Home Is Where Your Trees Are

Repairing Tree Wounds. Part 2

If the decay goes back into heartwood only a short distance and downward no farther than your chisel can reach, you may elect simply to cut open an exterior V channel through which you can be sure of excavating and painting thoroughly. (See Fig. 9.) If the cavity's vertical depth is great, you may decide to establish drainage by enlarging your test hole and inserting a tube (copper or galvanized), meantime carving back the cavity's upper wall surfaces as best you can. (See Fig. 10.) Often this compromise is best, to avoid an ugly gape in the tree and conserve the sapwood shell. The decay remaining within can be slowed by flushing out the cavity with disinfectant (copper sulphate or mercury bichloride solution), and this process will give you a check on your drainage, through the tube. A dry hole rots much more slowly than a damp one. It does not take many years for a cavity the size of the one in Fig. 7, which started from a small branch stub, to enlarge to one the size shown in Fig. 11. Here the heartwood has been invaded so far as to cause structural weakness.

When such a cavity has formed in a branch or minor leader, the simplest procedure is to amputate the whole member below the cavity. In a main leader or trunk, salvage is still possible by full excavation of the decay, through a frontal channel down its whole length (which matters much less than its width), followed by the installation of internal iron bracing rods. These are criss-crossed, at different levels, at spots where the cavity's sapwood-and-bark shell affords good purchase.

Excavating and

Tree "surgery" as it was first sold years ago consisted largely, and more truly, in tree "dentistry": plugging up cavities with a variety of fillers, chiefly concrete, which were supposed to arrest decay and strengthen the tree. Seldom did cavity-filling do any such thing for trees. Unless a perfect seal is achieved, decay persists more surely in a "filled" cavity than in one left open, well drained and periodically painted. Structural strength is as often lessened as it is increased by the filler's inert, non-integral bulk, against which the tree's living tissues weave and chafe. Nowadays, cavities are seldom filled except for appearance's sake; and this work, which is at once the most expensive and least important aspect of tree surgery, should be left to experts only. With this exception: Where a cavity extends down a trunk into the root-crown, it often pays a tree owner - after he has cleaned out, painted, and rodded the hollow above-ground - to excavate the decay downward as far as he can, then lay a base of small stones and pour filler (an asphalt-sawdust mix) into the hollow until its surface rises a few inches above ground level.

When it hardens, this fill by its weight alone may improve the tree's balance and anchorage. The top of the fill can be kept sloped and moisture-sealed against the tree's butt shell with thick tree paint or a plastic. Besides butt cavities and the girdling roots, other troubles in his trees' lower extremities that a home owner can spot and attend to are burns, root scars, and cavities, animal damage (gnawing by rabbits, rubbing by horses and cows, antler-raking by deer), and insect invasions (ants, grubs, borers). Against these latter, potent poisons now come in aerosol form. A few squirts from the can's nozzle and you fill the beasties' tunnels and galleries with lethal DDT vapor - much more effective than the pastes and slurries we used to mix up and poke in.

Sometimes trees "bleed" persistently from old wounds that appear to be almost, but not quite, healed. The exudate smells foully and it discolors, even kills, all bark that it oozes down over. This is called "slime flux" and it comes from high sap pressure in poorly conditioned trees. Actually it is of two kinds, "brown" and "alcoholic." The former is a leakage of xylem (heartwood) sap from the root system, darkened by fungi and bacteria. It may be checked (but seldom cured) by boring holes into the heartwood at intervals directly below the old, fluxing wound, and inserting pipes, which should be long enough to carry the drip out away from bark and roots. The more curable "alcoholic" slime is just that - a leakage of phloem (outer layer) enriched sap from the tree's crown, in which sugars and starches are fermenting. This kind, white and bubbly, comes out low on the tree as a rule. It can usually be stopped by retracing and redressing (with shellac) the old wound that is exuding. All trees showing slime flux should be generously fed.