Comparing germination success and seedling traits between exotic and native pioneers: Cecropia pachystachya versus Macaranga gigantea

Abstract

Cecropia is a pioneer genus from the Neotropics, whilst Macaranga is an ecological analog with a center of distribution in Southeast Asia. In the past few decades, introduced populations of Cecropia spp. have spread rapidly in Singapore, Malaysia, and Indonesia. In Singapore, Cecropia pachystachya now occupies habitats that would have been expected to be occupied by Macaranga gigantea. We conducted germination experiments under 0, 20, 50, and 70 % shading and measured the survival rates and functional traits of the seedlings of these two species from material collected in Singapore. Seeds of C. pachystachya germinated in 3–12 days, whereas seeds of M. gigantea germinated from day 13 onwards. Germination success for C. pachystachya was between 90.3 % under full-light conditions and 55.8 % under 50 % shading, while for M. gigantea only 69.1 % of seed germinated under full-light conditions and germination completely failed when seeds were shaded by 20 % or more. The seedlings of C. pachystachya also had higher survival rates, faster shoot and root biomass accumulation, larger leaves, and lower total water content than those of M. gigantea. Thus overall, C. pachystachya possesses traits that may provide a competitive edge over the native M. gigantea and will be advantageous for its spread given the increasing proliferation of disturbed landscapes in tropical Southeast Asia.