| Zusammenfassung: | Forests cover about 31 percent of the global land area. Tropical forests account for almost half of the total forest area and are a major terrestrial carbon pool. Since they act as both carbon source and sink, they contribute significantly to the global carbon cycle. Although the rate of deforestation has been declining over the last three decades, deforestation and forest degradation continue at ... Forests cover about 31 percent of the global land area. Tropical forests account for almost half of the total forest area and are a major terrestrial carbon pool. Since they act as both carbon source and sink, they contribute significantly to the global carbon cycle. Although the rate of deforestation has been declining over the last three decades, deforestation and forest degradation continue at a high rate. Despite the positive trends at global level, forest loss and degradation continue especially in tropical countries, which account for 10-15 percent of anthropogenic carbon emissions. Commercial logging is the main cause of forest degradation in the tropics. At present, tropical forests are mainly managed through selective logging. Over the past 30 years, the concept of sustainability has increasingly been incorporated into tropical forest management. The concept of sustainable forest management (SFM) attempts to reconcile ecological, socio-cultural and economic management objectives with the Forest Principles adopted at the United Nations Conference on Environment and Development (UNCED) in 1992. In addition to Reduced Impact Logging (RIL), SFM measures also include silvicultural treatments. In 2005, the negotiations on the United Nations Framework Convention on Climate Change (UNFCCC) launched a discussion on the link between climate change and forest loss, which led to the concept of Reducing Emissions from Deforestation and Forest Degradation (REDD). By integrating the conservation of forest carbon stocks, sustainable forest management and the enhancement of forest carbon stocks, the REDD scheme was expanded to REDD+. Although the concept of SFM is widespread and strongly promoted, it remains unclear to what extent SFM contributes to the sustainable use of tropical forests and to what extent SFM measures contribute to reducing carbon emissions from forests and thus to REDD+. The three scientific papers constituting this cumulative dissertation examine the contribution of SFM to sustainability in tropical forest management. They also analyse silvicultural treatments in terms of their impact on economic added value and the carbon balance of tropical forests.
The first part of the comprehensive summary presents the thematic context of the three papers. The thematic context provides an introduction to the relevance and status of tropical forests and their contribution to the global climate, followed by brief introductions to timber exploitation, sustainable forest management in the tropics and the REDD+ concept. Uncertainties in sustainable forest management in the tropics and in the implementation of REDD+ are discussed and conflicts of interest in the implementation of REDD+ are briefly presented. After the thematic framework has been established, the main objectives of this thesis are presented. The main objectives are "sustainability of selective logging", "profitability of future crop tree release treatments" and "impacts of silvicultural treatments as REDD+ mitigation benefits". The second part of the comprehensive summary integrates the three papers into the thematic framework of the current cumulative dissertation.
The first paper focuses on the analysis of recovery times and sustainability in tropical forest management using the example of four forest tenure types in Central and South America: large scale concession, private forests, forests managed under the periodic block system and community managed forests. As an indicator of sustainable timber production, the recovery times expected under the initial conditions of the stands were calculated and discussed with the regard to currently practiced cutting cycles. The findings show that general harvesting codes do not guarantee sustainable forest management in the tropics. Local stand conditions must always be one of the guiding principles of sustainable timber production. The application of rigid rules that do not take into account the current conditions of the stands carries the long-term risk of forest degradation. With these results, the currently practiced, generalized production methods for tropical forests are questioned and the necessity of a paradigm shift towards an ecologically sound, sustainable forest management is justified.
The second paper examines the economic aspects of silvicultural release treatments and considers the growth of the remaining stand and the timber prices that should be achieved at the end of the rotation period to make a treatment profitable. In this context, release treatments are considered as an investment that must be amortised by the additional growth of the remaining forest stand by the end of the rotation period. The treatment costs were derived from time studies carried out in four tropical countries during the treatment. A reverse approach was used to determine the additional growth that must be generated by the released trees by the end of the 30-year felling cycle to cover the treatment costs. The paper shows that the expected improvement in tree growth alone is not sufficient to justify the application of silvicultural treatments. While the treatment costs are known at the time when the decision to implement the measures is taken, future timber prices and harvesting costs as well as the additional growth actually achieved are subject to uncertainty. These uncertainties have a significant impact on the assessment of the economic risk, which is reflected in the choice of internal interest rates. The paper shows that investments in silvicultural treatments involve a considerable financial risk and that the decision to invest in silvicultural treatments should always be the subject of a detailed investment calculation.
The third paper examines the extent to which silvicultural treatments affect the carbon balance of the forest stand and whether refinancing through any profits generated from carbon sequestration payments would be possible. As in the second paper, this paper investigates silvicultural release treatments used to increase the growth of selected trees by felling competing trees in their immediate vicinity. The felling of competing trees leads to a reduction in a forest’s carbon stock and thus represents a carbon loss. The paper estimates the time needed for the released trees to compensate for the carbon loss through felling competitor trees by increased growth. By using a recursive approach, it was examined whether the treatment costs could be offset by the financial carbon benefits achieved. The paper shows that silvicultural release treatments do not guarantee for an increase in forest carbon stocks. Furthermore, it is shown that refinancing of treatment costs is problematic and that silvicultural release treatments as a sustainable forest management measure are not suitable as REDD+ activities.
Based on the results derived in the papers and their discussion in the thematic context, conclusions are drawn with regard to the main objectives presented above. The complete versions of the three papers that, together with the comprehensive summary, constitute this cumulative dissertation and a short explanation of the personal contribution of the author to the papers are attached in the Annex. |
