Modeling climate change impacts and drivers on temperate and tropical forest productivity

Medientyp: E-Book

Titel: Modeling climate change impacts and drivers on temperate and tropical forest productivity

Beteiligte: Nölte, Anja [Verfasser]; Hanewinkel, Marc [Akademischer Betreuer]; Hanewinkel, Marc [GutachterIn]; Seifert, Thomas [GutachterIn]

Körperschaft: Albert-Ludwigs-Universität Freiburg, Fakultät für Umwelt und Natürliche Ressourcen ; Albert-Ludwigs-Universität Freiburg, Fakultät für Umwelt und Natürliche Ressourcen

Erschienen: Freiburg: Universität, 2023

Umfang: Online-Ressource

Sprache: Englisch; Deutsch

DOI: 10.6094/UNIFR/242329

Identifikator:

Schlagwörter: Klimaänderung ; Anthropogene Klimaänderung ; Forstwirtschaft ; Aufforstung ; Modell ; Waldökosystem ; Forstertrag ; Tropischer Wald ; Mathematische Modellierung ; (local)doctoralThesis

Entstehung:

Hochschulschrift: Dissertation, Universität Freiburg, 2023

Anmerkungen:

Beschreibung: Abstract: Climate change is one of the greatest threats to human well-being, and forests play an important role in the global carbon cycle and in mitigating climate change. The conservation of existing forests is particularly important to prevent the release of the carbon stored in them. Afforestation and reforestation hold great potential to remove carbon from the atmosphere and to act as carbon sinks. Overall, they are among the most important tools for climate change mitigation currently available. At the same time, climate conditions determine forest growth and productivity. Climate change may alter these climate-forest feedbacks, which could have adverse effects on climate change mitigation. Despite the importance of forests, several important knowledge gaps remain regarding their response to future climate change scenarios, particularly for tropical forests, but also for temperate forests. In the temperate climate zone, it was shown that the lengthening of the growing season under rising temperatures can increase forest productivity. However, there is a lack of quantification of the effects of a longer growing season on forest growth at the stand scale and on the interplay with other climatic drivers and CO2. In Central Europe, specifically Germany, sessile oak (Quercus petraea) is the second most common broadleaf species and one of the target species for forest adaptation under climate change scenarios. Therefore, this species was selected for analyzing effects and drivers of climate change scenarios, in particular effects of the growing season lengthening, on temperate deciduous forests. Globally, most of the climate change mitigation potential from reforestation is attributed to the tropics as they have fast forest growth rates and large areas of deforested and degraded land. Forest plantations are expected to play a major role in future restoration through reforestation, because they combine carbon sequestration with economic return. Yet, they are commonly planted with introduced species in monoculture, which has little value for biodiversity conversation. Native species and species mixtures have shown to be key elements for biodiversity conservation by forest plantations. Mixtures can have potential co-benefits of increased productivity, increased resilience and risk diversification under uncertainty. However, knowledge about growth and management of tropical mixed native tree species plantations is scarce, which is an obstacle to their implementation. In addition, the response of tropical forests in general, and tropical reforestation in particular, to climate change scenarios remains highly uncertain. Process-based forest growth models, i.e., models that represent the biological processes of forest growth, are powerful tools for analyzing the effects and drivers of future climate change scenarios on forest growth. They allow for the simultaneous analysis of a large number of causal relationships and the quantification of the net effects of changing and novel climate conditions on forest growth. Model development requires simplification and depending on the modeling objectives different degrees and types of simplification are chosen that have led to a large variety of process-based forest growth models. On the spatial scale this means models range from a global scale to the tree level. Climate change is a global problem, but with a strong local variation of its impacts. Thus, findings from global forest growth models should be complemented with findings from small scale models that are often more detailed in the representation of the analyzed forest system. In this thesis, managed forests and forest plantations were analyzed under climate change scenarios. Detailed forest management is typically better represented in rather specific, stand scale forest growth models. Thus, 3-PG, the most widely used species-specific stand scale model that includes a good forest management submodule was chosen and applied to a subset of locations and species that are meaningful to address the research gaps described above. To answer the research questions, the model was calibrated, validated and if necessary improved. Then, the model was used to simulate impacts of climate change scenarios on forest growth and to identify the most important climatic drivers. Finally, modeling uncertainties and practical implications of the results were discussed. For temperate