Plant Geographic Studies on Dipterocarpaceae in Malesia

Abstract

The primary lowland forest of tropical Southeast Asia west of Wallace's Line have the peculiar feature that they are dominated as regards the numbers of emergent trees and volume of timber by a single family, the Dipterocarpaceae. The timber produced by trees belonging to this family is often sold in the United States under the rather misleading name Philippine mahogany. Renewed interest in this family among scientists and environmentalists in the U.S.A. stems from the studies of military forest destruction in Vietnam, and the opening up of large new American timber concession holdings in Indonesian Borneo and Sumatra. There is an awareness that the Dipterocarpaceae are a unique object for biosystematic and plant geographic study besides being the most valuable renewable natural resources of extensive areas of Southeast Asia (Foxworthy, 1946; Slooten, 1961; Ashton, 1969b; Jong & Lethbridge, 1967). They are, as regards sizes of trees, biomass and number of species, the most successful family among all Angiosperm families in Southeast Asia. The unexploited forests of Borneo and Sumatra represent a fortune of many billions of dollars in timber value. From a purely scientific point of view, the Dipterocarpaceae are extremely interesting because they occur in areas which have had a relatively stable geology since the Cretaceous, probably the time of their origin. Since that time they have spread over Southeast Asia and over Africa; possibly they occur in disguised forms also in the American tropics as plants now considered to belong to Tiliaceae. In their leaf forms and indumentum they show Malvalean characters. The flowers of the African Monotes have short androgynophores, and their barks have slime ducts as in some Tiliaceae. The Dipterocarpaceae proper have resin canals in their woods and the flowers have calyx lobes which enlarge