The Oscar-winning actress is specifically backing a project aimed at securing the future of Nower Wood, as an "outdoor classroom" for generations.
The ancient woodland, in Leatherhead, serves as a wildlife and environmental education site for pupils from primary to A-Level age.
A fundraising drive aims to raise Â£470,000 to rebuild dilapidated classrooms.
Dame Judi said: "As a local Surrey resident with a love of wildlife, I'm delighted to be supporting Surrey Wildlife Trust and its Nower Wood New Build Project.
"I also recognise the importance of outdoor education and the need to inspire the next generation about wildlife and conservation."

The Dow Jones Industrial Average lost 20 points to end at 20,914.62, while the broader S&P 500 index dipped by just three points to finish at 2,378.23.
The tech-heavy Nasdaq Composite was unchanged at 5,901.
Among the individual shares to rise was jewellery firm Tiffany's after it reported better-than-expected results.
Strong demand in Japan and China, as well as higher prices, helped an overall rise in sales, but profit fell to $157.8m in the fourth quarter from $163.2m the same time last year.
Software company Adobe also saw its shares jump 3.8%, also after beating expectations with its earnings.

Fifty lodges from around Ireland, along with visiting Orangemen and women, attended the event.
The parade, accompanied by 30 bands, made its way along the rural coastal setting into the centre of the seaside village before a religious service.
Many families with young children gathered at vantage points along the route to take in the demonstration.
County grandmaster David Mahon said Donegal prides itself on being a family-friendly day with a relaxed atmosphere.
The parade is the traditional opener to the annual 12 July celebrations marking King William III's victory at the Battle of the Boyne in 1690.
Assistant Grand Master Stuart Brooker told the crowds the institution was "being challenged on many fronts".
"One of the biggest issues we currently face is organised opposition to our traditional parades, and in this respect, we are branded intransigent, and insensitive," he said.
"We have responded by challenging ourselves. And I believe that we have responded in a responsible manner, by reaching out to the wider community as never before."
He added that they have done so "in a spirit of openness and goodwill, evidenced in the success of the Twelfth here in Rossnowlagh."
Dame Judi Dench has been announced as Surrey Wildlife Trust's new patron.
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US shares dipped on Friday, as the rally prompted by the Federal Reserve's rate rise paused for breath.
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Thousands of Orangemen and women have taken part in their annual parade in Rossnowlagh in County Donegal.