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One of the major pushes to protect biodiversity while increasing the planet’s ability to store carbon is to revert unused farmlands to woodlands, and eventually, mature forests. However, that’s easier said than done, as a new study in the U.K. shows that ex-arable woodland planted a quarter century ago still has a biological makeup distinct from that of nearby semi-natural woodlands, including different soil chemistry, smaller fungal communities, and greater plant diversification.This isn’t all bad news, as the study also notes that while replanted woodland retains scars of its farming past, its chemical and species makeup grows increasingly similar to that of ancient woodlands over time.
When neolithic Britons meticulously constructed Stonehenge around 5,000 years ago, ancient woodlands made up 60 percent of what is now known as the United Kingdom. Today, such woodlands—defined as being untouched for more than 400 years—make up only a measly 2.5 percent of the country’s forests. And considering that ancient forests are well-known havens of biodiversity as well as excellent carbon-storing resources, this drastic disappearance is a big problem.
Bringing back such forests won’t be easy—after all, they’re ancient for a reason—but the U.K. wants to transform at least 200,000 hectares (772 square miles) of farmland into low-grade woodland by the year 2050 as part of the country’s net zero strategy. Now, a new study may highlight the best way to do it. In 1999, in Kent County in southeast England, a 12-hectare plot of ex-arable farmland, located near a semi-natural ancient woodland, was replanted with oak, ash, linden, and hornbeam trees, along with hazel and hawthorn woody shrubs. These native plants make up the W10 National Vegetation Classification (NVC) community and together they matched the composition of ancient woodland nearby.
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Then, at irregular intervals from 2001 to 2024, botanists carried out surveys of the newly planted woodlands that included soil samples, canopy photos, and tallies of species distributions across the habitat to create the first direct-observation study that tracked the transition from ex-arable farmland into woodland. The results of the study were published in the journal Forest Ecology and Management.
“The aim of this study was to directly examine the transition of plant communities and soil properties as farmland developed into ex-arable planted woodland, in comparison to nearby ancient woodland,” the authors write. “Our results showed that soil properties and plant communities in ex-arable and ancient woodlands remained significantly different 25 years after land-use change.”
Led by scientists at the University of Reading, the research team combed through the data and found that the replanted woodland had a higher pH, more available phosphorus, less nitrogen, and less total carbon than the ancient forest, but also relatively greater plant species diversity due to a lower carbon-nitrogen ratio. As was expected, ectomycorrhizal fungal communities (a symbiotic fungal group) remained richer in the ancient forest as the researchers positively correlated fungal richness with soil pH and species diversity.
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While the two plant communities remained distinct in significant ways, the researchers found that the replanted farmland’s composition was slowly becoming more like that of the ancient forest. However, they noted that the U.K.’s own Biodiversity Net Gain policy, which pushes developers to transform land into woodland within 30 years, might be too difficult to realize. They concluded by recommending that reforestation efforts target farmland located near natural or semi-natural ancient woodland.
“Our findings deepen understanding of how species and environmental factors interact during afforestation,” the authors write. “The insights gained can help inform the selection of woodland restoration sites and improve projections of woodland development, particularly where an accelerated transition toward ancient woodland conditions is a management objective.”
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.