PLANT CONSERVATION UNIT UNIVERSITY OF CAPE TOWN "Biodiversity of Africa - Observation and Sustainable Management for our Future!" International Congress, 29 September 3 October 2008, at Spier, RSA
THE LARGER CONTEXT 1. Local evidence for global climate change truths Cultivation Grazing 2. Anthropogenic versus climate change impacts PLANT CONSERVATION UNIT UNIVERSITY OF CAPE TOWN
Summary for cultivation Generalisations are difficult the historical and current impact depends on the region Decline in dryland cropping in more marginal Karoo environments since 1970s (Namibia, Namaqualand, Upper Karoo) Moderate increase in dryland cropping in renosterveld and Little Karoo Significant increase in irrigated lands (Orange River, Sandveld - 1,000 ha/year since 1989) PLANT CONSERVATION UNIT UNIVERSITY OF CAPE TOWN
What has happened to crop production in Namaqualand? Crop production (ha) in Namaqualand: 1911-1988 20000 18000 16000 14000 12000 10000 8000 6000 4000 2000 Wheat Oats Barley Rye Total ha 35000 30000 25000 20000 15000 10000 5000 0 1910 1920 1930 1940 1950 1960 1970 1980 1990 0 Significant decline in ha cultivated. Abandonment of croplands more in marginal lands than higher rainfall areas What are the implications for mass flower displays?
Steiner 1967
Rohde & Hoffman 2003
Grazing impacts Species Community Landscape
Arid savanna Desert Desert grassland Succulent shrubland Ephemeral rivers Selected from collection of >500 repeat photographs of southern Africa PLANT CONSERVATION UNIT UNIVERSITY OF CAPE TOWN
Bush thickening Little change Grassland pulsing Bush thickening Grassland pulsing Shrub thickening Bush thickening Fynbos/thicket pulsing
1899 Magersfontein 241 BUSH THICKENING 2003 An increase in Tarchonanthus camphoratus on the hillslopes and Acacia tortilis, A. erioloba, A. mellifera and a range of grasses on the plains
1914
Jürgens 2005
1939 Smorgenskadu (nr Aggenys) DESERT GRASSLANDS In some cases there have been quite dramatic shifts 369 For example, at this site there has been a shift from annuals,?succulent shrubs to grassland (Stipagrostis brevifolia) Hans Herre This biome shift has been strongly influenced by land use. 2005 This site is close to the farmhouse which in the early 20th century had the only source of water for a wide area. Borehole technology enabled farmers to rest the veld which resulted in an expansion of grasses Rohde & Hoffman
1963 27 km E of Springbok 198 Frank Steiner 2003 This pattern is repeated at a few other sites as well which have experienced a shift from annuals to Stipagrostis brevifolia grassland The pattern is strongly influenced by season and time of year Rohde & Hoffman
1920 N. Loeriesfontein 383 SHRUB THICKENING Pole Evans 2005 Significant increase in shrubs (e.g. Ruschia spinosa, Eriocephalus spinescens, Lycium cinereum, (spiny) Tripteris sp. Heuweltjie in middle distance has also thickened up a lot. Rohde & Hoffman
Rohde & Hoffman 1958 Nieuwoudtville-Calvinia 388 2005 Acocks General finding from the repeat photographs suggest that there has been an overall increase in cover relative to images that were taken in the early or middle part of the 20 th century This site shows very little change in composition but a slight increase in cover
1920 S. of Loeriesfontein 145 SHRUB THICKENING INTO SUCCULENT KAROO Pole Evans 2002 Rohde & Hoffman Reduction in prostrate succulent species (Cephalophyllum, Brownanthus) and an increase in non-succulent shrubs such as Zygophyllum microphyllum, Blepharis, Tripteris, Eriocephalus)
1957 Buffels River 303 EPHEMERAL RIVERS 2006 Acocks Ephemeral river systems which are vegetated have not changed much No evidence of large floods which have cleaned out the river systems (vide Laingsburg floods of 1981) Rohde & Hoffman
1939 Wiedouw River Hoffman 448 EPHEMERAL RIVERS 2007 Levyns Acacia karroo has increased considerably in ephemeral river systems which in earlier times were not wooded This particular ephemeral river also has a dense understory of Oleander
Total No. cattle, goats, sheep and LSU in the Karoo: 1918-1995 25000000 6000000 20000000 5000000 4000000 No. animals 15000000 10000000 Cattle Goats 3000000 2000000 No. LSU Sheep 5000000 Total LSU 1000000 0 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 0 Reasons for decline include: loss in productivity (degradation); stock reduction scheme of 1960s; shift to different breeds and increase in commercialisation; active extension service and increased conservation consciousness;
BUT CLIMATE IS ALSO IMPORTANT 28 climate stations managed by the ARC
120 100 80 60 40 20 0-20 -40 Winter Summer Annual Rainfall -60 y = 0.1995x - 397.37 R 2 = 0.02-80 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 +10 mm per decade Rainfall Increase Decrease NS Winter 4 0 24 Summer 4 0 24 Annual 4 0 24
% deviation 7 6 5 4 3 2 1 0-1 -2-3 -4-5 -6 Winter Summer Annual Tmax y = 0.0798x - 158.39 R 2 = 0.2781-7 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 +0.23 C per decade Tmax Increase Decrease NS Winter 20 0 8 Summer 22 0 6 Annual 23 0 5
% deviation 10 9 8 7 6 5 4 3 2 1 0-1 -2-3 -4-5 -6-7 -8-9 -10-11 -12 Winter Summer Annual Tmin y = 0.1414x - 280.85 R 2 = 0.3172 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 +0.19 C per decade Tmin Increase Decrease NS Winter 17 0 11 Summer 21 0 7 Annual 21 0 7
30 25 20 15 Winter Summer Annual Evaporation % deviation 10 5 0-5 -10-15 y = -0.4803x + 955.53 R 2 = 0.6886-20 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 25% decline since 1965 Evaporation Increase Decrease NS The Evaporation Paradox Winter 0 17 10 Summer 0 22 6 Annual 0 24 4
% deviation 30 25 20 15 10 5 0-5 -10-15 Winter Summer Annual Windrun -20 y = -0.91x + 1809.6-25 R 2 = 0.9123-30 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 26% decline in wind run since 1965 Wind Increase Decrease NS Winter 0 26 2 Summer 1 25 2 Annual 1 26 1
300 250 E-P (1965) E-P (2007) Precipitation (1965) Precipitation (2007) 200 mm 150 100 50 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 25% decline in evaporation over last 35 years but no change in rainfall This has tremendous implications for ecosystem water balance
SOME FINAL THOUGHTS We have relatively good historical reconstructions of past climates for some areas of southern Africa (although perhaps we rely too much on rainfall and temperature data only); Very weak reconstructions of historical landscapes; Very weak understanding of historical rates of change and the timing of change in response to land use and climate impacts; This is important since it guides management ( What are we managing for? ) PLANT CONSERVATION UNIT UNIVERSITY OF CAPE TOWN
TWO FURTHER PROVOCATIVE THOUGHTS There is little evidence from this work and most of the images in the repeat photographic collection that the impact of climate change is upon us OR that land degradation has occurred over large areas of the western parts of southern Africa in the last 50-100 years PLANT CONSERVATION UNIT UNIVERSITY OF CAPE TOWN