The effects of management on vegetation trajectories during the early-stage restoration of previously arable land after hay transfer

Abstract

The restoration of floodplain grasslands has benefited from many studies of the underlying mechanisms. Among the operational tools that resulted, hay transfer is now used increasingly to alleviate the effects of limited seed dispersal and recruitment. To improve this method, we still need to understand how it can affect restoration trajectories, and particularly their direction and magnitude during the early stages of restoration. Based on concepts from the field of community ecology theory, we investigated the effects of early-stage management through grazing or mowing on restoration trajectories after soil harrowing and hay transfer. We established a randomized block design experiment and quantified several community-related metrics to formalize restoration trajectories for 3 years after hay transfer on a previously arable alluvial island in southwestern France. Whatever the management treatment, the species richness and evenness were significantly higher in hay-inoculated than in control plots. This effect was linked to the recruitment of species originating not only from the reference grassland through hay transfer, but also from the seed bank, a well-known effect of soil harrowing. Although generally oriented toward the reference grassland, the origin, direction, and magnitude of the trajectory of hay-inoculated plots all depended on the management applied. Sheep grazing applied at the same time as hay transfer enhanced the recruitment of reference species as from the first experimental year, because it controlled aboveground competition and maintained the window of opportunity open for a sufficiently longer period of time. Our findings show that the type of management applied simultaneously to hay transfer influences the origin of a grassland trajectory, while its direction and magnitude are dependent on the management applied in subsequent years. Grazing immediately after hay transfer may be appropriate to accelerate the recruitment of species from the reference grassland.

Keywords: community‐related metrics; ecological restoration; grazing; mowing; trajectory.

Figure 1

Mean (±SE) community structure integrity index (CSII) values in 2015 (white) and 2017 (gray) according to the five experimental treatments. C, control; DG, delayed grazing; IG, initial grazing; LM, late mowing; M, mowing. Different letters indicate significant differences between treatments

Figure 2

Nonmetric multidimensional scaling (NMDS) plot based on the Bray–Curtis dissimilarity of species composition between each experimental plot (40 plots × 5 treatments × 67 species); NMDS axis 1 is horizontal and NMDS axis 2 is vertical. Vegetation records are grouped according to year and management treatment. C, control; DG, delayed grazing; IG, initial grazing; LM, late mowing; M, mowing; 15: year 2015, 17: year 2017. Arrows represent vegetation dynamics between 2015 and 2017

Figure 3

Ternary plot of species groups represented in each treatment during the two monitoring years, 2015 (circles) and 2017 (triangles). Arrows represents the dynamic of each treatment between 2015 and 2017. C, control; DG, delayed grazing; IG, initial grazing; ISp, Initial species group; LM, late mowing; M, mowing; OSp, Other species group; RSp, Reference species group