Foliage structure and shoot growth in heathlands in the mediterranean-type climate of southern Australia and South Africa

Abstract

Three distinct strata (with occasional emergent plants) can be distinguished in heathlands in the mediterranean-type climate of southern Australia and South Africa. 1. The upper stratum is composed of deep-rooted nanophanerophytes (up to 2 m tall) with evergreen, broad sclerophyllous leaves and internodes 2-5 mm long, longer in emergent species. 2. The mid stratum is composed of relatively shallow-rooted nanophanerophytes (0.5-1.5 m tall) with evergreen, narrow semi-sclerophyllous leaves and internodes less than 1 mm long. 3 . The ground stratum contains a mixture of shallow-rooted chamaephytes, with densely -packed, small leaves, and evergreen, sclerophyllous “hemicryptophytes”, with varying numbers of culms/leaves in each clump (depending on the species). During calm, sunny days, the temperature of meristems on foliage shoots of dicotyledons increases above ambient air temperature, the increment being related to the density of packing of leaves on the foliage shoot. The temperature increment of meristems in rush-like, monocotyledonous clumps is related to the density of packing of the culms/leaves in the clump. Those plants with the highest temperature increment at foliage meristems grow during late winter to early spring ; plants with medium packing of foliage grow during spring ; while plants with sparse packing begin foliage growth in late spring through summer. The last group of plants must be deep-rooted to extract water from the deeper layers of the soil during the summer drought of the mediterranean-type climate.