Elephants are known to be ecosystem engineers that play a crucial role in creating and maintaining forest habitats by distributing nutrients, clearing the understory, recycling nutrients and browsing and dispersing seeds.
Ebony, which can reach a height of 25 meters, is listed as a vulnerable tree species in the International Union for Conservation of Nature Red List of Threatened Species due to its documented overuse in Cameroon. These slow-growing trees take about 50 years to mature and reproduce and require about 60 to 200 years to grow completely.
Elephants are known to consume these fruits, as fruit remnants are frequently discovered in the dung of these animals. The drop in elephant populations and its impact on seed dispersal distance is known as ‘megafaunal-syndrome’ — trees mainly depending on elephants for seed dispersal.
The researchers found that the decline in elephants caused both seed dispersal and small sapling recruitment potential. They found that a decline in the diametre at breast height of less than 10 centimetres, where elephants were rampantly hunted. These areas remained consistent with recorded elimination of elephants from the sites a few decades ago, considering the growth of ebony.
“We found evidence that elephants provide a nonredundant seed-dispersal service. Smaller dispersers, such as scatter-hoarding rodents and stomatochoric monkeys, did not contribute substantially to effective seed dispersal in the low-hunting forests and could not sustain species regeneration at levels achieved by elephants,” the authors of the report noted, adding their findings reveal ebony dispersal is primarily dependent on elephant.
The researchers found no evidence of hunting-resilient wildlife being substitute dispersers that could maintain ebony populations at levels similar to those supported by elephants, they noted.
The study said that a positive impact of elephant presence on the ebony tree was that the pulp digested from the seeds before they released dung increased survival and germination as the dung protected the seeds from its predators such as rodents.