Reconstruction of stand dynamics and climate in long-term forest ecosystem research plots

Rationale

Tree-ring research

• Why should tree-ring research be a component of long-term forest ecosystem studies?

Long-term forest ecosystem research (LWF) is growing in importance throughout the world. More and more sites are being established where detailed investigations of ecosystem function are being undertaken. A major problem with many such sites is that their history is largely unknown. This means that it is difficult to place the observations made at the sites within any sort of temporal context. Tree-ring analysis provides a means of obtaining such historical information. In Switzerland, LWF aims to investigate the inter-relationships between forest ecosystems, air pollution and climate change, and to assess the current condition and future development of forest ecosystems in relation to environmental and anthropogenic stress.

Stand history is critical for the correct interpretation of the data collected in other research projects within LWF (for example, soil nitrogen and carbon budgets may be affected by past forest management). Stand history in the plots (Fig. 1) is being reconstructed using dendroecology. Information about past climatic influences (events and trends), and past human impacts on tree-ring growth is being obtained.

Project aims

• What can tree rings tell us?

Tree-ring studies can help to answer a number of important questions in long-term plots. For example,

• How have tree-ring growth rates at the LWF sites changed over time? What is the nature of these changes? What might be the cause of any observed changes?
• How have the stands at the LWF sites evolved? What effects have stand dynamics had on tree-growth in the past? Is it possible to distinguish the role of human activities from the role played by other environmental factors (e.g., climate, genetics)?
• What kind of climatic events and trends have influenced tree growth at the LWF sites in the past? To what extent can climatic patterns be reconstructed from tree-ring patterns at the LWF sites?

Methods

A variety of methods are available for looking at stand history, including:

• Interviews with local foresters, analysis of forest management plans, and historical research.
• Ring-width measurements to the nearest 0.01 mm.
• Skeleton plot analyses with a stereomicroscope, using standard methods.
• X-ray densitometric analyses on cores sampled at high elevation sites.

Work plan

• SUMMER/AUTUMN 1996: sampling at five plots: Chironico (TI), Isone (TI), Novaggio (TI), Vordemwald (AG), and Bettlachstock (SO). Ring-width and wood density measurements.
• WINTER 1996/97, SPRING 1997: ring-width and wood density measurements, chronology building, data analysis and publication of results.
• SUMMER 1997: ring-width and wood density measurements, chronology building, and sampling at five plots: Alptal (SZ), Celerina (GR), Visp (VS), Lens (VS), Beatenberg (BE).
• AUTUMN 1997 and WINTER 1997/98: ring-width and wood density measurements, data analysis, and publication of results.
• SPRING and SUMMER 1998: sampling at five plots: Jussy (GE), Nationalpark (GR), Lausanne (VD), Othmarsingen (AG), and Neunkirch (SH) and data analysis and publication.
• AUTUMN 1998 and WINTER 1998/99: ring-width and wood density measurements, and data analysis, and publication of results.
• SPRING and SUMMER 1999: data analysis, and publication of results.
• WINTER 1999: publication of the final report.

Data

• An example from the Swiss Plateau: Vordemwald

Vordemwald is a high-forest site located on the Swiss Plateau. Dendroecological analyses have revealed that all the oaks (Quercus robur) germinated before 1850, whereas all the silver firs (Abies alba) germinated after 1880.

Fig. 1 - All the oaks germinated before 1850, all the firs after 1880.

The silver firs show evidence of growth releases: in 1943 a release after suppression occurred. As confirmed by forest management plans, thinnings took place in this forest compartment at the beginning of the 40s. The years 1946, 1947 and 1976 were characterized by drought and the trees grew slower. After those years, the ring widths recovered. 

Fig. 2 - This fir shows evidence of a growth release in 1943, following a period of suppression.

In the oaks, there was an abrupt growth release in about 1900, probably due to the removal of an old generation of silver fir, as reported by written records.

Fig. 3 -The oaks show an abrupt growth release around 1900.

Results

Results concerning past tree-ring growth and long-term growth trends will be useful to other LWF researchers, for comparisons with other results obtained in the LWF plots (cf. the project: "Biogeochemical cycling and ground vegetation", Anne Thimonier), and for development of tree and stand growth prediction models (Matthias Dobbertin and Norbert Kräuchi).

Participants

• Paolo Cherubini
• Matthias Dobbertin
• Werner Frey
• John Innes
• Felix Kienast
• Fritz Schweingruber

Contact

• Paolo Cherubini