Prospects of Philippine paleoclimate reconstruction through tree ring research applications on adaptation and mitigation to climate change

Dendrochronology is new to the Philippines. It is well developed in temperate countries especially in the United States where its modern form and substance metamorphosed from western ideas about annual growth rings of trees in Europe. The meaning of dendrochronology is evident in its etymology composed of three Greek words, dendro means wood, chromos means time, and logos means study of. It is the study of measuring and analyzing the variation of annual growth rings of trees to learn about past events such as past climate (paleoclimate), past forest disease and pest outbreaks, past historical events, past geological upheavals like volcanic eruptions and earthquakes and past episodes of floods. Not all trees exhibit annual growth rings. The trend is that more trees in very seasonal areas (like temperate zones and monsoonal tropics) have annual growth rings than in a seasonal areas (like in the ever wet tropics). There are however few trees in a seasonal areas which do have annual growth rings. Thus, a group of Columbia University scientists in relation to their tropical Asian monsoon research who were then using pine and teak wood rallied Asian scientists to help them do a reconnaisance survey on tropical trees with distinct rings as possible material for dendrochronology. The Philippines UPLB led collaborators from Sri Lanka, India, Thailand and Malaysia towards this direction with the sponsorship of the Asia Pacific Network (APN) based in Kobe, Japan. The output of this reconnaisance research will increase the geographic areas of erstwhile pines and teak as dendrochronology study areas (e.g. Himalayas and dry areas of Southeast Asia) extending even to the everwet areas of the Indomalayan region (e.g. archipelagic Southeast Asia including Malay Peninsula, Sumatra, Borneo, Philippines, New Guinea). There were 452 trees spread in 226 indigenous tree species from 54 families of seed plants and, out of this, 40 tree species were found to exhibit distinct growth rings. Trees that grow on exposed steep slopes and tree roots do not reach ground water because of the steep terrain usually record drought periods as very narrow rings. Conversely, trees or river banks display more or less equal ring widths and described as complacent (not sensitive). This principle of sampling from sensitive sites was done by sampling 20 pine and 20 teak trees in Carranglan, Nueva Ecija. The ring patterns of both pine and teak were compared with the El Niño Oscillation Index. It was found as expected that narrow rings coincide with El Niño events while the wide rings coincide with La Niña events. If this experience is extended to the 40 tree species found to have distinct rings, it is possible to capture 100 years space and time past climate history of the Philippines. The last 50 years instrumental record of climate (rainfall, ENSO, and flood years) can be correlated with sensitive corewood samples such that statistically significant autocorrelations may be used as proxy to extend interpretation of earlier 50 tree ring records or even earlier, for example, 200 years back depending upon the age of the tree. Knowledge of past climate at any given place in the country helps understand recent and present climate pulses. Faced by global warming trends, using past and present climate records for any given place in the country, it is possible to model what to expect in the near and far future. This would be useful in the design of adaptation and mitigation measures to climate change in the country.