River Edge and River Island Forest

River Edge and River Island Forest
Typical River Edge and River Island Forest showing multiple species of tall but skinny trees where cecropia trees of various ages are still a common member of this successional stage.

Definition: The river edge and river island forest is the successional stage type of forest that borders rivers and river islands in Amazonia. River Edge and River Island forests form a narrow band between the river bank and the more mature and diverse forest at higher grounds.

The width of this forest type is generally no more than 100 m wide alongside rivers courses but can encompass most of the area of a river-created island.

River edge and river island forest can be nearly as tall as the adjacent mature forest but is composed of tall and thin trees including Cecropia spp and fig trees (Moraceae), Ochroma pyramidale (Bombacaceae), Guazuma crinita (Sterculeacea), Sapium sp (Euphorbiaceae), Erythrina spp and various other tree species. The understory is thick as sunlight can penetrate the relatively sparse canopy. Characteristic understory plant species include Heliconia (Musaceae), Calathea (Marantanacea), and Renealmia (Zingiberaceae) among others.

sand bars - River Edge and River Island Forest
Sandbars are constantly being created and destroyed by Amazonian rivers. A sandbar marks the initiation of a succession that results in River Edge and River Island Forests.

How are River edge and River Island forests created?

This habitat type is a stage of multiple successional vegetative stages that start when Amazonian rivers form sandbars along river shores. Soon, several plants colonize the sandbars and become sorted into distinctive vegetation communities.

river created habitats
Three clear successional stages of a typical river edge habitat. The shorter stage is composed of grasses, followed by a midheight stage composed of mostly Tessaria spp.  The taller stage, which constitutes  River Edge and River Island Forest is largely composed of Cecropia spp trees.

Grasses occupy the outermost zone; the area nearest the water. Grasses are followed by Tessaria spp, a shrubby willow-like tree, Salix sp and canebrake Ginerium sp. The fast-growing Tessaria matures in three to four years and is rapidly invaded by taller Cecropia trees. In five to ten years, the Cecropia stands are is invaded multiple species specialized in colonizing this stage of the succession. So, proceeding from the beach at the lower end of the river bank toward the forest, each vegetation zone grows a little taller and lasts a little longer than the preceding one.

A similar photo of multiple successional stages as the photo shown above.  In this photo, the middle stage es dominated by canebrake of the genus Ginerium. The older and taller stage is not dominated by Cecropia spp trees.

If the river edges survive long enough, the figs become tall, and over time, other species of three begin to grow resulting in a more complex forest, which eventually reverts back to a forest type similar to the adjacent forest at higher grounds.

River edge forest can last for decades if the forest edges or the river island are not washed away again during changes in the dynamic of the river or after catastrophic floods.

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