Low browsing susceptibility but diverse responses to simulated herbivory in an insular endemic plant

Insular plants that are currently little browsed by ungulates may face increased damage if herbivore pressure rises and alternative forage becomes scarce. Understanding their responses to tissue loss is therefore relevant even when browsing is rarely observed. We investigated current goat browsing and responses to simulated herbivory in Hypericum balearicum L., a shrub endemic to the Balearic Islands. We combined a field experiment, monitoring exposed and individually fenced plants at two sites biweekly for one year, with an ex situ clipping experiment involving three treatments: no clipping, 50% and 75% aboveground biomass removal. Three months after clipping, we assessed survival, flowering, biomass, leaf traits, physiological performance and leaf chemistry. In the field, no signs of goat browsing were observed during the year of monitoring. In the clipping experiment, plants resprouted, and survival did not differ significantly among treatments. However, final shoot and root biomass were lower than in controls, and flowering was markedly reduced, with no flowers recorded after severe clipping. Physiological responses included increased chlorophyll content and maximum photochemical efficiency of photosystem II, while mass-based net photosynthesis remained unchanged. Severe clipping also increased specific leaf area, electron transport rate and lipid peroxidation, and clipping altered foliar secondary metabolite composition. These findings show that the absence of observed browsing under current field conditions coexists with a capacity for vegetative recovery after tissue loss, but recovery was accompanied by reduced biomass and flowering over the study period. Although future goat consumption remains untested, our results indicate that substantial damage could impose growth and reproductive costs on this currently little-browsed endemic shrub.