Abstract
Evaluation of long-term management regimes is important for guiding biodiversity conservation in salt marshes. However, such long-term experiments are sparse. Using a 46-year experiment in a salt marsh, we evaluated long-term effects of eight different management regimes (treatments; control, grazing, mowing, and their combinations) on the expansion of a late successional plant species (Elytrigia atherica), plant species richness and diversity, and community composition (species identities and dominance structure). Results show that E. atherica expanded strongly over time in the control treatment (without grazing or mowing) while plant species richness and diversity declined substantially. By contrast, E. atherica was greatly suppressed while plant species richness and diversity remained relatively unchanged in all other treatments except for the mowing, where species richness declined in the late season mowing treatment and plant diversity declined after 17 years in the both early and late season mowing treatment. Therefore, all management types except for the mowing were effective in conserving plant diversity. The trends for change in species identities reversed: change in species identities accumulated in the control treatment and exceeded that of other treatments 15 years after the start of the experiment. This suggests that results based on shorter-term (< 15 years) experiments may provide misleading conservation recommendations. Also, trends for change in dominance structure (taking abundance into account) were substantially different from those for species identities. Our results highlight the importance of long-term monitoring for guiding conservation management, and that monitoring should not only focus on the number of species but also community composition, to fully identify critical changes.
Highlights
Grazing and mowing are among the most widely used management tools for conserving biodiversity in terrestrial grasslands and salt marshes worldwide (Davidson et al 2017; Gedan et al 2009; Tälle et al 2016)
Using a 46-year experiment in a Wadden Sea salt marsh, we evaluated the long-term effects of different management regimes on the expansion of the dominant grass E. atherica, plant species richness and diversity
We evaluated these effects on community composition, given that the identities and abundance of the plant species can sometimes be as important as diversity in delivering ecosystem functioning and services (e.g. Winfree et al 2015)
Summary
Grazing and mowing are among the most widely used management tools for conserving biodiversity in terrestrial grasslands and salt marshes worldwide (Davidson et al 2017; Gedan et al 2009; Tälle et al 2016). Some studies show that grazing is better than mowing (Bakker 1985; De Cauwer and Reheul 2009; During and Willems 1984; Fritch et al 2011; Herbst et al 2013; Jacquemyn et al 2003), some show that mowing is better than grazing (Catorci et al 2014; Stammel et al 2003; Tälle et al 2015), while others show that both have similar effects Results from grasslands suggest the timing and frequency of mowing can modify the effects of mowing on plant diversity (Bakker et al 2002a; De Cauwer and Reheul 2009; Dee et al 2016). Studies, the long-term ones (decades long), from salt marshes comparing grazing, different timing and frequency of mowing, and their combinations on plant diversity are rare
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