New Zealand Journal of Botany abstracts
Temporal responses over 30 years to removal of grazing from a mid-altitude
snow tussock grassland reserve, Lammerlaw Ecological Region, New Zealand
Alan F. Mark
Katharine J. M. Dickinson
Botany Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
Abstract Monitoring of five representative sites in
the 144-ha Black Rock Scientific Reserve of mid-altitude (690-770 m) narrow-leaved
snow tussock (Chionochloa rigida) grassland over the 30 years since
its establishment has revealed, contrary to an early prediction, significant
increases in both cover and height of snow tussock. By contrast, co-dominant
shrubs have shown only a slight, generally non-significant gain, with Dracophyllum
longifolium rather than the predicted Hebe odora as the only significant
increaser. Several sub-dominant shrubs (Coprosma cheesemanii, Leucopogon
colensoi, Gaultheria macrostigma) plus some mosses (Hypnum
cupressiforme) and lichens (Cladia retipora, Stereocaulon ramulosum)
have increased significantly while some rosette herbs (Brachyglottis bellidioides,
Oreomyrrhis colensoi, Plantago novae-zelandiae, and the adventive
Hypochoeris radicata) have declined. The generally aggressive exotic
flatweed Hieracium pilosella remains as yet a minor component. These
changes in subcanopy cover probably reflect the obvious increase in shade
and dampness of the micro-habitat. The height-frequency sampling indicates
an overall decline in vascular species diversity since losses have significantly
exceeded gains over the 30-year period of monitoring. Our results confirm
that low- to mid-altitude snow tussock grassland ecosystems can be sustained
for at least several decades, for their conservation, landscape, and water
yield values. We question the interpretation of a general lack of tussock
grassland below treeline in immediate pre-human times, and its widespread
downslope replacement of forest following Polynesian fires, since it is at
variance with the known ecology of the dominant grass species, evidence from
relevant pollen records, and results from the present study. Rather, we interpret
the available evidence as indicative of succession to a vegetation mosaic
of non-woody and woody dominants related to physiography and disturbance,
as currently being debated for north-western Europe. We hypothesise that
such a mosaic would more closely reflect the pre-human situation below treeline
which would have been moulded by periodic fire and avian and invertebrate
herbivory, in the absence of land mammals.
Keywords conservation management; fire; floristics;
herbivory; monitoring; native grassland; succession
B02062; Received 12 September 2002; accepted 9 May 2003; online publication
date 26 November 2003
New Zealand Journal of Botany, 2003, Vol. 41: 655-668
0028-825X/03/4104-0655 $7.00 © The Royal Society of New Zealand
2003
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