Today Portsdown Hill has a mosaic of vegetation types, ranging from fine species-rich chalk grassland, through tall grassland and scrub to woodland. Chalk downland species are characteristic of thin topsoils where vigorous plant growth is limited by the alkalinity of the soil, and lack of water and nutrients. Plants that are adapted to these conditions can grow close together. Nationally, up to forty species may grow in a square metre of short turf. Where the topsoil is thicker the more competitive "coarse" species take over, with much less variety.
The soil profile and thin nature of the topsoil show up well on the M27 (preferably from a passenger seat) where the motorway has been widened.
Although the short grassland contains more species than the other habitats, tall grass and scrub add to the site's overall diversity. Each habitat supports a range of associated species and many animals exploit different habitats during their life cycles. For instance the larvae of many beetles live in wood, but the adults forage for nectar and pollen in flower-rich grassland. Even specialist downland insects benefit from the shelter provided by taller vegetation.
Grazing also has a major effect. Ongoing removal of leaves by livestock is another sort of stress that the specialist downland plants are able to cope with but nutrient demanding plant species are not. Therefore, the proportion of each vegetation type changes with management as well as soil depth. Grazing livestock also remove nutrients as they graze, thus favouring the specialised downland species. Although animals return some nutrients back to the ground in the form of dung and urine, they incorporate most into their bodies. Dung can be seen as a form of modified compressed vegetation from which many nutrients have been extracted, and is an essential habitat for many uncommon insects, e.g. the Hornet Robberfly. Even so, it is useful to remove dung where possible since many areas of the hill are over-rich in nutrients.
We've attempted to divide the various habitats found on the hill into four types. Nature isn't very good at being pigeon-holed, and so there are really continuous transitions which change with time and management.
Short grass on thin topsoil has many species of plant
packed together. A great variety of insects feed on the flowers
and benefit from the sun-warmed ground.
Typical plants are Red Fescue, Sheep's Fescue, Horseshoe vetch, Autumn Ladies tresses, Wild Marjoram, Pyramidal Orchid, Quaking Grass and many others. Animals include Common Lizard, Skylark and Chalk-hill Blue butterfly.
Tall grass may have a dense layer of previous years' leaves forming a thatch that prevents the sun warming the ground. Small hawthorn bushes begin to invade. It supports far fewer species than short grass, consisting typically of Upright Brome, False Oat grass and Cock's foot grass. Included in this category and shown in the picture is the regrowth after scrub-clearance, with tall plants such as Hemp Agrimony, Wild Parsnip and Ploughman's Spikenard. Invertebrates such as Marbled White butterfly shelter in the tussocks while mice and voles have runs through the grass.
Scrub consists of tangled bushes of Hawthorn, Dogwood and Wild Privet with scrambling plants of Bramble and Dog Rose. Although scrub generally gets a bad press, many birds such as Whitethroat and Willow Warbler nest in it. The Great Green Bush Cricket can be found here. Pictured are bramble in flower and a rather small variety of apple, which has probably grown from a discarded core.
Here are pictures of all the berries you are likely to see on the hill.
Woodland trees emerge from the scrub. These can be found on the lower slopes of the hill where the topsoil is deeper. Holm Oak, Sycamore, Elm and Ash are most frequent, with occasional Common Oak and Turkey Oak. Holm Oak and Sycamore are regarded as undesirable because of their tendency to spread rapidly. Turkey Oak gets the thumbs-down because its not a native and acts as a host for the knopper gall on Common Oak. Ash can also get out-of-hand but is sufficiently rare at the moment to get careful attention. The picture shows us felling Holm Oak towards the fire rather than into other trees. It was used for fence posts, before its tendency to rot was realised. Now it is stacked up for firewood or as habitat piles.
The lists show species which have been found and photographed on the hill, the vast majority by Hilma Miles. Common names are used, and are generally listed in order of the main part of the name. For example, Common Knapweed will be found under K. Short notes are being added to the photos.
An aside on the use of capital letters.
The common names have been capitalised here, but this practice seems to have a considerable number of opponents. Flower books, some societies, e.g. BSBI, and some magazines, e.g. British Wildlife, use capitals. Others, such as Natural England and Plantlife, do not. The first word of the scientific name is always capitalised.
|Butterflies and moths
|Fungi, Galls, Spiders and
Grasses and sedges
|Flowering plants, Agrimony to
Flowering plants, Deadnettle to Medick
Flowering plants, Melilot to Scabious
Flowering plants, Selfheal to Yew
With financial support partly from the Friends, Bryan Pinchen has now carried out two surveys for insects.
In the latest survey he found the Nationally Scarce Conopid fly Leopoldius signatus, a late summer species typically found at Ivy. The bumblebee Bombus humilis has again been found, this is much rarer than the similar-looking Common Carder bumblebee, Bombus pascuorum. The 2015 report is here.
In 2014, Bryan carried out a survey of the Top Field and three compartments within the SSSI area. His report is here.
The Wildlife and Management pages make use of a lot of
material which was created by a regular volunteer, Hilma Miles.
She took hundreds, possibly thousands of photographs, and was
keen to help with the various daily tasks such as moving cattle
and scrub clearing. She died in her sleep while on holiday
trekking in the Himalayan foothills of Bhutan.
An obituary was published in the Southampton Daily Echo on 6th December 2008.