Abstract
For boreal forests in colder climates, changes in environmental conditions are hypothesised to substantially affect ecosystem processes. In this study, trends of top height growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were analysed using permanent sample plot data from more than 300 long-term experimental sites distributed from temperate zones to the boreal forest conditions in Sweden. By regression analyses, the effects of temperature-sum and precipitation-sum on top height growth were assessed in the period 1986–2018. A significant upward temporal trend in height growth was observed for both species, with the trend more pronounced after the millennium shift. The magnitude of the annual relative height growth after the millennium was about 16.92% and 9.54% higher than expected, respectively for Scots pine and Norway spruce. A potential climate response on height growth was found for both species with temperature-sum positively correlated with top height growth. No significant effect of precipitation-sum on height growth was observed for either species. Our results suggest improved growing conditions and forest sites became more productive in response to increasing temperature in the northern temperate and boreal regions. The increasing growth trends may offer shorter rotation periods and increased forest value for Norway spruce and Scots pine, coupled with contributions of boreal forests to the emerging bio-economy and the regulation of global atmospheric carbon.
Highlights
In recent years, the growth of forests under changing environmental conditions has been a major concern across the globe
This study has shown that top height growth of Norway spruce and Scots pine increased during the last 30 years in the Swedish forests
The increase in growth was more pronounced after the millennium
Summary
The growth of forests under changing environmental conditions has been a major concern across the globe. In Europe, changes in forest growth in temperate and boreal forests during the latter part of the 20th century were investigated and summarized in Spiecker et al (1996). In boreal forests of northern Europe, increases in the forest growth have been reported (e.g. Elfving and Tegnham mar, 1996; Salminen and Jalkanen, 2005; Solberg et al, 2009; Kauppi et al, 2014; Henttonen et al, 2017). In the Finnish forests from 1971 to 2010, Henttonen et al (2017) found differences in forest management and changes in environmental conditions explained 67% and 37% respec tively of the observed increase in annual volume growth (8.98 million m3 year− 1)
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