New Zealand Journal of Botany abstract
North Island seral tussock grasslands. 3. The influence of heather (Calluna
vulgaris) on rates of change from tussock grassland to shrubland
G. M. ROGERS*
J. R. LEATHWICK
Manaaki Whenua - Landcare Research
Private Bag 3127
Hamilton, New Zealand
*Present address: Department of Conservation, P. O. Box 5244, Dunedin, New
Zealand
Abstract The cover of the adventive heath Calluna vulgaris
in seral tussock grassland of northern Tongariro National Park and the
influence of C. vulgaris on the rates of indigenous shrub invasion of
the grasslands were assessed by relating species canopy cover and height to
environmental and temporal factors using generalised additive models. C.
vulgaris now dominates virtually all of the area previously covered in
Chionochloa rubra tussock grassland below 1200 m over
52 km2 on the northern ringplain. Only on basin floors, and the
even frostier or poorly drained hollows, does C. rubra persist as a
conspicuous species, but at generally less than 10% crown cover. Native shrubs
are invading C. vulgaris shrubland in a process partly explicable in
terms of time elapsed since the last fire, slope, topographical position, and
altitude. On sideslopes at 900 m a.s.l. Leptospermum scoparium and
Dracophyllum longifolium colonise and exceed the cover of C. vulgaris
38 years after burning; on crests the native shrubs take at least 60 years
to dominate; and they take 75 years on basin floors. At 1100 m the times
for this transformation are almost doubled. These slow rates of change, coupled
with the extensive areas of early seral vegetation and the topographical
dominance of crests and basin floors, point to C. vulgaris remaining a
conspicuous component of ringplain landscapes for at least another 40 years.
Rates of native shrub invasion of tussock grassland without C. vulgaris
showed somewhat faster initial rates, but little difference after 70-80
years.
Keywords heather; Calluna vulgaris; tussock grassland; shrubland;
secondary vegetation; vegetation/environment relationships; stability; central
North Island; New Zealand
B95053
Received 7 November 1995; accepted 15 July 1996
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