Seed limitation of woody plants in Neotropical savannas

Abstract

The failure of seeds to arrive at all suitable sites (seed limitation) greatly affects plant distribution and abundance. In contrast to tropical forests, the degree of seed limitation in Neotropical savannas is unclear because empirical studies at the community level are scarce. We estimated seed limitation of 23 woody species from annual seed rain measurements along a tree density gradient in the savannas of Central Brazil. These savannas differ in tree density and canopy cover, from closed to open savannas, and are located along shallow topographic gradients. We also studied post-dispersal seed predation and removal of 17 representative woody species, and seed viability loss over time of 12 common woody species under dry-storage conditions. Annual seed rain was lower in open (410 seeds/m 2 ) than in closed savannas (773 seeds/m 2 ). Average seed limitation across woody species was higher than 80% along the tree density gradient. More than 60% of seeds of the studied woody species were predated or removed within 30-45 days in all savannah types. Seeds of most common woody species (66%) lost their viability in less than 12 months of dry storage. This study shows that Neotropical savannah woody plants are strongly seedlimited because of low and poor distribution of seeds among sites, post-dispersal seed removal, and short seed longevity. The high seed limitation of tree species in Neotropical savannas, particularly in open savannas, also may contribute to maintain their relatively low tree densities and help to explain the spatial variation of tree abundance along topographic gradients.

Crop size influences pre-dispersal seed predation in the Brazilian Cerrado

“…There is evidence that seed and dispersal limitation decrease the opportunities of recruitment of Xylopia and Erythroxylum to some extent (Christianini & Oliveira 2010;. However, the small amount of seeds lost to pre-dispersal predators does not seem to be enough to control the recruitment of these plants at the study site, with dispersal and establishment limitation playing a more important role (Christianini & Oliveira 2010; as well as for other species in Cerrado (Ferreira et al 2011;Salazar et al 2012).…”

“…Unless the regeneration of plants are seed limited (Ferreira et al 2011;Salazar et al 2012), pre-dispersal seed predators are unlikely to decrease substantially plant fitness by reducing the amount of seeds available for recruitment. There is evidence that seed and dispersal limitation decrease the opportunities of recruitment of Xylopia and Erythroxylum to some extent (Christianini & Oliveira 2010;.…”

“…Christianini & Oliveira 2010). However, the low availability of nutrients in soil probably constrains seed production, what decreases seed availability for dispersal and plant regeneration (Salazar et al 2012). Due to low nutrient availability increase in crop size is an unlikely plant strategy to satiate predators and decrease seed losses.…”

Semeadura direta de árvores do Cerrado : testando técnicas agroecológicas para o aperfeiçoamento do método

“…Apesar de ser significativo o aumento no crescimento nos tratamentos com cobertura de palhada, as diferenças entre os tratamentos não ultrapassam 6,1 cm em altura (Salazar et al, 2012b;Zida et al, 2007). Portanto, um procedimento de restauração que adiciona sementes e previne o fogo terá uma grande chance de sucesso para a restauração de savanas neotropicais.…”

“…Mesmo no ano sem fogo, a queimada anterior causa maior exposição das plântulas ao sol durante veranicos e durante a estação seca (Hoffmann, 1996). Na ausência do fogo, a sobrevivência de plântulas de árvores é alta , chegando a 80% para 16 41 espécies arbóreas em um ano (Salazar et al, 2012b). Quando sombreadas por copas de árvores (40-60% de sombreamento) a sobrevivência das plântulas nos primeiros oito meses é maior que com sombreamento intermediário (10-40%) e aberto (Salazar et al, 2012b).…”