(Reuters) - Outdoor apparel retailer Timberland is testing online shoppers' willingness to help the environment by slowing down delivery as Amazon.com AMZN.O drives retailers toward pricier, more polluting one-day shipping.

FILE PHOTO: Company logos are pictured outside a Timberland shop in Vienna, Austria, April 21, 2016. REUTERS/Leonhard Foeger/File Photo

New Hampshire-based Timberland, part of VF Corp VFC.N, since August has offered to plant a tree every time customers choose to have their orders delivered in 4-8 days versus the standard 3 days.

Customers hit the brakes on more than 18% of all Timberland orders during the holiday season’s Black Friday to Cyber Monday shopping spike. Acceptance has averaged about 14% and resulted in about 55,000 tree plantings so far.

The effort, part of the retailer’s commitment to plant 50 million trees by 2025, comes as shippers are under pressure to reduce transportation-related emissions that contribute to extreme weather, higher temperatures and rising sea levels.

“Hopefully it’s a step toward making a larger impact,” Tracy Smith, Timberland’s vice president for North America, told Reuters.

The race to deliver everything from televisions to toothpaste in one day could upend the emissions reductions that come from replacing individual car trips to the store with deliveries from a single truck. Experts say that fast deliveries require more trips with cars, vans and climate-damaging airplanes.

Timberland charges for fast shipping, an option less than 5% of its customers choose.

It did not quantify the cost savings from its tree-planting program. Experts said switching from 3-day delivery to a slower service could cut a retailer’s shipping costs by roughly 20% and create a halo of goodwill.

“Not only are you saving money, you’re being the good guy,” said Robert Passikoff, founder of Brand Keys, a marketing consultancy.

Timberland’s campaign is in line with shifting attitudes, said Passikoff, who polls tens of thousands of consumers each year. Apparel shoppers are becoming less interested in delivery speed and more interested in sustainability, he said.

Amazon.com has committed to putting 10,000 zero-emission electric vans on the road by 2021 and founder Jeff Bezos this week committed $10 billion to curb climate change. Meanwhile, the company is using more airplanes, the most polluting mode of transportation.

The world’s biggest online retailer is quietly encouraging shoppers to slow down deliveries. It offers $1 credits toward music or other digital purchases if shoppers choose “no-rush” shipping.

Amazon declined to comment on how many customers choose that slower shipping option.