D. H. Ashton

Catastrophic influences on the vegetation of the Valdivian Andes, Chile

In association with a devastating earthquake in 1960, thousands of debris avalanches, landslides, and mudflows occurred in the Andes of south-central Chile. Catastrophic mass movements associated with seismic activity have affected the Andes of south-central Chile several times in the past 400 years and have profoundly influenced the regional vegetation. The most widespread forest types in the Andean Cordillera of the Province of Valdivia (latitude 39°25′ to 40°40′ S) are dominated byNothofagus spp. andEucryphia cordifolia and characteristically have an intermediate layer of shade-tolerant trees. These forest types represent relatively early successional phases following forest destruction by catastrophic phenomena. The supporting evidence for this interpretation includes: (1) the nature of the colonization of the surfaces exposed by the 1960 mass movements, (2) the structure of the existing forest vegetation, (3) the ecological characteristics of the dominant trees, and (4) the historical frequency of similar catastrophic events in the Andes of south-central Chile.

Plant Succession in a Timberline Depressed by Vulcanism in South-Central Chile

The vegetation of the Antillanca Valley in the Andes of southcentral Chile consists of high altitude fellfields, species-rich scrub grasslands, Nothofagus krummholz, deciduous N. pumilio forests, and mixed evergreen deciduous NVothofagus forests. Catastrophic vulcanism has depressed the timberlines an average of 100 to 300 m and greatly affected these vegetation types. Locally, timberline is determined under the influence of such disruptive factors as withthrow, unstable slopes, and avalanches. Succession is interpreted on the bases of species distributions in zones of environmental stress, population structures, and the observed responses of the dominant Nothofagus spp. to avalanche damage and burial by scoria deposition. This study thus documents the dynamic and transitory nature of the frequently-described vegetation zones of southcentral Chile.

Tree regeneration strategies in a lowland Nothofagus- dominated forest in south-central Chile

In the longitudinal valley of south-central Chile remnant stands of old-growth forest on well-drained sites at altitudes of 100-400 m between c. 390 and 410 S latitude are often characterized by scattered tall individuals of Nothofagus obliqua and Eucryphia cordifolia which project approximately 10 m above a main canopy formed by Aextoxicon punctatum, Persea lingue and Laurelia sempervirens. The regeneration strategies of these tree species are reflected by their size class and spatial distributions and were studied in an old- growth forest on the northwestern shores of Lake Villarrica. A. punctatum regenerates beneath the shade of the continuous forest canopy as well as beneath small openings in the canopy. P. lingue and L. sempervirens regenerate only beneath small canopy openings, and E. cordifolia beneath both small and large canopy openings. The regeneration of N. obliqua depends on complete or partial destruction of old-growth stands. The regeneration strategies of the dominant tree species form a continuum of responses to differing scales of disturbance and are appropriately perceived within a kinetic scheme of vegetation dynamics emphasizing repeated disturbance rather than progressive development towards a

The regeneration status of Fitzroya cupressoides in the cordillera Pelada, Chile

Abstract The large conifer, Fitzroya cupressoides (Mol.) Johnston, which is native to southern Chile and Argentina, has been intensively exploited for its valuable wood since European colonization in the 16th century. Today F. cupressoides persists only in relatively small, remote stands and reports of inadequate regeneration have given rise to considerable concern for its survival. A reconnaissance study of virgin stands in the Cordillera Pelada, Chile, indicates that regeneration by both seedling establishment and root suckering is generally adequate to assure local persistence. Regeneration following very light burning is also adequate; however, following intense fires where soil peat burns and bare areas on the sterile, podzolic soils are created, forest re-establishment is exceedingly slow. The presence of regenerating virgin stands of F. cupressoides in the Cordillera Pelada is a strong reason for this area to be set aside for in situ preservation.

