Soil Begins

 This young pine is growing out of an inch or two of granite dust, and pure granite. The red plant next to it is a succulent, probably Sedum obtusatum, a stonecrop.

There’s something elemental about high mountains. Everything’s stripped down.  Rock. Plants. Water. It’s a perfect place to see how soil begins.

As far as I know, soil starts in one of two ways: things rot (usually plants), or rock breaks down. Usually, both are going on at once.

Rock breakdown is slow; we rarely think of it in our gardens at home. But it must be the original place where soil starts. In many of the places where we garden, the rotted plant matter has accrued so much that the soil obscures the place where it came from. (Although in many places where I’ve gardened, the rock layer was not all that far below the soil, and needed breaking up with a pickaxe.) In the mountains, extreme climate and topography mean that soil-making is always in its infancy.

On bare mountain rock, threadlike parts of lichens make a strong acid which breaks down granite, feeding the lichen. High mountain conifers can grow in just a tiny bit of this crushed granite. They then break up more rock with their roots, drop needles and eventually wood which rot and make more soil, so that other kinds of plants can grow there. Animals feeding on the plants do contribute organic matter one way and another, but the bulk of rotting material is plants.

This is the same pine tree as in the picture at the top. This is its root, going straight into crushed and solid granite.

This juniper root gets its nutrients the same way, and has become a large tree.

This dead tree has helped create a small plant community around its roots. It will soon fall over and add to the soil by rotting. Probably rain will wash a great deal of its rotten wood into the lake below, but some will stay in flat places and crevices along the way.

Reference:

Tracy I. Storer and Robert L. Usinger, Sierra Nevada Natural History, University of California Press, 1963. (They have recently come out with a more recent version, but this is the one I own and still use.)