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Volume 88, 1960-61
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III Effect of Fire and Herbivorous Mammals on the Subalpine Scrub

A few small areas of scrub near tracks have been burnt. An area in the middle Toaroha, burnt 10 years ago, is a typical example. On a 35° slope Dracophyllum traversii, Olearia lacunosa and O. colensoi were co-dominant before the fire. Phormium colensoi is now the physiognomic species. Polystichum vestitum and Hypolepis millefolium are also important. There is profuse regeneration of shrubs, now 1–3ft tall. Seedlings examined had 6–7 growth rings. The most abundant seedlings are those of the light demanding Olearia ilicifolia which was probably rare or absent in the original scrub. Seedlings of Olearia colensoi are common. There are also hybrids between Olearia lacunosa and O. ilicifolia. Even where this fire extended onto a 70° slope, there is now dense vegetation dominated by Phormium colensoi.

Red deer and chamois both feed within the scrub zone, and their effects were not distinguished from each other. Though Hoheria glabrata is palatable, there does not appear to be much damage to trees in established Hoheria forest; but isolated Hoheria trees are usually badly damaged or killed through removal of bark by chewing and rubbing, and the animals are almost completely preventing regeneration and the establishment of new Hoheria communities on bared areas. The usual community of young alluvial fans and healing slips is now an open one containing Poa cockayniana, Helichrysum bellidioides, Danthonia cunninghamii and browsed, suckering Carmichaelia grandifolia; on steep slopes Hypolepis millefolium is dominant. These communities are being invaded gradually by shrubs, especially the browse-resistant Olearia ilicifolia.

In the true scrub communities the impenetrability and low palatability of most of the species discourage the deer and chamois. Therefore their activity is mostly confined to the formation of sharply defined tracks on the crests of spurs and ridges, leading from the forest to the grassland. Along these tracks, shrubs die and are not replaced. The tracks tend to enlarge into erosion channels, and such grassland species as Danthonia flavescens and Celmisia spp. enter. Away from the tracks there are surviving plants of highly palatable species, notably Nothopanax colensoi and

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Table I.—General Relationship between Environment and Grouping of Main Shrub Species.
Soil Drainage Soil Depth Soil Age Altitude Exposure Shrub Species Community
Deep Young O. ilicifolia H. glabrata H. glabrata low forest
Older O. lacunosa D. traversii O. ilicifolia H. glabrata Oleria low forest
Good High Alt. Extreme Exp. D. uniflorum D. uniflorum scrub
Shallow Exp. not extreme O. colensoi D.longifolum O.lacunosa D. traversii O. colensoi scrub
Poor O. colensoi D. longifolium D. biforme D. biforme scrub
Very Poor D. longifolium D. biforme Mosaic of boggy grassland and D. biforme scrub
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Table II.—Relationship Between Environment and Grouping of Main Shrub Species within Olearia Colensoi Scrub and Related Communities.
Altitude Aspect Exposure Soil Moisture Shrub Species Community
High Alt. Extreme Exp. D. uniflorum D. uniflorum scrub
Highly Exp. Nth. aspect O. colensoi D.longifolium D. traversii O.lacunosa D.uniflorum O. colensoi scrub transitional towards D.uniflorum scrub
Moderately Sheltered North Aspect Relat. dry O. colensoi D. longifolrum D. traversii O. lacunosa Scrub on slight spurs and terrace faces, with D. longifolium rising to co-dominance or dominance.
Moist O. colensoi D. longifolrum D. traversii O. lacunosa Fullest development of O. colensoi scrub
Moderately Sheltered South Aspect Relat. dry O.colensoi D.longifolium D. traversii. Scrub on slight spurs of south aspect, with D. longifolium rising to co-dominanceor or dominance.
Moist O. colensoi D. longifolium D. traversii Well developed O. colensoi scrub on south aspect.
High Alt. Moderately sheltered Sth. aspect O. colensoi Pure community of low growing O. colensoi

Explanation of underlining in Tables I. and II.

O. colensoi—Species is dominant.

O. colensoi—Species is co-dominant.

D. longifolium—Species is important, but not dominant or co-dominant.

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N. simplex. Along the margins between scrub and grassland, and in places where shrubs are scattered through grassland, less palatable species—especially Dracophyllum uniflorum— are heavily browsed in the winter.

From the point of view of the control of deer and chamois the scrub belt is important. Its position as a barrier between forest and grassland allows the animals to use the uppermost forest almost undisturbed by hunters, who work either from the valley tracks or from the grassland. This uppermost forest is severely damaged throughout the Hokitika catchment.

Hares are present, and in winter they probably make considerable use of the scrub, but their effects were not recognised.

Mature specimens of Hoheria glabrata, Olearia colensoi, O. lacunosa and O. ilicifolia growing within the forest zone are often badly defoliated and, at least sometimes, opossums are responsible. However, no serious damage to the subalpine scrub was noted, although the animals range throughout. There is an exception to this statement; on fault-shattered terrain above the Kokatahi gorge, areas of scrub have died. Opossums are notoriously thick in the forest below, and probably overpopulation has forced numbers of them into the scrub.

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