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Habitats Wharfedale and its tributary valleys provide a wealth of differing habitats. The major rock types, the limestone and the Millstone Grit, develop soils which vary widely in their acidity. In addition, the glaciation has scoured some areas and deposited boulder clays in others. The limestone region has mostly thin, dry soils. They are rich in calcium and this also increases the breakdown-rate of organic materials, producing little humus. Such soils are therefore low in nutrients such as nitrogen and are home to some quite specialised plants. Ash woodland on these thin, rocky soils is a feature of the Dales in general and Wharfedale in particular. The exposed limestone weathers into 'clints' and 'grikes', fissured flattish areas which are home to many plants which are more often found in woodland and may, indeed, be remnants of lost woods. The screes and rocks, constantly weathering, provide niches for some specialised plants. They are safe havens from the sheep which otherwise graze away much of the flora. The Millstone Grit soils also are typically low in fertility. The shales erode to form heavy clays, with very low calcium content, and poorly drained. These soils often remain wet for extended periods and minerals are leached out. The sodden soils are ideal for sphagnum growth. Low oxygen levels mean that the organic material cannot decompose and there is a build up of acidic humus and, typically, peat, on the flat and gently-sloping plateaux. Glacial deposits cover extensive areas, including the valley bottoms. Here, they are associated with alluvial deposits which were laid down by the lakes which the glaciers and glacial deposits dammed. These can be very fertile but are of variable quality, depending on their origin. Human activity, both agricultural
and industrial, has developed particular habitats. The hay meadows
of the upper dale are one special example and the spoil heaps from
former lead mines are another. The plantations, which cover quite
extensive areas in some parts, are now regarded as unattractive
but the reservoirs can be important, for bird life rather than flora. |