Douglas fir, an evergreen coniferous tree that grows in North America, will absorb less carbon dioxide, if the average temperature of our planet will increase, reported in the study in Global Change Biology. Predictions scientists have built based on the analysis of tree rings, which showed that tree growth in many regions will slow down the warming.
Forests cover about 30 percent of the earth’s surface, and their long-term response to climate change constitutes one of the key uncertainties in models that predict the absorption of carbon dioxide from the atmosphere. In the last decade, future ecosystem responses predicted based on their past response to fluctuations in temperature and precipitation, but it may not always be so clear.
So, some researchers are of the opinion that warming will cause stress in trees, leading to slower growth or death. Others believe that plants on the contrary will more effectively absorb carbon dioxide and grow more active — this effect, which many consider controversial, is called the effect of “carbon fertilizer”.
Stefan Clessé (Stefan Klesse) from the University of Arizona, along with colleagues proposed a new approach. Scientists have suggested that the growth of trees at warmer sites today can tell us about how the trees in cool places will increase with warming in the future. Therefore, data on the growth of trees in some areas were used to build projections for other regions. For example, the behavior of the Menzies fir — tree, which was chosen as the object of study — in Arizona, were used to predict response in Montana through the decades.
The researchers analyzed information for 1902-2016 years about 2.7 million of annual rings of Douglas fir Menzies, which forms vast forests throughout the Pacific coast from British Columbia to California. The width of annual rings characterizes the growth of the tree, which, in turn, connected to the surrounding conditions. The authors also examined how climate has varied in the past, and used existing forecasts for estimating plant response to climate change.
It was found that the increase in the average annual temperature will have different implications for trees growing in different regions. The greatest decline in ring width, and therefore the most noticeable slowdown was predicted for the Northwest of Mexico, the value ranged from 15 to 30 percent. In the North-West Pacific and along the West coast, which is considered the center of the environmental niche of the species, and where the growth of Pseudotsuga Menzies is currently the most high, the width of annual rings, according to forecasts, will be reduced by approximately 10 percent. But at high elevations in Montana is projected to increase in the growth rings of trees, as there is the domination of very low temperatures, so the warming on the contrary will create more favorable conditions.
Among the factors influencing tree growth include average temperature and average rainfall. Because of warming and increased stress from drought, according to the researchers, almost all of Douglas Menzies will have thinner annual rings, and hence, absorb less carbon dioxide.
Recently, scientists based on paleo-climatic analysis of annual rings came to the conclusionthat drought in the basin of the Missouri river at the turn of XX and XXI centuries were the most devastating in the last 1200 years, which underscores the human influence on them.