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Six Simulations of Forest Diversity

These JavaScript programs explore three hypotheses about the remarkable species diversity of trees in the canopy of forests. In the temperate zone many forests have 10 or more species of the tallest trees, and tropical forests can have 100 or more. This diversity seems to violate the ecological principle of competitive exclusion, which says that organisms competing for the same resources cannot permanently coexist in the same place.

The code accompanies the article "The Curious Diversity of Forest Trees" at http://bit-player.org/2020/the-curious-diversity-of-forest-trees. You can play with the running programs at that URL.

Code and text and illustrations Copyright 2020 by Brian Hayes.

The six directories:

fitness. A demonstration of competitive exclusion in action, with two species that differ in fitness, or adaptation to their environment.

coexist. Two species escape the rule of competitive exclusion because they compete for different resources.

ecodrift. Ten species are all exactly equal in fitness. Nevertheless, one species takes over the entire space and the others become extinct through random fluctuations.

immigration. Occasional immigrants from an external reserve can prevent the collapse of the ecodrift model, and even bring species back from (local) extinction.

socialdx. In this model trees of the same species avoid adjacent sites, because of the hazard of sharing pathogens. This has the effect of favoring rare species and allowing multispecies coexistence.

invasion. What happens when the social-distancing model is invaded by a species that doesn't need to do social distancing because it doesn't have pathogens?

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Simulations of forest diversity.

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