Fire in the Cape Region of South Africa - Fire in Mediterranean Ecosystems - page 171

30 000

fynbos
succulent karoo
thicket, forest
pine plantations

25 000

20 000

15 000

10 000

5000

0

0 500 1000 1500 2000 2500

Mean annual precipitation (mm)

Fig. 7.3 Aboveground biomass of Cape ecosystems along a precipitation gradient. Fynbos
shrublands show little variation in biomass along the gradient (solid line). Conifer plantations,
grown in the same fynbos landscapes, produce tenfold higher biomass than fynbos. Native
non-flammable thicket and forest have much higher biomass for a given rainfall than fynbos
(dashed line). (Data from: Kruger 1977 ; Le Maitre et al. 1996 ; Midgley & Seydack 2006 ;
Mills & Cowling 2006 ; van Laar 1982 ; van Wilgen 1982 .)

increases (>600mm), renosterveld is replaced by fynbos on clay-rich soils
(Kruger 1979 ).
Succulent karoo shrublands are by far the most extensive fire-resistant vegeta-
tion type, replacing fire-prone fynbos and renosterveld in more arid sites. They are
dominated by leaf succulents of the Mesembryanthemaceae and Crassulaceae,
along with stem-succulent Euphorbiaceae and evergreen shrubs of the Asteraceae
( Table 7.1 ; Taylor 1978 ; Rebelo et al. 2006 ). Thickets are broadleaf plant commu-
nities that contain a mix of evergreen, deciduous and succulent shrubs, many of
which are spiny ( Table 7.1 ). Thickets are common along the coast where they are
referred to as strandveld , but they also occur in mountain fynbos and intermontane
valleys. With increasing rainfall, thicket stature and plant cover increases and the
succulent and deciduous components diminish. Above 750 mm, the thickets are

replaced by closed forests with a high proportion of evergreen species ( Table 7.1 ) .
Small patches of forest or scrub forest are common in fire refugia such as on scree
slopes, at the foot of cliffs, and along stream banks, in most mesic fynbos
landscapes. These fire-resistant alternative ecosystem states of thickets and forests
occur on all soil types, nutrient-rich and nutrient-poor, across the entire rainfall
gradient (Kruger 1979 ). Within a landscape, there are often clear edaphic patterns
with fynbos on poorer sandy soils and thicket, scrub or forest on deeper, more
nutrient-rich soils, but the latter are also found on the nutrient-poor substrates
(Vlok et al. 2003 ; Cowling et al. 2005 ).

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