Dc. Bragg et al., RELATIONSHIP BETWEEN BIRDSEYE SUGAR MAPLE (ACER-SACCHARUM) OCCURRENCEAND ITS ENVIRONMENT, Canadian journal of forest research, 27(8), 1997, pp. 1182-1191
We tested the premise that the ''birdseye'' grain abnormality in sugar
maple (Acer saccharum Marsh.) develops from local environmental condi
tions, with special emphasis on the role of competition in birdseye fo
rmation. Previous experience with birdseye maple frequency and the inh
erent differences in stand structure between old-growth and managed no
rthern hardwoods led to stratification by stand type. Old growth conta
ined considerably more birdseye than managed stands, but the levels in
both types exceeded previously published frequencies. Unlike earlier
studies, we did not fmd greater local density (and, presumably, greate
r competition) surrounding birdseye maples (versus non-birdeyes) in ei
ther old-growth (31.5 and 30.9 m(2).ha(-1), respectively) or managed n
orthern hardwoods (25.0 and 23.7 m(2).ha(-1), respectively). Except fo
r diameter, no tree variable strongly correlated with birdseye occurre
nce. Two plot-level variables, stand density and percent hemlock stems
, strongly correlated with stand-level birdseye frequency primarily be
cause of differences related to stand type, not because they represent
ed causal factors. A logistic regression model was developed to estima
te the likelihood of birdseye occurrence in an individual tree. Model
performance varied, with non-birdseyes being predicted more accurately
than birdseye maples. No evidence in this study explicitly supported
a competition-birdseye linkage, but the frequency of birdseye in old g
rowth suggests that prolonged suppression may influence birdseye forma
tion from the extended exposure to a highly competitive environment. M
anagement apparently results in decreased birdseye occurrence, a trend
that might be ameliorated through retention of higher residual basal
area and structure similar to old-growth stands.