Ecology and distribution ofNothofagusin Deception Valley, Arthur's Pass National Park, New Zealand

Abstract

Isolated Nothofagus stands, varying in size from single trees to 10 ha, occur in the Deception Valley, Arthur's Pass National Park. Upper montane to subalpine stands of N. fusca, N. menziesii, and some N. solandri var. clijfortioides occupy sites with N to WNW aspect on the eastern slopes of the valley. S maller and younger N. fusca stands occur on alluvial sites on the valley bottom. Numerous documented cases of establishment after longdistance dispersal by wind, and the apparently selective occupation of warm aspect sites suggest at least occasional low-density seed falls up to 6 km from seed sources. Subsequent population growth and marginal spread of outlier stands appears to be limited by competition, however, and older stands have probably persisted for 1000–2000 years or more. Both the apparent habitat restriction and the mostly stagnant population sizes of N. fusca indicate that this species is approaching its ecological limit in the region. Subalpine N. menziesii stands reveal recent marginal stand expansion. More frequent outlier formation of N. fusca since 1650 AD may be related to decreasing precipitation and more extreme climates in the Taramakau-Otehake region.