New Zealand Journal of Botany abstracts
Snow tussock {Chionochloa) population responses to removal of sheep and European hares, Canterbury, New Zealand
A. B. ROSE
Landcare Research New Zealand Ltd
Maryborough Research Centre
Private Bag 1007
Blenheim, New Zealand
K. H. PLATT
Landcare Research New Zealand Ltd
P.O. Box 31 Oil
Christchurch, New Zealand
Abstract Snow tussock (Chionochloa macra and
C. flavescens ssp. brevis) population structures and
seedling regeneration were investigated in 10
montane-subalpine stands on formerly forested sites
in the Harper-Avoca catchment, Canterbury,
subjected to different histories of sheep grazing and
browsing by European hares. Population structures
were assessed by assigning individuals to four "age-
states" based on basal diameter, number of tillers,
height, and percent crown death: "seedlings",
"juvenile tussocks", "mature tussocks", and
"senescent tussocks". On areas subjected to c. 80
years of grazing by sheep, most snow tussocks had
been destroyed. Remaining tussocks were pre-
dominantly senescent and seedlings were infrequent,
suggesting a continuing decline in abundance. In
contrast, stands retired from sheep-grazing for 34
or 21 years were characterised by low proportions
of senescent tussocks and high proportions (>60%)
of seedlings and juveniles, suggesting the onset of
increases in tussock abundance. Population
structures inside and outside a 10 year old exclosure
showed that browsing by European hares alone was
capable of inhibiting C. macra recovery. In retired
stands, snow tussock seedlings were most frequent
within 70 cm of mature tussocks, on microsites
protected from frost-heave by short ground-tier
vegetation (e.g., bryophyte mats). A lack of seedling
regeneration on heavily grazed/browsed sites
reflected the low basal area and poor vigour of the
tussocks remaining as seed sources. Balanced
management of tussock grasslands for conservation
and production urgently requires further knowledge
of successional processes and how these are altered
by different levels of grazing and burning under
different environmental conditions. Age-state
analysis appears useful for assessing tussock
population responses to management. Comparison
of sites subjected to historically different manage-
ment offers an approach that complements experi-
mental or monitoring studies.
Keywords Chionochloa; age structure; population
dynamics; plant community analysis; browsing
damage; sheep; hares; Canterbury
B91045 ;
Received 24 October 1991; accepted 19 October 1992
New Zealand Journal of Botany, 1992, Vol. 30: 373-382
0028-825X/92/3004-0373 $2.50/0 © The Royal Society of New Zealand 1992
PDF file of entire paper: medium quality (772K); (scanned from paper original: notes about this process)
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