Tree growth and mortality after small-group harvesting in New Zealand old-growth Nothofagus forests.
Wiser, Susan*,1, Allen, Robert1, Benecke, Udo2, Baker, Gordon3, Peltzer, Duane1, 1 Landcare Research, Lincoln, New Zealand2 private consultant, Christchurch, New Zealand3 private consultant, Rangiora, New Zealand
ABSTRACT- The impact of small group-selection harvesting on residual tree growth and mortality was examined in old-growth hard (Nothofagus truncata) and mixed red-silver (N. fusca-N. menziesii) beech forests. In New Zealand, uncertainty about how the use of such silvicultural systems will influence growth and mortality of residual beech trees has caused controversy surrounding their sustainable management. Diameters of the three beech species were remeasured 8-9 years after harvesting to explicitly compare tree growth and mortality along small coupe (0.05-0.20 ha) edges with that in forest adjacent to these coupes and in nearby intact, unharvested forest. Proximity to coupes had a major influence on growth and varied with species and initial tree diameter. For all species, smaller trees (<60 cm dbh) grew more slowly in intact forest than large trees, but these growth relationships changed along coupe edges such that smaller trees grew 80-600% faster than in intact forest. In contrast, growth of large hard and silver beech, and intermediate-sized (60-80 cm DBH) red beech trees, did not vary with harvesting proximity, suggesting that these main canopy trees were growing at a maximum potential rate for the localities. Edge trees were more likely to die as their level of Platypus beetle infection increased, but overall mortality rates were unrelated to harvest proximity. These results demonstrate that complex tree mortality and growth responses to harvesting need to be incorporated into forest growth models upon which silvicultural systems are based, if such systems aim to sustain the structural, compositional, and functional characteristics of forests.
Key words: tree growth, tree mortality, group selection silviculture, Nothofagus forest
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