Bizarre Cecropia pachystachya (Urticaceae) hemiepiphytic growth on palms in the “Pantanal” wetland

Abstract

In this study, we describe for the first time facultative hemiepiphytism in Cecropia pachystachya Trecul growing on palms in the “Pantanal” wetland of Brazil and investigate ecological factors associated with this unexpected phenomenon. We sampled C. pachystachya seeds lodged in palm stems and recorded the seed rain to low stems, high stems and to the ground below and away from palms. We also tested seed germination on soil and stem substrates and measured the chemical composition of both substrates. Compared to freestanding conspecifics, hemiepiphytes of C. pachystachya were rare and displayed wider trunks but similar height. All hemiepiphytes were fixed on low stems by aerial roots encircling the palms and coalesced branches rooted into the ground. Most palm stems contained C. pachystachya seeds but a few concentrated seeds massively. Dispersal of seeds was 15 times greater to lower than higher portions of stems, and seven times higher below palms than elsewhere. Germination rates of C. pachystachya seeds did not differ between soil and stem substrates. The clayey stem substrate presented more Zn, K, P, Ca, Mg and Al than the sandy soil, which in turn presented more Fe and Cu. The exceptional occurrence of C. pachystachya as a facultative hemiepiphyte in the “Pantanal” wetland results from massive seed rain to lower regions of palm stems, where germination, mechanical stability and access to nutrients are conducive to establishment and subsequent growth. However, the rarity of hemiepiphytism in C. pachystachya indicates that opportunities for successful establishment rely on a combination of uncertain spatiotemporal conditions.