Conservation Management on Portsdown Hill
Portsdown Hill overlooks to the south the populous city of Portsmouth and its associated harbours. To the north are vews over the Forest of Bere to the South Downs. It is a small but beautiful stretch of calcareous grassland much of which is designated a SSSI (Site of Special Scientific Interest).
It is a pocket of rich but now uncommon biodiversity, containing 1000's of species. The vegetation is well adapted to the free-draining, low-nutrient habitat that develops on chalk outcrops subjected to long term grazing. A great variety of plants, gives rise to an even greater variety of invertebrates. Many species of insect benefit from the warm south facing aspect of the hill.
However, about 95% of this habitat has been lost to development and agricultural improvement, so it is increasingly important to protect and maintain what is left.
Some claim that "nature knows best" and the site ought to be left with no interference and to allow the natural ecology to regenerate. Left unmanaged scrub would continue invade the grassland and the scrub would in turn be invaded by woodland. The habitat produced would not only exclude the chalk grassland species but would also render the site inaccessible. Furthermore, it supports fewer species and it is easily and quickly replaced elsewhere. Chalk grassland on the other hand take many decades to develop and has been on the site for many hundreds of years. There is a historical precedent for its retention. The wildlife associated with the scrub habitat, e.g. birds and bush crickets, can be retained in smaller scrub blocks to form a mosaic of grassland and bushes
The management is largely related to scrub-control and removal. Over the past half-century of neglect, scrub has encroached over the grassland. Ideally, scrub-control should be by grazing, but given the current status and the urgency, man-power and machinery is also required.
Scrub clearance
For many centuries, Portsdown was covered mainly in chalk grassland, with small pockets of scrub. Scrub was restrained by domestic grazing, which had doubtlessly been practised on Portsdown since at least the Middle Ages. However, in the 1950's domestic grazing finally stopped as farming methods changed and the rabbit population died out due to myxomatosis. Until the early 1990's the site was effectively abandoned. In those few decades, scrub cover increased from pockets covering around 5% to nearer 70%. The remaining grassland was dominated by coarse grass species and the flower rich turf occupied only 5%. The aim is to change the the proportions of grassland and scrub, to get around 70% grassland and 30% scrub with other vegetation. Scrub provides habitats for plenty of wildlife, and it is not a bad thing in itself - but in moderation.
Since 1994 a concerted effort has been made to bring the scrub under control and restore the grassland to its previous extent. An enthusiastic team of volunteers, using mainly hand-tools, has been clearing it ever since. The scrub clearance has been aimed at connecting patches of grassland across the hill, and at preventing scrub encroachment onto particularly species-rich grassland.
Unfortunately, the use of hand-tools barely keeps the 'status quo': as more areas are cleared, previously-cleared areas become overgrown again. Initially a lack of funding, too few paid staff, and the impracticalities of all-year grazing on public-access area on the 'urban fringe' made it difficult to stay in front. The assistance of funding from Defra and the MoD has helped enormously and with a combination of winter grazing, machinery and volunteer effort, real progress is now being made.
Images of scrub clearance by volunteers using hand-tools can be seen within the Scrub Clearance page, while the Management Plan has a section about scrub and its clearance.
Grazing
In post glacial times, from 8,500 years ago Britain would have been grazed by the now-extinct aurochs, tarpan, deer, hare and other wild grazers. To what extent these herbivores would kept have the woodland at bay is a matter of conjecture. It is clear that Neolithic settlers (5,000 years ago) would have preferentially cleared trees on sites such as Portsdown Hill and introduced agriculture, including grazing livestock. Subsequent cultures would have continued this process to produce the extensive grassland found in the middle ages. So from at least the Middle Ages until the mid-1950's, domesticated sheep and other livestock kept the hill open, either 'in situ' or en route to Portsmouth, from where wool and meat has been exported for centuries. Many local people still remember Portsdown as an open, grassy area, with some pockets of scrub.
Since the middle of 1990s, 'conservation grazing' on the site over most winters has been introduced and increased in extent. Cattle have been borrowed from both conservation herds and local farmers, along with ponies and goats. This grazing largely occurs the winter, although it is now extending into the growing season.
The Portsdown SSSI is divided into 11 'compartments', from its west-most extent at Porchester Common along to the area bounded by the A3 to the east.
Annually, for ten years, an extra compartment has been fenced to allow grazing in another compartment.
A history of grazing can be read on the Grazing page, while the Management Plan has an extensive section about the advantages and disadvantages of grazing.
Fencing
To enable grazing, the site has been compartmentalised by fences. To this end, around 12 km of fence line has been erected since 1995, along with numerous water troughs and holding pens. Over forty access features such as field gates, kissing gates, stiles and squeeze points have been fitted.
Fence posts and other timber for the construction of estate furniture often comes from softwood plantations. They are felled, shaped, and treated with preservatives and then transported a considerable distance.
On Portsdown, a different, more sustainable, approach has been tried. Holm-oak from the site is felled, shaped and used. This tree is an invasive, non-native nuisance species that has to be cleared anyway.
The whole process, with many photographs, is detailed on the Fencing page.
Machinery Usage
While cattle and volunteer labour are the central to sustainable management, the realistic restoration of extensive grassland requires some mechanical assistance.
Between July 2003 - April 2004, new machinery purchased with grants from both English Nature, and Onyx via the 'landfill tax' scheme. These has accelerated scrub-clearance:
a flail mounted on an all-terrain tractor can clear a great deal more scrub than volunteers armed with billhook and ,importantly, mow off the inevitable regrowth.
However, there is still plenty of manual work to be done. Trenches and other steep terrain are not accessible by machinery, or "we can get it down the slope, but not up again".
Furthermore, some close work is still best done with hand-tools and more discriminating workers.
Rare plants, nesting birds and dumped motor-bikes may be recognised by human workers, but not by the flail teeth, the convergence of which would cause severe damage to one or the other.