Meetings of the Royal Botanical Society of The Netherlands

Pollen records from lake sediments from tropical montane and tropical lowland forest belts show that the floral composition of these ecosystems is subject to considerable change. During glacial-interglacial transitions (some thousands of years) arboreal compositions may adapt to changing precipitation regimes causing transitions from evergreen to semideciduous forest and natural changes in biodiversity, which is, e.g. evidenced by pollen records of Lakes Bosumtwi (Ghana) and Barombi (Cameroon) (Maley, J., 1991, Climatic Change, 19: 79-98). On long time scales, including several glacial-interglacial cycles (>200 000 years) natural adaptation of ecological requirements and migration cause important changes in the floral composition of ecosystems, causing changes in competition between floral elements (Hooghiemstra, H. & Cleef, A.M., 1995, In: Churchill, S.P. el al.. Biodiversity and Conservation of Neotropical Montane Forests, pp. 35-49, New York Bol. Card). Evidence from pollen records of anthropogenic disturbances of montane and lowland forests in the tropics is rapidly increasing. For several classical centres of civilization located in forested areas in the tropics (Inca culture in Peru, Tairona culture in Colombia, Maya culture in Guatemala, Aboriginal culture in Australia), pollen records show clear evidence of the impact of expanding and collapsing civilizations (Islebe, G.A. el al., 1996, The Holocene, 6: 265-271; Herrera de Turbay, L.F., 1984, Studies on Tropical Andean Ecosystems, 2: pp. 531- 545, Cramer, Berlin). Also evidence on the changing composition of crops in centres of civilization may be related to natural climatic change as well as to changes in farming techniques and forest degeneration (Chepstow-Lusty, A.J. et al., 1996, Antiquity, 70: 824-833), Growing palynological evidence shows that natural forest regeneration on century to millennial scale often involves a distinct change in the floral composition and biodiversity. Modem natural composition and biodiversity of ecosystems may be considered as a snap-shot in the course of evolution and these characteristics may be seen as variable on glacial-interglacial time scales. Human disturbance affects tropical montane and lowland forest belts selectively, affecting seriously our heritage of biodiversity.