Beauty, height and shade were some of the qualities of trees feted on Arbor Day at the Planting Fields Arboretum State Historic Park in Oyster Bay Saturday.

But 6-year-old Arnav of Hicksville, accompanied by his mother Nidhi Caplash, 36, pointed out another important gift from trees: “Oxygen,” he said.

The family, along with Andy Kowalik, 77, of Massapequa, were picking up a few of the many free seedlings the park handed out.

“I’m just going to stick it in the ground and see if it grows,” jested Kowalik.

Arbor Day was started in 1872 by J. Sterling Morton, an early Nebraska newspaper editor; trees are planted as a gift for future nature-lovers.

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“Each generation takes the Earth as trustees,” Morton said, according to the Arbor Day Foundation of Lincoln, Nebraska. “We ought to bequeath to posterity as many forests and orchards as we have exhausted and consumed.”

Saturday’s Arbor Day activities, attended by about 2,600 people, included stilt-walkers, live music, a miniature railroad, and rescue dogs performing tricks.

Kowalik’s seedling will replace a towering pine he got from the Planting Fields some 40 years ago, which suffered from superstorm Sandy’s salt spray in 2012 and had to be taken down because it was just 12 feet from his house, he said.

His new spruce could grow 18 inches high in three years, estimated JoAnn Flora, 70, of Baldwin, one of the gardeners offering advice.

The important thing, Flora recommended, is “the flare at the bottom of the tree,” because the roots need room to bow up a little to ensure they do not suffocate.

Linda Li of Jericho had her 10-year-old twins, Jordan and Madison Lee, look up the symbolic nature of Arbor Day beforehand.

“I don’t want the whole iPad” preoccupation, she said, watching them climb trees — assisted by ropes and some spotters.

Scott Goodman, 20, of East Meadow, summed up the day’s importance after his tree-climbing session.

“I love the outdoors,” he said.

Some youngsters focused on blowing dandelions or had to be warned not to pull one goat’s tail at the petting zoo.

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Though the goats at the zoo attracted lots of grass-offering admirers, Ariel Hardy, 10, of Central Islip announced, “I like the ducks more.”

Her stepfather, William Thomas, 52, pulling 3-year-old Nina and 2-year-old Nino Thomas in a red wagon, particularly enjoyed the Muttville circus dogs.

Brandon Hardy, 5, however, had another star in mind. “I like Batman.”