Functional assembly of tropical montane tree islands in the Atlantic
forest is shaped by stress-tolerance, bamboo-invasion and facilitation
Abstract
Aims: Amidst the Campos the Altitude (Highland Grasslands) in the
Brazilian Atlantic Forest, woody communities grow either clustered in
tree islands or interspersed within the herbaceous matrix. The
functional ecology, diversity and biotic processes shaping these
communities are largely unstudied. We characterised the functional
assembly and diversity of these tropical montane woody communities and
investigated how those communities fit within the Grime’s CSR (C –
competitor, S – stress-tolerant, R – ruderal) scheme, what trade-offs
they exhibit and how traits and functional diversity vary in response to
bamboo invasion. Methods: We sampled five leaf traits and wood density
along transects covering the woody communities both inside tree islands
and outside (i.e. woody plants in the grasslands community) to
characterise the functional ecology of the community. We used
Kruskal-Wallis test, t-test and variation partitioning to determine
effects of inside vs outside the tree island and bamboo invasion on
traits, woody species diversity and functional diversity. Results: We
found a general SC/S strategy with drought-related functional
trade-offs. Woody plants in tree islands had more acquisitive traits,
whereas woody plants within the grasslands had more conservative traits.
Trait variation was mostly taxonomically driven, and species composition
varied between inside and outside tree islands. Leaf thickness, wood
density and foliar water uptake were unrelated to CSR-strategies,
suggesting independent trait dimensions and multiple drought-coping
strategies within the predominant S-strategy. Bamboo-invaded islands
showed lower Simpson diversity, lower functional dispersion, lower
foliar water uptake and greater leaf thickness than non-invaded tree
islands. Conclusions: The observed functional assembly in response to
bamboo and facilitation have implications for future forest expansion
and response of the communities to climate change. Further studies on
eco-physiological and establishment traits and the mechanisms behind
biotic interactions are needed to better understand the response of
these communities to future environmental changes.