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| North Pennines |
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| Habitat: Rivers and streams (of local significance) |
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Rivers and streams from bank top to bank top, including the open water area, fringing vegetation and exposed sediments.
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Running water is an important element of the region's habitat resource. Rivers and streams act as 'natural' wildlife corridors, and the mosaic of habitats associated with the river valleys producesome of the most picturesque landscapes in the Pennines. Many of the Natural Area's ancientsemi-natural woodlands flank the steep-sided tributaries of the Tees, Wear, Derwent, South Tyneand the Allens whilst herb-rich hay meadows and pastures lie within their floodplains. Riverbanks are often lined with alders, oaks, ash and the tea-leaved willow.
These upland lengths of rivers are relatively clean and unpolluted. They are usually fast-flowingover rocky substrates and have a high oxygen content, enabling a wide variety of animals tosurvive. Upper Teesdale National Nature Reserve, above High Force, provides a classic exampleof a clean upland river. The abundance of pollution-sensitive aquatic invertebrates such asmayflies and caddisflies found along this stretch of river corresponds to the presence of waterbirds such as grey wagtail and dipper. Dippers are very characteristic of clean upland rivers andcan often be seen 'bobbing' or 'dipping' on the rocks which constitute the river bed. Alternatively,they are often the birds glimpsed flying away at high speed just above the water's surface. Where insects abound, bats are usually not too far away; riverside habitats are important feeding grounds for these nocturnal mammals.
Generally, flowing waters in the uplands are not characterised by flowering plants. Instead, theirrocky beds are often carpeted with lower plants, commonly including the mosses Rhacomitrium aciculare, Rhynchostegium riparioides, Brachythecium rivulare, the long green ribbons of Fontinalis antipyretica and the liverwort Scapania undulata. The rare moss Schistidium agassizzii is frequent in the most current-scoured parts of the Tees below Cauldron Snout, usually growing well-submerged. Its only two other British localities are in Scotland. Knock Ore Gill, within the Moor House NNR, also supports a rich bryophyte flora and is characteristic of the becks in the eastern Cumbrian fells. The shingles along the river margins have their own specialised plant community, particularly in areas influenced by heavy metals (see section on Inland rock).
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