Tree Islands in a Seasonal Inland Delta

Tree Islands in a Seasonal Inland Delta is an original illustration set in Seasonal Okavango Delta, Botswana. It lies in the tropics, where the climate is hot semi-arid steppe.

An aerial view shows dozens of oval islands rising from shallow seasonal floodwater, each edged by tall palms and broad-canopied trees around a drier pale center. Reed channels braid between flooded grass, several reddish termite mounds stand at island margins, and a narrow line of antelope crosses one exposed strip.

Why do rings of tall trees rise as islands from a flooded grassland?

Termite building and old channel sediments provide small initial rises above seasonal water, letting woody plants establish where roots can breathe. Trees then trap wind-blown dust and draw water upward; evaporation and mineral precipitation gradually raise and enlarge the island while salts accumulate toward its center. The concentric vegetation, pale interiors, termite mounds, and maze of shallow distributaries express a long feedback between organisms, groundwater, and sediment in the Okavango Delta.

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