Owing to the surface of the wood being in 

 contact with the air, the outer layers of wood become dry and 

 useless for conduction. This alone may ISOon render the water- 

 feupply insufficient in species with only a thin zone of sapwood, 



since 



true heart-wood is incapable of conducting the transpiration 

 II. On the other hand *^ sap-wood trees ' (i.e., those which 



stream 



form little or no heart-wood) can usually survive the operation of 

 ringing for a long time, e.g., several years. Among these the 

 progressive drying of the wood from without inwards may finallv 

 restrict the area of functional wood until it reaches the critical 

 point, or this result may be accelerated by a fungal disease attack- 

 ing the wood and rendering some of it useless. Again, in trees 

 which form heart-wood, the production of this accounts for the 

 loss of a. certain proportion of the wood available for conduction , 

 While no new wood is added at the level of ringing, and functional 

 wood is lost externally by drying, there is a further loss internally 

 owing to the yearly conversion of some sap-wood into heart-wood. 

 To summarise, bark-ringing eventually causes the death of the 

 upper part of the tree, because the water supply becomes in- 

 adequate, either through loss of conductivity in the wood at the 

 level of the wound, or through deficiency of absorption by the 

 roots. 



An interesting example of bark-ringing may be quoted here. 

 A forked pine-tree was chosen by Hartig"^ for an experiment. The 

 tree was 118 years old, and the trunk was forked at 4| m. above 

 the soil into two approximately equal stems. The bark was peeled 

 off all round one of these stems at about 3 m. above the point of 

 forking. When the tree was felled 18 years after this ringing 

 operation had been performed, it was seen that the crowns of both 

 stems were still sound, but that the foliage of the ringed stem was 

 thinner and weaker than that of the other stem. It was also 

 found that growth in thickness had practically ceased after ring- 

 ing on the side of the trunk situated below the ringed branch. The 

 reason for the long-continued life of the ringed stem is that the 

 roots attached to the base of the trunk on the side below the intact 

 stem had received normal nourishment, and therefore, having 

 remained healthy, had been able to supply the trunk with a good 

 supply of water. 



Hartig, Lehrbuch d. Anat. u, Phjs. d. PflaDzen, p. 2;34, 



i 



