? This is the boreal forest（北方森林）. The largest forest on Earth. 750 billion trees smothered by snow throughout the winter. This is the northermost boundary of an extraordinary world.

? I‘m standing at the edge of the Arctic Circle（北極圈）. To the north of me, lies a land dominated for most of the year by snow and ice. 3,000 miles to the south, the tropics, bathed the year round in warm sunshine, and in between, a very different world, dominated by relentless change.

? An endless cycle of four distinct seasons, each with its own challenges. The short, freezing days of winter give way to the urgent?awakening of spring. And the long hot days of summer yield to the cooling of autumn.?

? Opportunities will be brief. To survive these extremes, plants have not only got to be hardy and resilient, but many of them have developed special strategies in order to meet the demands of this seasonal world.

? To succeed, they must get their timing just right. For months now, this world has been asleep. But change is coming.

Seasonal Worlds

? ??Spring is on its way.?In Canada, the forests are starting to stir.

? Throughout the winter, the sugar maples（糖槭）?here have kept stores of nutrients ready for this moment. Now, as temperatures start to rise, those nutrients must be brought up from the roots. Sap is on the rise. Fuel for new green growth.

? But just as growth reaches full speed, robbers arrive. A sapsucker（黃腹吸汁啄木鳥）. A thief, in search of maple syrup.?

? The tree can tolerate hundreds of wounds, but if they completely encircle the trunk, the tree wil eventually die. The sapsucker's beak-in hasn't gone unnoticed.

encircle:?to form a circle around?:?SURROUND

? Hummingbirds（紅喉北蜂鳥）...

? squirrels...

? and insects all invade the supsucker's territory, trying to steal a meal. But unwittingly, they help the tree. Time spent chasing the competition means less time to drill new holes. The tree gets a chance to repair its wounds, and the sap can rise freely again.?

unwittingly:not knowing : UNAWARE

competition此處：one's competitors

? So this year at least, the tree will once more produce its leaves. Hundreds of miniature solar panels that collect energy from the sunlight. Each leaf is covered by millions of microscopic pores, stomata. They take in carbon dioxide and release oxygen and water vapour, in a process that produces high energy fuel. All the trees here can now use that fuel to grow over the coming months.

? As spring proceeds, the power of the sun increases.

? On riverbank across Europe, many plants have been lying dormant underground waiting for the earth to warm. And now a race begins.

? Among the first to start are nettles（異株蕁麻）, the sprinters. Then, only just behind, come the brambles（懸鉤子屬）. They are much more aggressive and have backward pointed hooks with which to scramble over their rivals. Last to come, the climbers（攀緣植物）. Hops（啤酒花）...and briony（瀉根屬）. They lasso their way towards the light.

scramble:to move or climb hastily especially on all fours

lasso(n.):?a rope or long thong of leather with a noose used especially for catching horses and cattle?:?LARIAT

lasso(v.): to capture with or as if with a lasso : ROPE

? Soon every inch of space and every patch of light has been claimed. But hidden in the shadows, another plant has been waiting to make its move. This, is dodder（歐洲菟絲子）.

? A hunter with an exceptional sense of smell. Moving swiftly, it searches for its prey. It detects the scent of a young nettle.?

? The dodder punctures the nettle's stem and sucks out the nutritious sap. And it doesn't stop at just one victim. With its energy supply assured, it multiplies.

? It's a parasite, with an insatiable appetite.

? But remarkably, its victims can now exploit the dodder when other springtime enemies appear.?

? Caterpillars！

? When under attack, a leaf sends out a signal telling the rest of the plant to start building defences, foul-tasting toxins that deter the caterpillars.?

deter:?to turn aside,?discourage, or prevent from acting

? In an extraordinary twist, the stems of the dodder interconnecting the plants are now being used as lines of communication to relay these warning signals from plant to plant. They respond by producing their own protective chemicals.?

relay此處:?the act of passing along (something, such as a message or ball) by stages

? Eventually the whole riverbank becomes one huge defensive network, and the one time rivals are now better off together.

? The first warm days of spring encourage some plants to flower and get ahead of the competition, creating beautiful displays throughout the seasonal world.

? From the spectacular cherry blossoms of Japan

? to the goldfield flowers of California（加州金原菊）

? But spring flowering is risky. If they flower too early, it may not be warm enough for pollinating insects to be active, but the common daisy gives them every opportunity.

? The warmer the flowers are, the more attractive they are, and they have a remarkable strategy in order to maximise this.

? They were closed up tightly throughout night, as a protection against the elements, but once they feel the warmth and the light of the sun they spring into action.

spring此處: to move quickly and suddenly towards a particular space; spring into actoon=start taking action

? It's a behaviour called heliotropism（向陽性）. They turn to keep facing the sun, absorbing as much heat as they can.

? This is a thermal camera, and it will tell me the difference between the surrounding temperature and the temperature in the centre of a daisy flower. The surroundings, 12 degrees, in the centre of a flower, 21.

? Pollinators such as bees and wasps prefer the warmed-up flowers, because they can get a share of the heat for themselves. As a consequence, they can collect more nectar from more flowers, pollinating as they go.

