Deferment associated to contrasting grazing intensities affects root/shoot biomass allocation in natural grasslands

Abstract

AbstractQuestions(i) How does a strategic deferment influence both shoot and root biomass in South American Campos natural grassland after a long time of contrasting livestock grazing intensities? (ii) How do functional strategies of plants to tolerate or avoid grazing affect patterns of aboveground and belowground biomass?LocationA natural Campos grassland in the Central Depression of Rio Grande do Sul State, Southern Brazil (latitude 30°05′27″ S, longitude 51°40′18″ W, and altitude 46 m).MethodsWe studied the effects of deferments (spring or autumn) at moderate and severe livestock grazing intensities (maintained by adjusting contrasting forage allowances during 25 years) on the cover of dominant species, and aboveground and belowground biomass. The experiment was arranged in a completely randomized design with three replications of grazing exclusions, applied simultaneously at moderate and severe grazing intensities. Measurements of above‐ and belowground biomass and the coverage of the five dominant species were performed before and after grazing exclusion periods.ResultsUnder severe grazing intensity, erect‐growing grasses were replaced by prostrate species, which were able at least to maintain the belowground biomass found at moderate grazing intensity. In response to deferments, severe grazing intensity changed toward a significant increase in aboveground biomass and in the coverage of plants with erect growing habit. However, total belowground biomass remained unaffected by exclusions in both grazing intensities. The relation of root:shoot biomass was lower under moderate grazing intensity, and showed a negative response to deferment treatments at severe grazing intensity.ConclusionLong‐term contrasting grazing intensities applied in South American Campos grasslands determine several changes in above‐ and belowground relationships. Prevalence of prostrate plants under severe grazing is associated with a high partitioning capacity of assimilates toward the subterranean biomass, higher than in the tall species predominant under moderate grazing. The fast recovery of aboveground biomass, the maintenance of the underground biomass and the increase of tall grasses in response to deferments reveals the high resilience capacity of this ecosystem after a long‐term period of overgrazing.