The Secret Life of Trees

We begin with the tallest trees on earth, the towering redwoods, which can stand as high as 115 metres, taller than the Statue of Liberty. Even these mighty giants start life as a seed just a few millimetres long. For many trees, the creation of new life starts with one of the most dramatic displays in the natural world: blossom. To learn how seeds are actually made, we travel to a beautiful elderflower orchard blanketed by hundreds of thousands of tiny white flowers, to learn that blossom is crucial to a tree ‘having sex'. And once a seed is formed, it uses ingenious ways, like the spiraling sycamore helicopter seed, to travel far from the parent tree. And then from the bare soil a brand-new tree will begin to grow. But the early years of young infant trees can be challenging. On the sunny Italian Amalfi coastline, we meet a lemon farmer whose young saplings must be looked after extra carefully. Their youthful ‘enthusiasm' to grow fruit when they're just a few years old can damage their delicate branches, so he builds scaffolding to support them. From Italy to Kew Gardens in London, where among its 11,000 trees, we learn how leaves are vital to helping trees grow tall and strong. Coming in all shapes and sizes, leaves allow trees to make their own food using the sun's rays. But a tree needs more than just sunlight to grow. Water is vital for a tree to survive, and many trees have found ingenious ways to quench their thirst in some of the hottest places on the planet, from absorbing it from the air to sending their roots deep underground to find it. And in a eucalyptus plantation, we hear the incredible sounds a thirsty tree actually makes when it ‘drinks'. Eucalyptus trees are so thirsty they can drink about a bathtub's worth of water every day. Some trees can reach maturity in a matter of years - the weeping willow grows eight feet taller in a single year, whereas the white bark pine can take 250 years, a quarter of a millennium, to reach their adult size! In the New Forest, historical tree graffiti on a 200-year-old beech tree reveals exactly how a tree grows; this tree, which was young at the time Britain was fighting sea battles against Napoleon Bonaparte, doesn't grow from the base of its trunk up, but from the top. The seasons play an important role in any growing tree's life. At the end of this chapter in the trees' story we journey to the National Arboretum at Westonbirt, as its acer trees burst into a magical display of autumn colour to reveal exactly how this firework display of reds and golds, emerges, following a long summer of growth into adulthood, as trees are preparing for winter.

In this second episode we discover how trees have developed the art of growing and ageing gracefully as they pass from their early years into middle age. We see how they do incredible things in the prime of their lives, how they talk to one another, and even work together to thrive in an often turbulent world. Arriving at adulthood is a major milestone in a tree's life. Some fruit trees get there early, maturing at as young as 5 years old, whereas some trees like North American hemlocks can take 300 years to become an adult. Early in the morning we see a glorious English Oak as it ‘wakes up', stretching its branches as much as 10cm with the rising sun. At 75 years old, this oak tree is just reaching adulthood, and already plays host to more than 2,000 different insects and creatures – more than any other native British tree. Every tree has ‘lodgers' but not all are friendly. In Scotland amongst an avenue of hornbeams, we reveal the incredible details of how trees communicate, using chemical ‘smells' to warn each other of attacking predators. Trees have found ingenious ways to thrive in all sorts of hostile landscapes, including our very busiest cities. The Cheapside Plane is believed to be the oldest living tree in the City of London. London plane trees have a nifty trick to thrive amongst the capital's polluted streets: sloughing off their bark after it has absorbed the grime around them. Trees can overcome many perilous conditions; on the edge of the Arctic circle entire forests of dwarf willows and birches grow no taller than a metre to protect themselves from the freezing winds. And in the summer heat of Tuscany, Cypress trees produce cones that only open with fire or extreme heat; an amazing way to survive against the growing threat of wildfires. But it's often below the ground where trees hold their greatest secrets. In the rolling hills of Dorset, beneath the tree line, is a magical sunken lane called a Holloway. It's here that the wonderful world of tree roots are on display. A growing tree can have up to 30 miles of roots, 90% of which are actually found in the top 10cm of the soil, working hard to feed the tree and keep it upright as it battles the elements. But there's even more to a tree's underground world. In Wales there's a rare piece of rainforest. The forest floor is covered with colourful mushrooms and toadstools; this is all we can see of an incredible network of fungi that runs underground with threads that connect the roots of many different trees. Some experts believe that these networks actually allow trees to ‘talk' to each other, or even help each other by passing nutrients between them. Finally, at Kew Gardens, we learn how trees can ‘heal' themselves when they are damaged. We meet Kew's ‘unluckiest tree', a Corsican pine, that has been struck by lightning twice. The energy of a lightning strike can be as much as a million volts, splitting a tree in two. Luckily the strike on the pine was just on its bark; when trees are injured they are vulnerable to infection but remarkably trees like the Corsican pine can seal their wounds to stop the infection spreading. Trees can survive extraordinary things, from wildfire to lightning strikes, and time after time they show their incredible strength and resilience to live incredibly long lives.

The concluding episode reveals how trees can extend their lives by 'walking' across the land and planting new roots. Plus, how they can 'learn' from trauma, and how a decaying tree has the miraculous ability to nurture new life. In Scotland, Tony Kirkham explores a magical collection of Yews - the UK's longest living trees. He also explores a grove of Monkey Puzzle trees, and explains that the unusual, scale-like leaves of this prickly species are an adaptation to protect it from hungry dinosaurs.