Compositional variation in understorey fern and palm communities along a soil fertility and rainfall gradient in a lower montane tropical forest

Abstract

AbstractQuestionsFerns and palms are key components of tropical wet forest understories. The distributions of these groups are influenced by variation in rainfall and soil properties, although the degree to which their resource requirements overlap remains unclear. Palms and ferns also represent extremes in a spectrum of reproductive traits, which may impact habitat requirements and compositional turnover. We asked whether: (a) environmental variables influence fern and palm distributions in a similar manner across a gradient in soil nutrient availability; and (b) larger propagule size and lower reproductive output in palms result in greater spatial aggregation of populations and, consequently, greater distance–decay rates in community similarity in palms than ferns.LocationOld‐growth premontane forest, Fortuna, western Panama.MethodsAll ferns and palms were sampled in fifteen 5 m × 5 m subplots in each of 12 one‐hectare plots. The plots span a strong gradient in soil nutrient availability related to parent material. Light, precipitation and soil variables were measured in each subplot. Species associations were analyzed using ordination and regression, as well as Procrustes and Mantel tests.ResultsParent material significantly impacted compositional similarity of both ferns and palms, with fern compositional variation related to total soil N:P ratio and red:far red (R:FR), and palms with bulk density (p < 0.05). Palm and fern abundances were not correlated; however, tree fern abundances showed an opposing abundance relationship with total soil N:P and R:FR compared to herbaceous ferns and palms. Distance–decay rates in compositional similarity were slightly higher for palms than ferns.ConclusionsFerns and palms show similar patterns of compositional variation in response to resource availability but were related to distinct environmental factors. Soil fertility and light availability emerged as key factors in predicting the abundance of plant groups, with clear partitioning of environmental gradients only apparent when tree ferns were compared with other groups.