This article, Mats and Nets – Patterns from the Dunes, describes two different patterns of plant succession on the sand dunes along the Oregon coast, and how those relate to certain permaculture strategies. It’s really lovely and clear writing about the growth of plant communities – I had a really easy time envisioning what was going on as the first plants spread and provided appropriate conditions for new species, and how the “islands” of growth in what was really barren sand expand and increase in complexity. Here’s a portion:
. . . In these quiet patches, ecological succession begins with clumps of red fescue grass that colonize bare sand. The grass mounds create miniature windbreaks, stopping air movement near the ground. This offers a welcoming environment for a type of moss that loves sunny, dry sites. Incoming spores sprout quickly. When I picnic or write in these sheltered spots, I’m often surrounded by thick crusty mats of these ancient organisms.
The growing moss, in the pattern of ungratefulness familiar to ecologists and parents everywhere, eventually crowds out its older benefactor—the fescue nets that nurtured it. As the seasons pass, the carpet of moss alternately dries and renews, crumbling nutrients into the sand. Lichens move in next, and add their crop of organic matter. The resulting patch of shelter and soil tailors an ideal habitat for the subsequent occupant: kinnikinnik, a creeping evergreen shrub with red berries.
Kinnikinnik sprouts from bird-dropped seed or from dormant tendrils left over from earlier colonizations. Like the moss, this trailing shrub grows in a mat shape, but on a larger scale, and eventually smothers the shade-intolerant moss. The moss is now relegated to the margins of the expanding kinnikinnik mat, and creeps outward into the sunny, protected edge, transforming more sand into soil.
The overall pattern, of islands of plant life forming and growing and perhaps eventually merging and disguising portions of the dunes completely, reminds me of something I read once about how plants started to regrow on Mt. St. Helens in the area most affected by the eruption. People had been expecting that things would regrow from the outside, unaffected edge back in, but that was not the case. There were also many tiny islands of surviving plants within the blasted area, where plants had been sheltered by something – like a rock outcropping – and so regrowth in the overall area was much faster than originally expected, as it could happen outwards from many small islands, as well as inward from the edges.