Transhumance

Why do herders climb the mountain on a schedule set by snowmelt rather than the calendar?

Ask an alpine herder when the cattle go up and you rarely get a date. You get a condition: when the snow is off the middle meadows, when the grass has come, when the ground will carry the animals. Ask why not simply fix a date — the twentieth of May, every year, and be done with it — and you get something like a shrug.

That shrug is worth taking seriously. A fixed date is enormously convenient. It lets you hire help, arrange transport, tell your neighbours. Communities that live by seasonal work usually love fixed dates. So why does this particular movement resist one? What is the mountain doing that a calendar cannot represent?

Begin with what altitude does to climate. Air cools as you rise — on average around six and a half degrees for every thousand metres of the free atmosphere — so a slope is a temperature gradient stood on end. A valley floor and a pasture a thousand metres above it are, in thermal terms, a long way apart, and the growing season at the top is shorter by weeks.

Now the consequence that matters. If spring is a threshold in temperature, and temperature falls steadily with height, then spring does not arrive on the mountain at one moment. It arrives at the bottom first and creeps upward over the following months. Ask yourself what that means for a grazing animal: the same early stage of growth is available at different heights at different times. The season is not a moment on a slope. It is stacked vertically.

Why should the early stage matter so much? Because grass is not a constant food. Young growth is high in protein and low in indigestible fibre; as the plant matures towards seed, that reverses, and the same field that fattened an animal in June barely maintains it in August. So the best forage is not a place, it is a narrow window — and that window sweeps up the mountain as the snowline retreats. A herd that stays put gets a few good weeks. A herd that climbs at the right pace can ride the leading edge for months. Biologists studying wild ungulates gave this the obvious name: surfing the green wave.

Now we can see why a date fails. The wave's sequence is fixed — low ground always greens first — but its phase is not. Snowmelt in a mountain basin can vary by several weeks between a warm year and a cold one, and the grass follows the melt, not the almanac. A fixed date is a bet on the average, and it loses at both ends. Arrive too early and there is nothing to eat, and worse, the ground is saturated: hooves on wet soil cut the turf and compact it, so an eager herder damages the pasture for the rest of the summer. Arrive too late and the best growth has already gone past, uneaten.

There is a second reason to leave, and it is easy to miss because it happens behind you. What limits a mountain household is not summer grass at all — it is winter feed. Every animal must be fed through months when nothing grows, from hay cut on the valley meadows. But you cannot cut hay from a meadow the cattle are standing in. Taking the herd uphill vacates the low land so it can grow the winter crop. Do you see how the two ends of the year are locked together? The climb is not only a search for food; it is also a withdrawal that makes the following winter survivable.

Coming down is the same reasoning run backwards. The first hard frosts stop growth at altitude, and lingering high on the mountain risks being caught by early snow with animals that must be walked, not carried. So the descent tracks the end of growth, and lands the herd back on ground that has by then been cut and has regrown a second time.

One honest complication. Plenty of transhumant communities do name dates — saints' days, customary alp-opening days, and in Switzerland dates written into grazing contracts. That is not a contradiction, but it is a different job. Common pasture is shared, and a hundred households cannot each decide privately when to arrive without chaos over who grazes what. The date solves the coordination problem; the snowmelt solves the ecological one, and in practice the customary date is the anchor that gets adjusted when the season runs early or late.

The tempting misreading is that transhumance is nomadism — wandering in search of whatever can be found. It is close to the opposite. The routes, the huts, the grazing rights and the order of movement are typically fixed for generations; what varies is timing, and only timing. It is a settled system with one flexible parameter.

The second refinement is that this logic is not really about snow. Snow is the local signal for a general problem: forage quality peaks briefly and in different places at different times, so the herd must move to stay on the peak. Where the limiting factor is summer drought rather than winter cold, the same institution appears with the direction reversed — the long Iberian droveways carried flocks north to mountain pastures for the summer and back to the warm south-western plains for the winter, because there the lowland fails in August rather than in January. Same reasoning, different signal.

And the sharpest way to hold the whole thing: the herd is not chasing grass. It is chasing a stage of grass, and stages have a schedule the calendar only approximates.

• How grazing rights on shared alpine commons were governed without exhausting them — and what that says about common-pool resources generally.
• What happens to a snowmelt-triggered system when the melt advances faster than the customary dates and the social calendar can follow.
• Horizontal transhumance and its infrastructure: the droveways, their legal protection, and what became of them.

Every term the collection defines is gathered in the glossary.