If you came across the "Christmassy" article in the Times of India published September 28, you would have read the fascinating story of thousands of Christmas trees being deliberately dumped into a lake in Finland.
In the southeastern part of the country, scientists set out to find how this unusual experiment would impact aquatic life by submerging 1,500 spruce specimens in Lake Saimaa.
The project began in 2021, when researchers from the Finnish Environment Institute (SYKE) placed groups of these conifers on the bottom of the lake. The aim was to determine whether the trees could create an underwater habitat for organisms and fish, effectively turning parts of the lakebed into a kind of submerged forest.
Three years later, researchers retrieved the trees and examined the areas where they had been placed.
What they found was a dramatic increase in life around the submerged trees, particularly among organisms living on or near the lakebed.
The trees were placed in groups of six to eight and submerged at a depth of about two metres. Bricks were used to keep them in position underwater. The experiment was designed to examine whether the natural structure of the trees could provide shelter and food for aquatic organisms.
Kari-Matti Vuori, the scientist leading the research, said the experiment resulted in a major increase in benthic production in areas where the trees had been submerged.
Benthic organisms are animals and other living organisms that live on, in or close to the bottom of aquatic ecosystems. They form an important part of the food chain, providing food for fish and other species.
According to Vuori, the number of individual benthic animals increased tenfold in areas containing the submerged trees. Species diversity also increased dramatically, rising by as much as five times compared with the conditions recorded before the experiment.
The difference was identified by comparing benthic samples collected from the lake before and after the trees were introduced.
The submerged trees appeared to provide a new physical structure for organisms to colonise. Microbial and fungal communities developed around the wood, creating an additional source of food and helping establish a more complex underwater habitat.
The effects were also noticed higher up the food chain. Local fishermen told Vuori that they had observed a considerable increase in the number of fish in areas where the trees had been placed. While the observations from fishermen were not the same as controlled scientific measurements, they added to the researchers' interest in how the submerged trees were influencing the ecosystem.
The experiment also highlighted how natural materials such as discarded Christmas trees can potentially be repurposed rather than simply thrown away. Once submerged, the trees provide branches and surfaces that can be used as shelter by aquatic organisms.
As the wood gradually breaks down, it can also support microbial and fungal growth, creating food sources for smaller organisms that are themselves eaten by fish.
The Finnish experiment was therefore not simply about disposing of old Christmas trees. It was designed to investigate whether the trees could contribute to aquatic biodiversity by creating additional habitat in the lake. The findings also connect to a broader environmental question: what happens to Christmas trees after the holiday season?
Christmas trees are organic material and contain carbon absorbed by the trees as they grow.
Environmental experts have warned against sending them to landfill because decomposing organic waste can contribute to methane emissions. John Kazer, a footprint certification expert at the Carbon Trust, told the BBC that Christmas trees should be kept out of landfill because they can contribute to greenhouse gas emissions as they decompose.
Nonetheless, the Finnish experiment does not imply that Christmas trees should just be unceremoniously tossed into lakes.
The trees utilized in the Lake Saimaa study were purposefully submerged under meticulously controlled conditions as an integral part of scientific inquiry. Rather, this groundbreaking experiment provided a unique insight into how a seasonal item, often seen as a mere decorative object, can integrate into and contribute to an aquatic ecosystem.
After three years had passed since 1,500 spruce trees were placed beneath the surface of Lake Saimaa, researchers discovered that these underwater structures had transformed into vibrant hotspots for benthic life. Specifically, they observed a remarkable tenfold increase in the number of individual organisms and an impressive rise in species diversity, which soared as much as fivefold.
What initially started as an experiment focusing on repurposed Christmas trees had effectively illustrated how submerged wood can create new habitats while fostering and supporting complex aquatic food webs.
