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Developed in conjunction with Stand and site factors associated with birdseye sugar maple, a cooperative study between the School of Forestry and Wood Products, Michigan Technological University, and the USDA, Forest Service, North Central Forest Experiment Station.

North Central Forest Experiment Station Forest Service--

U.S. Department of Agriculture
1992 Folwell Avenue
St. Paul, Minnesota 55108
Manuscript approved for publication February 11, 1994


Field Identification of Birdseye in Sugar Maple (Acer saccharum Marsh.)
Don C. Bragg Douglas D, Stokke

Birdseye grain distortions in sugar maple must be identified to capture the full value of a timber sale throughout the economic range ofbirdseye's occurrence. Even when relatively common, birdseye veneer typically makes up less than 1 percent of the harvested volume, but may account for one-half of the value of the sale *1*. With prices *2* recently reaching $50,000 per Mbf for prime logs *3*, omission of birdseye (when present) from cruise data could cause significant economic loss for the forest landowner. But figured wood can sometimes be detected in standing timber (Pillow 1955). Field identification of birdseye sugar maple is critical for two principal reasons: (1) it allows for the enumeration of a valuable resource that may influence management decisions, and (2) it may prevent improper manufacturing of logs at the job site. Both factors should help increase overall timber sale return. The objective of this paper is to provide a background on birdseye sugar maple and a detailed sequential methodology for field identification of birdseye in standing trees.


Little is known about birdseye, from its geographical range to regenerative capabilities to
causative factors, although various hypotheses have been proposed since at least the turn of the century. Some authors (e.g., Wangaard 1950) believed that birdseye resulted from birdpeck, other researchers have discounted this theory (Anonymous 1929, 1987; Pillow 1930; Record 1921). Others have attempted to link it the production of adventitious buds or adventitious root primordia (Betts 1944, Borthwick 1905, Edlin 1969, Fink 1982, Strasburger et al. 1898, Werthner 1935), but these references appear to misinterpret the phenomena (Beals and Davis 1977, Davis 1961 *4*, Pillow 1930, Stokke 1992). Many texts have suggested that birdseye formation may be attributed to localized deactivation of the cambium due to fungi (Hale 1932, 1951; Harris 1989; Jane 1970; Record 1934), yet this has apparently never been substantiated. Shigo (1986) noted a similar condition in grafted fruit trees called stem pitting that is associated with viruses. Holmberg (1933) believed birdseye formation was a result of suppression early in the tree's existence. His examination of logs at a veneer mill found that trees with birdseye grew slower in the first century of life than non-birdseye specimens. Righter (1934), unconvinced that suppression had resulted in the diameter discrepancy that Holmberg (1933) found, felt that genetics or environmental factors could just as likely have caused the diameter differences. Mroz et al. 1990) did not detect the slower growth rate that Holmberg (1933) noted, but did find that birdseye maple trees tend to grow in stands that have higher basal area in the immediate vicinity of the birdseye trees. Mroz et al. (1990) also found statistically significant differences (p < 0.10) in the percentages of sand (p = 0.073), silt (p = 0.055), and organic matter (p = 0.054) between paired birdseye and non-birdseye maples, but did not find differences in levels of soil nitrogen, phosphorus, calcium, magnesium, or potassium, Boyce (1961) noted that a similar grain abnormality of birch in northern Europe was believed to originate from climate or soil conditions. These settings resulted in " internal gummosis... in which the cell walls or contents are not dissolved."

Birdseye has been described in a number of species, including other maples (Acer campestre (Boulger 1902), A. rubrum (Brown et al. 1949, Panshin and deZeeuw 1980, Pillow 1930), A. mandschuricum, A. platanoides, and A. pseudoplatanus (Korovin and Zuikhina 1985), yellow birch (Betula aUeghaniensis [Betula lutea]), white ash (Frax/nus americana L.) (Brown et al. 1949, Panshin and deZeeuw 1980, Pillow 1930), Betula pubescens, B. kylowii (Harris 1989), black walnut (Juglans nigra L.) and Cuban mahogany (Sweitenia mahoganO (Beals and Davis 1977), and probably in American beech (Fagus grandifolia) (Shigo 1986), and Kaxelian birch (Betula pendula var. carelica) (Korovin and Zuikhina 1985). The occurrence of birdseye in these species, while not as common or valuable as in sugar maple, may indicate that a particular sugar maple birdseye subspecies does not exist, even though certain trees may be genetically more susceptible to the formation of birdseye. Birdseye would then seem an acquired feature attributable to environmental or pathological conditions.



Birdseye figure is due to a pattern of indentions in the growth rings. If the wood is split
tangentially {i.e., the plane of the split is essentially parallel to the growth rings), conical projections or elevations are revealed, with corresponding indentations on the matching piece (figs. la-lb). These projections and indentations extend inward toward the pith, generally beginning in the bark and extending through the wood for an indeterminate number of growth rings. Birdseye is classified by Beals and Davis (1977) as a "figure related to indented growth rings,'" and indeed, close examination of the cross-sectional surface of birdseye reveals that the growth rings do appear to be indented (fig. 2). It is as though a blunt conical instrument were used to cause a localized indentation in the bark, cambium, and wood. These areas contain the same types of cells as found in the surrounding "normal" wood, but the longitudinal cells are not vertically oriented as their counter parts in the normal tissue (fig. 3). Because these projections and indentations generally extend into the bark, trees can be examined for the presence or absence of birdseye with little physical damage, A variation of birdseye called "fingernail" or "thumbnail" is also found in sugar maple. Fingemail birdseye appears as long grooves in the bark and xylem of sugar maple {fig. 4), which look like a fingernail has been dragged across the surface of a piece of wood. It is unknown how similar this type of birdseye is to "normal" birdseye, but this variation apparently does not add ornamental value.


*1* Reed, D.D. 1992. Personal communication with D. Bragg.

*2* Prices on birdseye veneer logs typically range from $10,000 to $20,000 per Mbf. Price quoted here repre sents an exceptional quality and size log.

*3* Dougovito, J. 1993. Personal communication with Bragg, March 24.

*4* Davis, E.M. 1961. Some observations on bird's-eye maple. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. Unpublished manuscript on file with: Forest Products Laboratory Library, One Gifford Pinchot Drive, Madison, WI 53705-2398.

*5* Stokke, D.D. 1992. Birdseye figure in sugar maple. Carbondale, IL: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. Unpublished manuscript onfile with: Forestry Sciences Laboratory, Southern Illinois University at Carbondale, North Central Forest Experiment Station, Carbondale, IL 62901-4630.


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