We quantified the effects of position within treefall gaps, gap size,
and sapling size on sapling radial increment (most recent 5 yr, using
tree cores) for two species of Nothofagus (southern beech) on the Sout
h Island, New Zealand (42 degrees 13' S). Mean radial growth rates of
the two species and characteristics of the gaps in which they occurred
were similar. Based on regression analysis, stems (1.4-26 m tall) of
both species grew faster in larger gaps than smaller gaps (canopy gap
area range 16-528 m(2)) and larger stems grew faster than smaller ones
, the latter more true of N. fusca than iV. menziesii. N. fusca grew f
astest near gap center; N. menziesii grew fastest south of gap center.
Smaller stems of both species grew faster south of gap center and lar
ge ones faster at, or even north of, gap center. For all size classes,
the optimum location for N. menziesii growth was further south than f
or N. fusca. N.fusca grew faster than N. menziesii near gap center; N.
menziesii grew faster than N.fusca south of gap center. These results
are intermediate between literature predictions of best growth in gap
center (based on soil moisture, soil nutrients and diffuse radiation)
and best growth near the south gap edge (based on direct beam radiati
on and without considering shading).