How Soil Is Formed - Soil: Reflections on the Basis of our Existence - page 26

know this due to scientific studies of soil formation in the Costa Rican rainforest, where
leaves and other matter that collects in tree forks gradually forms a soil base in which
seeds can germinate. It was several centimetres down inside the soil of one such fork
that researchers found ash originating from the Mount Saint Helens eruption.
On arrival at Seattle airport, I am greeted by American colleagues who are to take
me to Lyman Lake, which lies at an altitude of eighteen hundred metres near Glacier
Peak Wilderness National Park—a journey of many hours by car and then boat. This
pristine area was formed by meltwater from a glacier that has retreated at a rate of eight
to twelve metres per year during the last century and now lies some distance from the
water's edge. We are here to study pristine soil never previously exposed to the elements
and answer a host of questions, such as the impact of rainwater when it seeps through
the soil, what species of plants colonise the area and what happens to the soil when veg-
etation takes hold. Thanks to photographs, we know the exact position of the glacier's
edge and how it has shifted over the last hundred years.
On our way to the lake, we hike through dense deciduous forest that gradu-
ally turns into sparse fir woodland. Yellow wolf lichen grows on the boughs of the
Tentative steps towards new soils. When a glacier melts and recedes, it leaves behind an assort-
ment of fine and coarse soil particles—everything from clay to rocks. Known as moraine, this
mixture slowly becomes soil due to the action of the elements and as plants take root. The stony
moraine contains plenty of phosphorus and potassium but lacks nitrogen. Plants must therefore
find another way to access this critical element. The yellow plant in the foreground—alpine
birdsfoot-trefoil—lives in symbiosis with bacteria that capture nitrogen from the air. The nitro-
gen content in the ground accumulates when these plants decay, facilitating the establishment of
other plant species