A curious group had assembled for my Planting Ecology workshop at the nature center. I passed out oil pastels and white sheets of paper to enhance their diagraming, doodling or whatever they were doing as I quickly slid into a rant. They politely listened as I flailed about, wildly covering my flip chart with arrows and circles aimed at displaying the essence of rhizosphere interactions. That is, the intense zone of chemical and biological activity associated with living roots.
The group included a consulting arborist, a nature librarian, a government natural resources specialist, a massage therapist and yoga instructor, an environmental educator, an organic farmer, a jazz musician, a theoretical ecologist and a Peace Corps volunteer preparing for a conservation assignment in Africa. Each of them was open to the idea that a tree is a community unto itself and that soil is very much alive, and that a good tree planter knows this. That’s why they came.
A foundational principle of native tree planting is that the living members of the rhizosphere community—the countless species of microflora and microfauna, down to every living cell—act in many ways like a single organism. Rhizosphere symbiosis is so integral to every native plant growing in a native habitat that some ecologists have suggested a conceptual model, a singular “rhizo-organism,” that includes symbiotic soil organisms and the plant itself. Bur oak (Quercus macrocarpa) lives this reality so largely that it can’t be ignored. And thus, rhizosphere symbiosis is the central doctrine in my Bur Oak Manifesto.
Obviously, an old bur oak would be the best teacher of the Manifesto. But the morning was brisk; the yogi-farmer eco-jazz green book club peace coalition patiently abided my remonstrations and continued to doodle and draw as I ranted on. One particular group of soil bacteria is particularly fascinating because they produce and exchange the plant growth regulators auxin and cytokinin for food in the form of sugary mucus exuded by root tips. These growth regulators stimulate the growth of more root tips, and the production of more exudates that results in more auxin and cytokinin. Granted, this is a simplified explanation, but it shows how root form and function are determined, to large extent, by symbiotic bacteria.
The muffins were gone and my espresso was wearing off, but there were more wonders to tell. After fielding a few questions and accepting corrections from the young theoretical ecologist, I continued. The evolution- ary history of plants indicates that the first land plants required root infections from symbiotic fungi (mycorrhizae), and still do to this day. Roots without mycorrhizae function poorly, and uninfected roots in nature are rare. Mychorrizal fungi, like rhizosphere bacteria, feed on exudates and stimulate increased production of root tips that are, in turn, infected. Fungal strands (hyphae) form a network that grows between root cell walls and is called the Hartig net. The internal net connects to an external network of hyphae in soil. Energy, water and chemical communication flow both ways through this ever-growing web. The influence of the bur oak rhizosphere on ecosystems is too large and complex to calculate or imagine.
Adaptive rhizosphere symbiosis has empowered bur oaks to have the widest range and occupy the most diverse habitats of any oak. However, each local population (ecotype) sustains and is sustained by a distinctive rhizosphere community. Each ecotype produces a unique exudate formula and a distinct community of soil organisms, determined by soil type, rainfall, temperature, day length and environmental cues. If you want to plant an oak, matching ecotype to ecosystem is paramount.
This was just the beginning; the rhizosphere hosts countless symbionts. By now the morning had brightened and the local oaks had much to tell. I feared that my oakniks had grown weary of my flailing gyrations and cluttered flip chart that looked like a poor imitation of a Jackson Pollock painting. I looked around the tables at the formerly white sheets of paper. I saw rainbow root diagrams with scribbled notes. I saw cartoon bacteria and protozoa that looked like gummy bears. The bookish types had made neat columns, and the paper belonging to the theoretical ecologist was covered with equations. I wondered if the jazz musician would take his home and play it. We grabbed shovels and hand lenses and entered the warming woods.
As it happened, their quirky graphics proved to be much more instructive than mine. The bright abstractions and written lines foreshadowed the vibrant woods before us, though all the words and crayons in the world would be lacking. As we entered a story written in oak, organic improvisations made autumn jazz. Even the sheet of mystifying equations taught me something as I recalled that Thoreau believed “the most distinctive and beautiful statement of any truth must take at last the mathematical form.”
The canopy made autumn greens flavored with butter and pumpkin. Smilax and woodbine twined about our feet as we shuffled aside duff to scoop the loess soil. We looked at oak roots with infected tips. Cottony webs and squirming things told the story of a world made by oak. We lingered, but noon approached. We hiked the ridge back to the nature center, and there we planted a bur oak sapling grown from an acorn we collected the previous autumn just a few meters away.
Every manifesto delivers a charge, and ours is to plant native oaks into the communities that created them. Even the oak you plant in your own backyard should be grown from a wild acorn collected nearby. There may be other ways and reasons to plant, but ours is true to oak. I stayed behind to water the sapling as the nascent planters, having embraced their destiny, went to lunch.