“Habitat fragmentation in the Amazon rainforest has caused measurable declines in wildlife and plant biodiversity and has disrupted ecosystems.”

“Here we show that forest fragmentation provokes surprisingly rapid and profound alterations in Amazonian tree-community composition. In less than two decades after fragmentation, nearly a fifth of the more-common tree genera have declined significantly (P < 0.01) in abundance, whereas over a tenth of the common genera have increased significantly… Our findings suggest that habitat fragmentation will have pervasive, long-term impacts on the species and functional composition of Amazonian forests… suggesting that compositional shifts are reducing carbon storage in fragmented forests, above and beyond the carbon losses that result from elevated tree mortality.”

The BDFFP, begun in 1979, is the only experimental study of the process of habitat fragmentation under way in the Amazon basin. As one of the longest-term projects evaluating the impacts of human activities in the Amazon, the BDFFP is both a cutting-edge study of forest fragmentation and a model for similar investigations in other regions.

“Over two decades of study in the Biological Dynamics of Forest Fragments Project reveal that Amazonian forest fragments undergo ‘ecosystem decay’… Many species of large mammals, primates, and birds have disappeared or declined sharply in small fragments, whereas generalist and edge-tolerant species have increased… Fragmentation has also altered forest structure, microclimate, and ecological processes, indicating that ecosystem functioning is being disrupted in fragmented Amazonian landscapes.”

This study was conducted within the Biological Dynamics of Forest Fragments Project (BDFFP), the world's longest-running experimental study of habitat fragmentation. The authors state that fragmentation and associated microclimatic seasonality affect forest structure and canopy understory dynamics, and they note that carbon losses from forest degradation already exceed those from deforestation in the Amazon.

We concluded that forest species should maintain a threshold of approximately 30% of habitat to avoid a significant abrupt decline in overall connectivity. We were able to demonstrate that below 32% habitat, overall regional connectivity in Southeastern Amazonia erodes, disturbing the ability of species to track environments within their climatic limits.

Researchers found that, between 2000 and 2022, the Brazilian Amazon lost about 30,000 km², or 10%, of natural non-forest vegetation. “These ecosystems are among the least protected in the Amazon biome,” lead author Cassiano Messias said. “The continued loss of these ecosystems, many of which occur as isolated islands within the Amazon rainforest, represents a significant loss for both scientific knowledge and the biodiversity of the biome.”

Summarizing results from the Biological Dynamics of Forest Fragments Project, the article notes: "Results suggest that edge effects play a key role in fragment dynamics, that the matrix has a major influence on fragment connectivity and functioning, and that many Amazonian species avoid even small (<100-m-wide) clearings." It states that "The effects of fragmentation are highly eclectic, altering species richness and abundances, species invasions, forest dynamics, the trophic structure of communities, and a variety of ecological and ecosystem processes." It also emphasizes that forest fragmentation interacts with hunting, fires, and logging, "collectively posing an even greater threat to the rainforest biota."

Overall, natural vegetation cover declined from 90.9% to 62.7% between 1986 and 2020, and fragmentation greatly increased, generating more than 70,000 fragments of forest vegetation and 90,000 fragments of non-forest vegetation. We warn that these environmental impacts on a landscape scale have severe ecological and socioeconomic consequences, especially for traditional and Indigenous peoples.

“In Central Amazonia, 9 to 19 years after fragmentation, we recorded species richness and net seedling recruitment rate in forest fragments of 1, 10, and 100 ha and in continuous forest… Species richness of tree and herb seedlings in Central Amazonia, recruited 9 to 19 years after fragmentation, is significantly lower in fragments than that recorded in continuous forest. The results not only suggest that loss of plant species will occur, but also that a qualitative change in life-form and species composition in forest fragments is occurring.”

Reviewing long-term datasets from fragmented Amazonian forests, the article notes that fragmentation has led to "persistent changes in tree community composition, with declines of shade-tolerant, large-seeded, and late-successional species and concomitant increases in fast-growing, disturbance-adapted taxa." It states that these community changes are associated with "reduced aboveground biomass and carbon storage, and altered regeneration patterns," indicating that fragmentation has both reduced tree biodiversity and disrupted key ecosystem functions such as carbon cycling.

