Climate change alters slug abundance but not herbivory in a temperate grassland

moisture (CS-616 time domain reflectometers; Campbell Scientific, Logan, UT, U.S.A) at 5 cm below the soil surface were recorded in each plot at 15-minute intervals for the duration of the project. Heated plots were consistently maintained on average +2.8–3˚C (air and soil tempera- ture) compared to non-heated plots. Added precipitation plots were consistently wetter than non-irrigated plots by 3–15% volumetric water content with differences between treatments in soil moisture being greatest during the summer and autumn (Fig 1). The field was managed as a hayfield, and all plant material was harvested (6 cm above the soil surface) three times each year and removed offsite. Over the duration of this experiment, harvests occurred on October 5, 2011; May 21, July 30, October 8, 2012; and May 21, August 5, and October 14, 2013. Exclosure design To quantify the effects of slug herbivory on pasture productivity, areas of slug exclusion were constructed and paired with control structures that did not exclude slugs in each experimental plot. The exclosures were modeled after those described by Strauss et al. [36]. Strauss et al. used 50 cm wide rings made of 20.3 cm aluminum flashing, but rings of this size were too large for the established plots. To accommodate two rings in each of the 3 m diameter plots, the ring diameter was reduced to 37.5 cm. Height was proportionally reduced 25% to 15.2 cm to pre- vent over-shading. Slug exclosure rings were rimmed at the top with a 5 cm wide band of cop-

per tape as copper provides a repellant effect on slugs [37]. The control rings lacked the copper tape and had three 4×8 cm sections removed from the base to allow slug movement in and out of the ring. The rings were installed in the plots on August 5, 2011 (S1 Fig). The rings were fas- tened flush to the ground with several stakes made from bailing wire. There were two rings per plot (one exclosure and one control) for a total of 40 rings. The aboveground plant biomass was also harvested from within the rings during the tri-annual harvests of the field. Slug her- bivory was quantified as the difference in aboveground plant biomass between each set of Fig 1. Soil moisture (upper lines) and soil temperature (lower lines; both taken at 5 cm depth) in climate treatments during 2013, as well as ambient precipitation received at the site and amounts of added precipitation applied to the +precipitation treatments. https://doi.org/10.1371/journal.pone.0283128.g001 PLOS ONE Slug herbivory & climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0283128 March 14, 2023 4 / 17