The southern hills are bald on the ridges and forested in the folds

Two habitats interlocked, not one habitat with gaps

Above roughly the level where mist becomes permanent, the high ranges of the southern Western Ghats look wrong to anyone expecting tropical forest. The rounded ridges are open grassland, and the forest is confined to the hollows and stream courses between them, in dark compact patches with an almost drawn edge.

Those patches are called sholas, and the combination of the two is a single system rather than forest with clearings in it. The boundary between grass and trees is remarkably abrupt, often a matter of a few metres, and it sits in the same place decade after decade.

Inside a shola the character changes immediately. The canopy is low and dense, the trunks are covered in moss and epiphytes, the ground is spongy and permanently damp, and the temperature drops as you step in. They act as sponges, holding water through the dry months and releasing it into streams that feed a great deal of the country below.

Why the ridges have no trees is a genuine argument

The explanations offered are frost, wind, fire and shallow soil, and they aren’t mutually exclusive. Cold air pools on open ground on clear nights at these altitudes and frost kills tree seedlings on the ridges while the hollows stay warmer, which fits the observed pattern well.

Fire is the other main candidate, since grassland burns readily and shola edges do not, and repeated burning would hold the boundary where it is. How much of the fire has been natural and how much of it has come from centuries of grazing and management is not settled.

What is agreed is that the system is old. This isn’t a landscape that was cleared and failed to grow back, and treating the grassland as bare ground awaiting trees has produced some of the worst decisions made in these hills.

Plantations rewrote the high ranges

From the colonial period onwards, large areas of high grassland were planted with tea, and later with fast-growing exotics grown for fuel and for pulp. Tea plantations now cover much of the accessible high country in the Nilgiris and around Munnar, and they are what most visitors actually mean when they describe the scenery.

The planted exotics have caused more difficulty than the tea. Several of the species used spread readily into grassland on their own, and once established they shade out the grasses and change the water behaviour of the slope. Removing them is expensive and slow, and there is disagreement about how far it should go.

The result is a landscape that reads as natural and is heavily manufactured. Knowing which is which turns a drive through the high ranges into something much more interesting than a scenic road.

What lives up there is largely found nowhere else

The Nilgiri tahr, a stocky mountain goat, is the animal most associated with these slopes, and it depends on exactly the open cliff-and-grassland combination that the system provides. Several birds of the high Ghats are similarly restricted, which is why birdwatchers come here for a small number of specific species rather than for variety.

The shola patches carry their own set of frogs, small mammals and invertebrates, many of them with tiny ranges confined to a single massif. Isolation is the mechanism: each high range is an island of cool wet habitat surrounded by warm lowland, and things marooned on those islands went their own way.

The kurinji shrub, which flowers en masse at long intervals and turns whole hillsides blue when it does, belongs to this habitat too. The flowering years draw very large crowds to a few slopes, which has become a management problem in its own right.

Seeing it without simply driving past it

The high country is reached through the hill stations — the Nilgiris around Ooty and Coonoor, the Anamalais, the Palani hills around Kodaikanal, the high ranges above Munnar — and the grassland and shola begin above the town in each case rather than in it.

Mist is the defining condition, and it usually builds through the day, so the clear window is early. Afternoons in the wet months can close down to a few metres of visibility, and the same slope that was open at eight in the morning is a white wall by two.

Much of the best habitat lies inside national parks and reserves where access is by permit, on set routes, or with a guide, and the arrangements differ between states and change from season to season. Look up the current rules for the specific park, and treat any account written a few years ago as history rather than as instruction.