“Although habitat fragmentation is widely associated with biodiversity loss, a subset of species can benefit from the creation of edges and small forest patches… In Neotropical forests, several studies have reported higher abundances or species richness of bats, some generalist birds, and disturbance-tolerant plants in fragmented habitats or along edges compared to forest interiors… These findings caution against assuming uniformly negative biodiversity responses to fragmentation and emphasize taxon-specific and context-dependent effects.”

In this study of 1200 saplings from 337 species, the authors found that "There was a positive and significant effect of forest fragment area on herbivore damage, with plants from continuous forest having twice as much damage as plants in the smallest fragments studied (1 ha)." They suggest that forest fragmentation may affect the dispersal of insect herbivores and "reduce their abundances on small forest isolates." The paper concludes that "Altered patterns of herbivory on tree saplings may have important consequences for forest structure and dynamics," indicating disruption of plant–herbivore interactions and ecosystem processes, even though in this specific case herbivory is lower in the smallest fragments.

Discussing the consequences of deforestation and fragmentation, the authors state that "Forest fragmentation and edge effects have already degraded large areas of remaining forest, leading to increased tree mortality, changes in species composition and loss of biodiversity." They further note that fragmentation "disrupts ecological processes such as pollination, seed dispersal, and nutrient cycling" and warn that continued landscape fragmentation could push many Amazonian species towards local or regional extinction.

They found that since 2001, between 40,000 and 73,400 square miles of Amazon rainforest have been impacted by fires, affecting 95% of all Amazonian species and as many as 85% of species that are listed as threatened in this region. Since the 1960s, the Amazon has lost about 20% of its forest cover to deforestation and fires.

“Their meta-analysis revealed consistent negative effects of forest fragmentation on mammalian species richness and community composition, highlighting the pervasive influence of habitat fragmentation on mammalian biodiversity… Studies indicate that species richness tends to decrease as fragmentation increases, primarily due to habitat loss, reduced connectivity, and edge effects… Fragmented landscapes consistently supported lower densities of large mammals, underscoring the vulnerability of large mammal populations to habitat fragmentation.”

“Nonvolant small-mammal assemblages in Amazonian forest fragments showed reduced species richness and altered community composition compared to continuous forest… Edge and matrix-tolerant species often became more abundant, whereas forest-interior specialists declined or disappeared from smaller, more isolated fragments… These patterns indicate that habitat fragmentation in the Amazon can lead to measurable biodiversity loss and community reorganization in small mammal communities.”

Results suggest that edge effects play a key role in fragment dynamics, that the matrix has a major influence on fragment connectivity and functioning, and that many Amazonian species avoid even small, 100-m-wide clearings. The effects of fragmentation are highly eclectic, altering species richness and abundances, species invasions, forest dynamics, the trophic structure of communities, and a variety of ecological processes.

We synthesize findings to date from the world’s largest and longest-running experimental study of habitat fragmentation, located in central Amazonia. Over the past 32 years, Amazonian forest fragments have shown pronounced edge-related changes in microclimate, tree mortality, and species composition, indicating that fragmentation alters ecosystem structure and functioning.

“A study examining responses of Amazonian bats to varying degrees of fragmentation indicated higher species abundance and richness in fragmented versus continuous forests (Klingbeil & Willig 2009). The findings were attributed to positive edge effects, such as higher forage availability and refuge from predation near forest edges… These results highlight that not all taxa respond negatively to fragmentation and that some groups can benefit from increased edge habitats.”

The paper directly examines forest fragmentation in an Amazonian landscape that has been fragmented for over a century. It frames fragmentation as a long-term disturbance affecting ant community composition, abundance, and species turnover, which is relevant evidence of biodiversity change from habitat disruption.

A new paper in The Condor: Ornithological Applications summarizes four decades of data from the project about how Amazonian bird communities respond to habitat fragmentation. The work reports that fragmentation changes bird community composition and reduces the abundance of some forest-dependent species.

Long-running experimental and observational studies in the Amazon, especially the Biological Dynamics of Forest Fragments Project, have repeatedly found that fragmentation changes species composition, increases edge effects, and reduces abundance of many forest-dependent animals and plants. The strongest contrary view is usually not that fragmentation has no ecological effect, but that the magnitude of impacts varies by species, habitat type, and landscape context.