Grassiness of the Eastern Karoo - part of a cycle or here to stay? (Platform)

Rainfall and grazing are drivers of vegetation composition in the False Upper Karoo, an ecotone between semi-arid grasslands and Nama Karoo.  Vegetation includes the growth forms: grasses (C 4 ), dwarf shrubs (C 3 ), and ephemeral dicotyledons (C 3 ).  All forms grow when moisture is available: grasses and ephemerals mainly in summer; dwarf shrubs throughout the year but less in mid-summer and mid-winter.  Early summer rain specifically advantages grasses.  Grazing in summer by livestock reduces grass abundance, while grazing in winter increases grass abundance and may reduce dwarf shrub abundance. Trials investigating influences of livestock grazing systems (notably season) on plant composition of Karoo veld were established at Grootfontein in  1934 (Camp 6 trials, ongoing) and 1941 (Seligman trials, terminated in 1985).  Quantitative surveys began in the 1950s and repeated intermittently until the early 1970s.  The trials were each re-surveyed twice between 2011 and 2016.  Rainfall data (1888 to present) are available.  Rainfall data indicate a wave-type cycle in rainfall with clear periodicity but variable amplitude.  Rainfall from 2000-2013 was generally significantly higher than before that, and since 2014 has been relatively low.  Rainfall has mainly been concentrated earlier in the season (Dec/Jan) than before (Mar/Apr). Plant composition data from 2011/12 indicated a biome shift from dwarf shrubland to perennial grassland, correlated with the high rainfall.  Abundance and diversity of shrubs decreased, while those of perennial grasses increased.  The perennial grass Eragrostis lehmanniana dominated, and the palatable grasses Themeda triandra , Digitaria eriantha , Sporobolus fimbriatus , and Heteropogon contortus ingressed.  Grazing effects were manifest in the perennial grass component.  Winter grazing favoured Themeda triandra , which formed large near-monoculture patches.  The 2015/16 surveys indicate a partial reversal of the trend of increased grassiness, correlated with low rainfall. Results indicate that, in the Eastern Karoo, rainfall has been the major driver of vegetation change, with grazing giving a modifying influence.