We report a novel weathering mechanism in South African sandstone formations, where cryptoendolithic cyanobacteria induce weathering by substrate alkalization during photosynthesis. As a result, the upper rock part is loosened and then eroded away by physical forces such as wind, water, trampling. This special type of ‘exfoliation’ is widely distributed and affects the geomorphology of whole sandstone mountain ranges and outcrops across several biomes. We show, that this weathering type is initiated by bioalkalization because of the photosynthesis of cryptoendolithic (i.e. those organisms living in small tight open spaces between the sand grains) cyanobacteria causing pH values high enough to enhance silica solution in the cryptoendolithic zone. As modern cyanobacteria are the initial photoautotrophic colonizers of bare rocks in arid and semiarid landscapes, it is possible that they may also have played a significant role in shaping sandstone landscapes in the geological past.

No abstract

No abstract

The composition of the plant species eaten by kudu (<em>Tragelaphus strepsiceros</em>) determines the diet quality, which impacts on kudu condition and mortality levels. The yearround diet composition of kudus in the Limpopo Province, a mopane (<em>Colophospermum mopane</em>) dominated area, was determined by faecal analysis. The most important dietary plant species were <em>Colophospermum mopane, Grewia bicolor, Terminalia prunioides, Tinnea rhodesiana, Boscia albitrunca</em> and <em>Combretum apiculatum</em>, with <em>C. mopane</em> comprising on average 39.2 % of diet per month. Small amounts of herbs, grasses and seeds made up the remaining part of the diet. The contribution of <em>C. mopane</em> in the diet was negatively correlated with precipitation. <em>Colophospermum mopane</em> was consumed, irrespective of its high condensed tannin load (5.2–9.8 % DW) for the majority of the months. No seasonally significant differences were detected for modelled kudu diet crude protein, tannin or phenol concentrations. <em>Colophospermum mopane</em> showed significant seasonal differences with lowest values of protein, tannin and phenols in the late wet season. Surprisingly, crude protein concentrations were positively correlated with high levels of tannins and phenols for <em>C. mopane</em>. The diet of kudus comprised of significantly more species during the wet season compared to the dry season. Diet diversification, instead of protein maximization, seems a potential tool to satisfy protein requirements while reducing potential toxic effects associated with a high intake of secondary compounds. A significant positive correlation was therefore detected between the tannin concentration of <em>C. mopane</em> leaves and the number of plant species in the diet

A field experiment was conducted in which Mopane (Colophospermum mopane) trees were subjected to three different canopy treatments:felling of trees at a mean height of 0.7m above ground level, felling at a height of 2m, or pruning of selected branches. These treatments were intended to simulate wood harvesting by local communities, pollarding by elephants, and browsing by herbivores, respectively. The foliar concentrations of total phenol, condensed tannin and protein-precipitating tannin were tracked for three consecutive years after treatments were effected. Coppicing, pollarding and pruning induced chemical defences in Mopane tree foliage. The order of magnitude of the response was positively related with impact severity: coppicing > pollarding > pruning > control. Differences between treatments remained the same for the duration of the study. The effects of canopy treatments on phenol and tannin concentrations were small compared to the seasonal and inter-seasonal fluctuations. The protein precipitation capacity of the secondary metabolites increased significantly with increasing impact. We concluded that secondary metabolite concentrations in Mopane foliage are dynamic and can be explained satisfactorily by season, year and treatment severity, with a high explanatory power (r 2 = 0.94-0.98). Findings of this study have consequences for current harvesting, animal production and conservation practices.