Fjölrit RALA - 05.12.1999, Blaðsíða 129

KevinF. 0‘Connor etal.
127
continental lowland and montane central Otago, forests which had developed since the
Pleistocene were destroyed before the arrival of man some 1000 years ago, possibly
by lightning fire, leading to formation of grasslands (McGlone 1988). Elsewhere in
eastem and southem South Island, forest destmction by fire during Polynesian occu-
pation (Molloy et al. 1963) led to tall tussock grasslands, dominated by species of
Chionochloa (Connor 1964, 1965, Connor and MacRae 1969, Wardle 1991, Mark
1992).
The extent of tall tussock grasslands in the South Island high country at the begin-
ning of pastoral settlement is a matter of some dispute. At the present time, there is
general agreement among botanists and ecologists that in the semi-arid interior of
Otago where mean annual precipitation is less than 350 mm, grasslands were charac-
terised by abundant Elymus apricus and the absence of tall tussock species of Chiono-
chloa. Many scientists believe that Intermediate in soil or climate conditions between
this semi-arid grassland and the more extensive area of tall tussock grasslands, there
was a substantial area of short tussock grassland dominated by Festuca novae-
zelandiae or Poa cita. Others, including ourselves, hold the view that, apart from
some specific situations, such short tussock grasslands did not occur naturally but
were induced from tall tussock grasslands, shrublands, scrub and forest, by the com-
bined impact of early pastoral fire and sustained grazing. The specific situations which
we recognise as exceptions were the semi-arid grasslands of Elymus apricus, the
coastal grasslands dominated by Poa cita, and the ofiten sparse grasslands of stony or
recent ground in dry sub-humid sectors of Marlborough or Waitaki where Elymus so-
landri, some forms of Poa colensoi, and some species of Rytidosperma were promi-
nent.
Outside the semi-arid zone proper, in virtually all areas with annual precipitation
greater than 500 mm, grasslands existing prior to the coming of Europeans appear to
have been characterised by one or other tall tussock species of the genus Chionochloa.
Attention in ecological research has been given mostly to the snow-tussock species of
existing pastoral lands, Chionochloa rigida, C. macra, C. flavescens, and C. pallens.
The frequency of remnants of red tussock, C. rubra, especially in the montane zone
wherever the terrain is well watered in early spring, betrays its former significant ex-
tensive role, even in dry sub-humid climate to the borders of the semi-arid, as well as
in more humid regions. Most tussock grasses of the genus Chionochloa are slow-
growing and long-lived. Where they grew in dense stands, they tended to suppress the
density and frequency of inter-tussock grasses. These included species of Festuca,
Poa, Agrostis, Deyeuxia, Dichelachne, Koeleria, Lachnagrostis, and Elymus. Other
inter-tussock herbs included species of Luzula, Celmisia, Ranunculus, Geranium, Vi-
ola, Wahlenbergia, Gentiana, Helichrysum and Gingidia. Many of these inter-tussock
plants and possibly some dwarf-shrubs had apparently accompanied the dominant
Chionochloa species in their migration into former forest lands.
The significance of fire
In many situations, such grasslands induced by Polynesian buming of forest also in-
cluded woody species. Such shrubs and dwarf-shrubs principally belonged to the gen-
era Olearia, Brachyglottis, Discaria, Podocarpus, Phyllocladus, Hebe, Dracophyllum,
Coprosma, Carmichaelia, Cassinia, Aciphylla, Kunzea and Leptospermum. Dense