A post by CM SHAW
The open moorland on the tops of the hills in the Calderdale area were formed by a combination of environmental, biological and human factors, over the past 10,000 years. Humans have been present throughout this time and brought about extensive deforestation of the landscape, especially from about 4500 to 2000 years ago (Bronze Age and Iron Age).
The underlying rock in this area is millstone grit, which tends to have soils which are acidic and poorly draining. In geologically recent times, this land was covered with snow, ice and glaciers, until the end of the last Ice Age, about 10,000 years ago. Erosion led to the flattish summits we see today – with shallow lakes and waterlogged soil – with exposed rock formations. As the ice melted and receded, there would have been bare rock – a “clean slate” – with valley formation as the water drained away. The first ecosystem to develop would have been Tundra, with animals like reindeer and moose moving in from across the European land mass.
The climate would have been very cold, wet and windy, but warmed up slowly over the next 1000 years from an average temperature around -2.50 C to about as warm as now. (There were fluctuations and at times it was a bit warmer / cooler than now, and often wetter). The important thing is that it remained generally cool and wet – the climate required for peat formation (see later).
Between 8,500 and 7000 years ago, as the climate improved, trees and shrubs progressively colonized the valleys, lower slopes, and higher ground. Predominant trees were hazel, birch, pine (cold tolerant) and then more elm, alder and oak. Woods were patchy, with clearings and margins which shifted depending on climate changes, trees dying and regenerating. Animals included aurochs (large wild cattle), red deer (replacing moose and reindeer left from the ice age), wolves, bears, boars, beavers (important for tree felling effects). Whilst there were dense woods lower down (including oak, alder and elm), further up the hills, as the temperature was lower, trees were more sparse and there was more scrub than woodland, with species like hazel and birch dominating, together with shrubby plants like heather.
The margin between scrub and woodland was variable, and gaps would have opened up in the woods by natural means – beavers felling trees, large herbivores grazing and trampling vegetation, wind blowing down trees, fires due to lightening strikes … In patches without trees, more light getting in meant grasses and other plant species could flourish, increasing biodiversity.
Throughout this time, humans were present, migrating into the area from across Europe (England was connected to the continent by a land bridge until 7,800 years ago) and although the population was low (20,000 people in England about 5000 years ago) they begin to have an impact on the landscape and ecology. These people were hunter-gatherers, and took steps to expand the grassy clearings favoured by large herbivores like Aurochs in order to improve hunting opportunities. They used fire to clear scrub and increase grass cover, and felled trees by ring-barking. They also cut branches for fodder to attract prey. Concentrations of large herbivores would have further reduced regeneration of trees. As well as promoting open areas, the people “probably prevented woodlands advancing up slopes as far / as fast as the climate would have allowed” (Simmons 2003). Humans continued to use this land for hunting, although there is some evidence of them growing crops in the openings in the woods.
Once the flattish upland landscape had few trees, and little scrub, looking quite open as we would see it today, the land became more waterlogged, and boggy. There would have been a mixture of grassy patches with varying amounts of heather and bracken, shallow lakes and pools. Wetter conditions and poor drainage enabled invasion by sphagnum moss and cotton grass and the growth of blanket bog, and eventually, the specific conditions required for peat formation (see box).
Over the next centuries humans in England began to undertake agriculture – about 5000 years ago onwards – and in the uplands they began to grow cereals in the openings in the mosaic of mire, scrub, and woodland. However these areas were primarily still used for hunting.
Human impact on the uplands, and the expansion of the moors, really intensified from about 4000 to about 2000 years ago: the Bronze age (2500-800 BC) and Iron age (800 BC to 100 AD). There were far more people, and they greatly increased their efforts to de-forest upland areas primarily for food production. Some cereals were cultivated above 300m, but mainly woodlands were replaced with grasslands for grazing. Aurochs became extinct and red deer numbers declined; domesticated animals increased (cattle, sheep, goats, pigs). In addition, the climate was cooler and wetter and areas of blanket bog and peat formation expanded, especially above 400m. So during this time, the moors and peat bogs on the tops of the hills, probably became as extensive as they are today, whilst most of the slopes of the hills were still covered in woods, albeit with extensive clearings.
From the Roman era (2000 years ago) into medieval times (500 years ago), the main change was the development of agriculture, and deforestation of the rest of the uplands. Hill slopes became farmland as woodland was cleared and converted to fields for pasture, hay, and cereal production (especially oats). The few woods remaining were used for wood-pasture, firewood and construction, but trees only regenerated if livestock were excluded. The predominant system was ‘in-fields’ (most intensively cultivated) nearest the farm buildings, ‘out-fields’, and common grazing on the open moors in summer (transhumance). Cattle were the main livestock grazed on the moors in the central / south Pennines. Moorland species included many grasses, heather, crowberry, gorse as well as sphagnum. Peat and gorse were used for fuel.
More recent changes from 1700 to the present day:
Through the 1700s and 1800s moorland was taken out of public ownership and into the ownership of individuals through a legal process known as ‘enclosure’. This resulted in open grasslands being portioned up into smaller sections, separated by dry stone walls. Land management practices also included drainage to bring about “improvement”, and burning to create more grasslands.
Beginning in the mid 1800s, sheep replaced cattle as the primary type of livestock farmed on the moors, and in more recent times numbers of sheep and intensity of grazing have increased due to the provision of farming subsidies.
From the 1840s onwards moorland also started to be managed for grouse shooting, for rich people arriving by train. This included burning to produce shorter heather to feed high density grouse populations (1860s onwards) and killing of birds of prey, and other predators of grouse by gamekeepers.
Industrial processes taking place in the moorland included:
- Quarrying for construction
- Limestone for lime
- Water – reservoirs for major towns (Halifax, Huddersfield)
- Textile industry, mills
- Canals and railways
The moorland has also been affected by erosion (particularly of peat) by acid rain, and more recently, by the consequences of climate change.
Simmons I.G. ‘The moorlands of England and Wales’. Edinburgh University Press 2003.