Doom of the elephant-dependent trees in a Congo tropical forest

Abstract

In an evergreen lowland rain forest of the Cuvette Centrale, DR Congo, at the LuiKotale Max-Planck research site, forest elephants (Loxodonta cyclotis) are close to extinction. Between January 2009 and June 2011 we investigated the influence of elephant decline on sustainability of elephant-dispersed tree populations. For this, we explored how trees with the megafaunal syndrome reproduce without seed dispersal by elephants and how does this affect the demography and spatial distribution of these tree species. We studied alternative partners for functional replacement of the elephant. Overall, 18 tree species presenting the megafaunal syndrome were identified and studied. They represent 4.5% of the local tree diversity with a density of 28.2 ± 2.7 tree/ha. Seventy-eight percent (14/18) of these megafaunal-tree species are elephant-dependent and do not recruit enough young for self replacement, either under the parent or beneath other tree species. For 12 of these species populations, the first cohorts were absent in our plots. For species able to recruit, the spatial structures of the young generations are more clumped than adults while they are not different for control tree species. There is no alternative partner for seed dispersal for the majority of the megafaunal trees which are actually elephant dependent. We discuss the likely consequences of the loss of elephant dispersed tree species and propose alternatives for species survival to bridge the time until efficient conservation strategies take effect.