A groundbreaking study led by Nils Henriksson at the Swedish University of Agricultural Sciences has shed new light on the complex relationships between trees and the fungal networks that interconnect them.
These networks, known as mycorrhizal networks, are formed by symbiotic fungi called hyphae and play a crucial role in determining the nature of forests and their response to climate change.
The study re-examines the increasingly popular “mother-tree hypothesis,” which posits that these networks also function as a means for trees to help their offspring and other tree-friends.
The mother-tree hypothesis,has attracted significant attention from both the scientific community and the media, with many outlets presenting the idea as established fact.
According to the hypothesis, the largest and oldest trees in a forest, known as mother trees, use the mycorrhizal network to share carbon and nutrients with saplings growing in particularly shady areas where there is not enough sunlight for adequate photosynthesis.
This network structure should also enable mother trees to detect the ill health of their neighbors through distress signals, alerting them to send these trees the nutrients they need to heal. In this way, mother trees are believed to act as central hubs, communicating with both young seedlings and other large trees around them to increase their chances of survival.
However, the new study has found that the empirical evidence for the mother tree hypothesis is actually very limited, and theoretical explanations for the mechanisms are largely lacking.
The researchers re-examined data and conclusions from publications both for and against the mother tree hypothesis in an effort to reconcile the hypothesis with existing theory. They found that while big trees and their interconnections with their neighbors are still essential for the forest ecosystem, the fungal network does not work as a simple pipeline for resource sharing among trees.
Instead, apparent resource sharing among trees is more likely to be a result of trading between fungi and trees rather than directed transfer from one tree to another. In many cases, this trading even results in aggravated competition between trees rather than support of seedlings.
This research, which is published in New Phytologist, has important implications for our understanding of forest ecosystems and how they respond to climate change. By re-examining the evidence for the mother tree hypothesis and questioning its validity, the researchers have contributed to a more accurate understanding of the role fungal networks play in forests.
While the concept of mother trees helping their offspring and neighbors may be a romantic and appealing notion, it is crucial that our understanding of these complex systems is grounded in rigorous scientific analysis.
Study co-author Oskar Franklin is a researcher in the Agriculture, Forestry, and Ecosystem Services Research Group of the IIASA Biodiversity and Natural Resources Program.
“We found that mycorrhizal networks are indeed essential for the stability of many forest ecosystems, but rarely through sharing and caring among trees. Rather, it works like a trading ground for individual trees and fungi, each trying to make the best deal to survive,” said Franklin.
“The forest is not a super organism or a family of trees helping each other. It is a complex ecosystem with trees, fungi, and other organisms, which are all interdependent but not guided by a common purpose.”
“Although the narrative of the mother tree hypothesis is scarcely supported by scientific evidence and is controversial in the scientific community, it has inspired both research and public interest in the complexity of forests. It is vital that the future management and study of forests take the real complexity of these important ecosystems into account.”
Trees communicate with each other in a variety of ways, both directly and indirectly. One primary method of communication is through the mycorrhizal network, also known as the “wood-wide web.” This network consists of symbiotic fungi that form connections between tree roots, allowing them to exchange nutrients, water, and chemical signals. Here are some of the ways trees communicate using these networks and other methods:
Trees can share essential resources like nutrients and water through the mycorrhizal network. This can be particularly important for seedlings and trees growing in harsh conditions where resources may be scarce. The fungi act as intermediaries, facilitating the exchange of nutrients between trees in return for carbon from the trees.
Trees can release chemical signals into the air, soil, or through the mycorrhizal network to communicate with other trees. For example, when a tree is under attack by insects, it can release volatile organic compounds (VOCs) into the air, alerting neighboring trees of the threat. In response, the neighboring trees can produce defensive chemicals to deter the insects.
Trees can send electrical signals through their vascular tissue to respond to environmental changes and coordinate their activities. These signals can be generated in response to physical damage, herbivory, or other forms of stress, and can help trees react and adapt to changing conditions.
Some trees can produce and release allelochemicals, which are chemicals that inhibit the growth of other plants nearby. This is a form of chemical communication that helps the tree secure its resources by reducing competition from neighboring plants.
It is important to note that while trees can communicate with each other in these ways, their communication is not equivalent to human communication or consciousness. Rather, it is an evolved mechanism that allows them to interact with their environment and other organisms to improve their survival and reproduction.
As scientists continue to research and uncover more about tree communication, we can gain a deeper understanding of forest ecosystems and their complex dynamics. This knowledge can be crucial in managing and conserving these ecosystems, as well as in developing strategies to combat climate change and other environmental challenges.
Trees play a vital role in maintaining the health of our planet and supporting human life in various ways. They provide a range of ecological, economic, and social benefits that are crucial for our well-being and the environment. Some of the key importance of trees to humanity and the Earth include:
Through the process of photosynthesis, trees convert carbon dioxide (CO2) into oxygen, which is essential for all aerobic organisms, including humans. A single mature tree can produce enough oxygen to support two people.
Trees absorb and store carbon dioxide from the atmosphere, helping to mitigate the effects of climate change. Forests act as carbon sinks, reducing the overall concentration of greenhouse gases in the atmosphere.
Trees provide habitats and food sources for a wide variety of plant and animal species. Forest ecosystems are among the most diverse and complex on the planet, supporting millions of different species. Biodiversity is essential for maintaining ecosystem resilience and overall planetary health.
Tree roots help stabilize the soil, reducing erosion and landslides. Additionally, fallen leaves and other organic matter from trees contribute to the formation of nutrient-rich humus, improving soil fertility and structure.
Trees play a critical role in maintaining the water cycle. They help regulate local and global water supplies by absorbing and releasing water through the process of transpiration. Forests also act as natural sponges, capturing and filtering rainwater, and reducing the risk of floods and droughts.
Trees help regulate local and global climates by providing shade, reducing surface temperatures, and moderating the effects of heatwaves. They also help to balance atmospheric humidity through transpiration.
Trees provide a variety of resources that contribute to the global economy, including timber, paper, and non-timber forest products such as fruits, nuts, and medicinal plants. Forest-based industries generate employment and income for millions of people worldwide.
Trees have been an integral part of human culture and spirituality throughout history. They are revered in many religious and spiritual traditions, and often serve as symbols of life, wisdom, and fertility.
Studies have shown that exposure to trees and green spaces can have a positive impact on human mental and physical health. Benefits include reduced stress, improved cognitive function, and increased physical activity.
Trees contribute to the beauty of landscapes and urban environments. They enhance the visual appeal of our surroundings and provide a sense of tranquility and connection to nature.
The importance of trees to humanity and the Earth cannot be overstated. Protecting and conserving our forests, as well as promoting reforestation and sustainable management practices, are essential to ensure the long-term health of our planet and the well-being of current and future generations.