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Aim To determine how the distribution of species richness is associated with environmental factors for the four major C4 grass lineages in South Africa, as a means to explore the mechanisms responsible. Location South Africa, Lesotho and Swaziland. Methods The geographical distributions of species richness for four major C4 grass lineages (Aristidoideae, Chloridoideae, Andropogoneae and Paniceae) were sourced from a recently published flora that divided the study region into different vegetation types. Mean values of potential environmental correlates were calculated for each vegetation type, and the relative importances of these were determined using single- and multiple-predictor generalized linear models, with and without control for spatial autocorrelation. Model selection of the multiple-predictor generalized linear models was conducted using an Akaike's information criterion-information theoretic approach. Association with wet, intermediate or dry, shady or open, and disturbed or undisturbed habitats was also determined for each C4 grass clade using habitat data for all the grass species, and analysed using chi-square tests of independence. Results Andropogoneae and Paniceae are most species-rich in areas of high precipitation and in mesic habitats. Andropogoneae are associated with high fire frequencies. Species richness in Andropogoneae decreases and in Paniceae increases in relation to livestock density. Chloridoideae species richness is relatively constant across South Africa, but is highest where there are infrequent fires, high temperatures and basic soils, and in mesic and disturbed habitats. Aristidoideae are most species-rich in arid regions and in habitats with high temperatures, and are associated with disturbed habitats. Main conclusions Environmental variables other than precipitation, including temperature, fire frequency and grazing pressure, are strongly associated with the contrasting distributions of species richness for the various C4 grass clades in South Africa. Our results suggest that ecological sorting is an important determinant of phylogenetic patterns in the species richness of these C4 grass lineages. [ABSTRACT FROM AUTHOR]

The author reflects on how editorial views of the journal changed over time since the first issue was published in 1902 until the issues in 2011 regarding forest fires. The author mentions an article in 1906 by F. E. Weiss that discusses the importance of fires in vegetation in Natal, South Africa that cites the fire resistant Vellozia plant and the use of fire to control cattle tick infestations. The author adds that after 100 years, fire importance to vegetation is still an interesting topic.

Global climate change is expected to shift regional rainfall patterns, influencing species distributions where they depend on water availability. Comparative studies have demonstrated that C4 grasses inhabit drier habitats than C3 relatives, but that both C3 and C4 photosynthesis are susceptible to drought. However, C4 plants may show advantages in hydraulic performance in dry environments. We investigated the effects of seasonal variation in water availability on leaf physiology, using a common garden experiment in the Eastern Cape of South Africa to compare 12 locally occurring grass species from C4 and C3 sister lineages. Photosynthesis was always higher in the C4 than C3 grasses across every month, but the difference was not statistically significant during the wettest months. Surprisingly, stomatal conductance was typically lower in the C3 than C4 grasses, with the peak monthly average for C3 species being similar to that of C4 leaves. In water-limited, rain-fed plots, the photosynthesis of C4 leaves was between 2.0 and 7.4 μmol m(-2) s(-1) higher, stomatal conductance almost double, and transpiration 60% higher than for C3 plants. Although C4 average instantaneous water-use efficiencies were higher (2.4-8.1 mmol mol(-1)) than C3 averages (0.7-6.8 mmol mol(-1)), differences were not as great as we expected and were statistically significant only as drought became established. Photosynthesis declined earlier during drought among C3 than C4 species, coincident with decreases in stomatal conductance and transpiration. Eventual decreases in photosynthesis among C4 plants were linked with declining midday leaf water potentials. However, during the same phase of drought, C3 species showed significant decreases in hydrodynamic gradients that suggested hydraulic failure. Thus, our results indicate that stomatal and hydraulic behaviour during drought enhances the differences in photosynthesis between C4 and C3 species. We suggest that these drought responses are important for understanding the advantages of C4 photosynthesis under field conditions., (© 2014 The Authors Global Change Biology Published by John Wiley & Sons Ltd.)