Chalk heath


Chalk heath is a rare habitat, in the temperate grasslands, savannas, and shrublands biome, formed of a paradoxical mixture of shallow-rooted calcifuge and deeper-rooted calcicole plants, growing on a thin layer of acidic soil over an alkaline substrate. Chalk heath is intermediate between two much more widespread habitats, chalk grassland and heathland.

Ecology

Chalk heath occurs where a thin layer of acidic soil overlies a basic one, such as chalk. Shallow-rooted plants grow only in the acidic soil, and so these are species characteristic of acidic habitats. Deeper-rooted plants can reach the underlying alkaline substrate, and so these include species characteristic of alkaline habitats. Plants also occur which are able to tolerate both acidic and basic conditions. There are no plants restricted entirely to chalk heath, and the animals are also those characteristic of chalk grassland and heathland. The vegetation structure of chalk heath resembles grass heath, being short grassy vegetation with heather growing up through it, with some scattered heather bushes.
Chalk heath often occurs at the tops of slopes, at the thin margins of acidic deposits which often cap the flatter tops of chalk hills. It usually gives way to chalk grassland on lower slopes where these deposits have been eroded away, and often to heathland on the hilltops where the acidic deposits are thicker. Chalk heath tends to occur as narrow strips and scattered fragments, being limited to places where the conditions are exactly right for its development and survival.
Chalk heath is a grazing habitat, created and maintained by livestock and rabbits.

Vegetation

Chalk heath in southern Britain includes calcicoles such as salad burnet, dropwort and common milkwort, and calcifuges such as bell heather, ling heather, heath grass, sheep's sorrel and betony. It also includes plants which can tolerate both acidic and basic conditions, such as common bent, wood sage and sometimes juniper.

Conservation

Chalk heath has suffered a parallel decline to those of heathland and chalk grassland, but because of the scattered and fragmented distribution of suitable soil conditions it has declined even more than those habitats. Many examples have disappeared due to agricultural improvement, or to a lack of grazing management, which leads to replacement by species-poor scrub and woodland. Chalk heath is especially sensitive to soil disturbance such as ploughing, which mixes the thin layer of acidic soil with the chalk beneath.

Example locations