On an island filled with weird and wonderful living things, the spiny forest has to be Madagascar's most unusual ecosystem. Endemic to the south of the island, the forest is distinguished by tall, virtually branchless plants with dagger-like spikes, and dumpy succulents with swollen trunks. Elegant sifaka lemurs leap from tree to tree with ease, effortlessly avoiding the lethal thorns.
Squeezed into a cosy nook between its neighbours Nepal, China and Bhutan, the mountainous ex-kingdom of Sikkim is India's greenest state; a thick carpet of pine forest covers much of this mysterious Himalayan region. Cloaked in cloud for much of the year the moist canopy is dripping with epiphytes and beautiful wild orchids. Believed to be the stomping ground of the mythical yeti, other inhabitants include cute red pandas and shy clouded leopards.
The granddaddy of all rainforests, the Amazon is the largest and most biodiverse tropical forest on Earth. Giant anteaters, pink dolphins and jaguars all make the trees and rivers here their home, though many of the plant and animal species are still unknown. It is culturally diverse too: home to over 300,000 indigenous people, some still uncontacted, speaking over two hundred languages. The Brazilian Amazon even has its own world-famous opera house, in the humid city of Manaus.
Few natural spectacles are as striking as the Vermont fall foliage season (from mid-September to October). The air is crisp, plump apples hang heavy on the branches and maple, poplar and birch trees turn brilliant shades of crimson, amber and gold. Widely considered the region's best area for leaf-peeping, Green Mountain National Forest is right in the heart of the action. Leaves change colour from north to south; check www.yankeefoliage.com before heading out.
Next time you complain that you feel old, spare a though for the giant redwood trees of foggy northern California, which can live for over 2000 years. Redwood National Park's Hyperion tree is also the world's tallest. With its head firmly in the clouds, it's bigger than many skyscrapers, at 379.1ft, and a relative teenager at between 700 and 800 years-old. Hyperion's exact location is known only to scientists, but you can still try and hug many of the park's other giants.
Damp, green, vibrant and extraordinarily beautiful, Ecuador's Bellavista cloudforest, high in the Western Andes, feels like the prehistoric habitat of dinosaurs. Veined by silvery waterfalls, the mountains are shrouded in heavy mist for at least part of each day, and covered in mosses, bromeliads and orchids. The forest’s primary attraction is the superb birdlife: there are well over 300 species here, including the masked trogon, tanager-finch, moustached antpitta, plate-billed mountain toucan and countless hummingbirds.
The largest mountainscape in the UK, Cairngorms National Park also contains a quarter of Scotland's remaining ancient Caledonian forest. Once the domain of brown bears and wolves, the native woodland was largely destroyed by climate change and hordes of Vikings, among other foes. Alpha predators no longer roam the forest, but the remaining Scots pines are home to rare red squirrels, capercaillie, beavers and ospreys.
It's hard to keep your eyes on the tarmac as your cruise Maui's Hana Highway – all along the roadside are stunning groves of Rainbow Eucalyptus trees. As the name would suggest, the tree's bark peels off in summer to reveal beautiful traffic-light-coloured ribbons of red, amber and green. The view is even more stunning when the tree trunks get wet from the rain, making the colours really pop.
The largest cactus species in the USA, the unmistakable forked arms of the saguaro give it the "hands-up" appearance of a startled shopkeeper at a Wild West hold-up. Protecting part of the Sonoran Desert, Saguaro National Park is the best place to see these iconic cacti en masse. Standing up to 50ft-tall and with a lifespan of 200 years, many of the best specimens are micro-chipped against poachers.
Home of the cuckoo clock and source of the celebrated Danube River, the Black Forest, stretching 170km north to south, and up to 6km east to west, is Germany's largest and most beautiful forest: so good they named a cake after it. The endless pine trees were once an eerie wilderness – a refuge for boars and bandits – but nowadays the region and its spa towns are much easier to visit.
West of Kyoto lies the pleasant, leafy suburb of Arashiyama. Originally a place for imperial relaxation away from the main court in central Kyoto, the palaces were later converted into Buddhist temples and monasteries. Modern-day visitors come here to explore these temples and the area's stunning bamboo grove. A well-constructed trail meanders its way through the statuesque green trunks, which sigh and whisper in the wind.
Standing tall and strong as Maori warriors, New Zealand's kauri trees are a sight to behold. Once felled sustainably for boat materials and gum by the Maori, the kauri suffered huge deforestation at the hands of European settlers. Waipoua is one of the country's best-preserved pockets of kauri woodland. It's also home to its mightiest tree, the 2000-year-old Tane Mahuta, or "God of the Forest" – a vast wall of bark 6m wide rising nearly 18m to the lowest branches, which are covered in epiphytes.
The mountains running southwest of Rio's Sugar Loaf mountain are blanketed with tropical trees. This is the Parque Nacional da Tijuca, a man-made urban forest of some 120 square kilometres. The original trees here were cut down for hardwood, but the area was re-afforested between 1857 and 1870 to reduce landslides. Now home to reptiles, ocelots, howler monkeys, agoutis, three-toed sloths and myriad birdlife, many believe that Tijuca is the world's largest urban forest.
The muddy and mysterious tidal waterways and mudflats of the Sundarbans comprise the largest mangrove forest in the world. Slinking with ease between the tangled vegetation and labyrinthine islands, there is a large population of handsome Bengal tigers here who pay no regard for the international border between India and Bangladesh. Resolutely wild and untamed, despite being sandwiched between two of the world's most populated countries, crocodiles, pythons and Ganges river dolphins are also resident here.
Quite possibly the oldest rainforest in the world, a visit to Taman Negara is unforgettable. Listen to the cacophony of insect chirps, marvel at giant buttressed tree roots and peer into the understory of palms, luminous fungi, giant bamboo and odorous giant rafflesia flowers. You don't have to go far to encounter the local wildlife either; leopards, rhinos, monkeys, Asian elephants, tapirs, mouse deer and a host of smaller creatures can be found amongst the tangled foliage.
A mermaid's paradise, the giant kelp forests of California's Monterey Bay have an otherworldly beauty. The kelp enjoys the cool nutrient rich waters in these parts and forms an underwater cityscape for its aquatic residents, growing up to 175-feet-tall in places. Small air-filled bladders keep each frond afloat, providing rockfish, leopard sharks and sea otters with an anchor during storms, and a place to hide from predators.
The jungle hereabouts is humid, muggy, dense and very hard to access; it's easy to see why its inhabitants went completely un-contacted until the 1970s. The indigenous Korowai people give a whole new meaning to the phrase high-rise living. They have adapted to this extreme environment by building their homes over 100ft up into the treetops, well away from the forest's vicious mosquitoes. Each house is shared by up to a dozen people and access is via a long series of spindly ladders.
The wide, sparsely populated plains of Alentejo are dominated by vast forests of bushy cork oak trees. The crooked oaks live for up to 25 years, and every nine years their bark is stripped and harvested to make the corks we use in our wine bottles. With the advent of new bottle-corking materials, these woodlands and their resident wild cats, boar, storks and vultures are at serious risk of deforestation and habitat loss.
The high altitude evergreen cedar forests around Azrou shelter several troupes of Barbary apes, one of the wildlife highlights of a visit to Morocco. They roam the forest Planet of the Apes-style in troupes of up to a hundred monkeys. The cedars themselves can lives for over 400 years and grow an impressive 200ft tall, with an attractive canopy of bluish needles. You'll find a Christmassy mix of juniper, holly and fir trees growing on the forest floor.