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Abstract:
Initial plant diversity might control subsequent community assembly processes and plant productivity. To
study these effects, we used a biodiversity experiment (Jena Experiment) with subplots of different sown
diversity that were never weeded and spontaneously colonized control plots of different size (3.5
×
3.5 m,
20
×
20 m) with and without mowing in an 8-year study. On non-sown bare plots without mowing, colonizer
accumulation depended on plot size resulting in a loss of diversity in large, undisturbed (unmown)
control plots after initial colonization. On sown plots that were mown, species richness converged to
high levels due to the accumulation of internal colonists (species belonging to the experimental pool of
sown species), while initially high species richness of external colonists (species not belonging to the
experimental pool) and residents (species sown on the plot) declined over time. The convergence of total
species richness at higher levels was paralleled by increased taxonomic (Simpson index, QSimp), phylogenetic
(QPhylo) and trait (FDQ) diversity, whereby FDQ was greatest on plots with low resident species
richness after several years. Rates of change in terms of species colonization and extinction decelerated
over time irrespective of resident species richness, mowing or plot size. While the contribution of residents
declined and that of colonists increased, community biomass production did not change over time.
The biomasses of residents and colonists were greatest at higher levels of species richness, partial QPhylo
and FDQ of the respective species group, but community biomass was consistently weakly related to
total species richness and diversity indices. Our study shows that in contrast to the period of succession,
“mature” plant communities resulting from natural assembly processes, favouring the coexistence of
multiple species and thus high biodiversity, do no longer show significant relationships between species
richness and variables related to ecosystem functioning such as primary productivity.
