SCATTERED across the Highlands are ancient forests where the last wild Scots pine trees grow.

These Caledonian pinewoods provide refuge for some of Scotland’s rarest wildlife, from iconic capercaillie to tiny lichens.

Enter one and you’ll see that each old tree looks different than the next – the product of centuries of exposure to the elements and high levels of genetic diversity.

These remarkable woodlands have been shaped and valued by people for centuries. They often have Gaelic placenames, and are part of Scotland’s environmental, cultural and historical DNA.

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Once, thousands of years ago, wild pinewoods covered an estimated one million hectares of Scotland.

Today ­– mostly because of a long history of deforestation – just some 2% of this precious habitat is left, broken down into small and isolated fragments, many now under threat and in poor condition.

Over four years, I have surveyed 71 of the 84 officially recognised Caledonian Pinewoods that survive, walking some 800 miles to gather data from over 1200 survey plots – from Loch Lomond to Ullapool to Glen Ferrick near Aberdeen.

These detailed surveys formed part of the first major study into the health of the pinewoods in over 60 years, carried out as part of Trees for Life’s Caledonian Pinewood Recovery Project in partnership with Forestry and Land Scotland, NatureScot, Scottish Forestry, Scottish Land And Estates, and Woodland Trust Scotland.

The headline finding from our research is that urgent action is needed to prevent many areas of ancient pinewood, home to descendants of trees that first appeared some 10,000 years ago, from disappearing forever.

A quarter of Caledonian Pinewood is now critically threatened, with young Scots pine failing to grow up and replace old trees as they die.

These unique woodlands can no longer support their full range and abundance of wildlife. Neither can they adapt to the seismic changes that are impacting our environment, not least climate change.

The main reason for the pinewoods’ decline, and the biggest barrier to their much-needed recovery, is Scotland’s artificially large deer populations.

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Other threats – including the spread of non-native conifers and emerging impacts of climate breakdown – are all playing their part. But we found high impacts of over-browsing by deer in almost two-thirds of the plots we studied.

Browsing – the eating of tree seedlings by animals – is a natural process that has shaped woodlands for millions of years.

It’s why holly has prickly leaves, birch foliage is difficult to digest, and Scots pine needles taste bad – plants invest heavily in physical and chemical defences to protect themselves.

But browsing levels in the Highlands today are so high that they completely overwhelm these age-old defence mechanisms.

Deer have become desperate – eating the millions of young trees that sprout each year, regardless of how prickly, digestible, or tasty the saplings may be.

It’s a particular problem because the pinewoods have been subject to this kind of intense pressure for so long.

Browsing levels have been sufficient to prevent young trees from growing across much of the Highlands since at least the Highland Clearances, when people were forcibly removed from the land and their livelihoods replaced by large-scale sheep farming.

Sheep stripped much of the tastier vegetation from the hills during the 1700s and 1800s, before giving way to deer during the 1900s as sport shooting became dominant.

Deer were encouraged by careful management and winter feeding which – combined with the eradication of natural predators – allowed populations to soar.

The consequences were clear in many of the pinewoods I visited, where ancient “Granny pines” – reaching the end of their natural lives – no longer have young pines growing nearby to replace them.

The deer are also stripping away other trees, and the diverse range of woodland plants that make up a natural woodland – including wildflowers and berry-producing vegetation such as blaeberry, dog-rose, and honeysuckle.

In the 1990s, there were huge efforts to restore pinewoods by fencing deer out of them. Behind these fences, pinewoods started to recover. But deer have since got inside, preventing further recovery and in some cases reversing it.

One of the saddest things I saw during surveys were fences where 30 years’ worth of pine regeneration was now being killed by over-browsing and bark stripping. This was most often the case in the west, where Scots pine regeneration happens slowly.

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While it is vital for now to repair the fences that have been breached, this is a short-term fix. Fencing off the pinewoods from the wider landscape is also a sign of how perilous their future has become.

A far better approach is to learn from the minority of pinewoods that are recovering well. In parts of the Cairngorms, deer numbers have been reduced at landscape scale, leading to dramatic pinewood recovery and expansion.

Young pines are reclaiming lost ground, connecting patches of old-growth woodland and sprouting at higher altitudes. This allows pinewoods to “move” up mountains and across landscapes to cooler areas more suited to them – giving them the chance to survive the threats posed by climate breakdown.

Reduced deer numbers also helps other ancient woodlands, peatlands, montane scrub, and wildflowers recover, creating a mosaic of wildlife-rich habitat at landscape scale. Whole ecosystems are being put back together.

Deer themselves also benefit, as vegetation recovery increases the amount and quality of food and shelter, allowing them to maintain good condition and survive winters.

This also means there are greater opportunities for skilled deer managers in the Highlands, and experience has shown we can both restore  woodlands and protect rural livelihoods.

The future of Caledonian Pinewoods across the Highlands is tied to our ability to better manage deer populations at landscape scale.

Faced with the overlapping nature and climate emergencies, restoring these unique woodlands has never been more vital.

Achieving this will require leadership from the Scottish Government and commitment by landowners, who could become the generation that pulls these pinewoods back from the brink.

James Rainey is a senior ecologist at rewilding charity Trees for Life (