Calderdale has two distinct natural areas, the South Pennines and Coal Measures, with their own characteristic species. This provides a mix of habitats, which is home to an estimated 8,000 species occurring on land and in freshwater, an estimate based on a data from a study in Rotherham District. During the 20th century we have lost over 100 species, including 4 mammals, according to records held by the Halifax Scientific Society. Many of the remaining species have suffered marked declines and it is important that we take action urgently to reverse these trends.
It should also be remembered that along with the changing face of the district, there have been similar changes in the flora and fauna. Some of these changes can reflect natural changes to habitats, but many are undoubtedly due to factors related to human actions. However, particularly in the urban context, many of the new arrivals, often termed ‘aliens’, can make a valuable and colourful contribution to the local biodiversity, as can be readily seen in the urban floras found at many urban waste ground sites.
A long tradition of natural history recording, dating back to 1874, has culminated in a number of important publications, including the West Yorkshire Plant Atlas (1994) and the Birds in Calderdale 1900-2000 (2001). In addition, the reports published by organisations such as the Yorkshire Naturalist Union, Halifax Birdwatchers Club and the Halifax Scientific Society provide regular updates and summaries of records. Amateur and professional naturalists constantly update the biological records. Through their reports and newsletters a picture of the changes taking place within the area can be built up. The Yorkshire Naturalist Union also issues ‘The Naturalist’ quarterly with ‘The Bulletin’ half yearly. West Yorkshire Ecology holds many of these and other records, and others are held within the Countryside and Forestry’s Unit Recorder Database. Halifax Scientific Society also has partly computerised records.
Table 1 presents summary totals of the biological resource in Calderdale derived from records held by Halifax Scientific Society. Although we have a high level of knowledge for some groups, notably birds and vascular plants, for other groups (such as invertebrates and lower plants) the totals must be viewed as incomplete. Also the Priority Species criteria vary between groups so it is difficult to compare different groups.
|Table 1: Number of species (excluding viruses and bacteria) recorded in the District|
|Taxonomic Group||Species recorded||Priority Species||Extinct|
|Vertebrates Total||290||84||7 at least|
|Butterflies & Moths||628||15||No data|
|Arthropods||225||No data||No data|
|Other Invertebrates||271||26||5 at least|
|Invertebrates Total||1976||81||3 at least|
|Ferns & Club mosses||41||9||9|
|Vascular Plants & Grasses||952||32||36|
|Mosses and Liverworts||409||29||38|
|Algae||211||No data||No data|
|Plants Total||3142||79||93 at least|