PRELIMINARY INDOMALAYAN TREE RING CHRONOLOGIES AND THE SOUTHERN OSCILLATION INDEX
By Nestor Baguinon
December 28, 2009
Northern Luzon pine and teak ring series synchronously follow the El Niño and La Niña pulses. The Indian ring series of Albizia lebbeck and Dalbergia latifolia were superimposed. Certain agreement between the Indian and the Philippine tree ring widths is apparentalthough this should be substantiated by more tree ring data-points spread across the Indomalayan region. Crossdating corewood samples in the existing SSEADENDRO xylarias is just one stepping stone. From this leads to more studies that would shed light to the Tropical Asia Monsoon. This serves as springboard to a better designed collaborative dendroclimatological research using the expanded array of tree species that allow greater data points. Greater data points, in turn, enable greater resolution of information leading to superior modeling of climate in the region. [click to enlarge] |
While the main objective of the Project , "Collaborative Studies in Tropical Asian Dendrochronology: Addressing Challenges in Climatology and Forest Ecology" is reconnaissance for tree species with distinct growth rings, two of the five SSEADENDRO teams, the Philippines and India, attempted to graph tree ring widths with time to find evidence of crossmatching. Team Philippines selected a Benguet pine Pinus kesiya tree naturally growing on a cliff and another tree Teak Tectona grandis in Carranglan, Nueva Ecija growing on a hilly plantation to test crossmatching between two species. Carranglan, Nueva Ecija is one of the seasonally variable and driest places in Luzon due to rainshadow effects offered by two nearby mountain ranges, the Caraballo and Sierra Mountain Ranges.
The growth ring series of Benguet pine and Teak trees when plotted against time show clearly they crossmatch very well. Then when the Southern Oscillation Index is overlaid to the pine and teak plots, it clearly showed that during La Niña events the growth rings are widest while during El Niño events the growth rings are narrow. This observation supports the fact that deprivation of water during drought periods in the El Niño events limit growth hence the narrow ring widths. The converse is true during La Niña events when water is not limiting hence the very wide ring widths.
When Team India's Albizia lebbeck and Dalbergia latifolia chronologies were overlaid with the aforementioned graph, it is surprising to note more general agreement than contradictions. Considering the distance between the Philippines and India, what is being observed here is in favor of the hypothesis that the El Niño Southern Oscillation phenomenon has very wide teleconnections in the Indomalayan region.
This observation however needs to be justified by more replicated research. Now that there are about a hundred potential tree species with distinct growth rings that can be crossmatched and crossdated, the future is bright that dendrochronologists in the Indomalayan region may again collaborate to provide more data points and therefore more statistically reliable information can be generated to enable a higher resolution model for the tropical Asia monsoon.
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