Research has found that warming temperatures are affecting the way trees grow. But what does this mean for our fight against climate change?
A study, published last month in PLOS ONE, examined the growth rates of 7 tree species in Ohio, North America, over the past 100 years, along with changes in temperatures and precipitation. This was made possible by records of Thomas Mikesell, a local farmer, who kept records on all of these factors between 1883 and 1912. The team compared Mikesell’s findings to modern-day measurements and found in 5 of the 7 species that growing season length had increased in correlation with warming temperatures of climate change. Trees were growing for up to a month longer than they had over 100 years ago.
This increase was due to a delay in leaf browning. Leaves stayed on trees 15% longer than in the 19th Century. Interestingly this is different to previous work which has focused on the earlier formation of leaf buds as the causative factor of prolonged growth. Lead author Prof. Calinger-Yoak suggests her team’s findings highlight a previously under-researched area of tree life cycles that could help us better understand how plants are affected by climate change.
What does this mean for our fight against climate change? The authors don’t conclude the exact implications for these longer growing seasons, but since forests are natural carbon sinks, able to absorb CO2 from the atmosphere, they suggest it could have positive impacts on slowing the rate of global warming.
A similar study in Germany in 2018, also found trees growing at a faster rate than over a century ago. However, whilst growth rates had increased by 77%, the density of the wood formed had reduced by 12% in some species. Therefore, whilst increased growth rates could have positive implications for reforesting initiatives, the resulting trees are less robust and may not be able to withstand the onslaught of storms and other extreme weather, which due to climate change is on the rise in both frequency and severity in many countries.
Interestingly, the 2018 study measured how CO2 absorption had changed in trees since 1870. The researchers did this using dendrochronological techniques. This refers to the study of tree rings, which many already know to be informative about the age of a tree. What’s fascinating is that they can tell us much more about how the tree lived and died. Researchers were able to measure how much carbon trees in southern Germany absorbed each year. Since 1870, CO2 absorption has decreased by 50%. Trees absorbed less CO2 as their growth rates increased, likely due to reduced wood density.
These findings directly contradict the suggestions of Calinger-Yoak and colleagues: that increased growth periods would lead to increased CO2 uptake by trees. This calls into question the effectiveness of reforestation methods in fighting climate change. However, others have suggested that the lower level of carbon absorption in trees is insignificant. These effects could be offset by the increase in reforestation allowed by fast tree growth. Increasing tree numbers could reduce the impact of less efficient carbon capture.
The scientific community remains undecided on the exact implications of altering tree growth but all agree there should be a push for future research. Forests have been identified as one of the major carbon sinks and could be a significant tool in our fight against climate change. Therefore it is important to understand how rising temperatures are affecting these trees to develop better-informed technologies and techniques.