We build supralong tree-ring chronologies

We have three climatically sensitive main tree species: Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula pubescens). Scots pine is the only tree species that preserves unrotten in cold waters for thousands of years. The oldest megafossil pine (ancient pine remnant) we have found so far, started its growth 7642 years ago (5634 BC) in Lake Iijärvi, north of Inari (Northern Finland). These old logs have given us a possibility to spesialize in building and analysing supralong tree-ring chronologies.

We were enough lucky to build in the ADVANCE-10K project a year-exact 7642 years lomg timberline Scots pine chronology. It is the longest conifer tree-ring chronology in Eurasia, and the second longest in the world! Only the 8800-yr Bristlecone pine chronology in the USA is longer. We know Scots pine arrived in Finnish Lapland some 9000 years ago. That is why we wish to be successful in extending the chronology by some hundreds of years, or even by more.

Growth of timberline Scots pine is sensitive to June-July temperature. This strong climatic signal that can be tracked year-exactly over a 7500-year period, has made our pine one of the most important data sources in climate change research.

The chronology is not complete yet. It is good for dating, but needs more replications in order to fulfil statistical accuracy requirements in dendroclimatic research. The weakest points in the Advance-10K pine chronology have less than 10 observations. From the statistical point of view, we would need for a ±10 % index accuracy at 95% level over 60 samples! We still have to do some special analysis and calibration in order to be able to extract the low frequency temperature signal from our data. The task is quite challenging because we have to build a new calibrated tree-ring width chronology focused on the present pine timberline.Then we can apply trend analyses like the RCS or Age Banding methods.

We try to be strict in our dendroclimatic analyses. We have e.g. published a summary about the strengths and weaknesses of the millennial tree-ring archive of Fennoscandian forest-limit Scots pine. Despite of some problems in our data we are now building a low-frequency June-July temperature model based on the whole 7642-yr data. We need to calibrate the scattered Advance-10K data of about 80 lakes (sites) on the both sides of the present timberline to one hypothetical timber line. We, hopefully, can highlight the ups and downs (e.g. Holocene optimum, Roman Warm Period, Medieval Warm Period, Little Ice Age and Modern Warming) more detailed than at this time. Well controlled data quality is one concern in successful chronology building. We have developed a system to control the strength of climate signal. Check Our Method to Qualify on the Saima databank website.

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