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Effects of artificially established depth to water table gradients and soil type on the growth of Cape fynbos and forest plants

1992; Elsevier BV; Volume: 58; Issue: 3 Linguagem: Africâner

10.1016/s0254-6299(16)30866-3

1727-9321

P. T. Manders, R.E. Smith,

Ecology and Vegetation Dynamics Studies

Different responses of forest and fynbos species to water table depth and soil nutrient status may restrict forests to moist, sheltered habitats in the fynbos region of the Cape. To test this hypothesis, Cunonia capensis L. (a mature forest species) and Kiggelaria africana L. (forest precursor) and fynbos shrub species Protea neriifolia R. Br. and P. nitida Miller were cultivated in an experimentally established range of depths to water table in forest and fynbos soil types. Fynbos species grew at all depths to water table in the fynbos soil, but K. africana grew very poorly and C. capensis died in dry situations in this soil type. Growth of all species, especially the forest species, was greater in the forest soil than in the fynbos soil and was little affected by depth to water table. Protea species had taproots reaching to the water table with little development of lateral roots, even where water was plentiful. Forest species had well-developed roots in the forest trough, but not in the fynbos trough. Pre-dawn leaf xylem potentials of forest species were similar to fynbos species in both troughs and did not fall below – 1.5 MPa. This study supports the hypothesis that forests are limited to sheltered habitats by dry conditions in exposed habitats that restrict root development and plant growth. The enhanced development of forest in areas with greater soil moisture availability and more nutrients is therefore related to the establishment requirements of the species. Forest precursors are more able to persist in less optimal conditions than mature forest species, possibly because of more rapid root development. Die uiteenlopende reaksies van woud- en fynbosspesies op die vlak van die watertafel en die vrugbaarheidstatus van die grond mag woude tot klam, beskutte habitatte in die fynbosstreek van die Kaap beperk. Om hierdie hipotese te toets, is Cunonia capensis L. (’n volwasse bosspesie), Kiggelaria africana L. (’n woudvoorloper), die fynbosstruikspesies Protea neriifolia R. Br. en P. nitida Miller aangeplant in woud- en fynbosgrondtipes waar eksperimenteel vasgestel is dat die watertafeldiepte wissel. Fynbosspesies het by al die watertafeldieptes in fynbosgrond gegroei. Waar hierdie tipe grond egter droog was, het K. africana baie swak gegroei en C. capensis afgesterf. Al die spesies, maar veral die woudspesies, het beter in die woudgrond as in die fynbosgrond gegroei en is min deur die vlak van die watertafel beïnvloed. Protea spesies het penwortels tot by die watertafel ontwikkel met min sywortels — selfs waar baie water beskikbaar was. Woudspesies het goed ontwikkelde wortelstelsels in die woudgrond ontwikkel maar nie in die fynbosgrond nie. In beide grondtipes was die blaarxileempotensiaal voor dagbreek van die woud- en fynbosspesies dieselfde en het nie onder – 1.5 MPa gedaal nie. Hierdie studie ondersteun die hipotese dat woude beperk is tot beskutte habitatte aangesien droë toestande in blootgestelde habitatte wortelontwikkeling en plantgroei aan bande lê. Die feit dat woude beter ontwikkel in gebiede waar meer grondvog beskikbaar en waar die grond vrugbaarder is, staan dus in verband met die vestigingsvereistes van hierdie spesies. Woudvoorlopers groei beter as volwasse woudspesies onder minder gunstige toestande, moontlik as gevolg van vinniger wortelontwikkeling.