The assumption that climate change positively affects plant growth due to an increase in warm days has been challenged by a recent study conducted by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL). The study found that while climate change may extend the vegetation period of plants, it does not necessarily lead to increased growth in trees. The seven tree species studied in Switzerland only grow on average for 29 to 77 days per year, meaning that a longer vegetation period would not result in more growth. In fact, evidence suggests that an earlier start to growth before April and a later end after October could actually decrease overall growth. The study also found that negative factors such as heat and drought affect needle trees more than leaf trees.
The researchers analyzed growth data from 160 trees at 47 locations over eight years and found that trees generally experience the strongest growth from April to mid-June, with a significant decline just before the summer solstice in June. This decline is likely due to decreasing daylight signaling the end of the growth period and the start of other processes such as fruit and bud formation. The study also revealed that temperature, light conditions, and water availability are the main factors influencing growth. The researchers were surprised to find that all seven tree species studied only grow for an average of 29 to 77 days per year, with the highest daily growth rate of 25 micrometers per day achieved by the spruce, which only grows for 43 days per year.
The study’s findings have implications for the assumption that climate change will increase carbon uptake by forests. While climate change may extend the vegetation period of plants, it does not necessarily lead to increased growth in trees. The study also highlights the vulnerability of needle trees to negative factors such as heat and drought, which could have significant implications for forest management in the future.