deciduous forests, first, I improved the 3-PG model by adding a phenology submodule that included a dynamic, temperature-dependent growing season length. The original model version was developed for evergreen species and, thus, the model modification was an important contribution for modelling deciduous tree species under climate change scenarios with 3-PG. I calibrated and validated the improved model for sessile oak on 10 sites in Southwest Germany as that region is a climate change hotspot in Germany. The model calibration and validation were successful with an average model error of 6.6% and model underestimation of -4.7%. Lengthening of the growing season was the most important climatic driver under future climate change scenarios, when CO2 fertilization effects were excluded. It increased accumulated volume growth by about +3% for each degree of warming. However, the overall effect of the growing season lengthening on future sessile oak growth was rather small with +3% to +8% by the end of the century, depending on emissions scenario and stand age. Generally, sessile oak growth remained largely unchanged under climate change scenarios. The one site with very low soil water holding capacity and reduced precipitation throughout the growing season, showed a clear negative effect of climate change on forest growth. In conclusion, the simulations showed that sessile oak may be well adapted to future climate conditions in Southwest Germany except on sites with strong water limitation. Analysis of CO2 fertilization effects showed this process is not sufficiently well represented in 3-PG. Future forest mortality rates and response to elevated atmospheric CO2 concentrations are major uncertainties for forest growth projections under climate change scenarios with 3-PG and in general. According to the literature, sessile oak mortality may increase slightly under future climate scenarios. The mixture version of 3-PG (3-PGmix) was calibrated and validated for native species forest plantations in mixed and pure plots in Costa Rica and Panama. Tropical forest plantations with mixed and/or native species are generally rare, but several examples can be found in these two countries. To calibrate 3-PGmix for neotropical native species, I collected a very large database of 947 growth observations from 107 plantations throughout Costa Rica and Panama. This database was supplemented with field measurements of leaf dynamics and crown dimensions. This allowed a robust calibration of 3-PGmix with an average model error of 9% and -2% model underestimation. Providing extensive yield tables based on the results from the calibrated forest growth model has filled an important knowledge gap for the cultivation of forest plantations with native and mixed species in Central America. Simulation results from 69 sites showed that sensitivity to climate change scenarios was higher for reforestation in the tropical dry forest climate zone compared to the tropical moist and rain forest climate zone. Reforestation growth under a low emission scenario (SSP1-2.6) was stable (losses of -7% or below) in all climate zones until the end of the century. Reforestation in the tropical dry climate zone showed moderate losses (-17%) in biomass growth under an intermediate emission scenario (SSP2-4.5) and alarming losses (-43 %) under a high emission scenario (SSP3-7.0). In the tropical moist and rain forest climate zone, reforestation growth also remained stable (-2% to -3%) under SSP2-4.5 and showed moderate losses (-10%) under SSP3-7.0. However, the variability among individual sites was very large, ranging from +35% to -71% in biomass growth for sites in the tropical rainforest climate zone alone under SSP3-7.0. In all climate zones, high growth losses were associated with high temperatures. A sharp decline in forest growth was observed at temperatures above 29°C mean annual temperature (-11% per 1°C of warming). This temperature threshold was consistent across all the analyzed species and climate zones. By the end of the century, 54% of the land area within the study region and 62% of the pan-tropical land area could exceed this temperature threshold under a high emission scenario (SSP3-7.0). An indirect temperature effect, i.e. rising vapor pressure deficit, was found to be the main driver of this growth decline. Major modeling uncertainties are future forest mortality and response to elevated atmospheric CO2 concentrations, both of which were excluded from the simulations due to insufficient representation in 3-PG. Instead a sensitivity analysis and literature review were conducted, suggesting that future losses might be roughly 10% lower when considering CO2 fertilization effects. Yet, the strength and persistence of CO2 fertilization effects is highly uncertain. In addition, future trends in mortality and CO2 fertilization might cancel each other out, at least partially. Results of this thesis raise concern about the future efficiency of reforestation as a climate change mitigation tool under intermediate and high emission scenarios. In addition, they show the importance of following a low emission pathway to prevent growth declines which would reduce the mitigation potential of reforestation efforts. Thus, immediate emission reduction and increased reforest

Zugangsstatus: Freier Zugang

Nur in Feld suchen:

Zuletzt gesuchte Begriffe: