Biosphere, Soils and Ecosystems: Biodiversity and Conservation in Island Environments
Domain 8 links soil formation to vegetation zones and island biogeography, then to conservation. The exam's favourite angle is why the Canaries concentrate so much endemism, what threatens it, and how protected areas and legislation respond.
Soil formation
Soil = mineral matter + organic matter + air + water + organisms, developed by weathering under climate, relief, organisms and time. Horizons: O, A (humus), B (illuviation), C (weathered parent rock), R (bedrock). Canarian soils: andisols on volcanic ash (allophane, very fertile, high water retention), aridisols and calcisols in arid lowlands, entisols on recent lava and jable, leptosols on steep slopes. Threats: erosion after fires, salinisation, terracing abandonment, sealing by urbanisation.
Ecosystems and vegetation belts
Coastal halophytes and tabaibal-cardonal (Euphorbia) in arid lowlands; thermophilous woodland (palms, junipers); monteverde laurel forest (Garajonay, UNESCO) in windward cloud belts; Canary pine forest (Pinus canariensis), fire-adapted with thick bark, above the laurel belt; high-mountain broom scrub above the tree line; afromontane-type relict species in inaccessible cliffs.
Island biogeography and endemism
Species–area relationship; colonisation and extinction balance (MacArthur & Wilson); isolation drives endemism and disharmonic biotas (many plants and birds, few large mammals). Examples of endemism: Pinus canariensis, Drago (Dracaena draco), Canary Islands chat, giant lizards. Threats: invasive alien species (rabo de gato, Pennisetum setaceum; picudo palm weevil), habitat fragmentation, wildfire, overgrazing, mass tourism and coastal development. Conservation: four national parks (Teide, Garajonay, Caldera de Taburiente, Timanfaya), Canary Islands Network of Protected Natural Areas, Natura 2000, Red List categories, LIFE projects and ex situ seed banks.
Worked example
Why does Garajonay hold laurel forest while nearby low ground is scrub? Reasoning: laurel forest needs high humidity, mild temperatures and rare frost; it occupies windward slopes within the trade-wind cloud belt where the inversion supplies fog drip. Lower ground is warmer and drier with high evaporation; higher ground lies above the inversion and suffers frost. So the forest is a narrow altitudinal and windward belt - an island relict of the Tertiary laurisilva, now dependent on cloud, making it vulnerable to changing wind and humidity patterns.
Traps that cost marks
Saying soil is simply 'ground rock'. Confusing endemism with abundance. Listing a park without stating what it protects. Ignoring that isolation cuts immigration as well as emigration.
- Monteverde needs fog drip from the trade-wind inversion.
- Andisols from volcanic ash are the most fertile Canarian soils.
- Invasive species are the top threat to island endemics after habitat loss.
- Four Canarian national parks: Teide, Garajonay, Caldera de Taburiente, Timanfaya.
- Species–area: larger, closer islands hold more species.