Special Feature: Functional Diversity
Shifts in functional traits and functional diversity between vegetation and seed bank
Does the seed bank have a different functional trait signature to the vegetation and is this difference affected by productivity and disturbance? Do functional diversity differences exist between the vegetation and seed bank and are the differences modulated by productivity and disturbance.
An area of diverse land use on the west coast of Scotland.
Parallel vegetation and seed bank surveys were carried out across 30 sites contrasting in land use, and hence productivity and disturbance regime. Data were analysed to assess overall differences between the seed bank and vegetation in community-weighted mean for selected functional traits and to test if the difference was affected by productivity or disturbance. Three functional diversity indices were calculated for each seed bank and vegetation sample – functional richness, functional divergence and functional evenness – and each index was assessed for overall differences between the seed bank, the vegetation and differences modulated by disturbance and productivity.
There were clear differences in many community-weighted mean traits between the seed bank and the vegetation. Plants in the vegetation were characterized by increased stature, more conservative leaf traits, wind pollination and by being perennial, whereas plants in the seed bank had higher seed longevity, higher seed masses and were more frequently insect- or self-pollinated. There was no difference in functional richness between the seed bank and the vegetation, and while both the seed bank and the vegetation functional richness were significantly lower than expected, the vegetation showed a bigger deviation from expectations compared to the seed bank. The functional diversity indices revealed different relationships between seed bank and vegetation against productivity and disturbance. Functional divergence (and its standardized effect size) indicated stronger habitat filtering for the vegetation at high levels of productivity or disturbance, while the effect size of functional richness and functional evenness suggested stronger filtering on the seed bank at high levels of productivity and disturbance.
The significant difference in traits between the seed bank and vegetation mean that following disturbance this is likely to have a considerable impact (at least in the short term) on ecosystem function. Functional diversity patterns were less clear, with conflicting evidence on habitat filtering, depending on the metric chosen.