Abstract
Dispersal is an important factor in plant community assembly, but assembly studies seldom include information on actual dispersal into communities, i.e. the local propagule pool. The aim of this study was to determine which factors influence plant community assembly by focusing on two phases of the assembly process: the dispersal phase and the establishment phase. At 12 study sites in grazed ex-arable fields in Sweden the local plant community was determined and in a 100-m radius around the centre of each site, the regional species pool was measured. The local seed bank and the seed rain was explored to estimate the local propagule pool. Trait-based models were then applied to investigate if species traits (height, seed mass, clonal abilities, specific leaf area and dispersal method) and regional abundance influenced which species from the regional species pool, dispersed to the local community (dispersal phase) and which established (establishment phase). Filtering of species during the dispersal phase indicates the effect of seed limitation while filtering during the establishment phase indicates microsite limitation. On average 36% of the regional species pool dispersed to the local sites and of those 78% did establish. Species with enhanced dispersal abilities, e.g. higher regional abundance, smaller seeds and dispersed by cattle, were more likely to disperse to the sites than other species. At half the sites, dispersal was influenced by species height. Species establishment was however mainly unlinked to the traits included in this study. This study underlines the importance of seed limitation in local plant community assembly. It also suggests that without information on species dispersal into a site, it is difficult to distinguish between the influence of dispersal and establishment abilities, and thus seed and microsite limitation, as both can be linked to the same trait.
Highlights
Dispersal into plant communities has been identified as one of the major factors influencing plant community assembly
For species in the regional species pool surrounding each site on average 36% (SE61.7%) were found in the local propagule pool and on average 78% (SE62.5%) of species in the local propagule pool were found in the local community
A majority of species in the local propagule pool were already a part of the local community at a site, whereas 12% came from the regional species pool surrounding each site and 11% came from further away (Fig. 1)
Summary
Dispersal into plant communities has been identified as one of the major factors influencing plant community assembly (i.e. seed limitation [1,2]). Null models investigate if a local plant community is a random or non-random sample from a regional species pool. These models often explore how species are assembled into communities based on functional traits i.e. measurable morphological, physiological and life history characteristics of the plant that influence plant fitness through their effect on reproduction, growth and survival [5,6]. If a trait related to species establishment or competition abilities exhibit a non-random distribution, this would indicate microsite limitation. Some traits, such as seed size, can be both linked to species dispersal [7] and establishment [8,9,10], complicating the distinction between seed and microsite limitation. This complication could be resolved by including measurements on species dispersal into communities in these models
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