IDENTIFICATION PROCEDURES

We suggest three basic stages (see table 1 for a summary) for determining birdseye sugar maple: the external, exocambial, and xylemic investigations. These stages represent different degrees of examination of an individual tree for the presence (or absence) of birdseye. The procedures were developed and found to be reliable as a means of birdseye identification in standing sugar maple during research into stand and site factors that may influence birdseye production, and are similar to methods used in many millyards to identify birdseye in logs.

The stages can be further subdivided into five distinct steps, depending on the depth of the research. Any one stage or step by itself is not necessarily sufficient to identify a tree containing birdseye--all should be performed to achieve a reasonable level of certainty. The inconsistent nature of birdseye's occurrence within a tree makes it difficult to unconditionally guarantee the quality or distibution of figured wood in the stern. Birdseye often occurs at inconsistent distributions within trees and at varying degrees at different locations within individual trees (Brown et al. 1949, Panshin and deZeeuw 1980), making identification difficult at times. For example, birdseye figure may be present on one side of a log but not the other, may be found in the butt log but not the second log, or vice versa, or may be present internally in the tree but not evident on the surface. Another point to consider is that while a tree may exhibit birdseye, the expression may not be extensive (or intensive) enough to add ornamental value, or tree quality may be too low to provide the desired product. In these cases, birdseye may provide little to no additional value, or could actually represent a
degrade in log value.

Stage 1: External examination

Stage 1 is a preliminary examination of the bark's surface and general tree form for useful indications of birdseye. External examination begins by observing the sugar maple's stem from a distance of a few feet, allowing the viewer to determine the presence (or absence) of the "Coke-bottle" lower bole form noted by many field foresters and Mroz et al. (1990) as a possible birdseye indicator (figs. 5a-5b). However, not all birdseye maples exhibit this bole form, and some diseases of sugar maple may cause a bole form that imitates this "Coke-bottle" appearance. One may, in certain cases, notice birdseyes at this distance, especially if the lighting is appropriate {fig. 6). Birdseye maples that can be identified at short distances typically reflect a substantial birdseye presence in the wood, but these trees are relatively rare. The crossbark must usually be viewed at close range for birdseye identification. In most cases, at least some of the birdseyes have been expressed through the bark and are visible on the surface (figs. 7a-7b). Note that the number of birdseyes on the bark's surface does not necessarily reflect the frequency present in the xylem, and that the presence (or absence) of birdseyes in any section of the bark is not a guarantee of what exists on the surface of the wood (fig. 8).

Stage 2: Exocambial examination

Stage 2 requires the removal of outer bark tissues (rhytidome) to further establish the presence of birdseye. The first step involves the extraction of loose fragments of outer bark, which may be removed by hand but sometimes need to be loosened by force {fig. 9). The exterior and interior of the removed fragments should then be examined for signs of birdseye, expressed externally by indentations (fig. 7a) and internally by protuberances (fig. 7b). This step may not prove sufficient, however, if the birdseyes have just begun to form and do not
reveal any expression through the phloem tissues (fig. 10). Further sampling of phloem tissues to the cambium is then done to determine if birdseyes are present at the cambial level. Birdseyes at this level will also appear as conical elevations on the internal face of the phloem (fig. 7c) and typically have a brownish color, contrasting with the lightly colored fresh inner bark (fig. 11). Disruption of phloem tissues, however, provides an avenue for infection to the tree, so care must be taken (see cautionary section in stage 3).

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