Record of Pinus forest in the coastal lowlands of Northern Luzon, Philippines
2004
Stevenson, J.(Australian National Univ., Canberra 0200 (Australia). Dept. of Archaeology and Natural History, RSPAS)E-mail:[email protected] | Siringan, F. | Madulid, D.A.
The palaeoenvironmental history of Paoay Lake in northern Luzon [Philippines] is being examined through an analysis of pollen, diatoms, charcoal, mineral magnetics and AMS dating. It is a large coastal lake in the northwest of Luzon, cut off from the sea around 6,000 years ago. Analysis of sediment cores has found that coniferous forest, dominated by Pinus, grew at the lake until around 4,500 years ago, when the pollen signature changes to that more indicative of an open landscape (primarily grass). Charcoal is as an indicator of fire is abundant throughout record, although the highest levels occur during the period of forest decline. Pinus pollen continues to be present in the record in small amounts up until the present day, reflecting regional pollen transport from the Central Cordillera. The discovery that Pinus was growing at Paoay between 6,000 and 4,500 years ago would seem significant, as it is only found above 600 m in the present day environment, which is considered as the altitudinal limit of Pinus in Luzon. The finding also raises the question of whether the forest decline at 4,500 BP [calibrated years before present] is associated with human activity or a climatic shift, possibly an increase in climatic variability, as no evidence for agricultural plants (e.g. rice) is found until around 2,000 BP. The only other quarternary pollen record from the Philippines comes from Laguna de Bay, south of Manila. Laguna de Bay only became a fresh water lake around 3,500 years ago and, although the pollen composition is quite different to that of Paoay Lake, there is an interesting shift to greater grassland after 5,000 BP suggesting that a significant regional event occurred around this time.
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