Activities such as forest inventories, surveys, and research experiments have generated technological innovations and new efficient methods of gathering ecological information. Conventionally accepted methods have developed from these many innovations as a way of standardizing procedures to allow the comparison of results. As in all aspects of life, conventional methods must be continually re-evaluated, especially in terms of unintentional but avoidable harm they may cause in the name of furthering science and knowledge.
Increment boring, the removal of a cylinder of wood of about 0.2 inch diameter and extending from the bark to the pith of a tree, has become standard operating procedure for determining tree age, examining patterns in annual diameter growth, determining site index, and developing chronologies of events such as fires that leave scars marking the year of occurrence. While the information provided by increment boring is important, common sense suggests that wounding a tree, like wounding a human, would invite infection, ultimately leading to ill health and a shortened life span. The scientific literature supports these common sense expectations.
Many pathological defects are caused by increment boring. The most important of these include discoloration and softening of the wood surrounding the wound, decay of the heartwood or sapwood, and infection of surface wounds by canker-causing organisms (1). The extent and type of discoloration is variable by tree species. American Beech (Fagus grandifolia), for example, exhibits a brown, watery discoloration, while Cucumbertree (Magnolia acuminata) is stained deep blue (2). In a study of 135 trees that had been bored, 100% of the trees exhibited discoloration (1). Open channels left by increment boring also provide infection courts for bacteria and fungi. Research indicates that decay from heart-rotting fungi in increment borer wounds may progress from year to year until the entire trunk is hollow (4). Bacteria and fungi colonizing surface wounds often cause cankers and retard or inhibit wound closure. In the Southern Appalachians, most of the diffuse-porous hardwoods that were bored developed cankers which slowed healing to such a degree that after ten years wounds were still open in four species (2). Similarly, increment boring of Trembling Aspen (Populus tremuloides) in Newfoundland (3) and of birch (Betula pendula) in Europe (6) always led to serious decay. In a comprehensive study, 85% of bored beeches and 57% of bored Sugar Maples (Acer saccharum) exhibited decay, and 100% of bored Red Maples (Acer rubrum), Sugar Maples, and American Basswoods (Tilia americana), had open surface wounds at the end of the first year of growth following boring (1). These statistics are overwhelming, and indicate that boring is truly hazardous to the health of trees.
Increment boring does, however, provide information that is essential, or at least useful, to the preservation and management of forests, such as data describing a stand's age-distribution. But must we be so exacting? Must we accurately document that a tree is 254 years old, or can we accept an estimated age range of 220 to 290 years, that is, can we accept a 10 to 15% error? The authors believe this degree of accuracy is reasonable for most purposes, and recommend the following system for estimating tree ages and gathering growth information without harming living trees.
Trees that have recently died or that have been recently wind-thrown should be opportunistically increment bored as encountered. At the same time, these trees and the site on which they occur should be carefully examined to "train" the eye to associate age measure by increment boring with tree characteristics such as diameter and height and distinctive crown and bark features, and with site characteristics such as location in the landscape and soil depth and fertility. In other words, ages measured by boring dead and fallen trees should be used to teach us to recognize a 254-year-old White Oak on a dry south slope, or a 70-year-old Sugar Maple in a rich cove. Such education has been shown to be effective in a study where volunteers who initially estimated tree age with a 40% error reduced their error by one-half after a brief on-the-ground training session; the study concluded that with a little more training, errors <15% could be consistently achieved (5).
Human nature strives for knowledge and understanding. This natural tendency must be controlled and tempered by our moral obligation to minimize the impact of our activities on the ecosystems of which we are a part. Wholesale boring of living trees, especially rare species, old-growth trees, or trees on stressful sites, sacrifices the trees in the interest of gathering abundant and accurate information. Opportunistic boring of dead and fallen trees, combined with a continuing effort to develop an "eye" for tree age, renounces a dependence on a convenience and an exaggerated sense of accuracy in the interest of protecting the trees.
References
(1) Campbell, WA. 1939. Damage from increment borings. Division of Forest Pathology. Bureau of Plant Industry, U.S. Department of Agriculture Mimeo. 7pp.
(2) Hepting, G.H., E.R. Roth, and B. Sleeth. 1959. Discolorations and decay from increment borings. Journal of Forestry. 47:366-370.
(3) Laflamme, G. 1979. Discolored wood of aspen caused by increment boring. European Journal of Forest Pathology 9:15-18.
(4) Lorenz, R.C. 1944. Discolorations and decay resulting from increment borings in hardwoods. Journal of Forestry. 42:37-43.
(5) McGee, Charles E. 1989. Estimating tree ages in uneven-aged hardwood stands. Southern Journal Applied Forestry. 13:40-42.
(6) Vuolki1a, Y. 1976. Boring of standing trees
as a source of defects. Folia Forestalia, Institutum Forestale Fenniae.
282. 11pp.
Paul Kalisz is an Associate Professor of Forest Soils & Silviculture in the Department of Forestry University of Kentucky. Amy Carrico and is a forestry graduate of the University of Kentucky.