Walking Underground with Staghorn Sumac
Some trees create conditions that favor their own progeny. These climax species (e.g. sugar maple, eastern hemlock) are typically long lived, slow growing, and shade tolerant. White cedar, which thrives on calcareous bedrock, have calcium-rich needles that make the soil less acidic as they decompose, which in turn creates conditions better suited for future white cedar. Hemlock canopies cast a thick shadow that almost exclusively supports hemlock regeneration.
Other species, the rock star species, live fast and die young. They’re shade intolerant so can’t regenerate under their own shade. They occupy a site for a generation and rely on their seeds being scattered far and wide in the hopes of winning the habitat lottery and finding another suitable site. Typically these species are less tied to soil/bedrock types and more towards disturbance.
Staghorn sumac is one of the rock stars. It rarely lives past 25-30 years and is generally shade intolerant (link 1, link 2). Each of those prominent red cones, or “bobs” on female trees (and there can be dozens per individual) holds 100s of fruits, which are dispersed primarily by birds. Their seed coats are extremely tough and require heat and/or passing through an animals digestive tract in order to germinate. Even if these conditions are met, germination rates are still low. Sumac relies on vegetative reproduction to spread horizontally and dominate a suitable site.
Clonal Stand Formation
If a sumac seed does successfully germinate, in its first year it sends up a single lead shoot that hardly branches at all, and its shallow roots radiate out in a circle. In its second year, the main stem continues to grow vertically, but it also sends up new shoots at the margins of its roots. It continues to do this in subsequent years resulting in an umbrella shape to the clonal stand, with the largest, oldest stem in the middle and the youngest shoots at the margins.
My wife and I paddled out to Appletree Point in Burlington a couple weeks ago and I noticed that this growth pattern was being used in a slightly different way. Suitable microhabitats are extremely patchy and could never support a large clonal stand. The likelihood of a viable seed successfully being deposited in a small pocket of soil is effectively zero, so the roots act like probes, snaking through cracks in the rocks. Small patches of soil collecting in the rocks super the development of lateral roots which then send up shoots, exactly as seen with the runners on strawberries. The isolated individuals growing on the shale were still clones, but the roots connecting the individuals had broken away as the shale crumbled away.