New Zealand Journal of Botany abstract
Seasonal changes in semi-arid vegetation of Central Otago, New Zealand
SUSAN WALKER
J. BASTOW WILSON
ALAN F. MARK
Botany Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
Abstract Seasonal changes in the semi-arid grassland
vegetation of Central Otago, New Zealand, are examined using data collected in
nine pairs of spring and autumn sampling dates at five long-term plots, and
data from consecutive autumn, spring, and summer surveys across an
environmental gradient. Seasonal changes are small in relation to those
occurring in the vegetation from year to year, and to spatial differences in
vegetation across the landscape. Seasonal changes in community characteristics
and in the abundance of most species differ between years. Climatic control of
seasonal change appears to be complex and site-specific. Greater seasonal
variation, in both species presence and species abundance, is found in shady
sites and on deeper soils. Spring vegetation tends to be more variable and less
well structured than autumn vegetation. It is suggested that the annual soil
moisture cycle of winter recharge and summer depletion leads to a random
element in the spring vegetation (i.e., the relatively widespread germination
of distributed seed under temporarily favourable climatic conditions) and that,
by autumn, species are more strongly confined to particular environments
according to their tolerance of moisture stress.
Keywords seasonal changes; New Zealand; Central Otago;
semi-arid; community structure; moisture stress; long-term monitoring
B98055
Received 22 September 1998; accepted 17 February 1999
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