Abstract:
Compositional and functional plant community characteristics can strongly govern some ecosystem
processes. These community characteristics, may, in turn, be related to multiple environmental
variables, including edaphic, climatic, and topographic conditions. However, there is still an
incomplete understanding of how environmental conditions affect plant community composition and
functioning and, therefore, how species composition and trait expression potentially link habitat
conditions to ecosystem processes. This is particularly true for grasses, despite this taxon having
considerable ecological and economic importance. The grass family (Poaceae) is a species-rich taxon,
with close to 10 000 species occurring worldwide, and is chiefly responsible for providing the key
ecosystem service of grazing provisioning since grass species make up the bulk of the herbaceous plant
growth in grasslands and savannas. The grazing quality of grasses is assumed to vary strongly between
species, with intra-specific variation in grazing quality often ignored, resulting in grass species often
uniformly being categorized as being of high or low grazing quality. There is, however, an increasing
debate about the validity of this approach since many grass characteristics (including plant functional
traits; PFTs) vary intra-specifically along environmental gradients. Therefore, this study examined the
relationship between 19 environmental factors and community composition and cover, community weighted
mean (CWM) trait values, intra-specific trait variation and the grazing quality in two C4-
dominated savanna grass assemblages.
This study demonstrated that the relationships between grazing quality and PFTs and environmental
variables are typically weak and highly idiosyncratic at both the community- and species-level. Cover
and soil (particularly soil nutrients) variables were most consistently influential environmental
variables. Grazing quality (i.e. nutritional value) differed significantly between grass species, with large
proportions of the variation in all grazing quality components being explained by the identity of
species. However, within species, few environmental variables explained intra-specific variation in
grazing quality. Additionally, plant functional traits were also weakly related to intra-specific variation
in grazing quality. Therefore, these findings suggest that grass grazing quality and PFTs do not respond
consistently to environmental variables frequently quantified in ecological studies and that, contrary
to results from C3-dominated temperate grasslands, leaf dry matter content, specific leaf area and
force to tear are not useful proxies of grazing quality. More broadly, this study highlights that there
may be considerable intra-specific variation in grass grazing quality, but that this within-species
variation is not related to commonly recorded environmental conditions or easily measured plant
traits, and, therefore, remains challenging to predict.
