This thorn tree, Vachellia karroo, and others positioned like it will drown young or never start, if rivers maintain even water levels all year round.
Seasonal rainy cycles and quick flood run-off ensure that some bold saplings, unwittingly chancing their luck in a riverbed or near it, stand a chance. Life by the river can be adventurous or risky, interesting to those that check what copes here.
Equally interesting is seasonal stream vegetation of dry areas. In such places, like the Arabian world where dry streambeds are called wadis, plants may live where moisture is for years confined to deep sand or clay only. Climate and the vicissitudes of weather dictate the conditionality of plant and other life along watercourses, whether water is abundant or scarce.
Many inland streams and watercourses are adorned by trees adapted to river life; in karoid parts of South Africa often also this kind.
River islands may retain their vegetation for years, but start over after those memorable big rains when inhabitants all sorts are deposited downstream or in the sea.