Oceans and Forests: A New Discovery
Written by: Alejandra Hart
A temperate rainforest coastline where forest meets sea. Credit: Bull and Wolf
Working with associate lecturer Dr. Benjamin Phillips from the University of Exeter, the Woodland Trust has discovered a groundbreaking glimpse into the important interactions between oceans and forests. Until now, these ecosystems have often been studied separately. But by drawing together more than 270 peer-reviewed studies from around the world, the Ocean Forest Links report highlights a far more connected picture of the natural world.
This research shows that when we restore forests - particularly temperate rainforests in places like Cornwall and Devon - we support healthier coastal and marine ecosystems. These relationships are complex but vital, offering new opportunities for a more interconnected restoration approach in land and sea recovery.
1. Forests Feed the Sea and Increase Fish Stocks
Forests do not end at the shoreline. Nutrients carried by rainwater, groundwater, and even wind, travel from trees to tides. Fulvic acids from decomposing forest soils help ocean plankton unlock iron, phosphorus, and nitrogen, forming a natural “forest tea” that supports the base of the marine food web. Studies show that plankton biomass can be up to 10 times higher in estuaries with healthy forested land, offering a richer food supply for fish and other marine life.
Japanese fishers have long observed what scientists are now confirming: healthy forests upstream contribute to abundant fish populations downstream. This relationship has inspired a movement of community reforestation known as Uotsuki-rin, or "Fish Forests".
Like a tea bag slowly releasing nourishment, forests infuse the land and gradually add nutrients to rivers. But when forests are degraded or removed, this process becomes unbalanced. Nutrients flow into waterways too quickly and in the wrong proportions, leading to “ocean malnutrition”: algal blooms, poor water quality, and oxygen-depleted zones that harm marine life.
Salmon populations rely on nutrient-rich freshwater ecosystems sustained by healthy forests, forming a vital link between land and sea. Credit: Brandon
2. Forests Protect Kelp and Seagrass
Cornwall and Devon hold the richest remnants of intertidal oak forests in the UK. These forests, along with woodlands in the wider catchment all the way up to the headwaters, act as natural buffers to pollution run off. Their roots stabilise soils, reduce runoff, and help keep sediment out of rivers and estuaries. Their canopies shade streams, cool water temperatures, and contribute to stabilising coastal chemistry, helping to reverse 'ocean desertification'. All this benefits seagrass meadows and kelp beds, which are highly sensitive to water quality.
Seagrass and kelp are essential habitats: they absorb carbon, support biodiversity, and provide shelter for young fish. But they struggle to thrive when coastal waters become turbid or overloaded with nutrients.
DEFRA has identified over 790 hectares of potential seagrass restoration sites in Devon and Cornwall. The report suggests that combining forest and marine restoration - particularly in catchments near these sites - could bring multiple benefits: cleaner water, healthier marine ecosystems, and stronger carbon storage across both land and sea.
Waves wash over kelp-covered rocks on a temperate coastline. Credit: Greg Rosenke
3. Salmon and Seabirds Feed the Forest
Just as forests send nutrients to the sea, the sea gives back by supporting life on land, particularly through animals like salmon and seabirds.
Atlantic salmon begin life in freshwater streams, migrate to sea, and return to the same rivers to spawn. Along the way, they carry ocean-derived, including nitrogen and phosphorus, back into river ecosystems. Studies from the Pacific Northwest show that trees growing along salmon-rich rivers grow up to three times faster than those along salmon-free rivers. In fact, up to 25% of the nitrogen in trees near healthy salmon populations is derived from the ocean. This remarkable boost is thanks to bears and birds, which catch salmon from the rivers and leave behind nutrient-rich remains in the forest. These nutrients feed the soil, accelerate tree growth and support a web of life including mosses, insects, and birds.
Forest-nesting seabirds, such as the Marbled Murrelet in North America and Manx Shearwater in the UK, play a similar role. They feed at sea and return to nest inland, linking land and ocean food cycles.
In Britain, salmon numbers have collapsed, but we still have migratory birds, otters, and sea eagles - species that reflect these land-sea connections. With the right restoration efforts, these vital links can be strengthened once again.
The Manx Shearwater on a body of water. Credit: RSPB
4. Forests Hold Water and Reduce Pollution
Forests play a vital role in regulating how water moves across the landscape. They store rainfall, reduce surface runoff, and allow water to soak slowly into the ground. This helps lower the risk of flooding and prevents pollutants like sediment, heavy metals, and excess nutrients from reaching rivers and the sea.
During the Industrial Revolution, and in the 1970s, an area the size of Dartmoor was drained in the UK every year. Restoring even a portion of these lost habitats could significantly reduce downstream pollution and improve water quality.
By restoring native woodland and rewetting peatlands, we can help rivers flow more steadily and stay cooler through summer months. In a time of climate instability, this natural capacity for water management is becoming increasingly important.
Forests act as natural sponges, holding water and reducing pollutants before they reach rivers and oceans. Credit: Rapha Wilde
Call to action
While the Ocean Forest Links report is a milestone, it is also the beginning of a new body of research. Most of the studies come from Japan, Patagonia, and the Pacific Northwest. Europe, particularly temperate regions like ours, remains understudied.
To restore the temperate rainforests of Britain and Ireland, we must better understand their role in coastal health. If we want abundant fish, clean seas, and a stable climate, we must look upstream and beyond. To the trees. To the mosses. To the soils.
The Woodland Trust, as part of the South West Rainforest Alliance, aims to triple temperate rainforest cover in Devon and Cornwall by 2050. This new research strengthens the case for linking rainforest restoration with ocean recovery.
Education, collaboration and ecosystem restoration are our tools. But the first step is vision: to see the land and sea as one interconnected ecosystem. To see that when we plant a tree, the ocean drinks. And when we lose a forest, the tide turns.
→ Read the full Ocean Forest Links report by Dr. Benjamin Phillips, commissioned by the Woodland Trust and supported by players of People’s Postcode Lottery. Let this be the start of a new conversation; from forest to fish, stream to sea, tree to tide.
Rainforest Recovery is the South West strand of The Rainforest Restoration Project. It is being led by the Woodland Trust in partnership with Plantlife. This project is funded as part of the Government's Species Survival Fund. The fund was developed by Defra and its Arm's-Length Bodies. It is being delivered on behalf of Defra by The National Lottery Heritage Fund.