It is for all the above reasons that human mangement of fens is essential for their survival. Wheeler and Shaw (1994) examined the relationship between species richness and soil fertility across a large number of fens, split into subsets of summer-managed and unmanaged vegetation, using linear regressions. The results suggest that; in unmanaged vegetation, species richness is negatively related to fertility. When vegetation is managed, the species-richness can be just as great in nutrient-rich sites as in nutrient-poor sites and that the number of rare fen species tends to be smaller in more fertile conditions, even when the vegetation is managed. For these reasons, management of nutrient rich systems can support high biodiversity, but few rare species and in low fertility systems, little or no management is needed to preserve high biodiversity.
However, some management is required and these human activities maintain the biodiversity of the fen. Species-richness of fen vegetation is related to above ground crop mass, which can be strongly influenced by management regimes. Summer managed fens in the UK have a greater number of rare species and overall species, than do unmanaged fens.
Fens are also managed to prevent seral development into fen woodland, which hosts fewer species than fen. Once fen develops into fen woodland it cannot be converted back and therefore its succession needs to be prevented.
Fen management by human activity generally involves grazing. Thomas et al (1981) showed that in the Ouse Washes, Cambridge, increased grazing was associated with an increase in botanical diversity. There is also evidence that grazed fens can be richer in birds than ungrazed fens. Two Loch Lomondside fens in Scotland demonstrate this. Crom Mhin, consists of more plant species and hosts more bird species then Aber bogs, with less plant and bird species.
The Norfolk Broadland forms the largest area of lowland fen in Britain, containing a large variety of plant species. Parts of the broadland fens are maintained by human cropping activities in the area, for the two main crops, reed and sedge, that are both used for thatching. Reed is mown in winter, usually every year, or every second year. Reed is deciduous so harvesting removes dead material. Sedge is mown every summer, usually on a 3-5 year rotation. Harvesting removes biomass during the growing season and has a big impact on the character of vegetation. Wheeler and Giller (1982) examined the relationship between vegetation mangement and species richness and crop mass in broadland.
It seems likely that in these fens human activity helps determine and maintain biodiversity, probably through its impact upon the above ground crop mass during the growing season, and the impact that this has upon the interception of light.
Moorland conservation and management is another example of how human activities are important in maintaining semi-natural ecosystem biodiversity. Moorlands have developed on acidic soils. Moorland habitats cover more than 1 ¼ million ha of upland Britain and support a range of bird species, including the red grouse and golden plover.
Moorlands were traditionally used for cattle grazing, but most now are grazed by sheep. They are mainly managed for grouse, as grouse shooting is currently worth about 21 million p a. Their abundance is affected by many factors, but principally the abundance of young Calluna vulgaris, its food source. Breeding density is strongly correlated with heather coverage. It is for this reason that management is essential, to maintain such species biodiversity. Rotational burning is used to maintain younger heather. Picozzi (1968) showed that the mean number of recently burned blocks of heather positively correlated the average number of grouse shot per year.
Grassland management is essential to ensure its biodiversity is maintained. There are three main types of grassland in Britain, acidic, neutral and calcareous. Over the past century there has been a change in the character of permanent grassland through human activities, mainly farming. In 1939 98% of permanent grassland was ‘old’. By 1959, only 42% were ‘old’.
Limestone grassland is a focus of conservation interest because it is scarce, species rich and contains many rare species. The soils are infertile and much of this grassland has been lost recently due to nutrient enrichment through fertiliser application. Areas of calcareous grasslands have become fragmented and therefore require human activity through mangement to conserve them from further depletion. Wells (1971) reports the result of a 6-year experimental management trial:
Control: became over grown, lost some species and reduced performance of others.
Grazed: Persisted as original chalk grassland
Clipped: no species were lost, but proportions changed.
His experiments showed that management maintained the biodiversity of the grassland.
Species richness of much grassland is threatened by succession. The science and art of grassland management is to arrest/ and or harness the succession process in such a way that particular plant and animal assemblages are favoured.
Human activity has a positive effect on maintaining grasslands, by promoting their biodiversity.
Human activities can also have negative effects on the maintenance of semi-natural ecosystem biodiversity. Afforestation of moorlands leads to soil drainage, which undoubtedly dries the peatland surfaces. Once trees have established they continue to drain the moorland. Such drainage also affects rates of erosion and sediment transport, increasing both, having negative effects on the moorland.
Industrial pollution through human activity also plays an important role on the maintenance of semi-natural habitats and their biodiversity. The blanket bogs of the southern and central Pennines are highly impoverished in plant species. Much of the peat of these areas is formed by Sphagnum species, which is now absent from large areas of the surface. This loss of sphagnum is correlated with the appearance of much soot in the upper most peat profile and has been attributed to industrial pollution. Ferguson Lee and Bell (1978) found that the bog-building species of sphagnum were sensitive to high concentrations of bisulphite. They suggest that SO2 pollution is responsible for this loss of sphagnum. However sphagnum is still rare in the area even though SO2 pollution has greatly declined. This could be due to the increasing amounts of nitrogen pollution supplied via precipitation. Another possibility is that the peat bogs have been damaged through human activity via peat extraction and no longer possess an acrotelm with effective hydroregulation, making sphagnum re establishment difficult.
However, not all human urbanisation leads to negative effects on semi-natural ecosystems, as it has done in the case of pollution and afforestation. Many man-made industrial habitats have led to the increase or maintenance of habitats.
Industrial habitats provide relict habitats, replacement habitats, new habitats and migratory corridors. Industrial habitats sometimes form reservoirs of species that have disappeared from, or declined in, their natural habitats.
Chalk and limestone quarries provide replacement habitat for calciole species and can be very species rich. For example Barnack Hills and Holes, Cambridgeshire, a series of roman limestone workings provides on of the best examples of grassland on Jurassic limestone in eastern England.
Gravel pits provide important sites for birds, and a number of bird reserves. The Little Ringed Plover first bred in Britain in 1939, in reservoir margins, but has since colonised much of Southern England, using gravel pits as its main breeding habitat.
Disused canals, mainly constructed in the 18th and 19th centuries, are narrow and shallow, and rapidly undergo hydroseral colonisation, becoming important wetland habitats. Murphy and Eaton (1983) reported 67 macrophyte species in a survey of British Waterway Board canals. Some of the aquatic species are exotic and occur particularly where heated water discharges into canal from adjoining factories. Murphy and Eaton (1983) demonstrate a negative effect of traffic intensity on the biomass of submerged aquatics.
Reaches with the most traffic were most species poor. Species present in the intensive traffic were tolerant to physical damage. Boat traffic may also reduce the crop of aquatic plants by turbidity. However, insufficient traffic may lead to choking of the waterways and succession to less wet habitats. Modest traffic may therefore be the best in maintaining the aquatic plant populations of canals.
Human activity is important in maintaining semi-natural ecosystem biodiversity. Management practices prevent succession, increase species richness and promote rare species. Although human activities try to produce positive effects on biodiversity, negative effects are also produced through human activity resulting in pollution.
Many man made habitats however have led to an increase in biodiversity by creating new habitats and replacing lost old habitats.
Human activities are essential to conserve many endangered habitats.
