Abstract
Andropogon lateralis is a tall and highly plastic tussock-forming grass native from southern South America. It is a frequent component of Campos and Subtropical highland grasslands that often becomes dominant under lax grazing regimes. The aim of this work was to analyze the response of species diversity and forage production of a natural grassland dominated by A. lateralis to a wide range of grazing intensity. We hypothesized that species diversity and forage production would both peak at the intermediate canopy heights determined by grazing regimes of moderate intensity. A grazing experiment was conducted in a highland grassland with mesothermal humid climate at 922 masl (Atlantic Forest biome, Santa Catarina state, Brazil) that comprised 87 species from 20 families but had 50% of its standing biomass accounted by A. lateralis. Four pre-/post-grazing canopy heights—12/7, 20/12, 28/17, and 36/22 cm (measured on A. lateralis)—were arranged in a complete randomized block design with four replications, and intermittently stocked with beef heifers from October 2015 to October 2017. Andropogon lateralis cover decreased (from 75 to 50%), and species richness increased (15–25 species m−2) as canopy height decreased. Grazing intensity did not affect annual forage production (4.2 Mg DM ha−1). This natural grassland dominated by A. lateralis had a high capacity to adjust to grazing regimes of contrasting intensity, maintaining forage production stable over a wide range of canopy heights. However, to prevent losses in floristic diversity, such grassland should not be grazed at canopy heights higher than 28 cm.
Highlights
Humid natural grasslands, which have become rare worldwide, harbour a large diversity of fauna and flora
Andropogon lateralis Nees is a tall tussock-forming perennial C4 grass native to South America. It is well accepted by grazing animals, presents an extremely high phenotypic plasticity showing large variations in specific leaf area (SLA) and leaf dry matter content (LDMC), and being able to display either a competing or a resource-conservation functional strategies depending on environmental c onditions[11]
We hypothesized that species diversity and forage production would both peak at the intermediate canopy heights determined by grazing regimes of moderate intensity, because under lax grazing intensity, species able to become tall and unpalatable, and conserve nutrients, would become dominant, whereas under too intense grazing only a few species with prostate habits would survive
Summary
Humid natural grasslands, which have become rare worldwide, harbour a large diversity of fauna and flora. In southern Brazil, natural grasslands are the base of complex agroecosystems that support extensive livestock production and a range of other valuable environmental services in the Pampa and Atlantic Forest biomes In the latter, the mesothermic humid Highland grasslands that extend at altitudes above 800 masl over some 1.374 million hectares[1,2], characterized by estepe formation, are the habitat of 1161 species, of which 107 were endemic[2], and 76 listed as endangered. Influences the botanical composition and the harvested yield of p astures[5,6,7,8,9] For this reason, agroecosystems based on the use of highly diverse natural grasslands aim to design grazing management strategies that couple high enough animal production so that economic sustainability is ensured with the preservation of native species that provides the basis for r esilience[10]. The replacement of few dominants by several subordinate species often occurs due to moderate grazing intensity and alleviating light limitation[4]
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