Present-day global land cover and its change since the last ice age

What counts as 'land cover' and where it is

Land cover is the physical material on the Earth's surface — it is what is naturally there (or what has grown/formed there), as distinct from land use, which is the human purpose the land is put to. A single land cover (forest) can carry many land uses (timber, recreation, conservation). For Unit 3 AOS1 you need the present-day spatial distribution of these categories:

• Forest — concentrated in three belts: the equatorial tropics (Amazon, Congo, Southeast Asia), the temperate mid-latitudes, and the high-latitude boreal/taiga band across Canada and Russia.
• Grassland — the semi-arid mid-latitude interiors (African savanna, the Eurasian steppe, North American prairie, Australian rangelands).
• Tundra — the treeless high-latitude fringe of the Arctic and sub-Antarctic, underlain by permafrost.
• Bare lands — the hot subtropical deserts (Sahara, Arabian, Australian interior) at roughly 20–30° latitude where descending dry air dominates.
• Wetlands — scattered but globally significant (the Pantanal, Sundarbans, peatlands), high in biodiversity and carbon.
• Land covered by ice (Antarctica, Greenland, alpine glaciers) and land covered by water (lakes, rivers, reservoirs).

Use the concepts of distribution and spatial association to explain these patterns — land cover associates closely with latitude, climate and altitude.

Land cover at the Last Glacial Maximum and the Holocene Climatic Optimum

The exam expects you to compare distributions over time using two reference points:

• Last Glacial Maximum (LGM), ~20,000 years ago — the coldest, driest phase. Ice sheets covered far more land (the Laurentide sheet blanketed Canada and the northern USA; the Fennoscandian sheet covered northern Europe). With so much water locked in ice, sea levels were roughly 120 m lower, exposing land bridges (e.g. Sahul joining Australia and New Guinea). Forests contracted toward the equator and into refuges; grassland, tundra and bare land expanded.
• Holocene Climatic Optimum, ~8,000 years ago — a warm, moist phase a few thousand years after deglaciation. Ice had retreated to near present extents, forests expanded poleward to their maximum, the Sahara was a green 'savanna' with lakes (the 'African Humid Period'), and sea levels were close to today's.

The point to drive home: present-day cover is the product of long-term natural climate change, and the contrast LGM → Holocene → today shows land cover is dynamic, not fixed.