Effect of soil and canopy factors on vegetation of Quercus robur woodland in the boreo-nemoral zone: A plant-trait based approach

The aim of the study was to determine the effect of soil and canopy on the understory vegetation of Quercus robur stands in Latvia, located in the boreo-nemoral zone. To determine the main processes regulating formation of the plant communities, the understory vegetation of Q. robur stands was described using plant traits. Vegetation and soils were described in 24 plots representing contrasting soil types and tree species composition. Redundancy analysis was used to determine the relation between vegetation, described using plant traits (proportion of species with each trait), and soil and canopy factors. About 50% of the variation in vegetation described by plant traits was explained by soil factors, which were collinear with canopy factors. Species characteristic of ancient forest were generally abundant. A smaller proportion of autochorous species, which have limited seed dispersal distances, occurred in secondary forest on previous agricultural land with higher soil pH in the upper soil horizon. A typical nemoral herb layer with greater proportion of ant-dispersed species and hemicryptophytes was associated with soils that had higher clay content. Forest management for conservation to maintain the nemoral aspect of deciduous woodland should focus on woodland that has developed on silty clay loam soils.