Forest fragmentation reduces recruitment of large-seeded tree species in a semi-deciduous tropical forest of southern Mexico

Abstract

Abstract:This study tested whether the reduction in the number of large-bodied seed dispersers is correlated with shifts in the taxonomic and functional (e.g. dispersal mode and seed size) traits of the seeding communities within small fragments of semi-deciduous forest, southern Mexico. In five fragments (2.3–640 ha) and one continuous forest site we sampled tree and seedling species in 40 (20 × 20 m) and 120 (3 × 3 m) plots respectively, and recorded the incidence (presence/absence) of the disperser fauna (three common large-birds and >500-g mammals). Tree and seedling species were categorized according to dispersal mode, seed size and whether they originated from local (i.e. from dropped) or immigrant (i.e. from actively dispersed) seeds. Fragment size negatively correlated with number of species of medium to large vertebrate seed-dispersers and number of seedlings of large-seeded species, but had no influence on functional traits of the adult-tree community. Between 41% and 61% of all seedlings were considered as immigrants and the proportion of immigrant seedlings of large-seeded tree species was negatively correlated with forest size. The results suggest that biased defaunation in small forest fragments may seriously reduce recruitment of large-seeded tree species (>1.4 cm length) dispersed by vertebrates, negatively affecting successional trajectories of small forest fragments.

Habitat fragmentation and the future structure of tree assemblages in a fragmented Atlantic forest landscape

“…Pütz et al 2011;Tabarelli et al 2008), (4) some native pioneer species are proliferating at multiple spatial scales , particularly Byrsonima sericea, Bowdichia virgilioides, Cupania oblongifolia and Cupania racemosa. Although it has been shown that tree assemblages in small forest fragments are predominantly comprised of small-seeded species (Melo et al 2010;Santo-Silva et al 2013;Santos et al 2008), our results suggest that production of large numbers of small seeds in itself does not necessarily confer the ability to proliferate in small fragments.…”

“…In particular, mechanistic explanations on nonrandom compositional drift are likely related to reduced dispersal movement of large seeds at multiple spatial scales (Cramer et al 2007;Melo et al 2006;Melo et al 2010;Peres and Palacios 2007;Silva and Tabarelli 2000), persistently low seedling recruitment of shade-tolerant old-growth tree species (Santo-Silva et al 2013), increased mortality of large trees due to uprooting and physiological stress (Laurance et al 2000), and hyperproliferation of light-demanding species facilitated by high propagule pressure and increased light availability . These mechanisms are likely to account for the prevalence of canopy, rather than emergent, hardwooded pioneer tree species among the ten top-ranking SF/MF ratios, such as those from the genus Cupania.…”

“…Therefore, human-modified landscapes have attracted increasing interests from conservation biologists, particularly as complementary landscape elements such as biodiversity corridors or biodiversity-friendly matrices . In this context, recent research efforts have identified: (1) several ecological or functional groups sensitive to human disturbances, most of which referred to as forest-dependent species (Girão et al 2007;Lopes et al 2009;Melo et al 2010;Santos et al 2008;Tabarelli et al 2010a), (2) the presence of altered but rather impoverished communities in taxonomic, ecological and phylogenetic terms along edge-affected habitats (SantoSilva et al 2013;Santos et al 2010;Santos et al 2008), (3) landscape and patch metrics correlated with species abundance and patterns of community structure such as habitat connectivity, forest cover and core forest to forest edge ratio (XXX). Population declines, species extinctions, shifts in community structure, and collapse in forest structure proceed rapidly as soon as forest edges are created.…”

Chuva de sementes em remanescentes florestais de Campo Verde, MT

“…Resultados similares foram obtidos por Stefanello et al (2009) em trecho de vegetação ciliar (Floresta Estacional Semidecidual), no meio e na foz do rio Pindaíba, em Mato Grosso, onde 85,7 e 77,5% das espécies desses ambientes não utilizam o vento como forma de propagação (zoocórica). Altas proporções de espécies zoocóricas presentes na chuva de sementes são indícios de ambientes conservados (TABARELLI;PERES, 2002;MELO et al, 2010;URIARTE et al, 2011).…”

Trilhas e seu papel ecológico: o que temos aprendido e quais as perspectivas para a restauração de ecossistemas?

“…Quando as plantas não conseguem se adaptar às novas condições, há uma alteração na diversidade e composição de espécies (Harper et al 2005, Pütz et al 2011, Tabarelli et al 2012, cuja dimensão irá depender do grau e amplitude do impacto sofrido (Hamberg et al 2009. Estudos feitos por Dupuy & Chazdon (2008), Melo et al (2010) e Dybizinsk & Tilman (2012) demonstraram como essas novas condições ambientais são capazes de interferir no recrutamento de plântulas, propiciando que espécies que antes não ocorriam no local que sofreu impacto, ou eram encontradas em baixas densidades, sejam capazes de ali se estabelecer.…”