Permanent plot studies have shown remarkable increases in above ground biomass of intact rainforest stands across the tropics. Furthermore several studies have found indications of accelerated tropical forest turnover and increased tree recruitment and mortality.
Both of these observations have been linked to the effect of climate change and CO2 fertilization. However, several potential biases regarding the permanent plot studies have been put forward, mainly concerning the small number of measurements and the relatively short time scale on which such studies have been carried out: i.e. no more than a few decades. These and other limitations to the study design have made conclusions on the long term trend of increased tree growth and accelerated forest dynamics a point of dispute.
More high resolution, long-term data on tropical tree growth is therefore needed. The use of tree rings has long been recognized as an adequate and reliable proxy for long term studies on patterns of tropical tree growth and tropical forest dynamics. In our project we use the tree ring approach to reconstruct pan-tropical forest dynamics over the past 200 years and assess the evidence for a long term trend of accelerated tropical forest dynamics.
My fieldwork area is situated in the Huai Kha Khaeng Wildlife Sanctuary in the Uthai Thani province of west-central Thailand. In the tropical seasonal dry evergreen forests of Huai Kha Khaeng I collect tree cores from five tree species all known to produce annual rings. These tree cores are exported to the Netherlands for measurements and analysis at the DendroLab in Wageningen.
In Wageningen tree ring data from Bolivia and Cameroon (see PhD projects of Peter van der Sleen and Peter Groenendijk).is added to the Thai dataset, giving our project the pan-tropical scope of the TROFOCLIM project. This tree ring data is then analyzed using various dendroecological techniques, for example suppression release analysis and analysis of growth autocorrelation. Growth rates of current juvenile trees is compared to juvenile growth rates of extant large trees in order to assess long term changes in juvenile tree growth. Additionally, we will try to link recruitment peaks to historical large scale droughts in South-East Asia. By doing so we expect to find simultaneous periods of stand initiation and large scale climate anomalies in the area.
- Bender, I.M.A. (2012). Climate-growth relations in trees of a tropical forest of western Thailand. Summary
Forensic forest ecology : unraveling the stand history of tropical forests
Wageningen University. Promotor(en): Frits Mohren, co-promotor(en): Pieter Zuidema; P.J. Baker. - Wageningen : Wageningen University - ISBN 9789461739421 - p.
Understanding recruitment failure in tropical tree species: Insights from a tree ring study
Forest Ecology and Management 312 (2014). - ISSN 0378-1127 - p. 108 - 116.
Disturbance History of a Seasonal Tropical Forest in Western Thailand: A Spatial Dendroecological Analysis
Biotropica 45 (2013)5. - ISSN 0006-3606 - p. 578 - 586.
Tropical forests and global change: filling knowledge gaps
Trends in Plant Science 18 (2013)8. - ISSN 1360-1385 - p. 413 - 419.