AGAWAM — When people take a walk in the woods on Robinson State Park Day, they may come across ancient trees, special birds, unique creatures and aquatic organisms.

Saturday, June 15, will be a day for visiting nature and hearing from environmentalists, in an annual event that brings people face to face with the park’s flora and fauna. There are trees more than a century old that are so big, it would take three adults holding hands to form a ring around the trunk. Others are as big as cars.

The stars of the show are tulip, pignut hickory and red oak trees.

“Tulip trees are the tallest tree in the forest,” said Rod Parlee, a conservation ecologist. “They have a yellow flower on top and Native Americans used to plant them to mark different areas of their land, because they stick out of the canopy.” Parlee is one of several experts who will be making presentations and taking people on trips through the woods.

Parlee said 450 plant and animal species have been identified and are living in the 800-acre park, everything from bears and coyotes to fisher cats and racoons. And beyond the mighty, there are microscopic organisms living in the pond. There are pollywogs there, too, for children to catch.

It’s nearly summer and the songbirds have arrived, their melodies mixing with life in a vernal pool.

“There’s a unique, small wetland called a vernal pool. They’re like nurseries for amphibians and attract mostly salamanders and wood frogs. It ends up being a breeding area, which if you ever hiked upon a vernal pool around sunset, it’s deafening, the quacking is so loud,” said Parlee.

The day starts at 7:30 a.m. with a bird identification walk led by Stephen Svec, a science teacher at West Springfield High School. Attendees should bring binoculars. The walk is appropriate for experienced birders and people who would like to learn about the birds that find habitat in the park. Vehicles should be parked on Colemore Street, across from the main park entrance.

Starting at 9 a.m., visitors can drive into the park at the main entrance at 428 North St., Agawam. Robinson Park Day events will take place at the Trestle Pavilion. Visitors are encouraged to bring their own chairs, food, water, sun and insect protection.

Between 10 a.m. and 3 p.m., Matt Largess, Susan Masino and Rod Parlee will lead “Big Tree Walks.” Largess will point out and identify the diversity of trees and explain why Robinson State Park is the “Yellowstone of the East.” He is an internationally certified arborist from Rhode Island who was named the “Tree Preservationist of the Decade” in 2006 by Yankee Magazine.

Masino will speak about the connection between brain health and forest health. She is a professor of applied science at Trinity College in Hartford, and a neuroscience and nature researcher and educator. Masino is interested in how public polices can improve brain health, with a special focus on New England’s forests. Forests have benefits for the brain, ranging from increased creativity and cognition to reduced blood pressure, anxiety, and depression.

Parlee will discuss the importance of pro-forestation and the benefits of natural area stewardship.

From 11 a.m. to 2 p.m., a craft station hosted by Maryanne Pacitti of Scattered Seeds Foundation will invite visitors to build Mason bee nests and bee feeders.

Kathie Breuninger lived across the street from the park and she remembers playing there as a child.

“I was fortunate. I had a mother that would say, ‘Go play in the woods,’ and so we always went down there. We hiked down to the pond where we would swim,” she said.

Breuninger is a member of the Friends of Robinson State Park, formed nearly two decades ago to fight a logger’s plans to cut trees and harvest wood from the park.

“They started marking all these trees and that’s when we started raising a ruckus. We went ballistic,” she said.

The environmentalists prevailed. The loggers were turned away, and Breuninger said that was the last real threat facing the park. Even so, the Friends are always on alert and can rally people if there is ever trouble in the woods.

“When we came together, everyone referred to is as ‘my park,’” she said.

By hosting Robinson State Park Day once a year, the Friends are inviting the public to see and connect with a treasured place worth fighting for.

“People go in there and walk with others, or by themselves. It’s quiet,” said Breuninger. “You hear the birds. It’s the whole tranquility of the place that gets people attached to it. It’s someplace where you can go and relax and sit by a brook or river. You can watch ducks. It’s just a very peaceful place to go.”