Response of community‐aggregated plant functional traits along grazing gradients: insights from African semi‐arid grasslands

Abstract

Questions Plant communities fulfil key functions in the ecosystem, which can be characterized by their plant functional traits. In functional ecology, plant communities are considered to hold a set of trait attributes reflecting a specific plant strategy adapted to persist in the environment to which they are exposed. In semi‐arid grasslands of the Republic of South Africa, we addressed the following questions: how are community‐aggregated plant functional traits (CPFT) shaped by grazing gradients; which plant strategies are associated with the response of CPFTs; and are environmental factors, such as soil properties and grazing management, interrelated with the functional response of vegetation to grazing gradients? Location Semi‐arid grasslands close to Thaba Nchu, Free State (Republic of South Africa). Methods Piosphere transects from a water point into the field were established to portray grazing gradients on two communal grazing areas with continuous grazing and two commercial farms with rotational grazing. Along each transect, six plots (5 × 5 m) were evenly distributed. The trait–transect sampling was applied to record 12 CPFT related to light capture and forage quality. A redundancy analysis was performed to derive relationship between CPFTs, grazing gradients and environmental conditions. Results Grazing intensity decreased along piosphere transects, from the water point into the field. Most CPFTs responded to this decreasing gradient of grazing intensity and so allowed derivation of trait syndromes that clearly reflect plant strategies of ruderal and competitive vegetation. Close to water points, plants had higher nitrogen concentrations, fewer cell wall components and higher specific leaf area, hence light capture might be faster and more efficient per leaf area and leaf mass. Plant communities exposed to intensive grazing were well adapted to defoliation, trampling and nutrient accumulation through fast growth rates and a quick return strategy. Conclusions In the sacrifice zone around water points, there is an ecological niche for vegetation communities exhibiting a strategy of fast growth, which is well adapted to intense and frequent grazing and is also associated with forage of high nutritional quality.

Spectral indicators of forage quality in West Africa’s tropical savannas

“…The negative correlation between fitted and observed forage variables (Table 4) agrees with previous observations of rangelands' decreasing forage quality with increasing biomass (Moreno García et al, 2014), and underlines the independence of both models.…”

Long-term Protection from Heavy Livestock Grazing Affects Ponderosa Pine Understory Composition and Functional Traits

“…Our results support this hypothesis: Protection from heavy grazing led to a shift toward more conservative leaf traits (low SLA, low foliar N mass , and high LDMC). Other research in grasslands around the world has shown similar patterns (Cingolani et al, 2005;Louault et al, 2005;Wesuls et al, 2012;Moreno García et al, 2014). A community-level shift in ungrazed communities toward reduced acquisition and increased conservation Table 2).…”

“…These species can be characterized as slow-growing perennial species that allocate a relatively small proportion of their energy to reproduction and produce litter that decomposes slowly (Reich et al, 1997;Wright et al, 2004). These findings contribute to a growing body of evidence that there are consistent shifts in community-level leaf traits under a variety of grazing regimens around the world (Louault et al, 2005;Laliberté et al, 2012;Wesuls et al, 2012;Moreno García et al, 2014). Species with low SLA are at a competitive advantage when protected from heavy grazing because they are able to reduce resource availability.…”

“…Vegetative height has long been a key functional trait thought to reflect a mechanism of grazing avoidance, with increased levels of grazing intensity consistently favoring shorter plants (Dyksterhuis, 1949;Arnold, 1955;Díaz et al, 2001;Díaz et al, 2006). Seed mass, SLA, foliar N mass , LDMC, and leaf toughness have been used to understand and predict the impact of grazing because these traits are thought to reflect a general trade-off in growth versus defense (Moles and Westoby, 2004;Adler et al, 2004;Cingolani et al, 2005;Louault et al, 2005;Laliberté et al, 2012;Wesuls et al, 2012;Moreno García et al, 2014). Some researchers suggest that generalizations of grazing impacts described by plant traits may be difficult (Vesk and Westoby, 2001), whereas others suggest that plant species' responses to herbivory might be idiosyncratic with regard to LHS traits (Butterfield and Callaway, 2012).…”

Inferring Aggregated Functional Traits from Metagenomic Data Using Constrained Non-negative Matrix Factorization: Application to Fiber Degradation in the Human Gut Microbiota

“…Investigating complex microbial communities from a purely functional point of view provides an interesting insight because their taxonomic diversity may be very high and varying in time while, owing to environmental selection pressure, their ecosystemic functions are often ubiquitous and much more stable in time. The functional profiling of microbial communities has motivated the adaptation of concepts borrowed from environmental and plant functional ecology to the framework of microbial ecology, such as community aggregated traits [9, 10], which can be quantified through abundance computation of specific genes or predefined pathways from WGS data. These taxon-free approaches allow the study of key processes at the ecosystem level and correlate environmental factors and ecosystem functions [11].…”