UC Santa Cruz

In recent years, tropical forest restoration has experienced a sharp rise in popularity as a means to combat forest loss. Governments, industry, and conservation organizations are investing billions of dollars annually to restore tropical forests, yet many ecologists caution that restoration efforts must move beyond simple tree planting to consider a variety complex ecological and social factors that influence restoration outcomes. Here, I examine three such factors with an emphasis on interactions between biota in restored forests and among actors involved in implementing incentive-based environmental policy.

First, within the context of a 15-year old forest restoration experiment in southern Costa Rica, I use two manipulative experiments to examine how plant-insect interactions affect seedling herbivory and mortality. I focus on mutualisms and antagonistic interactions between plants and insects as they are known to drive tree community dynamics in intact tropical systems but remain relatively unexplored in restored forests.

In my first chapter, I investigate how a mutualism between a disturbance-adapted ant and scale insect affects scale infestation, biological control of scales, and folivory on a hyper-abundant, early-successional seedling. When excluding the scale-tending ants, I observed increased herbivory and scale infestation on host seedlings. I also found that biological control of scales increased along with forest cover in the surrounding landscape but only on seedlings where ants were excluded. These results suggest that the presence of disturbance-adapted ants confers protection to a highly abundant seedling which may contribute to the proliferation of this early-successional species in restored forests.

My second chapter focuses on the influence of insect herbivory on tree seedling mortality. In restored and remnant forest fragments, I excluded insect herbivory from multiple tree species of different successional stages and found that seedlings exposed to insect herbivory suffered greater mortality than those in insect exclosures. Further, this effect was more prominent in remnant than restored forests suggesting that restored forests may have reduced insect herbivory that could affect tree community composition as succession continues.

My third chapter investigates how different intermediary actors in Costa Rica’s payments for ecosystem services (PES) program influence program implementation and whether payments are sufficient to support smallholder farmers who participate in tree-planting PES strategies. Through interviews with intermediaries, I found that NGOs and agricultural centers offer a different suite of PES strategies than private PES agents with the latter focusing on large-scale forest conservation as opposed to small-scale tree-planting. Yet, all PES intermediaries were constrained by low payment amounts that affected their ability to work with smallholders and tree-planting strategies. Interviews with farmers revealed that PES payments from tree-planting rarely covered opportunity costs from converting commodity crops to PES land uses. I conclude that for PES to be a viable option to restore small-holder landscapes in Costa Rica, the program should increase payment amounts for tree-planting strategies to better incentivize both intermediaries and farmers to participate.