PORTSMOUTH, N.H. (AP) -- A horse chestnut tree towers over a busy street in New Hampshire's main port city. It's known for its history more than its height; legend has it that William Whipple planted it after returning in 1776 from signing the Declaration of Independence.
But at nearly 70 feet (21 meters) tall, it is also big for a chestnut, and that is what brought Keven Martin out one rainy morning. Armed with tape to measure its circumference and a laser finder to calculate its height, Martin was here to find out whether the tree remained the state's biggest horse chestnut, a title it has held for decades.
"It is not only the biggest, but it's been around a long time," said Martin, who coordinates New Hampshire's Big Tree Program when he is not building boats. More than 700 champions in the state have been crowned. And while there may not be any redwoods out here, the state is home to 10 national champions, including the country's biggest black spruce and American mountainash.
"People appreciate a big tree more, and they have a lot of history to them. People have a connection with them, more so," said Martin, who has written a book on the big trees found on public lands. "They are just a lot more impressive when you see them in the woods or driving by."
Started in 1950, the state's Big Tree Program has been part of a nationwide network run by the conservation group American Forests that has logged some 721 champions across the country — 200 species still don't have a title holder. Created to raise awareness about protecting forest from threats like development and forest pests, as well as a way to better understand why some species grow so large, the effort today is driven by tree lovers like Martin.
They spend their free time scanning highways, historic sites and the state's hiking trials for the next big one.
To find a champion, an owner starts by measuring its circumference and submitting that data to the tree program. Then, Martin or another volunteer goes out to measure its circumference, height and crown, as well as its overall conditions, and come up with a point total. Winners earn a place in the big tree list, and the owner gets a certificate. Some even have their photos taken alongside the tree.
"It's like finding a rare tiger. There is a segment of the population that really connects with trees," said Ian Leahy, director of urban forest programs for American Forests who coordinates its American Biggest Trees program. "There is a just a deep, deep passion. In some ways, it's just out being in nature. It's like hunting, but without killing anything."
But it's not just the thrill of finding a big tree. These forest giants serve as role models of sorts, helping the public understand the outsized role trees play in nature by feeding and sheltering animals, protecting watersheds and providing a sink for carbon that helps to offset greenhouse gas emissions.
They are especially important in a state like New Hampshire, which is 83 percent forested.
"By starting to look at one tree and appreciate it, people start to understand their connection with the outdoors and nature," said Mary Tebo Davis, a natural resources field specialist at the University of New Hampshire Cooperative Extension, which runs the big tree program.
The big trees, like the horse chestnut in Portsmouth, are also popular because they are tied to a historical event or have proven so resilient — surviving sometimes for centuries.
"You can't imagine the number of people who had their picture taken under that tree, groups of kids who encircle the tree," Barbara Ward, the director and curator of the historic Moffatt-Ladd House, outside which the tree stands. "It's such a nice thing for children in particular. But even adults are just awed by the idea that a living thing has been here that long."
Martin was done measuring, and Ward looked on anxiously, wondering whether the horse chestnut had done enough to keep its title. More precise measuring techniques meant the tree had lost some height, but it appeared to have made up the difference by increasing its circumference.
"It's still a champion, yep," Martin said later, after he was able to tally up all the numbers. "It still beat out all the horse chestnuts in the state."