Abstract
The increasing dominance of competitive plant species may reduce species richness of plant communities. Yet, species richness may depend on spatial scale and the alien versus native status of the dominant species. To explore the dominance effects of alien versus native species on species richness, we sampled semi-natural grasslands in southwestern Poland. We established 100 m2 squares at different grassland sites, and in two opposite corners we placed two series of five nested plots (0.001, 0.01, 0.1, 1 and 10 m2), in which we recorded all vascular plant species. Next, we selected squares with a strongly dominant plant in one corner (high-dominance series) and with no strong dominant in the opposite corner (low-dominance series). The number of species per plot and the slopes of the species–area curves fitted to each nested-plot series were used to assess whether the alien vs. native status of the dominant species influences species-richness pattern across scales. We found a significantly lower number of species in the high-dominance series than in the low-dominance series, regardless of the alien versus native status of the dominant species. The slopes of the species–area curves indicated that the rate of species accumulation with increasing area was faster in the high-dominance series than in the low-dominance series; however, this pattern did not depend on the alien vs. native status of the dominants. Our study confirms that increasing dominance is linked to a decline in species richness, but reveals that alien dominants do not have a stronger impact than native dominants.
Highlights
Semi-natural grasslands are important habitats for biodiversity conservation in European agricultural landscapes (Duelli and Obrist 2003; Tscharntke et al 2005; Bonari et al 2017)
We asked whether the decline in SR depends on the presence of a strong dominant species in the plant community
The observed significant difference in SR can be explained by interspecific competitive interactions which lead to the dominance of a few or just one species in the community (Tilman and Pacala 1993)
Summary
Semi-natural grasslands are important habitats for biodiversity conservation in European agricultural landscapes (Duelli and Obrist 2003; Tscharntke et al 2005; Bonari et al 2017). Examples of native European grassland plants that are becoming dominant with negative effects on SR include Brachypodium pinnatum in semi-dry grasslands (Bobbink et al 1987), Molinia caerulea in wet meadows (Lepš 2004), Calamagrostis villosa in acidic sub-alpine grasslands (Hejcman et al 2009) and Calamagrostis epigejos or Stipa pulcherrima in steppe grasslands (Házi et al 2011; Ruprecht et al 2016). It is not fully understood whether dominant alien plants species have a stronger impact on SR than dominant native plant species
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