8 BULLETIN 490, U. S. DEPARTMENT OF AGRICULTURE. 



alone. Table I clearly shows that during the black-jack period the 

 trees are practically free from this rot, but as they grow older the 

 increasing number of dead branches makes them more open to the 

 attacks of this fungus ; that is, after the trees enter the yellow -pine 

 stage of their growth they are more and more subject to infection by 

 heart-rotting fungi. 



In the Cienega ranger district western yellow-pine trees up to 125 

 or 150 years old (the black-jack period) are rarely attacked by 

 western red-rot, for the reasons previously given, while trees over 

 200 years old show a much higher percentage of rot than the younger 

 trees (black jack). Any system of cutting that will take out most 

 of the older trees (yellow pine) and many of the larger black jacks, 

 as well as all suppressed trees, will do much to rid the future forest 

 of this serious heart-rot. It also follows that a short rotation will 

 be better for the future health of the forest so far as heart-rots are 

 concerned. It is a fundamental fact that the older a tree is, the 

 more liable it is to be attacked by heart-rotting fungi. 



SUMMARY. 



(1) A varying percentage of western yellow pines in Arizona and 

 New Mexico is affected by a serious heart-rot called in this bulletin 

 western t red -rot. 



(2) Western red-rot has three stages in its development: (a) An 

 initial stage, in which the affected heartwood is firm but shows red- 

 dish to dark-brown discolored areas; (b) an intermediate stage, in 

 which the diseased heartwood is whitish or gray in color and more 

 or less delignified; (c) a final stage, in which much of the heartwood 

 has disappeared, owing to the absorption of the delignified por- 

 tions, while the wood particles left are brittle and crumble easily 

 when handled. 



(3) Western red-rot attacks both the sap wood and the heartwood 

 of dead branches on living trees. It then travels down the dead 

 branches into the heartwood of the living tree. 



(4) No constant external signs were found which would abso- 

 lutely determine whether or not a given living yellow-pine tree was 

 attacked by western red-rot. However, trees growing on very thin 

 soil on steep south or east slopes where growth conditions are very 

 poor have a higher percentage of this rot than yellow pines situated 

 where the growth conditions are good. 



(5) Of the 1,815 black jacks examined for western red-rot, only 

 29, or 1.59 per cent, had this rot, while out of 563 yellow pines ex- 

 amined, 77, or 13.6 per cent, were attacked by this rot. 



(6) So far as heart-rots are concerned a short rotation is better 

 for the future health of the forest than a long one. 



WASHINGTON : GOVERNMENT PRINTING OFFICE : 1917 



