Experimental Assessment of Natural Enemy Impacts on Palm Regeneration at Forest Edge Versus Interior

Abstract

Aims

Forest fragmentation induces edge effects that alter the abiotic environment and plant–enemy interactions, with potential consequences for the regeneration of shade-tolerant species. Importantly, plant–enemy interactions are context-dependent, suggesting that fragmentation can differentially modify natural enemy pressure along edge-interior gradients, weakening some interactions while intensifying others. However, experiments quantifying how multiple natural enemies differentially affect seed germination and seedling establishment at forest edges versus interiors remain scarce. To provide a biotic mechanistic understanding of edge effects in plant regeneration, we experimentally evaluated how natural enemies (vertebrates, insects, and fungi) influence seed germination and seedling establishment of two shade-tolerant palm species, Prestoea decurrens and Synechanthus warscewiczianus, in forest edges and interiors within a highly fragmented landscape.

Location

Choco Forest in northwestern Ecuador.

Methods

In an enemy-exclusion experiment, we manipulated access by natural enemies using wire cages and pesticides and established control plots at 13 paired edge (0–10 m) and interior forest (90–100 m) sites. We monitored seed germination (radicle emergence) and seedling establishment (development of epicotyl and roots) weekly over 5 months.

Results

Germination and establishment were consistently higher in the forest interior for both species, highlighting strong negative edge effects on early recruitment. Insects emerged as the primary natural enemies; they negatively impacted the regeneration of P. decurrens in both edge and interior habitats, whereas for S. warscewiczianus, the impact was restricted to the forest interior. Conversely, fungi and vertebrates had no detectable effects.

Conclusions

Our findings demonstrate that forest edges and biotic filtering through insect predation limited the regeneration of the two understory palm species evaluated, reducing their regeneration potential in forest remnants within fragmented landscapes. Conservation strategies should prioritize maintaining interior forest conditions, minimizing edges when possible, and preventing seed and seedling damage by insects in restoration programs.