Old-growth moss mats cannot reestablish because only young twigs offer footholds

Evidence

Kent Davis and I began looking at how mosses get started naturally as epiphytes. Surely they must be able to colonize bare bark—otherwise how could these thick moss carpets ever develop? What we found surprised us. Mosses on young trees don’t colonize the bare bark at all. When we looked at tiny twigs and young branches, the bark was bare. But on virtually every leaf scar, bud scar, and lenticels there was a tiny tuft of moss. If you look closely at a twig, you’ll see that much of it is covered by bark, but it also is textured by its brief history. It is marked by a raised stub where last year’s leaf was held. This so-called leaf scar is minutely corky, with just enough texture to capture a spore or two. Twigs also bear a collection of closely spaced ridges which show where the bud used to be. This roughening also seems to provide a foothold for mosses. A young branch starts to collect its moss flora tuft by tiny tuft, leaf scar by leaf scar. Weobserved that the size of the tufts increased with the age of the branch. As the tree grew older, different mosses would colonize—not on the bare bark, but on top of the initial mosses. The thick moss mats of mature trees got their start on twigs. We found that colonization is much easier on rough young twigs and nearly impossible on old branches. Once the stem has aged and leaf scars become few and far between, the opportunities for attracting mosses have dwindled. We can infer, then, that the mats of mosses which weigh down the branches are probably almost as old as the trees themselves. — Robin Wall Kimmerer, Gathering Moss, 614

Categorization

• SEED: Article gleam: ‘leaf scars as landing strips’ — the textured micro-history of surfaces as the unseen scaffold for whole ecosystems; pairs beautifully with the disturbance-recovery theme running through the moss course.
• XREF: Directly explains Robinson’s disturbed-landscape recovery limits in earlier chapters — regrowth and succession always read the micro-texture of what came before. — connects to: Old-growth moss mats recover almost not at all once stripped from trees — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 607; Moss colonies establish only through a rare, poorly understood succession — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 519; A moss garden that needs wild harvesting is not self-sustaining — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 514 (+3 more)
• recurring: this claim recurs 2 times within its source

Broader Connections

• Stripped moss beds regrow only centimeters per year on smooth mature bark #corroborates (0.95) — Robin Wall Kimmerer, Gathering Moss, 613