Variation in the population structure between a natural and a human-modified forest for a pioneer tropical tree species not restricted to large gaps

Background

The study evaluates the distribution of Cyperus floribundus (a long-lived pioneer tree specie) individuals in the gaps and compared the plant density between a primary and an early successional forest to understand the pioneer plant distribution and niche preference under the variable environmental and biotic conditions generated by natural or anthropogenic disturbances.

Goals & Methods

The study was conducted in a permanent plot in a primary forest at Caetetus Ecological Station (CES), and in an early successional forest adjacent to the state reserve at Torrão de Ouro Farm, state of São Paulo, Southeast Brazil. This forest originally covered nearly the entire plateau in the state of São Paulo, and it is currently the most threatened forest in the State due to past fragmentation.

Conclusions & Takeaways

The results showed that population structure of C. floribundus, varied between areas with contrasting levels of human disturbance but not with the level of natural disturbance, showing no preference regarding gap size or gap age under natural forest conditions. The main ecological processes that determine the pioneer species distribution in natural and human-modified forests are responses to light associated with biotic interactions, seed dispersal, and colonization. C. floribundus shade tolerance capacity allows this specie to occupy a broad range of gap sized in the primary forest, but the unfavorable sites in the early successional forest for juvenile growth and herbivory competition may contribute to the high juvenile density in this forest. The intensive land use and posterior abandonment, created a large open are with possible barriers to plant establishment associated with a limited seed dispersal, decreasing the density of trees in the early successional forest. Furthermore, the distance from the source of seeds and barriers of seed dispersal influenced the density of juveniles in the primary forest.