Conservation of habitatsAQA A-Level Biology: Revision notes

Many valuable habitats, such as heathland, chalk grassland and meadows, exist at an early stage of succession. If they are left alone, succession continues and they are replaced by scrub and then woodland, which shades out the specialised species that depend on them.

Conservation of habitats therefore frequently involves management of succession: holding the community at an earlier stage. A community held in this way by human activity is called a plagioclimax.

The aim is to maintain biodiversity, protecting species that would otherwise be lost.

Management techniques are chosen to prevent succession or restore a habitat:

• Grazing by sheep, cattle or ponies removes tree seedlings and tall vegetation.
• Cutting or mowing, with the cuttings removed, prevents scrub growth and stops nutrients returning to the soil, so fast-growing species cannot dominate.
• Removing scrub and tree seedlings by hand.
• Controlled burning of heather to promote regrowth.
• Coppicing woodland to allow light to reach the ground flora.
• Re-wetting a drained habitat, for example blocking ditches on a bog, and replanting characteristic species.
• Restricting access (fencing, boardwalks) to prevent trampling, for example on sand dunes.

Humans use land and natural resources for food, fuel, housing, jobs and income. These needs often conflict with conservation, for example when a wetland is drained for farming, a bog is dug for peat or a woodland is cleared for building.

The key idea is sustainability: using natural resources so that they can be maintained for future generations. A resource is used sustainably only if the rate of use does not exceed the rate at which it is replaced. Peat, which forms at about 1 mm per year, is a clear example of a resource that cannot be used sustainably when extracted quickly.

The conflict must be managed by balancing the needs of people and wildlife.

Conflicts are managed through compromise that allows people to benefit without destroying the habitat:

• Zoning: allowing use in limited areas while protecting breeding sites.
• Licences and quotas on fishing or harvesting.
• Involving local people in decisions and providing alternative income, such as ecotourism.
• Using alternatives, for example peat-free compost.
• Restoring damaged habitats once use has ended.

Examples: grazing to keep heathland open; fencing and boardwalks to protect sand dunes from trampling; regulated sustainable fishing in a wetland.

You may be asked to evaluate evidence about a conservation issue where studies disagree. Consider:

• Source: is it independent, or does it have a financial or political interest (bias)?
• Sample size, duration and repeats: one summer or a small sample may not be representative.
• Comparisons: are there control areas or before-and-after data?
• Quantification: statements without numbers are weaker than measured values.
• Correlation or causation: other factors may explain the pattern.
• Scale and timescale: effects may extend beyond the site or take decades to appear.

Finish with a justified conclusion that weighs the evidence, and say what further data you would need.