Effects of a recalcitrant understory fern layer in an enclosed tropical restoration experiment

Luis C Beltrán,Henry F Howe,Karla María Aguilar-Dorantes

doi:10.3897/neobiota.59.51906

Abstract

Establishing mixed-species tree plantings and fencing them to protect seedlings from herbivory is a valuable strategy for reconnecting forest fragments separated by agropastoral lands. However, fencing may provide exotic plants with the escape from herbivory required to invade the understory of planted communities. Here we take advantage of such a situation to ask how the identity of planted species and the resulting canopy cover influenced invasion success by the Asian swordtail fern (Nephrolepis brownii Desv. Nephrolepidaceae) in a 13-year-old tropical restoration experiment. Through a seed addition experiment, we also evaluated the effects the ferns had on recruiting seedlings. We found that the invasion was most acute in the unplanted control plots where canopy cover was consistently scarce. Frond density correlated negatively with canopy cover, though most of the variance in the model is explained by the design of our experiment (r2m = .161, r2c = .460). Between planting treatments that differed in the dispersal mode of the planted trees, the wind-dispersed treatment had higher fern density and longer fronds than the animal-dispersed treatment. The animal-dispersed treatment had the highest recruiting species richness, which was negatively correlated with fern density (r2 = .748). The seed addition experiment confirmed that mortality rates increased where frond density was higher (F1,41 = 7.159, p = .011) and germination rates were lowered for the smaller-seeded species (F1,42 = 13.2, p = .002). To prevent recalcitrant understory layers from establishing in plantings in the future, we recommend: (1) establishing larger plantings or expanding existing ones to minimize edge effects (particularly light filtration), (2) supplementing young plantings with additional seedlings to prevent canopy gaps from forming, and (3) planting an assemblage of species that cover the full forest strata and have consistently full tree-canopies.

Highlights

Mixed-species plantings are established to enhance the natural succession of forests in degraded lands (Parrotta and Knowles 2001; Lamb et al 2005; de la Peña-Domene et al 2013)
Of the 384 1 m2 quadrats established for the census, 306 (80%) were recorded with N. brownii
Pairwise comparisons reveal that the control quadrats have significantly higher frond density than the animal-dispersed treatment (z = 3.417, p > .001) and marginally higher frond density than the wind-dispersed treatment (z = 1.729, p = .083)

Summary

Introduction

Mixed-species plantings are established to enhance the natural succession of forests in degraded lands (Parrotta and Knowles 2001; Lamb et al 2005; de la Peña-Domene et al 2013). These plantings can be used to reconnect forest fragments as a stepping-stone biological corridor, a design that provides greater flexibility of land use for local landowners than continuous biological corridors do (Rey Benayas et al 2008). Eliminating a recalcitrant understory layer is possible when a dense tree canopy cover has already been established, but this is time-consuming and labor-intensive (Hill and Silander 2001; Douterlungne et al 2010)

Methods

Results

Discussion

Conclusion