Seasonal progression of plant water relations in fynbos in the western Cape Province, South Africa

Abstract

Plant xylem pressure potentials and leaf conductances to water loss were measured in the spring and summer at two sites in the western Cape Province, Republic of South Africa. The measurements were to test the hypothesis that the fynbos of South Africa was equivalent to the chaparral of California, therefore a period of plant water stress, similar to the period measured in chaparral species, should occur in flynbos species during the dry summer. The measurements indicated little or no plant water stress in most fynbos species at both sites. The sites were similar in plant water relations in spite of a more than twofold difference in annual precipitation. The minor differences in plant water relations can be explained in terms of different vegetation cover and different vapor pressure deficits during the measurements. The results support the conclusion that the arid fynbos may be equivalent to chaparral, but the majority of the fynbos is equivalent to coniferous and broad-leaved evergreen forest in California.

Do low standing biomass and leaf area index of sub-tropical coastal dunes ensure that plants have an adequate supply of water?

“…These values are similar to those measured for other dune species of southern Africa (Pammenter 1983) and California (De Jong 1979) and deep-rooted fynbos species (Miller et al 1983;von Willert et al 1989). Chaparral species of North America and the shallow-rooted fynbos species Diosma hirsuta develop very negative water potentials (−3.9 to −6 MPa; Mooney et al 1977;Miller et al 1983), yet both live in environments that have annual rainfall not dissimilar to the amounts measured for Old Woman's River study site. This emphasises the apparent water availability in these dunes.…”

“…Ψ leaf of all three species recovered overnight (Table 3) to values that are comparable to predawn values measured for a wide range of species from different habitats (De Jong 1979;Jefferies et al 1977;Miller et al 1983;von Willert et al 1989). Recovery suggests an adequate supply of water and a resultant positive Ψp would have important implications for plant growth.…”

Measurement and modelling of evapotranspiration in three fynbos vegetation types

“…The projected future climatic conditions are likely to be more conducive to the growth and dispersal of the alien invasive plants (Hellmann et al, 2008). It is therefore not surprising that numerous studies in the fynbos biomes have mainly focused on the mechanisms by which plant species respond to seasonal patterns in moisture availability and how these vary along rainfall gradients (Miller et al, 1983;Richards et al, 1995;Richardson and Kruger, 1990;Von Willert et al, 1989) and during droughts (West et al, 2012). These studies have largely targeted specific plant species and few were conducted at the community or vegetation-type levels (Jacobsen et al, 2007;Midgley et al, 2002).…”

Patterns of vegetation and climate in the mediterranean zone of South Africa

“…These results were corroborated by those from similar investigations as yet unpublished from elsewhere in the fynbos. Miller et al (1983) therefore rejected the hypothesis that local water balance favours fynhos on high-rainfall sites. If physical environments were indeed analogous, fynbos that occurs between the 350 and 650 mm isohyets should be analogous in its physiognomy and water relations to chaparral, but fynbos in areas with rainfall exceeding about 650 mm yr-1 should be dunctionally equivalent to evergreen forest in Western North America», where one month or less of drought is experienced.…”

“…Shallow soils with low water holding capacity could reduce the effectiveness of high precipitation thus precluding the establishment of forest in humid climates and enabling persistence of fynbos. Miller et al, (1983) tested the corollary hypothesis, that plants in fynbos would show seasonal patterns of plant water relations similar to plants in the chaparral, despite higher · '-11 Specifically, the seasonal water relations of fynbos . This was donc at a site with around l 600 mm yr· 1 rainfall and l6°C mean daily temperature, and another with about 650 mm yr· 1 and l8°C.…”