Swiss artist Klaus Littman, who designed the installation, has called it For Forest - The Unending Attraction of Nature.
People can visit it at Wörthersee Stadion in Klagenfurt.
The forest was inspired by a drawing Littman came across by artist Max Peintner, which imagines a world in which nature is only seen in specific spaces like animals in zoos.
Littman said he wanted to take trees that people see every day and make people really notice them.
He said: "This forces people to question things that surround them and that they take for granted - in this case trees."
Littman isn't the only artist to have used his work to speak out about climate change and the environment, though.
Artist Olafur Eliasson and geologist Minik Rosing took 30 huge blocks of glacial ice from water surrounding Greenland and placed them outside the Tate Modern and Bloomberg's European headquarters in London last December.
The blocks of ice weighed between 1.5 and 6 tonnes - about the size of an adult elephant!
The pieces of ice, which were left to melt, were installed to remind people about the negative impact climate change has on the environment.
This pair of giant hands was showcased at the Venice Biennale art exhibition in 2017.
The sculpture, which shows two hands coming out of the city's Grand Canal in Italy, was created by artist Lorenzo Quinn. It represents how hands can be used to both destroy the world, but also save it.
"I wanted to sculpt what is considered the hardest and most technically challenging part of the human body. The hand holds so much power - the power to love, to hate, to create, to destroy," the artist said.
As part of the Global Climate March in 2015, 20,000 pairs of shoes were left on the streets of Paris.
That's because protestors weren't able to march in the city due to security concerns, but climate change marches were held outside of the French capital and across the world.
Irish artist John Gerrard created his piece called Western Flag to show the problems caused by increasing levels of carbon dioxide.
The installation - a digital simulation - shows a flag made of smoke flying from a flagpole.
The artwork was said to represent a site in Texas where oil was struck back in 1901. Oil gushed out of the ground for nine days straight before it was finally brought under control.