Human activities and deforestation have caused 80 per cent of tropical forests to become fragmented in the past two decades, a study has revealed.
The study, published in the journal Science, added that about 51-67 per cent of the forests globally have also become fragmented.
The researchers used fragmentation indices including Connectivity-based Fragmentation Index (CFI), Aggregation-based Fragmentation Index (AFI), and Structure-based Fragmentation Index (SFI) to come to the conclusions.
The assessment noted that fragmentation arises through multiple ways such as shrinking forest patches, splits and vanishing of stretches into complex shapes to distance themselves from each other. Such changes are observed in Amazonian deforestation, which directly affects biodiversity.
The impact on biodiversity depends on three mechanisms including change in microclimates and disturbance regimes, making forests warmer and drier. The other impact is the reduction of core areas, resulting in threatened species relying on large, intact habitats.
The increased patch isolation further disrupts the connectivity and reduced movement of wildlife, causing long-term population declines.
“While edge effects vary, losses of core habitat and connectivity consistently harm forest specialists found consistent tropical forest patch loss from 2001 to 2018, with smaller patches disappearing fastest,” the study said.
Edge habitat also expanded from 2000 to 2010, increasing exposure to disturbances, it added.
The researchers analysed the reasons for forest fragmentation and cover loss to find that fragmentation occurred for permanent conversion such as mining, energy development and urbanisation. Temporary disturbances are described as ‘agriculture conversion’, followed by abandonment for selective logging and wildfires.
The scientists integrated the data from the Global Forest Watch dataset which mapped primary deforestation drivers from 2000-2023 and found the results to be consistent with their previous assessments from 2000-2015.
The results confirmed the growing influence of anthropogenic disturbance, especially shifting agriculture, commodity-driven deforestation, and forestry, the study said.
The researchers used the CFI at 5-km resolution for their analysis and the subsequent assessment of protected areas, as it best aligned with ecological indicators of fragmentation.
They noted that globally, shifting agriculture indicated in 37 per cent of grids with increased fragmentation and forestry at 34 per cent were the dominant drivers of increased fragmentation.
Forest fragmentation was followed by wildfires and commodity-driven deforestation at 14 per cent each.
In the tropics, fragmentation was overwhelmingly driven by shifting agriculture at 61 per cent, while temperate forests were mainly affected by forestry at 81 per cent. In boreal regions, wildfires and forestry primarily contributed in 62 per cent and 38 per cent respectively, the study observed.
Permanent conversions from commodity-driven deforestation and urbanisation accounted for less than 15 per cent of fragmentation globally, it said.
With respect to protected areas in tropics, fragmentation remained lower with strictly protected areas seeing 82 per cent less fragmentation compared to non-protected areas. Less strictly protected areas saw 45 per cent reduction.
“These patterns align with reduced human activity: shifting agriculture was 59 per cent and 16 per cent lower in strictly and less strictly protected areas, respectively, while forestry was 10 per cent and 58 per cent lower,” the study found.
On the contrary, non-tropical forests demonstrated slightly higher fragmentation in strictly protected areas compared to non-protected ones, alongside a 63 per cent increase in forestry activity, the study said.
The authors said the results highlight effectiveness and significance of tropical protected areas to limit human-driven fragmentation and underline the urge need to expand protection in pan-tropical regions to achieve the Aichi Target 11 and the “30x30” goal of the Kunming-Montreal Global Biodiversity Framework international targets.
“Our analysis shows that permanent forest conversion accounts for only 15 per cent of global connectivity-focused fragmentation, while wildfires—intensified by climate change—contribute another 14 per cent. The remaining 71 per cent was primarily driven by agricultural and forestry activities that can often represent temporary transitions, highlighting opportunities for restoration,” the study observed.
Confirming widespread declines in forest ecological integrity in the past 20 years mainly by humans, the researchers underscored the urgent need to accurately assess the changes and address them using effective tools to guide conservation and reverse biodiversity loss.