Human Activity & Succession (AQA A Level Geography)

• The climatic climax community is attained, only if, natural conditions are stable and undisturbed - the UKs ancient woodlands is a good example of this
• However, there are times when an alternative community is formed:
  • Sub-climax - occurs when succession is interrupted through natural local factors
    • E.g. fire or the arrival of a new species
    • Vegetation is prevented from reaching its usual climatic climax and is held back at an earlier stage
  • Plagioclimax - occurs when human activity has permanently changed the final community of an ecosystem
    
    • Human activities have stopped natural succession in many areas of the UK
• Secondary succession - when an arresting factor is removed, (natural or human) the vegetation restarts/continues its progress 
• However, depending on the level of 'arrest', the final climax community may be changed permanently

Examples of Plagioclimax Communities

Activity	Impact	Change
Deforestation for timber, fuelwood or space for agriculture	Reduces soil quality, releases carbon into the atmosphere, reduced species and variety	Hardy shrubs such as heather
Farming - domesticated animals are kept for meat and other products and openly graze	Small plants and saplings are eaten or destroyed by trampling before being able to grow	Fast growing grasses, weeds and plants such as daisies and dandelions. Very few trees and shrubs
Clearance by fire - either for agricultural purposes or to control plant growth, can also be done to improve soil condition in areas	Ash is a fertiliser and can act as a soil improver, however, all plants are destroyed an only the fastest growing types of plants re-colonise the area	Heather, and fast growing hardy grasses and weeds
Afforestation - re-planting trees for commercial purposes such as timber, paper goods etc.	Some areas are cleared to make way for fast growing, non-native species. Only one species of tree is grown (monoculture) so this species dominates	Pines and managed plantations

Heaths and moorlands 

• Heaths - drier, mostly well-drained, lowland areas less than 250m in altitude
• Moorlands - wetter, upland areas greater than 250m in altitude, usually with a peat layer several metres thick
• Both habitats are manmade and examples of plagioclimax communities
• Heath and moorlands are areas of open country, devoid of trees and have a rich carpet of heather, that supports specialist wildlife and connects wooded habitats and grasslands
• Moor and heath lands have acidic soils and areas that are waterlogged and boggy, with heather and specialist plants such as sphagnum moss, the carnivorous Sundew plant, blanket bog and valley ferns
• Despite their natural appearance, heaths and moorlands are a managed ecosystem
• Burning and grazing maintains their biological, social and economic value

Heather

• Heather is a low growing, evergreen shrub, that thrives in acidic soil
• Their woody stems act as ground cover to reduce competition from other species
• They have adapted to grow in low-nutrient, acidic soils, by having fungi in their roots that help breakdown organic matter and minerals for absorption
• Heathers are found on both heath and moorlands and are managed through burning every 10-15 years, in small patches
  • Burning keeps a balance between the woody stem growth to edible evergreen leaves
  • Grazing also controls growth; although over grazing causes the heather to die rather than re-grow their leaves

North York Moors

• The North York Moors are the largest area of heather moorland in England, covering 1436 km2 of land
• Over 5000 years ago, the area was covered in deciduous oak woodland, on fertile, brown earth soil
• Heather was limited to small patches; and people hunted and gathered in the woodland
• Between 4000 to 2000 years ago, the growing population increased their demands for food, increasing need for more land
• As clearing rates continued, the ground was exposed to heavy upland rainfall, leading to heavy leaching and erosion
• The soil thinned and turned acidic, which restricted vegetation growth and allowed hardy acid loving plants - heather - to grow
• When sheep farming became a major form of agriculture on the moors 1000 years ago, the sheep trampled and ate young plants, shrubs and tree saplings before they could mature
• As heather is a fast growing plant, it was able to survive grazing and soon dominated the area

Controlled management

• Controlled burning keeps the heather in its most productive phase; a habitat for the red grouse and its partner - the game shooting industry
• The North York Moors are a national park and the area is carefully maintained for environmental and economic reasons
• The moors are an important habitat for rare plants
• They are a forage plant and staple food for deer, sheep and red grouse
• Without active management, the moors would revert to woodland, destroying the established community of plants and animals 
• Despite sheep grazing helping to maintain the moors, it does not prevent heather from becoming tough and 'woody' and eventually collapsing
• Controlled burning is the primary management technique, where  a few sections are burned each year in an 10-15 year cycle
• Burning encourages new, green shoots to grow; providing improved grazing for the sheep and grouse
• Burning ensures that the moors remain as a heather moorland ecosystem through supressing other less fire-resistant vegetation