Sussex Ouse
Flora & Fauna

The tidal Ouse above Hamsey - Picture by Mark Davis SOCS.

The beautiful Sussex Ouse above Hamsey

Lush vegetation along the River Uck, Uckfield.

River habitat, the Uck downstream from Uckfield

Habitat

Sussex is still one of the richest counties for wildlife. It boasts the highest percentage of ancient woodland cover in England and the Ashdown Forest is one of the largest remaining areas of lowland heath land in Britain. Another feature of the Sussex landscape are the rivers that flow from sources in the Weald, through the county to reach the English Channel. The Ouse is the second largest of the Sussex rivers with a length of approximately 62km, other principal rivers in the county are the Rother, Cuckmere, Adur and Arun.

Rivers are very important for wildlife as they provide a broad range of habitats, not only in the water, but also in the surrounding countryside with its varying land use from source to sea. They also provide a corridor for migration or dispersion.

In this section of the website we will describe the various types of habitat provided by the Sussex Ouse and by using photos, we will show what you are likely to see along the river. For each creature or plant featured we have provided some interesting facts and a description to help with identification. We plan to constantly update this section using photos that we have taken along the river and surrounding environment, as we take new pictures, a greater range of flora and fauna will be included.

Rivers and streams that form the Sussex Ouse

The river and stream habitats of the Sussex Ouse consist not only of the water course itself – the "wetted channel", but also the bank and associated land or “riparian zone", including wet woodland which is another habitat closely associated with waterways. Rivers and streams are flowing watercourses and in their natural state are dynamic systems, continually modifying their form. Confined by geomorphology, numerous small streams, or tributaries like the River Uck, Shortbridge, Bevern and Longford Streams, combine to form the larger main river, which flows from upland to lowland. The dynamic ecosystem of the river supports a diverse flora and fauna.

Habitat types found along the Sussex Ouse

Headwater of the River Uck at Hadlow Down.

Coarse sediment of a High Weald headstream

Headwater streams, those within 2km of their source, tend to have steep gradients and form riffle and pool systems, they tend to be relatively fast flowing and have coarse sediments. These streams rise on the South Downs or High Weald, they are often in valleys and have a variable strip of adjacent scrub or woodland. Many of the invertebrates living within these watercourses are adapted to this type of channel.

Further from the source, the River Ouse and its tributary streams widen, the sediments become finer, valleys broaden and adjacent land tends to support grassland that is often used for pasture. Other habitat types are often present as small fragments along the bank of the river. A wide range of plant and animal species are associated with this type of watercourse. Much of the habitat along the river is not natural however, it has been created by man re-engineering the watercourse for navigation, land drainage or flood defence.

River features and their importance for Wildlife

Migrant Hawker dragonfly - Photo by Mark Davis SOCS

Migrant Hawker dragonflies can be seen along the drainage ditches beside the lower Ouse at Southease

Many species that occur in watercourses are entirely dependent on the habitat for part or all of their life cycle and are unable to adapt to other environments.

Watercourses form important wildlife corridors, enabling dispersion and migration of species, the utilisation of fragmented areas of habitat by mobile species and the interconnection of fragmented populations.

The banks are an important part of the life of the river. They provide breeding sites for mammals and birds that feed in or near water, and a habitat for adult insects, such as dragonflies, emerging from the river. The basic composition of the bank may be layers of mud, shingle, sand or small rocks. The flowing water erodes the banks and can make them very unstable unless there is plenty of vegetation to hold them together. Trees, such as willow and alder, stabilize muddy and sandy banks with their network of roots. Reeds and grasses are also important stabilizers.

Bridges and tunnels along river and tributaries may provide roosting and breeding sites for bats and birds as well as an additional habitat for many other species. In towns like Uckfield and Lewes, urban rivers or streams and the surrounding riparian zone, where sensitively managed, are valuable habitats for many species. They are also a recreational and educational resource for the community.

Weir structures are a barrier to sea trout migration

Culverts, bridges, weirs and hard engineering of channels, as well as poor water quality and low flows, threatens the continuity of these important wildlife corridors. Weirs and impoundment present a real problem to sea trout migration, Hempstead Mill and Buxted Park on the River Uck are good examples. Water quality is significant to truly aquatic species, although river corridors may retain considerable value to wildlife even where water quality is severely impaired. In general, whilst having a lower wildlife value than most rural watercourses, urban rivers and streams form one of the few semi-natural habitats within the urban environment .

Associated Key Species

Mammals

Water Voles are making a comeback in certain parts of the catchment, they are known to be in the head waters of the Uck and mid reaches of the Ouse. Pipistrelle and Daubenton's Bats make use of the various structures along the river as roosts and feed on the rich insect life during the evening and night hours.

Birds

Kingfishers and Grey Wagtails are a fairly common sight along all parts of the river but other birds, such as Reed Bunting, Reed Warbler, Sedge Warbler, Little Egret and Redshank are confined to to the tidal reaches below Lewes. Cattle Egrets have also been known to visit the brooks near the estuary. Buzzards are now becoming well established in the area and can be frequently seen soaring overhead, especially near the South Downs at East Chiltington and also around Isfield. The river also supports a waterfowl population including Moorhens, Mallard Ducks and Mute Swans.

Trees

Probably the most common trees found along the river are Alder and Willow with good numbers of Ash, Oak and Field Maple. In the Isfield area there are a number of mature Black Poplars along the river bank with a small plantation at Sutton Hall on the river flood plain.

Plants and Flowers

Throughout the spring and summer months there is proliferation of flowers along the river banks. Of note are Purple Loosestrife, Marsh-Marigolds, Meadowsweet, Ramsons (wild garlic),Rred Campion, Hemp Agrimony, Water Mint, Water Forget-me-not and Water Violet, which is found on the brooks at Offham. The most common plant that is found everywhere in the catchment is Himalayan Balsam, growing to a height of over 2m and has attractive pink flowers (policeman's helmets). This is an invasive plant and a real problem, competing with native plants and causing over shading. In mid-summer it can be seen choking the channel of the River Uck below Uckfield.

Aquatic plants present in the river include Water Crowfoot, Water Starwort, Strap Weed and in the slower flowing sections, Yellow-lily.

Fish

In conservation terms, probably the most important fish associated with the river is the Sea trout. These migratory fish start entering the river in May and go on to spawn in the gravels of some of the accessible tributary streams during the winter months. Research indicates they have possibly the heaviest average weight of any English or Welsh river. They show exceptionally fast growth and differ in behaviour from stocks in other rivers. There is a good population of cyprinid fish in the main river and tributaries including Barbel, Bullheads and StoneLloach with Brook Lampreys found in the upper Uck and its tributaries. The river also supports wild Brown trout, with Grayling present in the upper reaches near Haywards Heath. Other migratory visitors to the river are Sea Lampreys and Twaite Shad. During the summer months large numbers of Grey Mullet accumulate in the lower tidal reaches from Newhaven, up as far as Hamsey.

Invasive Species

Like all rivers, the Sussex Ouse has its fair share of invaders or escapees. The list includes Himalayan Balsam, Japanese Knotweed, Pumpkinseed Sunfish, Rainbow trout and mink.

Sussex Ouse Flora & Fauna