Tree disk. Photo by Aster Gebrekirstos
Dendrochronology is the examination of tree growth rings as a method for scientific dating. It can provide accurate dating because, in principal, each ring represents a year in a trees life. Seasonality in climate is the main driver for growth-ring formation, which results in cambial dormancy, or a halt in active growth. Many tree species in the tropics grow under a seasonal climate and therefore experience cambial dormancy. Depending on climate seasonality and species, formation of rings in the tropics can range from indistinct to distinct and from annual to bi-annual.
Established in 2013, the World Agroforestry Centre's dendrochronology lab is housed within the Climate Change unit. We are involved in active research with the Agroforestry Systems, Environmental Services and the Tree Diversification, Domestication and Delivery science domains of the World Agroforestry Centre. We also seek to engage with national and international partners, as well as graduate students and Postdocs globally who are interested in Dendrochronology.
Arrows indicate annual ring boundry
Formation of double rings (the arrow marked red shows a false ring)
We seek to unravel the past to better understand the present and to be better prepared for the future.
Tree rings are history books and they can tell us many things about past climates, tree growth and vegetation dynamics, history of people and their landscapes, and the rise and fall of civilization, among many others.
Knowledge of the range of natural climate variability and the tolerance range of tree species to climatic stress is scarce, especially in the tropics and subtropics. Our goal is to carry out applied cutting edge research with primary focus on the following:
- Assessment of climate-growth relationships and evaluation of the effect of a changing climate on tree growth, agroforestry systems and forest development;
- Using tree ring data for proxy reconstruction of past climate conditions beyond the period where instrumental records are available, proxy evidence of past variation in the El Nino/Southern Oscillation and other large-scale atmospheric circulations;
- The analyses of radial growth increment and stable isotopes at the inter-annual and intra-annual scale together with tree physiological parameters to better understand the ecological relationships between tree growth, climate and site conditions;
- Determining cambial dynamics, carbon allocation patterns and changes in wood anatomy, and hydraulic conductivity at different spatial and temporal resolutions;
- Changes in river flow, source of water and hydrological fluctuations in relation to climate change;
- The study of past and present changes in wild fire by dating the fire scars left in tree rings to determine the frequency of fire occurrences.
- To link scientific with local knowledge (e.g drought histories and frequencies), and to quantify change and provide evidence which is meaningful to policy-makers (e.g. to improve access to index insurance , Normalized Difference Vegetation Index (NDVI) and length of growing season).
A microtome is used to cut thin sections from tree samples
Thin sections are dyed such that different cell types can be distinguished when viewed under a microscope. Here the computer image shows a picture of Faidherbia albida for qualitative and quantitative wood anatomy analysis using WinCELL 2012.
The Lintab TM combines with TSAP software for ring width measurement, cross-dating and basic statistics (right) and WinDENDRO attached to a scanner to acquire high resolution picture and measure ring width, density (left).
Dendrochronology, particularly in Africa, is still in its infancy. If you are interested in joining an active laboratory engaged in a wide range of dendrochronological research to further your graduate and professional careers, please contact Dr. Aster Gebrekirstosto discuss the opportunities we have available.
Currently we are working closely with:
- The University of Erlangen Germany (Prof. Achim Bräuning)
- The Wondo Genet College of Forestry Dendro lab (a lab established by Dr. Aster Gebrekirstos; contact Motuma Tolera)
- The University of Wageningen (Dr Ute Sass-Klaassen)
Acknowledgements: We recognize the CGIAR Research Program for Climate Change, Agriculture and Food Security (CCAFS) for funding the lab, as well as the University of Erlangen-Nuremberg for training a technician and helping with the lab setup.
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