Fig. 1.1 plots world vegetation belts against annual precipitation and annual temperature. Tropical rainforest occupies the corner of the graph with annual temperature around 25 to 30 degrees Celsius and annual precipitation above 1000, while the grassland belts sit at a similar temperature but with precipitation only around 200 to 600. What does the graph therefore show separates tropical rainforest from tropical grassland?
ASoil depth, which the graph plots on its vertical axis as a proxy for the moisture each belt receives each year.
BLatitude, which the graph plots along its horizontal axis in degrees north and south of the equator, so that the belts read off directly as latitudinal zones from the tropics to the poles.
CAvailable moisture, since the two belts sit at broadly the same temperature and are separated along the precipitation axis instead.
DTemperature, since grassland on the graph occupies a distinctly colder band than tropical rainforest does.
Explanation
On Fig. 1.1 both belts lie in the warm part of the temperature axis, so temperature does not separate them. They are separated vertically, along the precipitation axis: rainforest needs high year round rainfall from constant ITCZ convergence, while grassland occupies the drier band where seasonal rainfall is too low to carry a closed tree canopy through the dry season.
Derived from ZIMSEC Advanced Level Geography 6037/1 Paper 1, June 2023 session, Q1