Poaching of African elephants for ivory led to collapse in slow growing ebony forests: Report

The rapid decline in African elephant populations led to a significent decrease of ebony forests, a study has found, highlighting the critical role the species plays in seed dispersal.

A study published in the journal Science Advances has revealed that the collapse in populations of African forest elephants (Loxodonta cyclotis) by 86 per cent during the past three decades reduced the seed dispersal and recruitment of new plants by 68 per cent in Cameroon forests in the Congo Basin of Africa.

These elephants were poached for ivory trade between 1995 and 2021. The poaching of ivory has reduced the elephant population in the reserve from 0.56 individuals per square kilometres in 1995 to 0.04 per square kilometres in both 2018 and 2021, the study said.

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.

The researchers also found rotting ebony fruits in places where elephant poopulations have been wiped out. The chances of survival and germination of these seeds were lower compared to dispersed seeds, according to their analysis.

Elephants enable dispersal of ebony seeds across long distances away from parent trees, thus reducing risks of inbreeding and increasing spatial genetic flow, the report also noted.

Without elephants, long-distance gene flow is lost, as the limited range of pollen dispersal cannot compensate for the drastically reduced seed dispersal, the researchers said. In the absence of spatial distribution, it will encounter shifting mutualistic and predatory interaction dynamics at each stage of its life cycle, potentially affecting ecological and evolutionary processes.

The results of the study indicated that African ebony is transitioning from an elephant-dominated long-distance dispersal system to shorter-distance dispersal patterns, the authors of the paper concluded. These trends may worsen as the few remaining elephant populations collapse, they warned.