© 2004 Heron Publishing—Victoria, Canada
Use of modeled photosynthesis and decomposition to describe tree growth at the northern tree line
Frank Berninger (1, 2), Pertti Hari (1), Eero Nikinmaa (1), Markus Lindholm (3) and Jouko Meriläinen (3)
1. Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland / 2. Author to whom correspondence should be addressed (Frank.Berninger@Helsinki.fi) / 3. Saima Centre for Environmental Sciences, Linnankatu 11, FI-57130 Savonlinna, Finland / Received November 8, 2002; accepted July 11, 2003; published online December 15, 2003
Summary
Growth of subarctic Scots pine (Pinus sylvestris L.) trees was investigated by a combination of process-based models and dendroecological approaches. Tree ring width indices
were strongly autocorrelated and correlated with simulated photosynthetic production of the previous year and with organic
matter N mineralization of the current year. An autoregressive model, with photosynthesis and N mineralization as external
inputs, explained growth of the trees well. However, relationships for the period 1950–1992 differed significantly from relationships
for the period 1876–1949; the slope of the regression of tree ring width index and photosynthesis was lower for the 1950–1992
period. Also, the autocorrelation structure of the data changed. First-order autocorrelation decreased and second-order autocorrelation
increased from the earlier to the later period. This means that growth is becoming less sensitive to variations in photosynthetic
production, whereas the relationships between growth and N mineralization are remaining fairly constant. We postulate that,
although photosynthesis has increased in response to increasing CO2 concentrations, tree growth rate cannot parallel the increase in photosynthesis because potential growth rate is limited
directly by temperature.
Keywords:
climate change, reduced sensitivity, tree rings.
