Terrestrial pteridophytes as indicators of a forest-like environment in rubber production systems in the lowlands of Jambi, Sumatra

Abstract

Species richness of terrestrial ferns and fern allies (Pteridophyta) may indicate forest habitat quality, as analysed here for a tropical lowland area in Sumatra. A total of 51 standard 0.16 ha plots in primary forest, rubber (Hevea brasiliensis) agroforests and rubber plantations was compared for plot level diversity (average number of species per plot) and landscape level diversity (species–area curves). Average plot level species richness (11 species) was not significantly different amongst the three land use types. However at the landscape level the species–area curve for rubber agroforests (also called jungle rubber) had a significantly higher slope parameter than the curve for rubber plantations, indicating higher beta diversity in jungle rubber as compared to rubber plantations. Plot level species richness is thus not fully indicative of the (relative) richness of a land use type at the landscape scale because scaling relations differ between land use types. Terrestrial fern species can serve as indicators of disturbance or forest quality as many species show clear habitat differentiation with regard to light conditions and/or humidity. To assess forest habitat quality in rubber production systems as compared to primary forest, terrestrial pteridophyte species were grouped according to their ecological requirements into ‘forest species’ and ‘non-forest species’. Species–area curves based on ‘forest species’ alone show that the understorey environment of jungle rubber supports intermediate numbers of ‘forest species’ and is much more forest-like than that of rubber plantations, but less than primary forest. Species richness alone, without a priori ecological knowledge of the species involved, did not provide this information. Jungle rubber systems can play a role in conservation of part of the primary rain forest species, especially in areas where the primary forest has already disappeared. In places where primary forest is gone, jungle rubber can conserve part of the primary forest species, but large areas of jungle rubber are needed. In places where primary forest is still present, priority should be given to conservation of remaining primary forest patches.