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 applied them to improve the allocation of environmental impacts and emissions from grazing livestock. Methods We inferred an equation relating Net Primary Productivity (NPP) with ungulate biomass and enteric CH4 with data from 11 Spanish Protected Areas. We estimated theoretical baselines in Spain using other literature sources. We applied the equations to the Spanish open ecosystems that are currently grazable. 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 should therefore be complemented 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 equivalent to 36% of current grazing livestock biomass and 23% of their enteric CH4 emissions.