Growth and mortality patterns of the Neotropical bracken (Pteridium arachnoideum) and their response to shading in a savanna–riparian forest transition

Abstract

Although certain clonal species are often overdominant in disturbed tropical ecosystems, it is often unclear how this success is related to their patterns of clonal growth and how they respond to abiotic heterogeneity. Here we describe ramet growth and survival in an overdominant Neotropical bracken fern (Pteridium arachnoideum) and assess how these patterns resemble congeneric species and are affected by canopy closure in a savanna–riparian forest transition in southeastern Brazil. We measured frond length from early emergence to senescence during two consecutive years in three clonal patches dominated by P. arachnoideum and associated the resulting growth pattern with the local canopy closure. Pteridium arachnoideum exhibited average frond length and growth rate higher than previously reported for this species and for congeneric species. Frond mortality was generally high shortly after emergence from the ground, but was also much higher in one study site due to ant herbivory. Fronds of P. arachnoideum were higher, showed petiole elongation and higher mortality rate under high canopy closure, suggesting shading avoidance, in contrast to the shade tolerance reported for Pteridium aquilinum. Although our findings indicate that this species is unlikely to represent a threat to the biodiversity of undisturbed Brazilian savanna–riparian forest transitions with continuous canopy, they also suggest that introduction of fast growing tree species with dense canopy may accelerate the restoration of more disturbed and degraded sites.