Question: What are the tempo and mode of long-term succession and of demographic processes in an alpine community, especially: tenacity, transition patterns, predictions, growth of individual cushion plants, cyclic succession, spatial patterns?
Location: A low-alpine mixed cushion/turf/snow-tussock / shrub community in southeastern New Zealand.
Methods: The distribution of seven plant cover-types was recorded at 1024 fixed points in an 8 m × 8 m plot at approximately decade intervals for 50 years. The diameters of eight Donatia novae-zelandiae cushions were monitored.
Results: The process was essentially first-order Markovian. There was a change in transition frequencies about 1980. The tenacity of the two major cover types – cushion and turf – was high, but that of cushion decreased about 1980 as some of its area was taken over by turf. The original informal prediction of 1955 that the cushion / turf would increase proved to be correct, probably because of paludification of the site. A prediction of 1987 made from observed transitions that cushion would dominate over turf has proved untrue because of a change in the transition probabilities in the 1980s, of unknown cause. There is a ten-fold range in diameter growth rates among the eight cushions measured, but the mean rate of 5.3 mm.a−1 is similar to that reported from other alpine and arctic sites. As cushions aged, turf colonized their centres, and in two cases new cushions colonized into this turf: consistent with cyclic succession. The pattern of transitions was compatible with a general interpretation of cyclic succession, but not definitive.
Conclusions: Change is slow in this alpine community, and tenacity high. The change in transition frequencies about 1980, the invasion of individual cushions, and the decrease in spatial autocorrelation all suggest that cushions established on the site as a result of the clearance of woody vegetation after 1400 AD. Paludification may be causing some loss of tussock grass. A tendency for the cushions to break up, and the shallow peat accumulated below them, may indicate that they are the first generation of cushions on the site. Though these cushions are breaking up, other cushions are establishing, and cushions will continue to be an important part of the vegetation dynamics which may be part of a cyclic succession.
Nomenclature: Mark & Adams (1995) unless the author is explicitly indicated.
