Jeanne Drennan enjoys the memories that certain trees bring -- specifically the several hundred she has helped plant over the past 20 years.

"I see them growing bigger and bigger," the Wilkinsburg resident said, "and it makes me wonder what they mean to the people who put them there."

For Drennan and some other local tree planters, the trees are a reminder of how they have improved the world through a environmentally, physically and socially fulfilling activity.

Drennan plants trees both as a hobby and as a member of the Nine Mile Run Watershed Association. The nonprofit group plants trees in "tree-deficient" areas to improve the flow of water throughout the 6 1/2-square-mile watershed consisting of Wilkinsburg, Swissvale, Edgewood and parts of Pittsburgh, including Frick Park.

Jeff Bergman, program director, said trees aren't only planted for the aesthetic view, but to aid the flow of storm water, especially in urban areas.

While Drennan appreciates the environmental benefits, she also enjoys the social perks of participating in group plantings.

"The neat thing about the tree plantings is that it brings out a great mix in the community," she said. "You get to meet other people who are concerned about trees and the health of the urban forest."

Peg Seidel, of Confluence, has hosted private tree-planting parties on her property at least once a year to improve her Somerset County property, provide cover for animals and as a memorial for her late husband, George Seidel, an outdoorsman and statistician for West Virginia University's School of Agriculture and Forestry.

"He started this and I just thought it was something that I should keep going," Seidel said. "But it's more than that."

Seidel, 55, hosts at least one tree planting per year where anywhere from 20 to 30 friends and family show up to plant seedlings, enjoy nature and even pitch a tent.

"It's like a reunion," she said. "We have a beautiful view, have a fire and some folks even stay for the weekend."

At least 20 people are expected to help plant 100 trees in April.

Seidel's group usually plants hemlocks and red and white pines around her 66-acre farm, but also has added shrubby dogwood along a creek bed because it thrives in the wet environment.

Neighbor and family friend Bryon Shissler, a wildlife biologist, helps Seidel chose her trees. He recommends that beginning planters consider their needs and budgets.

Native trees such as pines, oaks and hemlocks are generally safe choices, he said. But Shissler says to be cautious of invasive insects and animals that may inhabit certain areas. Shissler advises novice planters to avoid letting roots dry out, ensure that the trees are planted at the right depth and to pack the soil around the roots without leaving air gaps.

"Most nurseries provide these instructions on how to plant them and take care of them," said Seidel, 56. "Some people don't take those instructions seriously, but they really should."

NMRWA generally plants native trees and some noninvasive non-native trees. Bergman said larger "shade trees" are most beneficial long-term, but urban street planting sometimes requires smaller "utility compatible" trees that won't disturb utility wires.

Honey locusts, pin oaks, elms, maples, hornbeams and crabapples are chosen because they are drought resistant and generally tolerant of road salt, soil compaction, air pollution, heat from asphalt and concrete.

NMRWA invites the public to help plant trees throughout Wilkinsburg and Swissvale on April 11 in the annual GreenLinks Tree Planting. Volunteers will plant 50 trees throughout urban areas. Trees. The trees are at least 2 inches in diameter and 12-15 feet tall, and are either donated or purchased with funds donated by local government and community groups.

TreeVitalize Pittsburgh, a partnership between Allegheny County, the City of Pittsburgh, the Western Pennsylvania Conservancy and Friends of the Pittsburgh Urban Forest, is hosting public plantings in 11 Pittsburgh neighborhoods most Saturdays through the end of April. Information about the program and how to join in can be found at www.paconserve.org or 412-586-2396.

Drennan will continue planting trees -- and making memories -- and encourages others to participate in their respective communities.

"The more you can get involved, the more you'll care," she said. "I've been involved in this for 20 years. I'm in pretty deep."