Habitat types on Portsdown Hill SSSI

The vegetation on Portsdown ranges from short species-rich grassland (chalk downland) to trees. Today, bushes and tall grass dominate, but it hasn't always been so. For many centuries the hill's grass was kept short by grazing sheep and other livestock.
The succession diagram immediately below shows how short grassland turns into dense scrub and woodland.
Below that, is a series of sketches representing the changes in the proportion of vegetation types on the hill. The series goes from the past (1900) to potential future (2050), depending on future management (or not)

Succession of short grassland into woodland in the absence of grazing


Short grass with many species of plant packed together. A great variety of insects feed on the flowers and benefit from the sun-warmed ground. On Portsdown this habitat is associated with areas where the top soil is thin and it is difficult for invasive plants to grow vigorously.	Tall grass with a dense layer of previous years leaves forming a thatch that prevents the sun warming the ground. Often with small hawthorn bushes beginning to invade. It supports far fewer species than short downland, but invertebrates shelter in the grass tussocks and small mammals, like mice and voles, have runs through the grass.	Dense Scrub made up of tangled bushes with scrambling plants. Birds like Whitethroat and Willow Warbler nest in bushes. Bushes have insects associated with them.	Woodland trees emerge from the scrub. So far these only occupy a small part of the Hill where the topsoil is deeper on the lower slopes of the Hill.
Species include: Horseshoe vetch Autumn Ladies tresses Wild Marjoram Pyramidal Orchid Bird's foot Trefoil Kidney Vetch Squinancywort Restharrow Fairy Flax Quaking grass Sheep's Fescue Bastard Toadflax Skylark Common Lizard Chalk hill Blue and many more!	Species include: Upright Brome (about 80%) False oat Grass Cock's Foot Grass Ploughman's spikenard	Species include: Hawthorn Blackthorn Buckthorn Dogwood Spindle Bramble Clematis Privet Whitethroat	Species include: Hawthorn Elm Sycamore Ash Holly oak

Vegetation cover of Portsdown Hill past, present and potential

1900: Closely grazed grassland with many species of flower and insect

1990: The Hill's vegetation is dominated by coarse grass and scrub. Diverse species-rich grassland accounts less than 5% of the hill

2050: With no management the scrub will spreads. There may not be any grassland left.

2050: If grazing and other management continues, then about 50% of the hill will support short grass, while the rest will be a mix of scrub and coarse grass.

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