? And the daisies, with the help of their pollinators, are able to have a particularly long flowering season. But when the window of opportunity is brief, even more ingenious tactics are necessary.?

window此處: ?a?period when there is an opportunity to do something窗口期

? Here in southwestern Australia. Summer temperatures can soar to up to 40 degrees Celsius.

? Now, for a brief moment in the cooler spring, flowering plants must get busy.

? And this Hammer Orchid（鉛色槌唇蘭） with its strange flower is doing exactly that. It needs to attract a?pollinator, but has no nectar and doesn't even look like a flower, unlike these neibouring, huge grass trees（刺葉樹）.

? These produce thousands of tiny white flowers, all dripping with nectar.

? But the orchid has a different strategy.

? It synchronises its emergence with the brief mating season of the thynnid wasp（刺臀土蜂）. The flightless female wasp produces pheromones（信息素） to attract males.

? This male detect a scent that seems to be hers, yet flies right on by.

? The orchid not only has the same shape and colour as a female wasp but it sits at the same height?as she does. It even mimics her smell and the beguiled male attempts to mate with it.

beguile: to persuade, attract or interest someone, sometimes in order to deceive them

? He hammers against the orchid's pollen sacks and the wasp leaves, doubtless a little shaken, only to be duped once again.

hammer此處：to hit or kick something with a lot of force

dupe此處: =duplicate;?to deceive or cheat easily

? The pollen on his back now sticks to this different orchid and the deception has worked. The orchid's imitation is even more intoxicating it seems, than the real thing.

intoxicating: making you feel excited, happy, and slightly out of control

? Eventually, the male wasps tire of the orchid's enticements. Now the wasps, both male and female, find the flowers of the grass trees to feed, and there, at long last, they mate.

? And as for the hammer orchid, pollination is complete.

?As summer approaches, the need of flower?becomes more urgent and nowhere more so than here in South Africa.

? This is the Fynbos（凡波斯）, part of the Cape（好望角）? Floral Kingdom, a great expanse of open healthlands（歐石南灌叢）??just North of the Cape.?

? Here, there are more?different species of plant than anywhere else in the world. Nearly nine thousand, many needing pollinators.

? They compete with one another for such help by flaunting extravagant shapes and vivid colours, all promising nectar as a sugary reward.

flaunt: to show or make obvious something you are proud of in order to get admiration

? But there is a plant here that avoids this crowded competition, and the rising temperatures of summer bring just what it needs.

? This is the first fire here for 15 years. Nearly all the plants are destroyed. Incinerated. It might seem from the smokes and the still smouldering embers that no plant could survive such an inferno.

incinerate: to make fire or damage with fire

smoulder(smolder): to burn slowly with smoke but without flames

ember: a piece of wood or coal, etc. that continue to burn after a fire has no more flames

inferno: a very large uncontrolled fire

? But just 4 days after the flames, rising from the ashes, a Fire Lily（垂筒花）.

??It has been lying dormant underground for 15 years, but now, awakened by the smoke, it flowers.

???The blooms may be small and unshowy, but that's all they need to be. In this charred landscape, pollinators such as these sunbirds（南方重領花蜜鳥） can spot these little red beacons from great distances.

charred: burned and black

?They are the only source of nectar around, and the more visitors the flowers attract, the more likely they are to be pollinated.

? It's just in time.?

? Within?a few months, the whole landscape is alive once more. In fact, all these plants need fire to survive. And as competitors return, the fire lily?fades.

? It now?returns underground and will rest there as a bulb until another fire awakens it.

?By the time, the long hot days of summer arrive, wildflower meadows are bursting with life, but autumn is not far away.

? So now, pollinated plants must use their remaining energy to produce the next generation, seeds.

? A dandelion clock contains around 200 seeds, each with its own tiny parachute.

? Few seeds can fly as far as these, some are known to have travelled over 60 miles. But to travel any distance at all, they need the wind to be just right.

? However, before they can get away, there is a risk. Voracious hunters live in this meadow.

Voracious: very eager for something, especially food

? Tiny harvest?mice（收割鼠）.?

? They love dandelion seeds. But they don't like to share.

? Finally, the sun warms the ground, and a gentle breeze blows in, creating an ideal updraft.

updraft: an upward movement of gas(such as air)

?Air flowing between the bristles create a vortex that lifts the seeds up.

? Heading off on a gentle breeze, this seed now?starts its travel.

? Plants use a variety of different techniques to spread their seeds as far as possible from themselves, and one of the most remarkable is this one. It's called Ecballium（噴瓜） and it's a relative of the cucumber.

? For several weeks now, pressure has been building up inside the pods, and so now they're as taut as a well pumped up bicycle tyre, all they need is just a slight nudge.

taut: tight or completely stretched

nudge: to push something or someone gently, especially to push someone with your elbow to attract the person's attention

? The further the plant can fire its seeds the better. If a seedling germinates close to its parent, the two will have to compete for nutrients and light.

