New Zealand Journal of Botany abstracts
Potential forest cover of New Zealand as determined by an ecosystem process model
Graeme M. J. Hall
Matt S. McGlone
Landcare Research
PO Box 69
Lincoln 8152, New Zealand
Abstract A forest biome map for New Zealand is
presented, based on the ecosystem process model LINKNZ. Climate
surfaces, landforms, slope, and soil types defined 88 933
homogeneous landscape units covering the North and South islands
(264 000 km2). Forest development (2000 years)
was simulated on each unit with 78 individually parameterised species
selected by ecological importance. Forest biomes for the units were
assigned by the relative biomass predicted for 21 plant functional
types, categorised from the available species. An assessment of model
performance against a systematic sample of 559 measured forest plots
was satisfactory (dissimilarity index = 0.25). Direct validation was
not possible over most of the landscape where native forest has been
removed, but performance was sensible against data from 136
pre-deforestation pollen sites (dissimilarity index = 0.20). The
modelled biome map reproduced the main characteristics of the current
forest distribution in New Zealand and departures from the observed
forest distribution were generally explained by omission of whole-stand
disturbance effects from simulations. The model reproduced lowland
areas of the striking “beech gap” in the west-central zone
of the Southern Alps, but not the distribution of Nothofagus
species in montane areas of this zone. The most likely explanation
supported previous conclusions that the absence was due to a slow
reinvasion of Nothofagus after exclusion during the Last Glaciation. Predictions of Nothofagus
across some regions of the south-eastern South Island where it was
nearly absent before settlement suggested that the ecological knowledge
of some competing conifer species was incomplete.
Keywords biome; forest ecosystem model; Nothofagus; Agathis; direct extrapolation; New Zealand; biogeography; biogeochemical modelling
B05033; Received 27 July 2005; accepted 20 March 2006; Online publication date 4 May 2006
New Zealand Journal of Botany, 2006, Vol. 44: 211–232
0028–825X/06/4402–0211 © The Royal Society of New Zealand 2006
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