Successional pattern above timberline in south-central Chile

In the above-timberline zone of south-central Chile, stepped microtopography commonly develops on slopes of unstable volcanic ash deposits. Between the Nothofagus timberline and the high-altitude sparse fellfields, a scrubgrassland vegetation dominated by prostrate shrubs such as Empetrum rubrum and Pernettya spp. and tussock grasses such as Hierochloe utriculata and Cortaderia pilosa characteristically occurs on the stepped microtopography. Species interactions and species-microtopography interactions during the course of succession on the recent volcanic deposits were investigated by means of pattern analysis. Scales of pattern associated with individual plant morphology and interspecific interactions are present but, in general, the scales of pattern attributed to environmental variation are more evident. Cyclic changes occur in the scrub-grassland under the influence of periodic burial by the unstable ash substrate and the life cycles of the dominant prostrate shrubs. Such cyclic changes are part of a long-term linear successional trend following disturbance by catastrophic vulcanism. In contrast to the basic assumption of classic successional theory, in both the short-term and long-term the physical habitat in the above-timberline zone of south-central Chile is fundamentally unstable.