The coconut palm, Cocos nucifera, impacts forest composition and soil characteristics at Palmyra Atoll, Central Pacific

Question: Cocos nucifera, the coconut palm, has a pantropical distribution and reaches near monodominance in many atolls, low lying islands and coastal regions. This paper examines the ecological correlation between C. nucifera abundance and changes in forest structure, floristic diversity and forest soil characteristics. Location: Palmyra Atoll NWR (USA), Central Pacific Ocean. Methods: Plant surveys were conducted on 83 transects (each 100m). All plants 5 cm in height were identified and counted; large plants were also measured and ground cover was surveyed. Major macronutrients, pH, macro-elements/base cations, micronutrients and pedogenic elements, and thermodynamic stability levels were quantified from soil samples taken at each transect. Results: Even in a low diversity atoll environment, we found that high abundances of C. nucifera corresponded with pronounced differences in forest communities including: lower diversity of established trees and regenerating understorey; higher stem density and stand basal area; lower abundance of major macronutrients; and differences in macro and trace elements and energy content of soil organic matter. Historical natural experiments document that the expansion of C. nucifera was the likely causative agent of these changes. Discussion: Cumulatively, these data show that C. nucifera has important impacts on floristic, structural and soil characteristics of forests where it becomes dominant. Given the high proportion of tropical coastal areas in which C. nucifera is now naturalized and abundant, this likely has important implications for coastal forest diversity and structure.