May 27, 2012

Forests depend on large mammals

java_rhino_lr_credit_arkive.jpgElephants and rhinoceroses are needed to maintain tropical forests in SE Asia

“Megaherbivores are the ‘gardeners’ of humid tropical forests,” according to Ahimsa Campos-Arceiz, lead author of a recent study published recently in Biotropica journal.  “They are vital to forest regeneration and maintain its structure and biodiversity.”


Rainforests here are so dense, with little light reaching the forest floor, and diverse in plant species that there simply is not enough space for all tree seedlings to germinate and thrive.  There is also little wind down there to aid seed dispersal.  So seed dispersal is mainly left to animals that eat the pulp of fruits.  They then scatter seeds simply by dropping them, regurgitating some or through defecation, often somewhere further afield.

The bigger the seeds and seed pods, the larger the mammal required to eat and transport the seeds.  This suggests that the largest, most important trees in the forest need the largest of the mammals to disperse their seeds; hence, the importance of elephants and rhinoceroses in maintaining and reproducing the tropical forests of SE Asia.

“If these megaherbivores disappear from the ecosystem, their contribution to ecological processes will too be lost and the path of the ecosystem will change irreversibly,” explains Ahimsa Campos-Arceiz ; “the most probable consequences are the change in the structure of the undergrowth and the forest and the loss of certain species.”

Large herbivores are essential for scattered distribution.  Otherwise,  new large seed plants will always grow near to the mother plant and be unable to colonise often more suitable available space in other forest areas.

Conflict with man has been the downfall of large mammals.  Both elephants and rhinoceroses are hunted by determined well remunerated poachers.  But habitat loss has been a contributing factor as road networks expand, logging accelerates and settlements appear and grow fast.  Elephants are suffering a 95% loss of historical distribution range while rhinos are just a step away from extinction with less than 50 Java rhinos and only around 200 Sumatra rhinos surviving at the present time.  Protecting megafauna against hunting is an urgent necessity if the remaining forests are to be maintained.

Source: Science Daily


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