Millenniumproject
Results
The Needle Trace Method, NTM, has been developed in Metla to reveal retrospectively the needle and growth history for the entire tree, originally Scots pine. Currently about 15 different time series are produced from each examined tree, from breast height to the top of the tree. The series are valuable parameters to study environmental, eco-physiological and other changes in time and space. In growth and yield studies less used height increment is one of the major products of the NTM, the height-increment chronology spanning hundreds of years back in Laanila, the pine growing site 80 km south from the pine timberline, where climate signal has proved to be very strong between height increment and the mean July temperature of the previous year, explaining up to 80% of the variation. By using this relation with height increment July temperature has been reconstructed back to AD 1570 from present. Intra-annually, 1 °C increase in mean July temperature will increase leader-shoot length by 1.5 cm in young pines aged below 50 years in Lapland. Temperature of the current season affects growth rate of the leader shoot and timing of ending of height increment but not to the final shoot length. Also other NTM parameters consist of climate signal. Annual shoot length explains most of the variation in needle density, which is a new method to study past disturbances and e.g. climate extremes.
Next to the northern timberline, Laanila has proved to be a region with a very strong climate signal, suitable for various tree-based proxies. Based on the stable carbon isotopes in latewood of the Laanila pine, there have been warmer summers in the period of 1660–1760 than in the 20th century. Neither the isotope proxies (C, O, H) nor the ones of tree-ring width or tree-ring density demonstrate the ‘Hockey-stick’ effect (Mann’s curve) of rapid temperature increase. The proxy findings are in accordance with the long Sodankylä climate record of 1908–2007, showing an insignificant increase in annual temperature of 0.48 °C only. If the summer temperature in Lapland increases evenly and permanently by 2 °C as compared to the normal period of 1961–1990, only the highest part in Käsivarsi and the laws of the biggest fells in Utsjoki will stay pine-less.
An innovative blue-reflectance method was developed to measuring tree-ring densities, allowing cheap production of the density series as compared to the traditional X-ray analysis. The NTM and its time series have proved to be good indicators of climate extremes in the past; already known events were confirmed and new occasions revealed. One of the most common phenomenons is the ring shake between the rings of 1790 and 1791 in nearly all older pines in northern Fennoscandia.
To support our climate-related studies Scots pine has been monitored intra-annually for both height increment and radial growth, too. Bud break occurs now 8 to 10 days earlier than in the 1960s in Lapland, where the buds break approximately in the first week of May, along with the time when temperature sum begins to accumulate. Radial growth begins four weeks later when about 12.5% of the long-term site-specific temperature sum, corresponding with 80 to 120 d.d., has been accumulated. At the time when height increment ends, 41% of the sum has been gained and pine shifts from forming earlywood to latewood. Radial growth (cell production) ends in late July to early part of August when 80% of the long-term site-specific temperature sum has accumulated. Thus the volume growth in Scots pine lasts 83 days at the Arctic Circle, 64 days in Laanila and even less at timberline.
Project leader:
Jalkanen, Risto
The Finnish Forest Research Institute,
Rovanniemi Office,
PO Box 16 (Eteläranta 55), FI-96301 ROVANIEMI, FINLAND
Phone: +358 29 532 4430
E-mail: risto.jalkanen@metla.fi
Other researchers:
Lindholm, Markus, RO (2009-13), Salminen, Hannu, RO (2008-11,2013)
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Updated 02.02.2013
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