Recent visitors downtown may have spotted them at the base of the newly planted trees along Main Street. But what are they? What are they for?

"I have no clue," said resident Janette Kinnally looking at the large green bag at the base of one of the trees. "If I had to guess, I think it's for keeping the trees stable," she added. "At the very least, it's interesting."

Janet Mamera, who just moved to Westport, was on her way to Town Hall with her grandson when she stopped to survey one of bags.

"I have no idea," said Mamera, tossing the question over to grandson, Matthew, 5. He just shook his head. "Seems he doesn't know either," Mamera said.

Dan Charnas, waiting for his wife while she shopped, thought they provided some protection for the trees.

While resident Lucy Rios said she knew the bags held water because she saw "water dripping from one of them" while she was walking her dog downtown, earlier in the day.

In fact, the bags, installed at the request of the town's tree warden, Bruce Lindsay, provide up to 20 gallons of water and can be refilled weekly to provide hydration to the new plantings needed through the harsh heat of summer.

He said the watering sacks will be replenished with an additional 20 to 30 gallons of water every other week.

"The initial growing years are hardest on newly planted trees, especially in difficult site conditions like Main Street due to the radiated heat from cars, asphalt and sidewalks," Lindsay explained. By providing adequate hydration now, he said the trees will be able "to acclimate to the environmental conditions they have been planted in and will root out, thus ensuring a healthy start to life."

Trees that previously lined Main Street, some of which had been in decline, were cut down in 2012. That decision was made by the town's previous tree warden in concert with the Downtown Merchants Association.

Removal of the trees became controversial when members of the Tree Board questioned the propriety how the decision was made and demanded that they be replaced. Avi Kaner, during his campaign for the Board of Selectmen last year, was also outspoken in favor of replacing them.

Last December, Lindsay received a donation of 34 trees from Planters Choice Nursery in Newtown, valued at about $8,000 to be used as replacements.

The trees that now line Main Street came from that donation.

Charnas, after learning what the bags are for, said it is a good idea. "It's important to protect them and keep them healthy and help them grow," he said.