by Nico Arcilla and Alex Glass
A yellow-browed sparrow (Ammodramus aurifrons) caught and released in a clearing in white-sand forest in Peru's Allpahuayo-Mishana National Reserve. Credit: Nico Arcilla.
Tropical forests host an estimated 62% of global terrestrial vertebrate species on less than 20% of the Earth's land area and provide resources that directly benefit ~1.5 billion people throughout the world.
Despite their incomparable importance for maintaining life on Earth, tropical forests have been subject to unprecedented anthropogenic degradation and conversion over the past century. Most of the world's forests are now logged for use as human commodities, and tropical forests are no exception.
While many logged forests are lost forever due to their subsequent conversion to agriculture or other human uses, some are protected, allowing them to recover and regenerate over time. This raises a question: What do the impacts of prior disturbance mean for wildlife in forests regenerating after logging or wholesale clearance?
To investigate this question, we worked together with Peruvian colleagues to take advantage of a unique opportunity to quantify changes in forest understory birds in areas where logged and cleared forests were allowed to recover after the establishment of the Allpahuayo-Mishana National Reserve. This 58,070-hectare protected area in northeastern Peru hosts rare white-sand forests and wildlife in Amazonia, the largest tropical forest region in the world.
Characterized by nutrient-poor sandy soils, high densities of straight, relatively short trees, and low species diversity relative to other areas of Amazonia, white-sand forests nevertheless make important contributions to regional biodiversity by hosting many endemic species, including globally threatened and near-threatened birds such as the Allpahuayo Antbird (Percnostola arenarum) and White-masked Antbird (Pithys castaneus), as well as the Iquitos Gnatcatcher (Polioptila clementsi), and Mishana Tyrannulet (Zimmerius villarejoi).
The discovery of this unique biodiversity inspired the establishment of the Allpahuayo-Mishana National Reserve after this area had become the subject of logging and land clearance starting in the 1980s, due to state-sponsored efforts encouraging human settlement in this region. Its designation as a protected area in 2004 put an official halt to logging and land clearance in the reserve, although some illegal exploitation has continued, especially around villages that were established prior to its founding.
In our study, we examined the extent to which bird communities and forest structure were affected by human impacts prior to the establishment of the reserve, sampling birds with mist nets to compare avian communities in undisturbed tropical forest, selectively logged forest, and secondary forest regenerating on abandoned agricultural fields.
We quantified birds and habitat structure at 12 study sites: three forest sites selectively logged between 1996 and 2000, three sites cleared in the mid-1980s to establish sugarcane plantations and later native fruit trees, and six undisturbed primary forest sites. White-sand forests in the Allpahuayo-Mishana National Reserve are interspersed with more common, nutrient-rich clay soils, and we conducted field research in both habitat types.
A path winds through white-sand forest in the Allpahuayo-Mishana National Reserve. Credit: Nico Arcilla.
We found that after a 19-year recovery period, selectively logged sites hosted similar bird communities to undisturbed sites, and within 26 years had recovered sufficiently to display similar bird communities and vegetation structures as nearby undisturbed primary forest sites. The recovery of these sites within this timeframe was enabled in part by the protection of these sites from post-logging human impacts and their locations within a primary forest landscape where interior-adapted birds could recolonize forests.
By contrast, forest regenerating from agricultural fields had lower bird species richness, with fewer insectivores and frugivores. Many Amazonian forest birds follow army ants (Eciton spp.) to hunt arthropods, and ant-following insectivores in particular declined with past disturbance intensity, likely due to the increase in ground cover vegetation in high-disturbance sites. More details of our findings are the subject of a recent publication in the journal Birds.
What does this mean in the bigger picture? We believe our findings offer reasons for hope in the conservation of tropical forests, as well as present a cautionary tale. Critical actions taken by the Peruvian government in this case included the protection of forests from post-logging disturbance due to the establishment of the reserve.
The white-plumed antbird (Pithys albifrons) regularly follows army ant swarms to hunt for insects and other small animal prey. Credit: Nico Arcilla.
In addition, the maintenance of adjacent uncut reserves and large contiguous forest tracts constituted a source from which bird species recolonized logged forests, so that logged sites were comparable to unlogged sites within two decades post-logging.
On the other hand, the most significant driver of tropical forest destruction worldwide has been its conversion to commercial agriculture. For example, many tropical forests have been converted to commercial plantations, including cocoa (Theobroma cacao) in West Africa, oil palm (Elaeis guineensis) in Southeast Asia, and coffee (Coffea spp.) in the Americas.
Our analyses suggest that in former agricultural plantations allowed to return to forest, bird species richness and composition may lag behind those of undisturbed forest sites even after a 40-year recovery period. Full recovery of forest biodiversity on former plantations may take much longer, primarily due to the slow rate at which many forest-interior specialists recolonize these habitats.
Meanwhile, forest regenerating on former agricultural plantations supported more nectarivores, such as hummingbirds, than other forest sites. Our results suggest that maintaining high tree density and a low proportion of ground cover vegetation are important for conserving forest-dependent bird communities, so these structural traits should be encouraged in regenerating forests to provide habitat for vulnerable forest bird species.
The great-billed hermit (Phaethornis malaris) is an nectarivore that may increase in abundance in forest areas with lower tree densities due to past logging and land clearance for agriculture. Credit: Nico Arcilla.
One important lesson from these examples is that all is not lost for biodiversity after logging, if decisive conservation action is taken in time. Forest frugivores such as the blue-capped manakin (Lepidothrix coronata) and insectivores such as the black-faced antbird (Myrmoborus myotherinus) were among the forest species that recolonized regenerating forests on old agricultural plantations within the first few decades of recovery.
In fact, one surprise during our fieldwork that delighted us was the capture of a black-faced antbird that wore a uniquely-numbered band from a previous research project in 2010, indicating that this individual was at least 13 years old! As the life histories of many tropical species remain very poorly known, our encounter with this individual was an exciting reminder of how much more we have to discover. We commend our colleagues in Peru for their timely intervention and hard work to protect the living treasure that is Allpahuayo-Mishana National Reserve.
The black-faced antbird (Myrmoborus myotherinus), one of the more abundant avian insectivores in the Allpahuayo-Mishana National Reserve, is one of many forest species that recolonized forest regenerating from agricultural fields Credit: Nico Arcilla.
This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate.
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