Influence of Post-Dispersal Seed Predation on Forest Regeneration in A West African Montane Landscape

The restoration of degraded landscapes has become one of our most valuable tools for conservation, however there are many factors which can restrict natural regeneration and impede active restoration attempts. The purpose of this study was to investigate how seed predation limits the establishment of forest tree species into fenced-off pasture protected from burning and grazing in Ngel Nyaki forest reserve, Mambilla Plateau. Removal rates of seeds from experimentally laid out seed piles varied among seed species, the habitat the pile was in, and the predator guild able to access the piles. Results indicate that these trends are driven by the ecology of the seed predator. Removal of seeds by vertebrates was highest in the core forest, while ant predation was constant across all habitats. Vertebrates removed the larger seeds (Entandrophragma angolense and Sterculia tragacantha) while ants preferred the smaller Celtis gomphophylla and Croton macrostachyus. Overall predation rates in grassland were lower than those in the forest, and the presence of remnant trees did not influence predation rates, a positive sign for regeneration and the survival of seeds dispersed into these areas. INTRODUCTION Post-dispersal seed predation is a major source of seed mortality in many tree species (Blate et al., 1998) and can be a major post-dispersal filter limiting seed survival (Myster, 2004). Predation rates in tropical systems are particularly high, often with over 60% removal in the first 30 days (Chapman et al., 2010; Salazar et al. 2012). However, predation levels are highly variable even within a system (Holl and Lulow, 1997), so general rules are hard to establish. Seed species, year, site, habitat, microhabitat, predator species, seed density, and season have all been found to influence predation rates (García et al., 2007; Pérez-Ramos and Marañón, 2008). While seed predation is an important process in forests, sustaining granivore populations and helping to maintain plant diversity (Hulme, 1998; Paine and Beck, 2007; Herrera and García, 2009) in regenerating systems, this balance is often disrupted, and seed predation can hinder regeneration. Seed predation affects recruitment of seedlings when a species is seed limited, i.e. when fewer seeds are dispersed to the area than would be able to germinate and survive (CalviñoCancela, 2007; Denham, 2008), a situation common in regenerating areas. Predation of seeds arriving into regenerating habitats may significantly hinder regeneration success. Moreover, any variation in predation rates among seed species (Barberá et al., 2006) can lead to the selective recruitment of some species (García et al., 2005), which may in turn affect the composition and population dynamics of regenerating areas (Holl and Lulow, 1997; Blate et al., 1998; Shen et al., 2008). In this study we investigated the influence of seed predators on passive restoration of submontane forest on the Mambilla Plateau, Taraba State. Large areas of overgrazed grassland adjacent to the forest edge have been fenced off to protect them from grazing and burning, natural forest regeneration is occurring through frugivore mediated seed dispersal. Small mammals, lizards and birds eat seeds from the ground, as do invertebrates including ants. Specifically, we looked at the effect of habitat type (core forest, edge, open grassland, under remnant trees), seed species and predator guild on the levels of seed predation to help answer the following questions:  Does seed predation vary between habitat types within the reserve area?  Does predation guild (vertebrate/invertebrate) have interactive effects with habitat type or seed species in the number of seeds removed?  What seed characteristics increase the likelihood of them being removed (predated)?  Are seeds below isolated trees in grassland subject to different levels of seed predation than those in the open grassland? Study site This study was undertaken in and around Ngel Nyaki forest, a 5.2km area of submontane forest on Mambilla Plateau, Taraba State. Three sites were selected in fenced grassland areas around the border of the forest (Fig. 1). Roselli et. al. Proceedings of 6 NSCB Biodiversity Conference; Uniuyo 2018 (273 278pp) 274 Figure 1: Map of Ngel Nyaki with approximate study sites marked. Adapted from Google Maps (2014).