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23. Longitudinal dissections of red oaks strengthened the developing
hypothesis that heartwood does wall off or confine discolored and decayed wood.
And even further, that insects such as ants that infest trees also stay within
the tissues present at the time of injury (arrow).
Microorganisms and wound-infesting insects apparently do not move "at will" in a tree.
24. Ants infested the column of discolored heartwood in this white pine. The discolored heartwood is surrounded by about 75 growth rings of sound wood. Dissections of oaks, cherries, pines, walnuts, and other heartwood-forming trees began to show more clearly that a fundamental survival process may be operating. And, it was highly ordered.
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25. Trees were dissected to determine patterns of discolored and decayed wood associated with old dead leaders, or old main stems that had died. A lower branch then began to grow as a new leader. The old leader stub was called a stem stub. The trees that had stem stubs acquired a characteristic curve. The diameter of the old leader at the time it died was the diameter of the column of discolored and decayed wood, and the column developed mostly downward. Some discolored wood developed upward in the new leader when the branch was large and had a close connection with the old leader. The diameter of the discolored wood in the new leader would be the diameter of the branch at the time the old leader died.
26. The old leader decayed completely on this yellow birch. Discolored wood in the new leader was associated with branch stubs higher in the stem. The decayed wood did not spread outward to the surrounding discolored wood on the inner side, or to the clear wood on the outer side. These observations led to questions about whether it was wise to break the hard rim or barrier zone when cavities are filled in trees.
27. Dissection of beech shows a connection of the decay column from the sprout with the main stem. Note that the decay does not move outward (large arrow). The sprout has been dead for approximately 50 years. Approximately 50 growth rings separate the decay in the trunk from the bark (small arrow).
28. A low sprout on a sugar maple. The sprout did not connect with the main stem aboveground, hence the sprout decay is separated from the main stem.
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29. Dissections of many large, old red maple sprout clumps showed that decay did not spread from the old parent stump to the sprout stems. Decay did spread from sprout stubs at the base of still-living sprouts. Most of the defects in the sprout stems were associated with old branch stubs. Fungi that cause canker rots, such at Polyporus glomeratus (arrow), were associated with the stubs. When a sprout stem is cut, and decay develops in the cut stub, the decay may spread to the still living sprout attached to the stub. The greatest diameter of decay in the still living sprout will be its diameter at the time the connecting sprouts are cut. For example, if a 2 inch diameter sprout is cut from an attached 3 inch diameter sprout, decay could develop later into the 3 inch core of the still-living stem.
30. Old decaying parent stumps of red oak were dug out and dissected to reveal the attachment of the sprouts. Decay from the stump did not spread into the sprouts. The heartwood attenuated as it developed downward. There was no heartwood in roots. Dissections of many oaks showed that what appeared as a single stem was really the coalescence of several sprouts.
31. As more trees were dissected, the important role of insects and other wounding agents became obvious. Insects infested this yellow birch after it was wounded. At the 4-foot position (section at right), the decay associated with the wound spread inward to meet the already present circular column of discolored wood. At 16 feet above the wound (section at left), the patterns of insect infestation were still obvious. The central column was very small at this height. Note also the slightly darker shade of the wood present at the time of wounding. This wood is slightly pink in birch and maple. No matter how such wood is dried, it will be a darker shade than the wood that continues to form after wounding.
32. The sugar maple borer is a major cause of damage to sugar maple. The beetle has a 2-year life cycle. The discolored wood associated with the beetle wounds often has margins of dark green to orange. The discolored streaks are often called mineral streaks. "Mineral streaks" are columns of discolored wood associated with wounds. In sugar maple, the major wounds that initiate so-called mineral streaks are caused by the sugar maple borer, squirrels, and yellow-bellied sapsuckers. Often these wounding agents occur in clusters.
33. Small ambrosia beetles often bore into trees weakened or stressed by other agents. The small drill-like bore hole in this red maple was caused by an ambrosia beetle. Discolored wood formed above and below the hole. Also in this sample are vessel plugs that form in discolored wood (arrow). The plugs look like small patches of cotton in the vessels.
34. This paper birch was attacked by many ambrosia beetles 4 years before it was cut. Note the many small drill-type holes around the trunk (arrow). The central column of discolored wood is called red heart (A). Bacteria and non-decay-causing fungi abound in red heart wood. The wood on the inner side of the insect attack zone was a light shade of pink (B). The wood that formed after the insect attack was bright (C).
35. Cambium miner, an Agromizid or type of fly, in paper birch. The larvae mine downward in the developing wood, and they leave their tracks as a thin dark line. The arrow shows a circle of darker pink wood associated with another wound.
36. Yellow-bellied sapsucker wounds on a Canadian or Eastern hemlock. The wood often separates along the growth ring that has the wounds. Such ring separations are called ring shakes. The ring shakes form only where many peck holes are inflicted, and after at least 15 to 20 years.
37. Another scale insect on beech, Xylococculus betulae causes a bark roughening. The scale often becomes established at the base of weak and dying branches. The branch collar is killed, and when the branch is shed, a sunken area remains (left). The roughened bark may also serve to harbor low populations of the beech scale, Cryptococcus fagisuga (upper right). The tree walls off the injured areas, but included dead bark may persist as a defect (lower right). Some beech trees are highly resistant to the beech scale, and the Nectria fungi, and even to X. betulae.
38. Canker-causing diseases are common on trees, especially on weakened or stressed trees. Swollen dead spots, or cankers, (left) are common on young and old maples. The canker-causing fungi seldom invade far above or below the canker (right). The discolored wood is very hard and heavy and often resists decomposition. Nectria fungi are commonly associated with such cankers. The cankers remain perennial as the fungus reinfects the bark, and a small amount of additional cambium is killed. After the cambium is killed, the tree responds by walling off the infected tissue, hence the circles or bands which give some cankers a target shape.
39. Walled-off Nectria canker on beech.
40. Fomes igniarius is a fungus that causes canker rots like those shown here on beech. The arrow shows the hard mass of fungus tissue that pushes into the bark as a wedge. When the wedge spreads in the bark, a seesaw action begins: some cambium is killed, and the tree responds to wall off the "enlarged wound". This action is repeated over the years. Some canker rot fungi such as F. igniarius, produce fruit bodies with spores. Other fungi, such as Poria obliqua (Inonotus obliquus) produce very large masses of fungus material, but no fruit bodies on the living tree.
41. The canker rot fungi produce hard wedges of fungus material out into the bark (arrows). The wedges "fan out" in all directions from the center of the canker. When they protrude more deeply above and below the canker, an elongated spindle-shaped canker results. When the wedges spread evenly into the bark around the center canker, a round, knob-like canker forms. Such round, swollen knob-like cankers are commonly associated with Polyporus glomeratus, as is the canker shown here.
42. A deep fungus wedge of Poria obliqua (Inonotus obliquus) on paper birch. Note the boundary tissue separating the wedge from healthy bark (small arrow). The large arrows show the old boundary bark tissue that confined the wedge before it broke out of its confinement. Note where the cambium has been killed and compartmentalization began (double arrow).