Detecting the effect of non-climatic factors on climatic sensitivity of Norway Spruce in Central Europe via a multi-parameter approach

MSc. Yumei Jiang

Doctoral thesis

Abstract:

In dendroecology and dendroclimatological research, tree rings are used as a paleo-climate proxy. A wide range of research can be conducted using this proxy archive, such as tree growth or forest dynamics monitoring, forest disturbance (e.g., fire history, windstorm, bark beetle, etc.) and paleoclimate reconstructions of various climatic variables (e.g., temperature, precipitation, drought, etc.). However, tree growth and tree ring formation are determined by a complex combination of various climatic and non-climatic factors, making it necessary to distinguish and account for the impacts of climatic and non-climatic sources separately to achieve specific research objectives. By using tree-ring records from an extensive range of Central European forests, this thesis aims to disentangle the impacts of these climatic and non-climatic factors on the growth of Norway spruce trees with a particular focus on the impacts of non-climatic factors on the climatic sensitivity of different tree-ring parameters. Firstly, I used a disturbance identification technique to detect disturbance signatures in datasets of multiple tree-ring parameters of Norway spruce (Picea abies) across the whole range of the Carpathian Mountains and evaluated to what extent natural disturbances influenced the temperature signals in those datasets (Subsection 3.2/ 4.1/ 5.1). Though the growth of forests in the studied region has experienced significant interference from various types of environmental events over the past centuries, the disturbance signatures in tree ring chronologies were more easily detectable in a smaller-scale scenario (i.e., at the site level) with reduced sample depth. Additionally, the detected disturbance signatures were mainly observed in tree-ring width chronologies during periods characterized by major growth releases. In contrast, Blue Intensity chronologies were generally less susceptible to disturbance impacts or not influenced at all. Blue Intensity chronologies also exhibited much stronger temperature signals compared to those in tree-ring width chronologies, and such signals were more stable over time. Secondly, considering the recent pollution history of the Czech Republic and neighboring regions, I examined the impact of pollution on the temperature sensitivity of multiple tree-ring parameters by using the same statistical approach applied in relation to natural disturbances in the Carpathians (Subsection 3.3/ 4.2/ 5.2). As part of the research covered in this sub-topic, tree-ring parameters of one additional technique, quantitative wood anatomy, were also included. Pollution-related growth suppression trends were mainly detected in tree-ring width chronologies, especially at sites that experienced severe pollution levels. Growing season temperature signals were well-represented by both latewood Blue Intensity and cell wall thickness chronologies. The climatic signals in those chronologies outperformed those of the tree-ring width chronologies and tended to remain more stable over time and, unlike tree-ring width, even retained a significant relationship with climatic variables during the period characterized by severe pollution levels. Lastly, I investigated the impact of recent drought events on the drought resistance of several Central European tree species, considering the distinct drought conditions of the Czech Republic (Subsection 3.4/ 4.3/ 5.3). This study helped to contextualize the relative importance of climatic and non-climatic factors for tree growth dynamics in the region. Drought-induced growth reductions were found in all studied species but with different levels of magnitude. Norway spruce was found to be more susceptible to drought impacts compared to other species as it showed the largest growth reduction. The main drivers of drought resistance for different species were also explored. The findings of this research indicated that under the circumstance of climate change, drought-related impacts on forest sys

Abstract:

tems will potentially threaten timber supply sustainability and other services. In addition, when comparing these drought-related impacts to the non-climatic impacts on tree growth, such climatic impacts were much more prominent, which indicated the significance of climate for tree growth. The overall findings of this thesis revealed that the impacts of non-climatic factors on tree growth and climatic sensitivity are non-negligible, especially when using the tree-ring width parameter. In the context of dendroclimatology, measures need to be taken to better understand and reduce the influence of such impacts. For example, the Curve Intervention Detection method can be used for the identification of growth impacts, whereas the utilization of multiple tree ring parameters can assist with selection of more robust parameters for climate research. This work indicates that Blue Intensity and cell wall thickness have more stable climatic sensitivity characteristics and, in turn, would be more suitable for climate reconstruction purposes in either disturbed or historically polluted areas. This thesis represents a useful reference and inspiration for future studies with regards to alternative tree-ring parameters for specific research purposes or distinguishing and accounting for non-climatic impacts. These observations and recommendations are especially pertinent as forest disturbance events are expected to increase in response to global climate change.

Keywords

Disturbance trend biases, Sulphur/nitrogen deposition, Drought resistance, Latewood Blue Intensity, Quantitative wood anatomy, Temperature signal, Curve Intervention Detection, Climatic extremes, Tree growth reduction

Language used: English

Date on which the thesis was submitted / produced: 30. 3. 2024

Thesis defence

• Supervisor: Miloš Rydval, Ph.D.
• Reader: Jakub Kašpar, externi, Jelena Lange, externi, Jiří Doležal, externi

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme:
Global Change Forestry