Forests found healing poorly from human incursion, worsening conservation headache

Road expansion and fires are weakening tropical ecosystems more than previously thought, and full recovery could take centuries, new research suggests, highlighting the disconnect between biodiversity goals and agricultural expansion.

Forest logging road
A dirt track running through a forest in Sumatra, Indonesia. Image: GRID-Arendal/ Flickr.

It doesn’t take much zooming in on satellite photos of tropical Asia or the Amazon to find wiggly beige lines – dirt roads – criss-crossing swaths of rainforest, linking towns and farms to larger cities.

New research published on Wednesday suggests such that slicing up of forests, especially for agricultural expansion, damages local ecosystems and harms their recovery more extensively than previously thought. 

European scientists studying tropical forests in Asia, Africa and South America found that farm and road expansions, and fires reduced trees’ biomass and height up to 1.5 kilometres from the forest edge. Previous studies had assumed such impacts dissipated after 120 metres.

The new results, published in Nature journal, observed that the “overall spatial impact of fragmentation across the pantropical belt is severely overlooked by at least 200 per cent”. The study estimated that impacted areas could represent just under a fifth of the global tropical forest area in 2022.

The study postulated that already weakened trees allowed damage to creep further into the forest. Forest fires for instance, were more likely to occur where previously burnt and dead trees helped sustain blazes.

Weakened forests could also be more accessible to hunters and loggers, thus enabling them to venture in deeper and cause more environmental damage, the study added. Fires were generally more destructive than selective logging.

Still, impacts were most pronounced right at the forest edges. Average tree canopies were up to 25 per cent shorter, while biomass fell by as much as 35 per cent – though huge variations within the datasets.

This latest research used a laser-based instrument on the International Space Station (ISS) to scan tropical forests, which captured more fine details compared to past studies that relied on satellite-borne optical sensors.

Compared to historical data, the ISS’s scans also suggested forests took longer than expected to fully recover from fragmentation or burning.

There was “no significant recovery” in biomass and tree height 30 years after a forest edge was carved out, researchers said. While there was some growth in shorter trees, tall specimens matching the height of surrounding healthy forest were rare. The data also suggested these weakened forests were more likely to be cut down later.

Full recovery after deforestation or degradation could be on “a centennial timescale”, the researchers estimated.

“Collectively, our findings call for greater efforts to prevent degradation and protect already degraded forests to meet the conservation pledges made at recent United Nations Climate Change and Biodiversity conferences,” they wrote.

Conservation challenges

For decades, agricultural expansion has been the main reason for tropical deforestation globally. In South America, soy plantations and cattle rearing are usually blamed, while common Southeast Asian culprits are palm oil and wood pulp businesses.

Countries such as Indonesia and Malaysia have managed to slow deforestation in recent years through tighter control over their farming sectors. But new deforestation drivers have emerged – such as nickel mining in Indonesia, and its new capital’s construction over forest areas in Borneo island.

At the end of 2022, nearly 200 countries agreed to help conserve 30 per cent of the Earth’s land and seas by 2030, with biodiversity-rich areas like pristine forests prioritised. Since then, the percentage of protected land and inland waters has only crept up from 15.8 per cent to the present 16.1 per cent, while the fraction of marine protected areas dipped slightly.

At the same time, a European Union law banning the import of commodities linked to deforestation and currently set to go live December 30 this year has irked trade partners globally. Indonesia and Malaysia, the world’s top palm oil exporters, complained that the law unfairly impacts smallholders, while the United States has reportedly asked the EU last month to postpone the measure.

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