Herbivory baseline estimates in Spanish Protected Areas, and environmental implications.

Abstract

Context. There are no estimations of herbivory baselines in Spain. Due to the bioclimatic conditions, ungulates have maintained Open Ecosystems until the Holocene. Pastoral tradition later fulfilled the niche of wild grazers, but this role is not considered in environmental assessments of grazing livestock. Objectives. We attempted to better understand the scale of herbivory in Spain. We aimed to estimate the weight of current wild herbivory and evaluate the role of domestic herbivory in these baselines. We apply them to improve the allocation of environmental impacts and emissions from grazing livestock. Methods. We inferred equations relating Net Primary Productivity (NPP) with ungulate biomass and enteric CH4 with data from 11 Spanish Protected Areas. We applied the equations to the current grazable areas in Spain and we analysed the ecological conditions to get the herbivory baseline. We also estimated the proportion of grazing livestock that would be part of such baseline. Results. We found relationships between NPP and ungulate biomass and enteric CH4 emissions. However, current abundances are several times below the estimated baselines and the carrying capacity. There are major constraints for herbivore populations to reach their baseline state, particularly the absence of migration and the extinction of grazers among wild herbivores. Structural maintenance of Open Ecosystems must therefore be led by domestic grazers that cannot be replaced by the extant wild, mostly browser, ungulates. Conclusions. We concluded that Spain is widely susceptible to being populated by herbivores that generate Open Ecosystems as baseline landscapes. Current grazing livestock accounts for a significant part of them, so baselines must be included in their environmental assessments. For the case of Spain, we propose a minimum baseline of 36% of the herbivore biomass and 30% of the enteric CH4.