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Disjunction of Tree Species in Mountain Forests, Southern North Island, New Zealand: A Review of Paleobotanical Evidence

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Title:Disjunction of Tree Species in Mountain Forests, Southern North Island, New Zealand: A Review of Paleobotanical Evidence
Authors:McQueen, D.R.
Date Issued:Apr 1992
Publisher:University of Hawai'i Press
Citation:McQueen DR. 1992. Disjunction of tree species in mountain forests, southern North Island, New Zealand: a review of paleobotanical evidence. Pac Sci 46(2): 269-275.
Abstract:Dominant trees of New Zealand forests, particularly Nothofagus,
which has low seed mobility, show major distribution gaps, associated with past
glacial and volcanic destruction of forest. In the southern North Island there are
forest tree discontinuities distant from volcanic destruction and subject only to
periglacial activity in the Pleistocene. Here there is absence of one taxon of
Nothofagus and of some mountain coniferous trees, including podocarps, with
bird-carried seeds, and Libocedrus, with winged seeds. The southern North
Island, from 40° S to 41 ° 30' S, shows a progressive southward loss in montane
and subalpine tree species. These species are common, often dominant, to the
north of the area described, and in the northern South Island. In order of
increasingly southern limits in the North Island they are Halocarpus bidwillii,
Nothofagus solandri var. cliffortioides, Libocedrus bidwillii, Halocarpus biformis,
and Phyllocladus alpinus. Their pollen and macrofossil history is reviewed.
Libocedrus bidwillii was present in the southern North Island 80,000 yr ago, and
Halocarpus and P. alpinus until ca. 10,000 yr ago. Various glacial episodes since
80,000 yr ago have severely limited their distribution. The postglacial reoccupation
by forest of southern North Island sites was influenced by rapid climatic
warming. This warming not only flooded the Cook Strait landbridge, cutting off
tree migration from the south, but also allowed lowlands around the gorge
bisecting the axial mountains to be occupied by temperate forest, effectively
blocking access southward by L. bidwillii and N. solandri var. cliffortioides. The
mountain podocarps, H. biformis and P. alpinus, now abundant just south of
the gorge, are in a particularly cloudy climate, which lacks Nothofagus. Farther
south, under less cloudy conditions, the rapid expansion of N. menziesii forest
from lowland refugia could have excluded the two small podocarps, which were
present in pollen records in the early postglacial.
Appears in Collections: Pacific Science Volume 46, Number 2, 1992

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