Songbirds perch in the canopy of the Portuguese Monumental Oak, which was planted in 1783 and is now approaching its 240th birthday.
But soon gangs of men brandishing axes will be coming for it amid the sweltering heat of the Portuguese summer. They move from tree to tree, swinging and striking their one-handed, fan-shaped axes with a precision built over many years.
They are not here to fell these ageing oaks, but to harvest a prized resource from the trunks.
First they cut deep into the bark, then twist their axes and use the handles to prise long cork planks from the ancient oak trees that cover Portugal's biggest province, Alentejo.
It's a skilled and demanding job in the hottest months of the year, when temperatures reach more than 40C. If they cut too deep, the tree will be damaged, risking future harvests and ultimately the tree's survival. Too shallow and the planks aren't good enough to make the finest cork stoppers for the wine industry.
Each group of cork cutters work together quickly and carefully to remove just the right amount of bark, stacking the planks for collection before moving on to the next tree. Each newly-cropped tree looks as though it has had orange socks pulled up its trunk, and the year of the harvest daubed on it in white paint.
Pause for too long in the dappled shade beneath the rows hundred year-old cork oak trees (Quercus suber, or sobreiro in Portuguese), and the men with axes will quickly disappear into the distance. It will be nine years before they return to this part of the forest to harvest the sobreiro again.
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In the meantime, the trees will quietly serve another, larger purpose. As the world clamours to reduce the amount of carbon dioxide (CO2) in an effort to slow climate change, the cork oak tree is standing tall.
Like all trees, cork oaks absorb CO2and through photosynthesis lock away carbon for many years in their roots and branches. Planting forests is a commonly used approach to offset carbon emissions by polluting industries, but when the trees are harvested they are usually cut down and much of their stored carbon is released back into the atmosphere.
But cork oaks are one of the few commercial forests not felled for harvesting. This means the cork tree's carbon storage capacity keeps increasing during the 200 or more years the trees can live.
Most of the carbon remains locked in the tree as it continues to grow. Although cork products contain some of the absorbed carbon, they can have a long life after being cut from the tree. Cork can be recycled and is slow to break down even when discarded.
"They are a carbon sink," says António Rios de Amorim, the fourth generation chief executive of the 150 year old Amorim cork empire – the world's largest producer. "For every single tonne of cork produced we are talking about 73 tonnes of CO2 that are captured."
His figures come from a report by consultants PricewaterhouseCoopers, commissioned by Amorim, which also claims 392g (13.8oz) of carbon is sequestered by every cork stopper. A separate study on cork insulation boards found it was the only material with a negative carbon footprint.
In fact, the Portuguese cork association APCOR claims cork forests retain and store 14 million tonnes of CO2 every year, while scientific research in Portugal by the Instituto Superior de Agronomia (ISA) has confirmed that cork products are indeed carbon negative – storing more carbon than is used in their production. But calculating the total carbon footprint of anything is complicated – transport, processing and the fate of every product made from that resource must be considered.
So, can making better use of cork do more to help the climate?
Cork was first used by the Egyptians and Persians for fishing floats, then by the Ancient Greeks and the Romans who also made sandals and used it to seal amphorae jars. It wasn't until the late 1700s before glass bottles became the wine vessel of choice and their intimate relationship with the humble cork stopper began. Today there are 2.2m hectares (8,494sq miles) of cork forests growing around the world, producing around 13 billion cork stoppers every year, which are used in about two thirds of the roughly 20 billion bottles of wine sold annually.
