Paper Reviewed
Giammarchi, F., Cherubini, P., Pretzsch, H. and Tonon, G. 2017. The increase of atmospheric CO2 affects growth potential and intrinsic water-use efficiency of Norway spruce forests: insights from a multi-stable isotope analysis in tree rings of two Alpine chronosequences. Trees 31: 503-515.

Introducing their study, Giammarchi et al. (2017) write that, "in the last decades, several authors (Spiecker et al., 1996; Karlsson, 2000; Jandl et al., 2007; Lopatin, 2007; Bontemps et al., 2009; Pretzsch et al., 2014a,b) have reported an increase in productivity of European forests," which increase is often ascribed to higher atmospheric CO2 concentrations, warming temperatures, changes in precipitation, and/or nitrogen deposition. Seeking to determine which of these environmental factors has been leading the charge in such growth, the team of four scientists say they "first assessed the changes in forest productivity of two even-aged Norway spruce forests," after which they examined "the role of several environmental drivers, such as atmospheric CO2 levels, temperature, and precipitation regimes on the intrinsic water-use efficiency (iWUE) temporal patterns of the above-mentioned forests."

The results of their analyses revealed there was indeed an increase in forest productivity at both sites since the 1860s, paralleled by a significant increase of iWUE (see figure below), which they say was "mainly triggered by a CO2-driven increase in photosynthetic capacity, rather than by a reduction of stomatal conductance."

Figure 1. δ¹³C-inferred iWUE of three different aged stands of Norway spruce at Nova Levante (South Tyrol, Italy) and Traunstein (Bavaria, Germany). Adapted from Giammarchi et al. (2017).

The above findings echo those found at locations all around the globe, revealing a CO2-induced greening of the Earth in which trees and forests are benefiting from the modern rise in atmospheric carbon dioxide concentrations. For more information, see the many reviews we have posted under the headings Forests (Growth Response to CO2) and Water Use Efficiency (Trees) in our Subject Index.

References
Bontemps, J.D., Herve, J.C. and Dhote, J.F. 2009. Long-term changes in forest productivity: a consistent assessment in even-aged stands. Forest Science 55: 549-564.

Jandl, R., Neumann, M. and Eckmüllner, O. 2007. Productivity increase in Northern Austria Norway spruce forests due to changes in nitrogen cycling and climate. Journal of Plant Nutrition and Soil Science 170: 157-165.

Karlsson, K. 2000. Height growth patterns of Scots pine and Norway spruce in the coastal areas of western Finland. Forest Ecology and Management 135: 205-216.

Lopatin, E. 2007. Long-term dynamics in growth of Scots pine and Siberian spruce in Komi Republic (European part of Russia). Dissertationes Forestales 53: 35. https://doi.org/10.14214/df.53.

Pretzsch, H., Biber, P., Schutze, G. and Bielak, K. 2014a. Changes of forest stand dynamics in Europe. Facts from long-term observational plots and their relevance for forest ecology and management. Forest Ecology and Management 316: 65-77

Pretzsch, H., Biber, P., Schutze, G., Uhl, E. and Rotzer, T. 2014b. Forest stand growth dynamics in Central Europe have accelerated since 1870. Nature Communications 5: 4967.

Spiecker, H., Mielikäinen, K., Köhl, M. and Skovsgaard, J.P. 1996 Growth trends in European forests. Studies from 12 countries. Springer, Berlin.