In my many years of tree studies, I’ve accumulated a vast and varied assortment of reasons to love trees. I present you here with yet another great excuse: larger trees in a forest actually protect and nurture seedlings and young saplings.
It all begins with a complex system that involves specially evolved intermediaries called mycorrhizal fungi. Their fungal strands form an intimate bond with the tips of tree roots, and help the tree absorb water and nutrients. In return, the tree supplies the fungi with sugars. This network forms a dense mat in the top six inches of the entire forest floor, connecting all the trees in that location. Biologists have known about this root/fungus relationship for a very long time, but new research reveals even more fascinating material: the existence of Mother or Hub trees.
Niagara Escarpment Woods #8 by Janusz Wrobel
In a dense forest, the germination and establishment of fresh trees is a challenge: larger trees take up most of the nutrients, and the canopy prevents penetration of light to the forest floor. Ground-level surfaces tend to be inhospitable, and soil quality is poor. What is a seedling to do? What else: it calls on its Mother. In effect, once a seed begins to germinate, it awakens components of the fungal mat that quickly colonize its roots. The seedling thus becomes linked with a large pool of nutrients that connects it to larger, older specimens that have access to light. The more shaded the area, the more resources a seedling can access.
Saplings form strong fungal connections with large, mature trees. Image by Prof Suzanne Simard.
When a mature tree declines and begins to die, she sends her resources back into the network, and it is time for the younger trees to begin nurturing their own young charges.
Fallen by Janusz Wrobel
Shows a mature tree, fallen and being absorbed back into the network
In even more recent studies, biologists are discovering that a mother tree actually favours her own offspring. At one of the research sites I visited in BC, Amanda Asay, PhD (Does kin selection play a facilitative role in regeneration of forests under climate stress?) was monitoring the survival rate of related and unrelated seedlings. How was this done? Several mature trees were harvested of their seeds. Around each tree was embedded a series of marked mesh bags filled with local soil, into which were planted either the tree’s own seeds, or those of others. Over the next few months, if bears and other wildlife hadn’t harvested them first, a tally of survivors was taken.
Here are a couple of those mesh bags. They are 8×5″ in size and allow fungi and roots to pass through.
At the site, I had the opportunity to see how scientific research really happens. In the muddy trenches of boreal forest, after months of exposure to climate, pests, weed growth and just plain attrition, those little mesh bags were a challenge to find. But yes! I found one! Then another, not too far away!… soon we were expert at detecting the minutest bit of white mesh buried in forest scruff. This and other adventures renewed my deep respect for biologists working in the field.
Here we are visiting Amanda’s research site, looking for tiny mesh bags of seedlings. Amanda is wearing the red jacket.
Of course, I love the idea that trees might be altruistic: it certainly captures the imagination. However, biologists are quick to share the truth: the evolution of the mycorrhizal relationship has much more to do with the health and survival of species and communities, than what we humans identify as true altruism. The chemistry behind these processes is well documented. Never mind! Scientific explanations are much richer and more engaging than any romantic notion I can come up with – eventually it all connects and makes its own wild beauty. Science is the real magic: as long as we have inquiring minds, our knowledge and appreciation of the world will continue to grow, and so will our sources of inspiration.
LifeLines 2015 30×10″ Lorraine Roy
Saplings thriving with the support of a mature tree in the forest. The fungal connections are just visible at the roots.
