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Abstract

In the southern part of Korup National Park, Cameroon, the mast fruiting tree Microberlinia bisulcata occurs as a codominant in groves of ectomycorrhizal Caesalpiniaceae within a mosaic of otherwise species-rich lowland rain forest. To estimate the amount of carbon and nutrients invested in reproduction during a mast fruiting event, and the consequential seed and seedling survival, three related field studies were made in 1995. These provided a complete seed and seedling budget for the cohort. Seed production was estimated by counting woody pods on the forest floor. Trees produced on average 26,000 (range 0-92,000) seeds/tree, with a dry mass of 16.6 kg/tree. Seeds were contained in woody pods of mass 307 kg/tree. Dry mass production of pods and seeds was 1034 kg ha −1 , equivalent to over half (55%) of annual leaf litterfall for this species, and contained 13% of the nitrogen and 21% of the phosphorus in annual leaf litterfall. Seed and young-seedling mortality was investigated with open quadrats and cages to exclude vertebrate predators, at two distances from the parent tree. The proportion of seeds on the forest floor which disappeared in the first 6 wk after dispersal was 84%, of which 26.5% was due to likely vertebrate removal, 36% to rotting, and 21.5% to other causes. Vertebrate predation was greater close to the stem than 5 m beyond the crown (41 vs 12% of seeds disappearing) where the seed shadow was less dense. Previous studies have demonstrated an association between mast years at Korup and high dry-season radiation before flowering, and have shown lower leaf-litterfall phosphorus concentrations following mast fruiting. The emerging hypothesis is that mast fruiting is primarily imposed by energy limitation for fruit production, but phosphorus supply and vertebrate predation are regulating factors. Recording the survival of naturally-regenerating M. bisulcata seedlings (6-wk stage) showed that 21% of seedlings survived to 31 mo. A simple three-stage recruitment model was constructed. Mortality rates were initially high and peaked again in each of the next two dry seasons, with smaller peaks in the two intervening wet seasons, these latter coinciding with annual troughs in radiation. The very poor recruitment of M. bisulcata trees in Korup, demonstrated in previous investigations, appears not to be due to a limitation in seed or young-seedling supply, but rather by factors operating at the established-seedling stage.

Intrinsic biotic factors and microsite conditions drive seedling survival in a species with masting reproduction

“…While it is hypothesized that masting could provide an evolutionary advantage through predator satiation and dispersal efficiency (Kelly & Sork, 2002), high seedling mortality is usually recorded shortly after germination, limiting recruitment (Abrams & Johnson, 2013;Green & Newbery, 2002). For both masting and nonmasting species, factors that determine recruitment can be complex, species-specific, and change along both temporal and spatial axes (Fricke, Tewksbury, & Rogers, 2014;Oshima et al, 2015;Zhu et al, 2018).…”

“…Another topographical site characteristic, aspect, has been shown to influence plant association (Badano, Cavieres, Molina-Montenegro, & Quiroz, 2005;Warren, 2008), but not adult tree survival or mortality (Wu, Franklin, Liu, & Lu, 2017). Recruitment following a masting event is commonly assessed as a percentage of seedlings that survive at a given point in time (for example, Frey et al, 2007;Green & Newbery, 2002). Studies that assess several predictors-both abiotic and biotic-to explain what is driving survival of a masting species along a temporal axis are rare (but see Cleavitt et al, 2014;Norghauer & Newbery, 2016;Oshima et al, 2015).…”

Indications of an Achaea sp. caterpillar outbreak disrupting fruiting of an ectomycorrhizal tropical tree in Central African rainforest

“…For every tree ≥ 10 cm DBH (diameter at breast height; these measured last in 2005; Newbery et al 2013), the crown edges were measured along six bearings (60° increments) to the nearest 0.5 m, aided by a right-angle prism. Then, four 1-m radius circular ground plots (each 3.14 m 2 in area) were set up midway along the tree crown extensions on the four cardinal bearings (N, E, S, W), this positioning preventing sampling pod valves possibly originating from a large neighbouring conspecific fruiter (an issue that arose in Green and Newbery 2002). In each plot, all found pod valves were counted (two valves = one pod), as well as their respective seed scars (Supplementary material 1).…”

Natural disturbances and masting: from mechanisms to fitness consequences

“…In subtropical South America, drought increased seed production of Araucaria angustifolia [39]. A study of masting in Microberlinia bisulcata in Cameroon rainforests showed a response of seed crops after drought [38]. Drought was shown to trigger mass reproduction of Shorea forests in Malaysia [49].…”