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Old forests are not replaceable

Governments around the world are too slow and too weak in their commitments to stop deforestation. And promises of restoration will not make up for the loss of old forests.

Another month, another record rate of deforestation in the Amazon. Far from coming down from its decadal peak in 2020, the first four months of 2022 have seen yet further increases. The trend is completely counter to Brazil’s signing of the commitment to end deforestation by 2030, made at the 2021 Glasgow COP26 climate meeting.

Much of the deforestation in Brazil and elsewhere in the world is to open up land for growing food crops or livestock grazing. We are rightly outraged over this permanent land-use change, but conversion of old forests to forest plantations should be met with equal consternation. Such degradation is harder to track, but evidence is mounting that not all forest cover is the same.

In this issue, Betts et al. document the detrimental effects on forest-resident bird species of 35 years of habitat change in eastern Canada. Assessing an area of 130,000 km2, the authors show that, since 1985, more than 30,000 km2 of the Acadian Forest has been clear-cut. Most of the area is now occupied by plantations that are dominated by single tree species or a mix of early successional tree species, resulting in a 39% decline in old forest. Yet, total forest cover increased by 6.5% and, from a wood-production standpoint, the area is classed as sustainable.

The authors show that this ‘sustainable’ management, and the net increase in forest cover, has not helped local birds. The authors use back-cast species distribution modelling to show that 66% of the 54 most-common species in the area have lost breeding habitat since 1985. Deforestation — defined as permanent conversion to another land-cover type — was not a primary driver of bird habitat loss in the region but, fitting with the data on tree-cover change, those bird species that were associated with old forest were the ones that had lost most of their species-appropriate habitat. Using data from the North American Breeding Bird Survey, the authors show a strong correlation between habitat amount and bird abundance for all but 3 of the 54 species, and that populations of 39 of the species are in decline.

Betts et al. even note population declines in bird species that are associated with regenerating-forest habitats. They describe this result as ‘particularly cryptic’, given that this habitat type is increasing, but suggest that species that prefer early seral stages may have been affected by climate change. An average of 1 °C of warming has already occurred in the region, and the authors suggest that the more open or shallow canopies of these regenerating forests may have greater than average increases in ambient temperatures, affecting bird physiology. Presumably, birds adapted to regenerating patches may also be adapted to using other services that are provided by the mosaic of old forest but that are lacking in regenerating areas following large-scale clear felling. The nuance of these interactions is a reminder of what the authors also emphasize: that coarse descriptions of forest change, such as simple cover loss, do not effectively quantify species-specific responses.

The paper joins an extensive literature demonstrating the benefits of intact forests over degraded forest systems. These benefits range from greater carbon sequestration and resilience to disturbance through to genetic benefits, lower wildfire risk and more stable hydrological services. Intact forests also provide homes, livelihoods and cultural importance for millions of Indigenous and local people, and are strong magnets for tourism.

The value of old forests must not be minimized by promises of forest restoration. Conversion of already-cleared land to timber plantation will, of course, bring some carbon sequestration and habitat services. And more-concerted efforts to genuinelyrestore forests beyond simple plantation use are hugely necessary and welcome. But even well-executed forest restoration cannot fully regain the functions of old forests over time scales that will compensate for the biodiversity and climate ramifications of their loss.

Yet despite these knowns, the conversion of old forest continues in many countries. It took only days after their signing of the COP26 deforestation pledge for the Indonesian government to clarify that they saw “multiple ways to define deforestation”, defending ongoing logging in their country for the purposes of economic development. And in Australia, the Victorian state government announced in 2019 that it would phase out native species logging — but only by 2030. This inexcusably slow commitment is at odds with analysis showing that the native logging sector in Australia sustains fewer jobs than the timber plantation industry, and that the economic value of the environmental and recreational benefits of leaving old forest in place is higher than its value as harvested timber.

A spokesperson for the UK government, in response to the Indonesian stance on the deforestation pledge, said that “what countries have committed to is to end net deforestation, ensuring that any forest lost is replaced sustainably.” The paper by Betts and colleagues provides one more strand of evidence showing that so-called sustainable forest replacement is mostly a misnomer. Old forests are irreplaceable. Governments worldwide must stop finding excuses to log the fragments of their own old forests that are left, and find innovative ways to support other nations’ development that do not rely on deforestation.

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Old forests are not replaceable. Nat Ecol Evol 6, 653 (2022). https://doi.org/10.1038/s41559-022-01806-y

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