Managed grasslands play an important role in European landscapes. They are often characterized by a high productivity and a low variability of traits between species. Though the relationship between traits and productivity has been investigated by various field studies, insight is still lacking in understanding the role of species trait variability.

This study combines species-specific traits with grassland modelling to investigate how variability in grassland species influences grassland dynamics and functioning. Based on a field experiment in Central-Eastern Germany, we parameterized an individual-based grassland model. We analyzed simulations of grasslands with four grass species and compared results with observed vegetation attributes (e.g., productivity, species composition and vegetation height). In a next step, we systematically added and removed interspecific variability in traits regarding (a) photosynthetic capacity, (b) mortality, (c) plant geometry, and (d) seed establishment and investigated the effect on different grassland attributes such as leaf area index and gross primary productivity.

We found that grassland dynamics are markedly influenced by species-specific differences in traits. Annual productivity was mostly driven by traits describing a plant's photosynthetic capacity and plant geometry. Some grassland attributes (like leaf area index and gross primary productivity) showed to be more sensitive to variability in plant geometric traits and traits describing seed establishment. Simulations with similar species traits resulted in a more balanced species composition, underlining the role of trait variability for interspecific competition processes. However, we showed here that different trait categories affect different attributes and functions of grasslands.

We demonstrated in this study that individual-based models can help to gain a deeper understanding of the relative importance of plant traits on community dynamics and ecosystem functions of grasslands.