Mother Trees and mycorrhizal fungi on Pender Island

Familial connections are something that was once perceived to be impossible in the plant kingdom, but further study into forest relationships has proven us wrong.

According to Dr. Rachel Holt, single mature trees in the Coastal Douglas-fir (CDF) biogeoclimatic (BEC) zone have a disproportionate ecological value compared to other BEC zones in British Columbia. This is because so little mature forest remains in this highly developed region at the edge of the Salish Sea. Projects like Raincoast’s Pender Islands Big Tree Registry (PIBTR) have been initiated in an effort to safeguard big trees and biological diversity in this region.1

September 20th, 2022, marked the two-year anniversary of the PIBTR. To mark the occasion, we asked big tree enthusiast and local Pender resident, Meredith Boyd, to share her experience using data collected via the registry to conduct an experiment inspired by the work of Dr. Suzanne Simard.2

Meredith Boyd stands in a forest looking at fungi.
Photo by Alex Harris.

Background: The original study

Mycorrhizal fungi are long strand-like chains of mycelium (produced by mushrooms) which connect trees and many other plants. This creates a communication network  between many species that together make up forest ecosystems. Mycorrhizal fungi’s role in forest ecosystems was first brought to wider public attention through a series of experiments led by Dr. Suzanne Simard involving  two tree species:  paper birch (Betula papyrifera) and  Douglas-fir (Pseudotsuga menziesii).3 These species are known to share many ectomycorrhizae (fungi specific to tree roots) covering over 90% of their root tips.

Using radio-labled carbon-13 and carbon-14, pathways of resource transfer between birch and   Douglas-fir trees were traced. Notably, Simard and team found that when Douglas-fir trees were exposed to deeply shaded conditions, preventing them from acquiring necessary nutrients through photosynthesis, nutrient transfer from birch trees increased up to 10%. Findings from this study indicated the existence of a “tightly linked plant–fungus–soil system”, ultimately demonstrating that though competition for resources plays a role in forest ecosystem function, so too does mutualism.4

These findings can be applied worldwide to the ways in which mycorrhizal fungi support plant life. The fungi create a system in which they help tree roots process vital nutrients from the soil, and the roots provide sugars back to the fungi. About 60% of the world’s trees are connected to other trees through ectomycorrhizal networks.5

Mycelium

Mycelium is the vegetative part of a fungus, and it is the base for all of the networks of mycorrhizal fungi that science has discovered. Mycelium can be used in a process called bio-remediation in which it is used to decompose oil and other toxic waste. The mycelium produced by mushrooms is able to suck up spilled oil, and neutralize it in a way that helps the mushrooms to grow. This works because the fungi are decomposers, meaning they break down the structure of organic material on the forest floor (or whatever environment they are in), and because oil is technically organic material the fungi has the capacity to break it down so it can be used as a nutrient.  The decomposing property of fungi is crucial in the process of bioremediation. 

Types of mycorrhizal fungi

There are two main types of mycorrhizal fungi, endomycorrhizal and ectomycorrhizal.  Endomycorrhizal fungi is associated with plants that have smaller root structures, while ectomycorrhizal fungi tend to be solely associated with trees, as they need a larger root to support their external hyphae (branching filaments that make up the mycelium of a fungus).

A close up of fungi on a tree.
Photo by Meredith Boyd.

Ectomycorrhizae form symbiotic relationships with the trees they are connected to, moving essential resources back and forth between themselves and the trees as needed. These fungal networks also connect the trees to one another. By carrying signals and nutrients between them, ectomycorrhizal networks allow trees to communicate with and nourish each other. Tracing these networks often reveals familial bonds between trees. Studies show that mother trees are able to recognize their kin, and often will send more nutrients to those young saplings that they identify as their own (Simard, 2021). The bigger trees associated with mycorrhizal roots have been very valuable for keeping saplings alive through increasingly long periods of summer drought, as they have deep tap roots which are able to pull water and nutrients from lower reserves and provide them to trees with shallower, less established root systems. This is why age diversity is crucial to a healthy forest ecosystem. 

Familial connections are something that was once perceived to be impossible in the plant kingdom, but further study into forest relationships has proven us wrong. 

A close up of fungi on the forest floor.
Photo by Alex Harris.

Learning lessons from Mother Trees in the Coastal Douglas-fir zone

The unique topography, geography, and climate of the southern Salish Sea region has resulted in a unique assemblage of ecosystems  known as the CDF zone. The forests of this zone are globally rare and characteristic to the Gulf Islands. Unfortunately, much of the old growth on the Islands has been logged, but that means we must work even harder to protect what is left. Due to human impacts on natural ecosystems, including the climate crisis, it is difficult to know whether we will ever see these forests become old growth ever again. 

In December of 2021,  I began looking into mycorrhizal fungi on my home island, SDȺY¸ES/Pender Island. I looked at 15 of Pender Island’s known biggest trees, identified by the Pender Islands Big Tree Registry, to see what fungal networks on the Islands look like. I collected samples of fungi from both sides of each tree. Then, I moved them onto prepared petri dishes to examine them under a microscope. I found mycorrhizal fungi at all 15 trees. I observed that in drier soil conditions there were far fewer mycorrhizal fungi, which does not bode well for the future as the effects of climate change are expected to increase severity of summer droughts. When I put the fungi samples on petri dishes however, they continued to grow, and this shows just how resilient these fungi can be. 

A small mushroom in a big forest.
Photo by Alex Harris.

Overall mycorrhizal fungi are much more crucial to not only our forest ecosystems, but just about any terrestrial ecosystem there is than we might realize and give them credit for. Prior to my project I had little knowledge that these fungal networks even existed, but the species diversity they support in a healthy forest is amazing. We must work to understand and protect them, because they are the underground life support systems for our forests.

Footnotes

  1. See An Ecosystem on the Edge.
  2. Simard, S. (2021). Finding the Mother Tree. Allen Lane – Penguin Random House Canada
  3. Simard, S.W., Perry, D. A., Jones, M.D., Myrold, D.D., Durall, D.M., & Molinak,R. (1997). Net transfer of carbon between ectomycorrhizal tree species in the field. Letters to Nature, 338, 579-582. https://www.nature.com/articles/41557.pdf
  4. See Letters to Nature, 338, page 581.
  5. Anthony, M.A., Crowther, T.W., van der Linde, S. et al. (2022). Forest tree growth is linked to mycorrhizal fungal composition and function across Europe. The ISME Journal, 16, 1327–1336. DOI: 10.1038/s41396-021-01159-7

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Coastal wolf with a salmon in its month.
Photo by Dene Rossouw.