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

Abstract

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.