Tropical forest is wetter and usually supports only knee-high fires that spread slowly through the understorey.

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The reverse would be true if protection from ultraviolet light were the answer, since the canopy is sunnier than the understorey.

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"Most of that reduction was in the smallest trees - such as the saplings and the smaller trees in the understorey, " Professor Enquist observed.

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If preventing fungal attack were the explanation, he argues, young red leaves ought to be more common in a forest's wet understorey, where fungi thrive, than in the drier canopy.

ECONOMIST: Young leaves, as well as old ones, are often coloured red

Odzala is characterized by a rich variety of habitats, including primary rain forest with a closed canopy (e.g. with Entandrophragma utile, E. candollei and E. cylindricum) and open understorey layer, forests dominated by dense formations of Marantaceae, forest clearings and savannas on the hilltops (e.g. with Hymenocardia acida, Annona arenaria or Hyparrhenia diplandra).

UNESCO: Biosphere Reserve Information