New Zealand Journal of Botany abstracts
Recovery, invasion, and decline over 37 years in a Marlborough short-tussock
grassland, New Zealand
Alan B. Rose
Upland Research
New Renwick Road
RD 2, Blenheim, New Zealand
Philip A. Suisted
Landcare Research
P.O. Box 69
Lincoln, New Zealand
Present address: 21 Hindmarsh St, Johnsonville, Wellington, New Zealand.
Chris M. Frampton
Christchurch School of Medine and Health Sciences
P.O. Box 4345
Christchurch, New Zealand
Abstract The composition of humid, unfertilised, short-tussock
(Festuca-Rytidosperma-Poa) grasslands was recorded on 42 permanent
transects in 1959, 1970-72, and 1995-96 in the Wairau catchment, Marlborough.
Changes in frequency of the most abundant plant species and bare ground were
analysed. Reduced levels of grazing, browsing, and fire prompted significant
recovery of native shrubs, tall tussocks (Chionochloa), and herbs.
Invasive exotics (Hieracium, Anthoxanthum, Agrostis)
also increased. Short native grasses (Poa, Elymus), a native
herb (Acaena spp.), and an exotic herb (Rumex acetosella) declined.
Hieracium pilosella, H. caespitosum, and H. lepidulum
were rare or absent in 1959. By 1996 they had established on half the transects,
but were still in the early stages of invasion (median frequencies ≤ 5%).
There was no correlation between the increase in Hieracium and decline
in other species, suggesting that other factors were driving the compositional
changes. However, Hieracium species can establish in vegetated microsites
and eventually dominate. Early in the invasion a lack of correlation may
reflect a capacity for short-tussock grasslands to “absorb” exotic species
before interference becomes intense. Compared with five documented examples
of more heavily infested tussock grasslands, the Wairau was the only one
where the proportion of increasing species exceeded the proportion that decreased.
This may indicate a threshold level of Hieracium, beyond which interference
becomes involved in species declines. These grasslands will continue to change
as native species continue to recover and potentially dominant Hieracium
and exotic grasses continue to invade. In such grasslands, conservation management
would benefit from integrating the inevitability of vegetation change with
the need to optimise indigenous biodiversity. In appropriate areas, actively
promoting long-term succession to native woody vegetation and tall-tussock
grassland would result in communities that have high conservation values
and higher resistance to exotic invaders such as Hieracium.
Keywords tussock grassland; vegetation change; plant
invasion; grazing; conservation management; Hieracium
B02048; Online publication date 30 March 2004; Received 3 July 2002; accepted
24 July 2003
New Zealand Journal of Botany, 2004, Vol. 42: 77-87
0028-825X/04/4201-0077 © The Royal Society of New Zealand 2004
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