Seed caching by rodents favours seedling establishment of two palm species in a lowland Atlantic forest remnant

Scatter-hoarding by rodents is expected to benefit palm recruitment by allowing cached seeds to escape predation and to colonize new areas, but evidence that seedlings emerge from cached seeds is scarce. We aimed to assess to what extent seedling establishment of two palm species (Astrocaryum aculeatissimum and Attalea humilis) is favoured by seed caching by rodents in a large Atlantic Forest remnant. We mapped the location of conspecific seedlings within circular plots of 15-m radius around five adult individuals of each palm species, checking if seedlings established from dispersed (>2 m from parent palms) or non-dispersed seeds (0–2 m from parent palms), and from buried or unburied seeds. We found a total of 42 A. aculeatissimum seedlings and 16 A. humilis seedlings. Nearly all (98%) seedlings established from seeds dispersed away from parents (mainly located 10–15 m from parents), and 83% and 75% of seedlings of A. aculeatissimum and A. humilis, respectively, established from seeds buried in the soil. Results show that both palm species depend almost entirely on caching of seeds by rodents to establish seedlings. Our study suggests that checking for endocarps associated with established seedlings can accurately estimate the process behind seedling establishment, improving our understanding about the net outcome of seed caching for large-seeded palms.

Increased female reproduction favours the large-seeded palm Attalea humilis in small Atlantic Forest fragments

Palms are important components of tropical forest plant communities, due both to their abundance (Henderson et al. 2000) and to the network of interactions with their pollinators and dispersers (Henderson 2002, Zona & Henderson 1989). Forest fragmentation alters the biotic and abiotic conditions of habitats (Ewers & Didham 2006, Fahrig 2003) and it has been observed that Attalea palms increase their densities in disturbed sites (Aguiar & Tabarelli 2009, Andreazzi et al. 2012, Lorenzi et al. 2004). Increased light availability (Salm 2005, Souza & Martins 2004), changes in seed dispersal and predation patterns (Andreazzi et al. 2012, Pimentel & Tabarelli 2004, Wright et al. 2000), and ability to recover after disturbance (Souza & Martins 2004) are among the main mechanisms that have been proposed to explain enhanced palm densities. However, how altered conditions following disturbances influence the dynamics of flower and fruit production is still little understood.

Detecting ontogenetic stages of the palm Attalea humilis in fragments of the Brazilian Atlantic forest

A study of the ontogenetic stages of the acaulescent palm Attalea humilis Mart. ex. Spreng was conducted in three fragments (1.6, 6.4, and 9.9 ha) of the Atlantic forest in southeastern Brazil. The fragments were damaged by fire during the study period (1996-1999). External macromorphology and quantitative measures of leaf number and length of the newest leaf's rachis allowed the distinction of five ontogenetic stages. Seedlings were attached to buried fruit remains and presented entire leaves. Juveniles possessed incomplete segmentation of the blade. Pinnatifid-leafed, non-reproducing individuals were morphometrically divided in two groups: immature, with fewer leaves and smaller but highly variable youngest leaf length, and virginile, with more and larger leaves, but more constant youngest leaf length; the critical crown size by which immature and virginile stages could be identified varied according to fragment and year. Reproductive palms bore identifiable reproductive structures. Seedlings, juveniles, and immatures had fewer leaves than virginile and reproductive individuals. Leaf length was similar between seedlings and juveniles but increased in later stages. The characteristics of each stage were fairly constant throughout the study years in the three fragments and were little affected by fire, indicating that the stages we define in this study are important in the developmental program of A. humilis.Key words: stage-structured populations, ontogenetic stages, forest fragments, fire, leaf size, leaf number.