Blog on Arbor Day Foundation website – written by James R. Fazio – February 15, 2018
Trees in a forest are usually thought of as fierce competitors, each struggling for control of available light and soil moisture, usually at the expense of neighboring trees. But Canadian researcher Suzanne W. Simard and her colleagues found that Paper Birch trees can actually aid their neighboring Douglasfirs.
Through carefully controlled research, Dr. Simard has documented the transfer of carbon (sugar) from the Paper Birch to nearby Douglasfirs. The transfer takes place through tiny underground strands of beneficial fungi called ectomycorrhizae. These appendages are common on most tree roots. They illustrate a classic symbiotic relationship in that both the host and the fungus benefit from the close association. The fungus obtains a small amount of carbohydrates and vitamins from the tree and in turn greatly increases the absorptive surface of the root. This increases the flow of water and essential elements into the tree roots, especially phosphorous.
Dr. Simard discovered that the mycorrhizae on Birch and Douglasfirs in her research plots interconnected. Sugars flowed between the tree roots, with a net gain for the Douglasfirs. She also found that the more the Douglasfirs were stressed by shade, the more of a sugar fix they received from the Paper Birches.
There may be management applications of this phenomenon. By interplanting the two species, or encouraging natural regeneration of both, the birches may help the longer-lived conifers get a growth boost early in life and at the same time help crowd out competing vegetation in a plantation. Eventually the birch could be harvested when overtopped by the Douglasfirs. As an added bonus, scientists have noticed that birches also have an “antibiotic” effect on soil pathogens that cause root rot.
The Hidden Network Beneath Your Yard
The link between paper birch and Douglas fir is one example of a much larger system. Most trees form partnerships with soil fungi called mycorrhizae, which wrap around or enter the roots and extend a vast web of fine threads through the soil. This web greatly increases the surface area a tree can draw water and nutrients from, especially phosphorus, in exchange for a small share of the sugars the tree makes through photosynthesis. In many forests these fungal threads connect neighboring trees, allowing resources and even chemical signals to move between them.
What This Means for a Home Landscape
You can support this underground partnership in your own yard with a few simple habits. Healthy soil biology depends on undisturbed roots, so avoid compacting or repeatedly digging the root zone. A layer of natural mulch feeds soil life as it breaks down and keeps roots cool and moist. Limit broad use of fungicides and heavy synthetic fertilizers, which can suppress the beneficial fungi trees rely on. Planting a mix of species rather than a single type also builds a more resilient landscape.
For help building a healthy, diverse planting on your property, call Hometown Tree Experts at 301-250-1033 to speak with a certified arborist.