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The Congo Rainforest Without Elephants: An Uncertain Future

By Emma Silva

African Forest elephant walking through the dense Congo Rainforest. © The Elephant Listening Project

It is no small secret that the African forest elephant population is declining. Poaching and deforestation pose a major threat to the extinction of these gentle giants. In the last decade, over 60% of the forest elephant population was killed because of poaching, and the remaining population roams less than 25% of their historic range.¹¹ The potential extinction of African forest elephants is a scary enough prospect for conservationists to rally people against poaching. However, the extinction of African forest elephants could also change the Congo Rainforest as we know it.

African forest elephants are considered “keystone species” in African rainforests, meaning that their impact to a particular ecosystem is greater relative to their biomass.¹ ⁶ They play a critical role in maintaining the structure and function of Afrotropical forests. Researcher John Poulson and his colleagues hypothesize that the decline of African forest elephant populations will drastically change the composition of Afrotropical forests.⁹

Elephants are the largest fruit-eating animals on the planet and may consume a greater variety of plant species than any other animal in the world.³ Elephants are monogastric gut fermenters, so breaking down defensive plant toxins common in tropical forest plants proves difficult for these creatures. Consequently, elephants increase their food diversity to prevent ingesting too much of any specific toxin.³

Forest elephants play a key role in seed dispersal within Central African forests. Elephants travel much farther distances before depositing seeds in comparison to any other dispersing agent.¹⁰ One study tracked 4 GPS-collared elephants through the Congo Rainforest, focusing on the distance of seed dispersal from ingestion to defecation. 88% of the seeds were dispersed over 1 kilometer away from where the seed originated, and some seeds travelled as far as 53 km before being dispersed.¹

Seedling growing from elephant dung. © The Elephant Listening Project

In addition, many seeds benefit from being ingested and defecated by elephants. Elephants tend to disperse large seeds and fruits characterized by fibrous pulps and hard seed coverings, plants that would otherwise find difficulty dispersing on their own.⁶ As a result of high predation, some plants develop hard seed coatings to protect themselves. Unfortunately, it also makes it difficult for the seeds to germinate.³ However, when broken down by digestive enzymes of the elephants’ guts, the seed may be able to germinate.³ In general, studies show that most seeds that pass through elephants’ digestive tracts show a reduced germination time, better growing rates, and greater seedling survival because of the nutrient-rich environment provided by elephant dung⁸ and the digestion of the seed coating.

Balanites wilsoniana in Kenya. This tree relies on elephant dispersal for its survival. © The World Botanical Association

For some plants, such as the Balanites wilsoniana, elephant dispersal is essential for survival.⁴ Elephants are this canopy tree’s only effective dispersal, and germination increases by around 4000% when ingested by an elephant. Without the elephants’ role in dispersal, plants like the Balanites wilsoniana would cease to exist.

Group of Forest Elephants at a mineral lick. Credit: Richard Ruggiero/USFWS

In addition to seed dispersal, forest elephants play a critical role in nutrient recycling. Because of their high dietary diversity, elephants cycle a large variety of nutrients within the forest ecosystem, providing plants with the nutrients needed to survive.² African Forest elephants also excavate termite mounds and salt licks, distributing minerals that may have previously been unavailable.⁷

Trampling through the forest canopy may seem destructive to the tropical forest ecosystem, but such damage actually promotes plant diversity. Elephants often break off branches and tree limbs, thinning the canopy and allowing sunlight to reach the forest floor for smaller and younger plants to grow. Elephants also trample smaller plants when moving from place to place, opening patches of the forest floor, ready to receive newly dispersed seeds and reduce root competition. Reduced root competition allows trees to grow very tall, increasing carbon stores.⁹

Dr. Poulson believes that there would be catastrophic effects to African tropical forests if African Forest elephant populations continue to decline as they are.⁹ Without seed dispersal by elephants, plants with smaller seeds would be favored over plants with larger and tougher seeds. Similarly, without these creatures, there would a smaller availability of nutrients in the soil, decreasing plant growth. Without plant destruction, shade tolerant plants will be favored due to reduced light availability, increasing root competition and hindering tree growth, reducing carbon stores in the forest significantly.

Central African rainforests are under threat as forest elephants are poached and as they are relocated to smaller protected areas. If all of the elephant populations were to be continually sequestered into protective areas, Poulson hypothesizes that as much as 96% of Central African rainforests may experience a change in species composition.⁹ If things continue as they are, we can kiss the Congo Rainforest and the rest of Central African tropical forests goodbye. Poaching and deforestation must be stopped together in order to preserve these diverse and important forests.

References:

¹Blake, Stephen, Sharon Lynn Deem, Eric Mossimbo, Fiona Maisels, and Peter Walsh. “Forest elephants: tree planters of the Congo.” Biotropica 41, no. 4 (2009): 459–468.

²Blake, Stephen. “The ecology of forest elephant distribution and its implications for conservation.” PhD diss., University of Edinburgh, 2002.

³Campos-Arceiz, Ahimsa, and Steve Blake. “Megagardeners of the forest–the role of elephants in seed dispersal.” Acta Oecologica 37, no. 6 (2011): 542–553.

⁴Cochrane, Erica Paige. “The need to be eaten: Balanites wilsoniana with and without elephant seed-dispersal.” Journal of Tropical Ecology 19, no. 5 (2003): 579–589.

⁵Feer, François. “Morphology of fruits dispersed by African forest elephants.” African Journal of Ecology 33, no. 3 (1995): 279–284.

⁶“Keystone Species — Definition and Examples.” Biology Dictionary. December 26, 2017. Accessed March 19, 2019.

⁷Metsio Sienne, Julia, Rainer Buchwald, and George Wittemyer. “Plant mineral concentrations related to foraging preferences of western lowland gorilla in central African forest clearings.” American journal of primatology76, no. 12 (2014): 1115–1126.

⁸Nchanji, Anthony Chifu, and Andrew J. Plumptre. “Seed germination and early seedling establishment of some elephant-dispersed species in Banyang-Mbo Wildlife Sanctuary, south-western Cameroon.” Journal of Tropical Ecology 19, no. 3 (2003): 229–237.

⁹Poulsen, John R., Cooper Rosin, Amelia Meier, Emily Mills, Chase L. Nuñez, Sally E. Koerner, Emily Blanchard, Jennifer Callejas, Sarah Moore, and Mark Sowers. “Ecological consequences of forest elephant declines for Afrotropical forests.” Conservation biology 32, no. 3 (2018): 559–567.

¹⁰Sekar, Nitin, Chia-Lo Lee, and Raman Sukumar. “In the elephant’s seed shadow: the prospects of domestic bovids as replacement dispersers of three tropical Asian trees.” Ecology96, no. 8 (2015): 2093–2105.

¹¹“The Lesser-known Forest Elephant Is Crucial to Its Ecosystem.” African Wildlife Foundation. December 13, 2018. Accessed March 19, 2019.  “); background-size: 1px 1px; background-position: 0px calc(1em + 1px); background-repeat: repeat no-repeat”>https://www.awf.org/wildlife-conservation/forest-elephant.