Disentangling the relationship of grass height with two classic grazing managements: implications for grassland bird conservation in the Flooding Pampa

Abstract

Natural grasslands are among the most threatened biomes due to land-use change andlimited protection. The Flooding Pampa, Argentina, harbors well-preserved grasslandsused for grazing. Cattle grazing creates habitats dominated by tall or short grasses, affectinggrassland birds. We evaluated the influence of two grazing management systems andgrassland height on species richness, composition and functional traits of grassland birdcommunities in winter and spring. Birds and vegetation variables were surveyed alongeight transects in six rotational and six continuous grazing ranches. We selected sevenfunctional traits to study their association with grassland height. Cluster Analysis and LinearDiscriminant Analysis identified the grassland variables that best described site groupingsbased on bird composition. Generalized Linear Models compared species richnessbetween groups obtained by Cluster Analysis, and nonmetric multidimensional scalingand fourth corner analysis explored relationships between groups and species compositionand functional traits, respectively. In spring, species richness and the richness of tallgrassland species were higher in tall grasslands (mean = 27.5 and 3.5, respectively) thanin short grasslands (mean = 21.5 and 0.5, respectively), regardless of grazing management.In winter, species richness was similar between tall and short grasslands (mean = 18 and18.1, respectively). Ranches with tall grass were associated with species associated withtall grassland traits and species of limited abundance. We recommend revising rotationalgrazing to ensure habitat availability for threatened birds. Conservation policies shouldaim to reduce stocking rates in continuously grazed short-grass fields and extend restperiods in rotationally grazed short-grass areas.