Viability of seeds of Eucalyptus obliqua and Leptospermum juniperinum from capsules subjected to a crown fire

Abstract Following crown fires near Anglesea, Victoria, about one third of the estimated viable seed survived within the capsules of Eucalyptus obliqua and Leptospermum juniperinum. Thickness of the capsule wall was much less than that of the bark of adjacent stems on which cambium was killed. Moisture content of seed and capsules, as well as the mutual packing of inflorescences may contribute to the subtleties of seed survival under such searing conditions. All E. obliqua seeds were killed in capsules heated to 290°C for 1 ½ minutes, whilst some Leptospermum seeds survived 4 minutes at 380 °C. Experiments point to the occurrence during crown fires of either very short exposures to high temperatures, or longer exposures to relatively low temperatures at capsule sites. Further work may enable a calibration of such fire environments within the crown.

NOTHOFAGUS STAND DEVELOPMENT ON IN-TRANSIT MORAINES, CASA PANGUE GLACIER, CHILE

Vegetation development was examined on in-transit morainic arcs (i.e., supraglacial debris) and on recessional and lateral moraines at Casa Pangue Glacier in Chile. Data were collected on floristic composition, densities of shrubs and trees, and tree population age structures at sites on glacial deposits covering a range of ages. On arcs of in-transit moraine, formed by the deposition of landslide debris onto the glacier surface, forest stands dominated by Nothofagus dombeyi develop. These stands travel down the glacier surface at an average annual rate of 22.5 m. Such transport of live trees down a glacier could invalidate dating glacial movement on the basis of wood found at the snout of a glacier. Despite considerable instability of the supraglacial debris, these stands are characterized by trees of up to 40 cm in diameter and ca. 70 yr in age. Three tree species and six shrub species are common in these stands which also contain numerous other vascular plants including ferns and lianas. Comparison

Problems of regeneration of the mature Eucalyptus regnans F. Muell, (The Big Ash) forest, in the absence of fire at Wallaby Creek, Victoria, Australia

Summary This paper is based on observations on the regeneration of a mature E. regnans forest begun in 1949 and extending over the next 50 years. Any regeneration of E. regnans in the unburnt, mature forest is confronted by a phalanx of obstacles. The formation of large gaps which synchronously involve the overstorey, shrub understorey and fern stratum are an essential prerequisite for establishment, although success may not be assured unless the seedbed has been favourably prepared by mechanical disturbance or fire. In this study, regeneration, which was initiated experimentally by a heavy sowing of seed, scarification of soil, addition of nitrogenous fertilizer, creation of moderately good light conditions and the removal of competition by seedlings of understorey species in the first season, failed completely after 10–11 years even though understorey species which germinated from the soil seed bank continued to thrive. Processes of seed germination and seedling development are explored in terms of seed...

Ecological gradients in forest communities on Groote Eylandt, Northern Territory, Australia

Vegetational changes over a series of geological boundaries through an area of managanese mineralization on the western side of Groote Eylandt, have been analysed using pattern analysis techniques. Hierarchical classification of data on the frequency of occurrence of plant species in the transects through each of the vegetational zones gave five ecologically identifable groups. The degree of interrelatedness between the sites was emphasized by ordination of the groups, incorporating minimum spanning analysis. The vegetational groups represent developments under different environmental conditions in which differences in water relations and the presence of an impermeable barrier in the soil profile were important. Comparison of the soil nutrient contents of the sites indicated major differences in the total manganese concentration in the topsoil. Even though manganese levels in Eucalyptus tetrodonta leaf tissue were high, no evidence could be found for an iron-chlorosis induced by a low Fe/Mn ratio. The levels of other nutrients in eucalypt foliage were similar to those measured elsewhere. In each vegetational grouping the frequency of occurrence of termite species varied according to site and food type. The role of termites in nutrient cycling needs to be further studied. The closed-forest maybe the climatic climax on the acid red earth soils since in the absence of fire it extends into the surrounding Eucalyptus tetrodonta open-forest. On the Sandstone and Manganese ares the stable state of the vegetation is likely to be composed of the Australian element of the vegetation modified to various extents by fire.

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.