April Fungus

The month of April is the first national holiday celebrating action toward a better future for our nature — Arbor Day. In Indiana, we celebrate Arbor Day on the last Friday of April. Here at Crown Hill Arboretum, we give away new tree seedlings the week of Arbor Day to celebrate and give folks a chance to add tree diversity to their own property.

Once a tree is in the ground, it becomes part of larger systems both above and below ground. Fungal mycelium (mushroom roots) and specialized structures called mycorrhizae can expand, enhance, and connect to the root systems of trees.

The relationship between mycorrhizal fungi and trees is generally species or genera specific. Meaning, if there is a mycorrhizal spore in the soil it will only germinate and connect with specific species of plants and trees. They have preferences!

Also, they don’t intentionally connect trees; it just happens that way.

Mycorrhizal fungi increase the root surface area of trees. That can help the tree take up more nutrients and moisture from the soil, but this benefit to the tree comes with a small fee. The fungi feed on sugars, starches and carbon held in the tree’s roots. The individual trees become connected as the fungi expand their mycelial networks and connect with multiple trees. In this process, the vascular systems of multiple trees can be connected. Once connected vascularly, trees will share or send chemical resources, pest warnings, etc. through the larger system.

As long as a tree is healthy, mycorrhizal fungi are a net benefit to trees. However, if trees are significantly injured or are stressed to the point of decline, these same expanding mycorrhizae will want the same energy resources and will damage the tree further.

So, the next time you’re visiting our trees in the arboretum, take a moment to think about the complex exchanges happening underneath your feet.