Blue Stain in Storm Damaged Trees
Storm damaged trees present a number of challenges. They are tipped over, broken off, twisted, broken and split. In addition, logs lying on the ground are susceptible to blue stain, a fungus which causes the wood to discolor. Blue stain, like many fungus flourish under hot and humid conditions. Wood that is harvested in the cold weather is not vulnerable to blue stain nor is wood that is processed and dried quickly.
Blue stain is considered a sap stain because it invades the sapwood, or outer region of the stem. Logs saw into lumber can loose substantial value due to blue stain. Wood degrade is primarily due to the color change of finished lumber, not the strength or other characteristics of the wood. Each year, the white pine industry in New Hampshire looses substantial lumber value due to blue stain. Many sawmills will sprinkle their log piles with water to discourage the formation of stain and the activity of insects. The water reduces the temperature of the log surface and also disrupts the oxygen supply. Although all species can be affected by blue stain, it is the pines and sugar maple that are most susceptible to value loss.
What causes blue stain?
Blue stain is caused by the Ophiostoma specie of fungus. It is spread by spores floating in the air or by attaching themselves to insects. The spores land on an acceptable surface and begin to grow. Blue stain fungus can invade a log either through the cut end of the log, a damaged area such as a break in the bark, or by hitching a ride on an insect which may bore into the wood.
How quickly will the blue stain develop?
In hot and humid weather blue stain will develop rapidly in logs lying on the ground; within a week is possible. Research conducted in Quebec, using Jack pine, found that the formation of stain varied tremendously from log to log but found that 34% of the Jack pine was stained by 4 weeks. An informal study conducted by Kyle Lombard, Forest Health Specialist with the NH Division of Forests and Lands, on wind thrown white pine in Grafton County NH (May, 2007), found that trees on the ground without roots attached could last from 3-6 weeks but trees that were still attached to their roots could last up to a year.
What should a landowner do?
After a severe weather event the most important concern is safety which may prevent a salvage operation from commencing within a short period of time. A careful plan of attack is necessary to prevent dangerous conditions, further damage to standing trees, and to maximize the value of anything salvageable. If possible, sawlogs that do not show obvious splitting or cracking should be salvaged as soon as possible in the summer months – within a few weeks. Other products, pulpwood and firewood do not need to move as quickly.
