Exotic ecosystem engineer alters ecosystem structure and function in Patagonia

Background/Question/Methods

Exotic species affect ecosystem structure and function, but their effects are stronger when the invading species introduces a novel disturbance. Old world wild boar (Sus scrofa) are now present in all continents except Antarctica, and in order to feed they overturn extensive areas of vegetation and disturb the underlying soil. This physical disturbance not only directly affects below- and aboveground structure and composition but also indirectly alters ecosystem functioning. Although previous research has shown that wild boar effectively alter some ecosystem properties, little is known about the effect of wild boar on ecosystem function. Using an exclosure experiment, we determined how wild boar disturbance affects soil physical, chemical and biological properties, as well as on plant community structure and composition in Patagonia, Argentina. To study the impact on soil, we collected 72 soil samples in fresh and old rooted patches, unrooted patches, and artificially disturbed patches, and measured temperature, water content, compaction, total C and N, extractable P, soil respiration, and N mineralization rates. To test if soil disturbance by wild boar affected decomposition rates and aboveground structure, we set up leaf litter decomposition bags and collected plant biomass in rooted, unrooted, and artificially rooted patches.

Results/Conclusions

Rooting disturbance significantly decreases soil compaction and decomposition rates, but had little impact on the other properties we measured. Rooting impacts on plant communities were stronger than rooting effects on soil properties. Rooting disturbance significantly altered plant community composition and plant biomass, which was 3.5 times greater in unrooted patches than in rooted patches. These results show that rooting disturbance by wild boar has strong aboveground effects that are diluted belowground. In Patagonia community characteristics prevail over the effects of rooting disturbance on belowground properties. However, in the long term ecosystem function is compromised by the strong changes on aboveground structure and composition, and the reduction of organic matter decomposition rates.