Functional diversity of algal communities from headwater grassland streams: How does it change following afforestation?

Pine afforestation of grassland streams may lead to changes in species traits and therefore functional diversity of epilithic algal community. Here, we studied trait-based responses in three grassland and three afforested streams in a mountain watershed of Córdoba, Argentina. We hypothesized that afforestation would reduce functional diversity through a simplification of periphyton architecture resulting from reduction in light availability, and that changes in hydrological periods would influence community responses. Algal samples were collected at each stream during two different hydrological periods (high flow and low flow), and physicochemical variables were recorded. Selected traits included strategies and morphological characters related to resource access and disturbance resistance (size, morphological guild, resource requirement, attachment mechanism and life-form). We calculated two indices of functional diversity: Rao’s quadratic entropy (FD Q ) and functional variance. Most trait categories showed a significant effect of one or both factors; 26 % discriminated between vegetation types, 26 % reflect the changes between hydrological periods, and 47 % were sensitive to both of them. Our results revealed some categories of traits that can be used to distinguish changes in riparian vegetation, such as unicellular life-form and high-profile guild. Functional diversity of single traits was affected differently by pine afforestation. However, the most integrative index, the FD Q mean, partially supported our hypotheses. Afforestation reduced FD Q mean by 50 %, but only during low-flow period. FD Q mean was high and similar between streams at high flow, when environmental factors, such as discharge and temperature, could prevail on differences in riparian vegetation.