? This Himalayan Balsam（喜馬拉雅鳳仙花）has seed pods that react rather differently, like catapults（彈射器）.

? As they dry out, they begin to strain along precisely positioned lines of weakness and then just the slightest disturbance, even a single raindrop is enough to trigger the mechanism.

? The east coast of South Africa. Summer here brings scorching temperatures.

?This Ceratocaryum（銀白鑷被燈草） has to get its seeds underground before it gets too hot and it has acquired somewhat unlikely allies.

? Dung beetles（蜣螂）.

?They have a particular fondness for antelope（羚羊） droppings.

? At this time of the year these beetles bury the dung and lay their eggs on it.?

? And the?fresher the better.

? Ceratocaryum's spindly stems send their seeds flying.

spindly: long or tall and thin, and looking weak

? They are the same size, shape and even smell remarkably like antelope dung.

? The beetles simply can't resist them.

? Dung beetles always bury dung balls at the same depth and it's one which suits the seeds very well. So effective is the seeds' deception that the beetles come back for more, time and time again.

? Most of the Ceratocaryum's seeds get safely buried exactly where they need to be.?

? As the sun begins to retreat, so autumn arrives. The cooler, shorter days are the cue for many seasonal forests to prepare for the winter shutdown.?

? The trees starts to divert their nutrients back into their roots, and there, other organisms await them.

? Fungi.

? Mushrooms are the familiar?face of fungi but they are merely the fruiting bodies（子實體）, some of them only last for a few days. There are however, evidence of the giant organisms that lies in the soil beneath.

? Just a single handful of soil may contain several thousand metres of their microscopic filaments.?

??It's only recently that we have discovered the extraordinary role that these fungi play in a forest like this.

? Their filaments plug?into the tips of the trees' roots, and nutrients?pass between tree and fungus thoughout the year. Some fungi have the ability to link with not just a single tree but with a whole group of trees, so that the entire forest may be linked together by these microscopic threads from what you might call a wood-wide web.

plug: to fill a hole with a piece of fuitable material

? Hundreds of trees? can be interconnected by these webs. Scientists call it the mycorrhizal（菌根）?network, and it might look something like this.

? They've discovered that trees not only send nutrients along it but chemical and electrical signals allowing them to communicate with one another.?

? But some?trees can also be selfish and steal from their rivals or even wage war by sending out toxins that will harm competitors.

wage: to fight a war or organize a series of activities in order to achieve something

? It seems however, that most trees do try to help each other. They raise the alarm when attacked by leaf eaters, giving other trees time to produce defensive chemicals. Those that are dying may send their food reserves to their neighbours and some individuals known as Mother Trees（母本樹） recognise their own offspring and will channel resources to them so giving their young the best possible start in life.

? As the harshness of winter approaches, temperatures woodlands（溫帶森林） from Russia to Canada are now in a race to shut down.

? The green pigment（葉綠素） in the leaves starts to break down and nutrients are withdrawn into the branches.?

? The chemicals substances that are left behind then create one of the most spectacular displays of colour in the whole of nature.

? The first freezing nights of winter bring with them a killer...

? Frost!

? Stems, when frozen, rupture, and flowers of ice form in the chilly air.

rupture: to (cause something to) explode, break, or tear:

? For some, winter brings dormancy, for others, it brings death. Another cycle of?the seasons comes to an end.

? Plants all cross the seasonal world have developed many different strategies for success, but they all depend on the seasons changing reliably year after year.

? It doesn't matter whether you live for 3,000 years or just a few months, everything depends on you getting the timing just right.

? But in our changing world, this is becoming a greater challenge every year, and even the most hardy and resilient of plants are starting to struggle.

? These sequoia trees?are the giants of the natural world, the largest living things on the planet. They can grow to almost a hundred metres tall and eleven metres across. Their bark alone can be over a half a metre thick.?

? They're also among the oldest, some living to over 3,000 years. And to achieve such age and size, they need very particular living conditions such as are found here in the Sierra Nevada mountains（內華達山脈） of California.

? Not only do they need energy from the sun, but critically they also require up to 4,000 litres of water a day, so they are almost entirely reliant on the seasonal snowmelt.

? But recent years have brought longer, hotter summers and their source of water is becoming increasingly unreliable.

? Scientists are discovering that even these seemingly indestructible giants are now starting to show signs of vulnerability. Some are shedding their needles（針葉） and branches as a way of conserving percious water. But for others, climate change has already been fatal.

cone（此處）: the hard oval-shaped fruit of a type of evergreen tree (= one that never loses its leaves), called a conifer:松果

? 10% of them have been lost in just the last few years.

? A single giant sequoia（巨杉） in its lifetime can produce a hundred million seeds. These, in my hand from one cone are more than enough to start a completely new forest.

? But they can only do such a thing in a world where the seasons change with some reliabilty. Today our climate is changing, bringing an unprecedented level of unpredictability, all across the seasonal world.

? The question is, can we curb climate change sufficiently to ensure that the seasons will continue? Only if we can do that, with the future of seasonal plants, including these magnificent trees, be assured.