Lately I have been considering the purchase of a mycorrhizal fungi inoculant to mix into the soil with my Fall/Winter tree plantings. It’s been well established that most plants in the world form associations with mycorrhizal fungi, in which the roots of the plants connect with the hyphae of the fungi, enabling the exchange of nutrients. The fungi depend on the carbon (sugars) they acquire from the plants. The plants benefit from increased access to moisture and essential elements like nitrogen and phosphorous. The agricultural industry has capitalized on these attributes in the form of mycorrhizal soil inoculants. For example, Mycorrhizal Applications, touts itself as the “world’s leading manufacturer and supplier of mycorrhizal soil inoculants . . . which accelerate plant performance by greatly increasing the surface absorbing area of roots, producing a healthier root system.”
But are these products a good idea? I’ve spent quite a bit of time surfing the web for information and have found various studies, including the use of inoculants to help forest tree seedlings in nurseries and trees planted in bare soil. For the use of inoculants in our own backyard forests, however, I’m inclined to follow the advice of Canadian Master Gardener Robert Pavlis who writes “there is just no good reason to buy mycorrhizal fungi for your garden,” and furthermore “it is never a good idea to import foreign species of any kind into your garden.”
If not inoculants, are there other backyard forest applications related to mycorrhizal fungi? One that makes sense to me is keeping a sharp eye out for volunteer tree seedlings and letting them grow where they are if possible. Dr. Suzanne Simard’s pioneering research showed how large Douglas Firs use mycorrhizal connections to nurture the seedlings growing near them. The “mother trees” basically feed their offspring, enabling them to grow in partial shade and withstand drought. Thus, I am especially pleased when I find volunteer Douglas Firs sprouting in the vicinity of mature trees, knowing they are likely to do better than any seedlings I could have purchased from a nursery and planted in the same spot.
Another possible application for the backyard forest is companion planting, the “close planting of different plants that enhance each other’s growth or protect each other from pests.” For example, Douglas Fir and Paper Birch can connect through mycorrhizal fungi, providing benefits to both trees. In the forests of central British Columbia, the birch is an early successional tree that quickly establishes itself in clear-cuts. In sites replanted with Douglas Fir, foresters have traditionally prescribed removal of the birch to prevent it from shading out the fir. Professor Simard’s research demonstrated the fallacy of this practice since the two trees actually help each other through their mycorrhizal connections. In another blog, I’ll speculate about other possible companion plantings for Douglas Fir, Western Hemlock, and Western Redcedar.