Researchers here are investigating how the trees use carbon, and it's difficult to find out.

In an unusual experiment, extra carbon dioxide is piped to the trees to create the kind of atmospheric conditions expected in the middle of the century, and instruments measure how the forest reacts.

I need to be very, very careful about what that thing effective.

So too, is the scientist in charge says.

There's still a lot to learn, and he worries.

Governments and companies are rushing to plant trees as an easy answer to climate change.

If you try and use trees to tidy up the mess that we're making front through emissions, you are putting those trees into a very rapidly changing climate on they will struggle to adapt.

This device tracks the movement of carbon dioxide in a healthy forest.

The gas is not only absorbed by the trees, but some is released as well.

What scientists here are finding out is that the way carbon flows into a forest and out of it is a lot more complicated than you might think.

So if mass tree planting is meant to be a solution to tackling climate change.

The trees are gonna have to be monitored and cared for over not just decades, that maybe centuries as well.

Of all the challenges, the task of planting is the simplest.

Shelby Barber from Canada could do an amazing 4000 trees in a day.

People talking about planting millions, billions of trees around the world.

Is it possible, do you think physically, it's definitely possible with the right amount of people there.

A group of people I've personally in three years pointed just over half a 1,000,000 trees.

You can see where we've got the open gap.

Once planted, the trees need to survive and experts of mixing different types to minimize the risks of disease.

It's a bit like making sure you don't put all your eggs in one basket.

You're spreading out your risk.

And then if one part of that woodland fails whatever reason, it gets disease or it can't tolerate feet to climatic conditions.

There are other parts of the forest that a healthy and able to fill in those gaps.

Suddenly, there's momentum to plant trees on a scale never seen before.

So what matters is doing it in a way that ensures the forest thrive.

So they really do help with climate change.

David Trochmann, BBC News.

In an unusual experiment, extra carbon dioxide is piped to the trees and instruments measure how the forest reacts.

This device tracks the movement of carbon dioxide.

The trees are gonna have to be monitored on Cared for.

It's a bit like making sure you don't put all your eggs in one basket.

You're spreading out your risk.

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