New Zealand Journal of Botany abstracts

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New Zealand timberlines. 2. A study of forest limits in the Crow Valley near Arthur's Pass, Canterbury

P. WARDLE

Botany Division, DSIR
Private Bag, Christchurch, New Zealand

Abstract The Crow is typical of many moun- tain valleys in that the Nothofagus forest clothing the valley sides narrows to a mid-slope wedge in the glacially broadened upper reaches. In a study of this phenomenon, temperatures near the ground were measured, and observations on winter death of shoots, seed fall, and distribution and growth of mountain beech (N. solandri var. cliffortioides) seedlings were made. On clear, calm nights, tem- peratures in the open close to the ground above the upper forest limits, or below an inverted timber- line, are lower than those measured in openings within the forest, and can be lower than the experi- mentally determined limits of cold tolerance of beech seedlings. Other factors influencing the posi- tion of the alpine timberline are a tendency for growth rates of seedlings to decrease with increas- ing altitude, winter die-back of exposed shoots (especially where snow drifts into the forest mar- gin), and poor seed dispersal beyond the forest margin. Below the inverted timberline, scattered beech seedlings become established on sites where frosts are less severe. Mixed subalpine scrub grows beyond the up-val- ley limits of beech forest. Seedlings of two prom- inent species, Phyllocladus alpinus and Dracophyllum longifolium, occur only sparingly, but both species persist in mature scrub by virtue of their longevity and ability to layer.

Keywords timberline; mountain beech; Phyllo- cladus alpinus; Dracophyllum longifolium; valley head; krummholz; frost

Received 25 May 1984; accepted 19 September 1984
New Zealand Journal of Botany, 1985, Vol. 23: 235-261
0028-825X/85/2302-0235$2.50/0 © Crown copyright 1985

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