Forest Vines to Snow Tussocks: The Story of New Zealand Plants
Internationally, the treeline is generally taken to be the lower limit of alpine vegetation. In New Zealand, where beech species are present, the treeline may be very clearly defined with the trees abutting directly onto either alpine tussock grassland, with or without an admixture of shrubs, or a narrow belt of shrubs which widens on steep, sunny, stony slopes and spurs. Where beech species are not present the treeline formed by montane conifer broadleaf forest species is both more diffuse and at lower altitudes than that of beech at comparable latitudes. Above such treelines there is usually a very wide zone of shrubs extending up slope for 1-300 m.133 Some consider that this zone is climatically suitable for beech forest and so refer to it as 'subalpine shrubland' implying that the climatic or 'regional' treeline lies at the upper limit of the shrubs. As a modification of this view, Wardle95 suggests that the regional tree line would lie at the upper limit of shrubs capable of becoming small trees. This implies that below such a line the shrubland is subalpine and above it alpine (Fig. 90).
It seems more convenient to treat the higher altitude shrublands as one entity and for this reason I use the non-committal term 'mountain shrublands'.