SAPLING DIAMETER GROWTH IN GAPS FOR 2 NOTHOFAGUS SPECIES IN NEW-ZEALAND

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 South 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 fastest near gap center; N. menziesii grew fastest south of gap center. Smaller stems of both species grew faster south of gap center and large ones faster at, or even north of, gap center. For all size classes, the optimum location for N. menziesii growth was further south than for 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 radiation and without considering shading).