New Zealand is no exception to the general rule that the upper limit of continuous woody vegetation (usually formed here by species of Nothofagus) is lower in the Southern than in the Northern hemisphere at similar latitudes. In the Tararua Range the upper limit of the beech is lower than expected, with a belt of scrub above it. Zotov (1938) suggested that this depression of the beech is due to frequent fog formation. Most areas, however, where there is a wide belt of sub-alpine scrub lack beech altogether. This scrub can be an impenetrable barrier of prostrate trunks and stiff interlocking branches. The main type, classified by Cockayne (1928) as “shrubcomposite” scrub is dominated by species of Senecio and Olearia. Also common are Phyllocladus alpinus (mountain toatoa, celery pine), Podocarpus nivalis (mountain totara), Hebe spp., and divaricating shrubs such as Aristotelia fruticosa, Myrsine divaricata and Pittosporum divaricatum.