Student - March 29, 2007

Lianas prefer seasonal forests

Lianas do better in seasonal forests than in evergreen forests. They do better during dry periods and ensure that the soil remains nutrient-rich thanks to their own leaf waste, discovered Dr Zhi-quan Cai during his doctoral research in south-west China.

Cai did field work in the forests of Xishuangbanna in Yunnan Province, where there are three different forest types: a seasonal wet forest, an evergreen broad-leaved forest and montane forest. He found 147 species of lianas (woody vines) belonging to 48 families. The lianas showed a great variety of habits and included stem twiners and scramblers, and to a lesser extent hook, tendril and root climbers. Cai’s research indicated that more lianas grow in seasonal forest: per half-hectare plot, forty species were found in the seasonal forest, 26 species in the montane forest and 21 in the evergreen forest.

Their preference for seasonal changes makes lianas the odd man out in the plant world. Most plants are less common where rainfall is low and where seasonal differences are greater. According to Cai, however, there is a simple explanation. Lianas do better than trees in the dry seasons that occur in seasonal forests. They store more carbon and absorb water and nitrogen more efficiently. In addition, the leaves of the lianas contain more phosphorus, which in turn enriches the soil when the lianas lose their leaves.

Large lianas in particular are good at adjusting to seasonal changes. After studying the growth reactions of seedlings of the local liana species Zizyphus attopensis Pierre, Cai discovered that the local light intensity is the most important factor in the seasonal changes in growth and photosynthesis. From a comparison of six smaller and larger liana species, he concluded that larger species can withstand a higher light intensity and therefore are better able to colonise open spaces in the forest.

It would be too simple, however, to conclude that lianas always differ from trees. There are differences, but Cai also discovered that within a family – he studied the Bauhinia family – plant growth is very variable. This variation depends in turn on the growth form and light requirements. / Martin Woestenburg

Zhi-quan Cai obtained his PhD on Wednesday 28 March. His supervisor was Professor Frans Bongers, chair of the Forest Ecology and Forest Management Group.