Long-term ecological research in southern Brazil grasslands: Effects of grazing exclusion and deferred grazing on plant and arthropod communities

Abstract

Grazing exclusion may lead to biodiversity loss and homogenization of naturally heterogeneous and species-rich grassland ecosystems, and these effects may cascade to higher trophic levels and ecosystem properties. Although grazing exclusion has been studied elsewhere, the consequences of alleviating the disturbance regime in grassland ecosystems remain unclear. In this paper, we present results of the first five years of an experiment in native grasslands of southern Brazil. Using a randomized block experimental design, we examined the effects of three grazing treatments on plant and arthropod communities: (i) deferred grazing (i.e., intermittent grazing), (ii) grazing exclusion and (iii) a control under traditional continuous grazing, which were applied to 70 x 70 m experimental plots, in six regionally distributed blocks. We evaluated plant community responses regarding taxonomic and functional diversity (life-forms) in separate spatial components: alpha (1 x 1 m subplots), beta, and gamma (70 x 70 m plots), as well as the cascading effects on arthropod high-taxa. By estimating effect sizes (treatments vs. control) by bootstrap resampling, both deferred grazing and grazing exclusion mostly increased vegetation height, plant biomass and standing dead biomass. The effect of grazing exclusion on plant taxonomic diversity was negative. Conversely, deferred grazing increased plant taxonomic diversity, but both treatments reduced plant functional diversity. Reduced grazing pressure in both treatments promoted the break of dominance by prostrate species, followed by fast homogenization of vegetation structure towards dominance of ligneous and erect species. These changes in the plant community led to increases in high-taxa richness and abundance of vegetationdwelling arthropod groups under both treatments, but had no detectable effects on epigeic arthropods. Our results indicate that decision-making regarding the conservation of southern Brazil grasslands should include both intensive and alleviated levels of grazing

The role of fire disturbance on habitat structure and bird communities in South Brazilian Highland Grasslands

“…Nevertheless, we found peaked DDR for most plant community descriptors, providing further empirical evidence that this is a recurrent response pattern of grassland plant communities to disturbance, even though the mechanisms behind this pattern may be different from those postulated in the IDH. Furthermore, the responses of species richness and habitat heterogeneity to fire management relaxation (i.e., lower fire frequency) that we have reported here are similar to what has been reported for grazing relaxation in the same region 41 . This is the expected response of grassland plant diversity to grazing intensity/frequency 54 , 55 , and it seems that fire disturbance can promote similar response patterns.…”

“…Vegetation sampling was carried out in February 2018 immediately after the sampling of birds. We classified plant species into three life forms: shrubs, forbs (i.e., non-graminoid herbs), and graminoids 41,[81][82][83][84] . We used plant species richness and abundance as plant community descriptors, as well as vegetation height, and the amount (horizontal cover in percentage) of bare soil, water, and rock.…”

“…In the absence of disturbances, grassland structure becomes homogeneous 14 , 39 – 41 , mostly dominated by tall, erect grasses 28 , 41 , and shrubs 41 – 44 . This structural simplification results in biodiversity losses for plant and animal species 14 , 41 . Several studies have used a functional approach to measure patterns of community reorganization after disturbances 45 , 46 .…”

Assessing the rate and reversibility of large‐herbivore effects on community composition in a semi‐arid grassland ecosystem

“…Globally, many long-term exclosure studies were established following a historical period of intensive grazing pressure from domestic livestock during European colonial expansion, for example in the USA, Uruguay, and Australia (Witt et al, 2011;Sayre, 2017;Ferreira et al, 2020). Early grazing experiments typically involved the establishment of exclosures or other protected areas, but did not examine the effects of adding or increasing grazing pressure (Milchunas, 2011).…”

Temporal changes in bird communities in areas with different histories of fire disturbance in highland grasslands of Brazil

“…It is known that in the absence of any disturbance (e.g., grazing or fire), grasslands show a high dominance of a few species of caespitose grasses (that form tussocks) and a low diversity of forbs, resulting in a homogenization of the vegetation structure [ 2 , 15 ] and a consequent reduction of the bird diversity [ 16 , 17 ]. In the long term, in abandoned grasslands (i.e.…”