Much of this site was formerly notified as part of the Poole Harbour Marshes, Mudflats and Islands SSSI, to which it is now adjacent.
It also adjoins The Moors SSSI and Morden Bog SSSI. The majority of the site lies within the Dorset Heritage Coast and Area of Outstanding Natural Beauty.
Description and Reasons for Notification:
The site comprises the grazing meadows along the lower reaches of the Rivers Frome and Piddle adjoining Poole Harbour. The flood plains are underlain by river alluvium over peat and are strongly affected by groundwater. The interest of the site is closely linked to that of Poole Harbour, as it provides one of the few large areas of permanent grassland adjacent to the estuarine system and, as such, is of great value for wintering birds as a feeding site and a high water roost. The river valleys are also of importance for breeding birds throughout the summer. Some of the grassland is of considerable botanical value and even where the fields have undergone agricultural improvement this interest is retained within the rich ditch system. Other habitats represented within the site include a heathland slope and an area of semi-natural woodland. The site is also of interest for its invertebrate fauna.
The meadows are an important part of the wider Poole Harbour site in terms of the populations of wintering wildfowl and wader that visit this area both for feeding and roosting. Numbers of the various species are largely influenced by factors such as the tidal cycle, the degree of waterlogging or flooding and the severity of weather conditions. The most significant species is black-tailed godwit Limosa limosa, with flocks representing up to 5% of the British wintering population regularly present. Also frequently present in large numbers are lapwing Vanellus vanellus, dunlin Calidris alpina, redshank Tringa totanus, snipe Gallinago gallinago and curlew Numenius arquata; the area is also one of the main south-western sites for ruff Philomachus pugnax, although the number of birds wintering here over the last few years has declined in line with a national trend. Birds known to breed within the site include the nationally rare Cetti’s warbler Cettia cetti, water rail Rallus aquaticus and bearded tit Panurus biarmicus, the latter being found in areas of extensive reed swamp.
The meadows to the north of the River Piddle support frequently waterlogged and herb- rich grassland which is influenced both by slightly acidic ground water and lateral seepage as well as base-rich river water. There are many species of grass, rush and sedge present which reflect the range of soil moisture conditions. The wetter areas have frequent reed sweet-grass Glyceria maxima and greater pond-sedge Carex riparia with creeping bent Agrostis stolonifera and soft rush Juncus effusus abundant elsewhere. The occurrence of blunt-flowered rush Juncus subnodulosus and a tussocky form of common sedge Carex nigra reflect the influx of base-rich water over the area. Characteristic herb species of these fen-meadows include meadowsweet Filipendula ulmaria, ragged-robin Lychnis flos-cuculi, marsh-marigold Caltha palustris and greater bird’s-foot-trefoil Lotus pedunculatus, with several species infrequent or local within Dorset being present such as water avens Geum rivale, great burnet Sanguisorba officinalis and marsh valerian Valeriana dioica. The ditch system throughout the meadows retains a rich assemblage of marginal and aquatic vegetation, again with several species of restricted distribution including tubular water-dropwort Oenanthe fistulosa, lesser bulrush Typha angustifolia and the only known Dorset locality of the nationally rare cut-grass Leersia oryzoides. The ditch lines also provide a refuge for many of the meadow plants lost from the fields of otherwise improved grassland. Mousetail Myosurus minimus, a nationally scarce plant of disturbed ground, has also been recorded from this site.
Several areas have swamp vegetation which is largely dominated by either common reed Phragmites australis or lesser pond-sedge Carex acutiformis. An additional characteristic and unusual feature of this site is that with increasing distance from the river channel there is a gradual transition from swamp to bog communities, with an area of relic heathland on the adjoining slopes.
A further interest of the meadows is the invertebrate fauna that is largely associated with the ditch system and riverside banks. At least sixteen species of dragonfly and damselfly have been recorded from the area including the local ruddy darter Sympetrum sanguineum, and the nationally scarce long-winged conehead Conocephalus discolor is one of several species of grasshopper found within the site. Also known to occur are the spider Argiope bruennechi which is confined to the southern counties and the local scarlet tiger moth Callimorpha dominula.