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Wiederherstellung der Pilgerodendron uviferum-Wälder auf der Insel Chiloé, Nord-Patagonien, Chile

abgeschlossen 11/2012


While the majority of peatlands and wetlands are concentrated in the boreal zone, millions of ha of these ecosystems are also found in subantarctic areas of the southern hemisphere. In spite of the extensive area of bogs in the southern cone of South America, there have been very few studies on structure and dynamics of conifer bog forests in this region, although many of them have been greatly changed by humans. Southern bog forests dominated by the conifer Pilgerodendron uviferum in Northern Patagonia are a typical case of an ecosystem with low resilience to disturbance by fire, which kills most trees and seeds. These forests, which have been burned to a large extent, cover an area of almost 1 million ha (6.8% of Chilean native forests).The aim of this doctoral thesis was to study fire-disturbed and undisturbed old-growth P. uviferum bog forests in North Patagonia in order to develop the scientific ecological basis for conservation and restoration strategies. Therefore the work focussed on three important aspects of restoration: a) understanding the processes occurring in undisturbed old-growth forests, b) analysing the natural rate of recovery of fire-disturbed forests, and c) exploring some options for restoration.
Using a multi-scaled approach, this study started analysing diameter and age structure, foliar and soil nutrient levels and the light environment in old-growth and fire-disturbed P. uviferum stands on Chiloé Island (43ºS) in North Patagonia. Secondly, the seed dissemination potential and effective seedling recruitment distance from seed trees of the species were quantified, the suitability of substrates for the germination of P. uviferum seedlings was assessed, and the spatial distribution of seed trees of the species at the landscape level was analyzed. Finally, restoration plantings were established in disturbed upland and bog forests, to evaluate growth and mortality as well as performance (foliar nutrients and photosynthesis) of P. uviferum seedlings in relation to different site conditions characterized by variations in micro-topography and canopy cover.
According to the findings of this doctoral thesis, longevity (>880 years), extremely slow growth (<1 mm diameter per year) and tolerance to shade and stress are the main mechanisms of P. uviferum to persist in an extreme environment shaped by low nutrient availability and frequently waterlogged conditions. Therefore, in contrast to propositions made in previous studies, old-growth P. uviferum forests are not a transitional phase in forest succession and may be maintained in the landscape for many centuries or millennia. However, although extremely stress-tolerant, the species is very sensitive to fire and recovery from this type of disturbance is very slow. Seventy years after high-severity fires in the study area, seed trees were extremely infrequent at the landscape level (0.3 trees/ha) and were aggregated at scales up to 30 m. Seed dissemination potential and effective seedling recruitment distance from individual P. uviferum seed trees was limited to 20 m, and seeds germinated best on moist Sphagnum or mineral soil substrate. This finding showed that high-severity fires can practically eliminate the species from parts of the landscape, where neither propagules nor seed trees survive. At the same time it points to the importance of biological legacies such as seed trees for the recovery of disturbed sites. Natural regeneration from seed trees can assist the recovery of P. uviferum populations following fire disturbance, but their effect is spatially limited at a landscape level. Therefore, restoration planting to complement existing seed trees may assist natural recovery of P. uviferum in disturbed bog forests and add to genetic diversity.
To examine conditions for successful restoration planting, trials were established in bogs and upland forest to assess whether manipulation of potentially limiting conditions may assist establishment of seedlings. Seedlings were planted on mounds or in depressions on bog sites to examine the effect drainage or beneath a canopy or in the open on upland sites to examine the effect of light. In bogs, there was no significant effect of micro-topography on growth and survival of P. uviferum plantings. However, fluorescence measurements indicated lower stress in seedlings established on mounds. Seedlings in upland areas established beneath a nurse canopy had lower mortality and higher relative shoot growth, higher foliar nutrients, higher photosynthetic light use efficiency and higher fluorescence values than those planted in the open. This indicates that seedlings of the slow growing P. uviferum may tolerate extremely wet conditions, yet suffer from stress when grown in the open. These results may improve restoration plantings of the species in disturbed bog forests.
The mixed passive-active restoration approach, relying on naturally regenerated parent trees complemented through low-density planting, which is suggested here, could be the most effective and efficient option to restore disturbed southern bog forests dominated by P. uviferum in North Patagonia. This low-cost approach may help managers of forest land to restore the species in the future. Furthermore, the multi-scale approach used in the present doctoral thesis studied the underlying ecological and physiological processes occurring in disturbed and undisturbed sites prior to planning a restoration program. In this context, it may be adopted for other ecosystems with low resilience and high degradation, where restoration is likely to be extremely expensive and the outcome uncertain. At the same time this study, which was inevitably limited in scope, showed that there are still very large knowledge gaps that should be filled to base management and restoration of these unique forests on a sound scientific basis.

Projektleitung: Prof. Dr. Jürgen Bauhus
Projektbearbeitung: Jan Bannister
Finanzierung: DAAD - CONICYT, Gobierno de Chile
Laufzeit: 10/2008 - 11/2012

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