Effects of insect herbivory on seedling mortality in restored and remnant tropical forest

Insect herbivory is one of the major drivers of seedling mortality in the tropics and influences plant abundances and community composition. Anthropogenic disturbance can alter patterns of insect herbivory with potential consequences on plant communities in restored forests. We planted seedlings of early- and later-stage successional tree species in 13–15-year-old restored and remnant tropical forests. We then either excluded insect herbivores or left seedlings exposed to examine how insect herbivory-affected seedling mortality. Early-successional seedlings experienced similar decreases in mortality when insect herbivores were excluded from both restored and remnant forest sites, but this effect was smaller and driven by only a few species in restored forests. Later-successional seedlings experienced a stronger decrease in mortality between open and insect-excluded treatments in remnant than restored sites. Our results suggest that herbivory-driven seedling mortality is lower in restored forests, particularly for later-successional seedlings. Results are encouraging from a restoration perspective because recruitment of later-successional seedlings is a key component of ecosystem recovery. However, if reductions in seedling mortality continue over the long term, this may affect tree community composition as succession progresses.

昆虫植食作用（insect herbivory）是热带地区幼苗死亡的主要驱动因素之一，同时可影响植物种群丰度与群落组成。人为干扰可改变昆虫植食作用的发生模式，进而对恢复林的植物群落产生潜在影响。本研究在13~15年生的恢复林与残存热带森林中，栽植了早期演替和晚期演替阶段的树木幼苗。随后分别设置昆虫植食者排除组与幼苗自然暴露组两种处理，以探究昆虫植食作用对幼苗死亡率的影响。在恢复林与残存林样地中，排除昆虫植食者后，早期演替幼苗的死亡率均出现相似幅度的下降，但恢复林中该效应的强度更低，且仅由少数物种驱动。相较于恢复林样地，残存林样地中晚期演替幼苗在自然暴露与植食者排除两组处理间的死亡率下降幅度更为显著。本研究结果表明，恢复林中由昆虫植食作用驱动的幼苗死亡率更低，针对晚期演替幼苗这一现象尤为明显。从森林恢复的视角来看，本研究结果令人鼓舞，因为晚期演替幼苗的定植是生态系统恢复的核心环节之一。但如果幼苗死亡率的降低长期持续，可能会随着演替进程改变树木群落的组成结构。