If you go What: ISA North American Tree Climbing Championship When: 8 a.m. to 9 p.m. Saturday and 8:30 a.m. to 5 p.m. Sunday Where: Thompson Park, 420 Bross St. Cost: Free More info: A full schedule is available at bit.ly/tree-climbing

It’s a bird, it’s a squirrel — it’s a competitive tree climber!

In fact, this week it might be Ray Rockett purposefully navigating among the limbs and leaves as he practices for the North American Tree Climbing Championship to be held over the weekend in Longmont’s Thompson Park.

Rockett, 30, is from Nederland and currently resides in Gunbarrel. He works part-time for Longmont’s forestry department and also freelances for various Boulder County tree-trimming companies as a professional arborist.

Arborists, sometimes called arboriculturists, use ropes and harnesses to manage the growth of tall trees in urban areas.

The North American Tree Climbing Championship is held by the Illinois-based International Society of Arboriculture, and Rockett is one of four competitive tree climbers from the Rocky Mountain chapter of ISA who qualified for this weekend’s event.

Rockett said he’s spending the week leading to the competition resting up.

“It’s my first time competing on this level. There are going to be some really great climbers from all over the country, so there’ll be some stiff competition for sure,” Rockett said.

He added that he feels like the competition’s Longmont locale will give him a slight, but not huge, home field advantage.

“Well, I won’t have to travel and I already live at this high altitude … but it’s not like I’m really familiar with the trees, so more or less, everybody is getting a fair shake out of it,” Rockett said.

ISA and city officials said they expect the two-day event, which will feature 43 competitive arborists from the across the United States and Canada, will draw between 300 and 500 spectators to Thompson Park.

The free event is open to the public and will kick off Saturday with preliminary events and an Arbor Fair.

ISA spokeswoman Sonia Garth said the Arbor Fair will feature food trucks, arts and crafts and a tree-climbing workshop for kids and adults. Some of the crowd-favorite events in the competition are the aerial rescue, in which competitors must safely retrieve a dummy stuck in the limbs, and the “Footlock,” in which climbers race up a tree gym-class style by pushing on a rope with their feet.

The winners of Sunday’s Masters’ Challenge will go on to compete in the international tree-climbing championships to be held in San Antonio, Texas, in April, Garth said.

Because the arborists will use ropes, rather than shoes with spikes to climb the trees, Thompson Park’s seven ash trees stretching between 70 and 90 feet into the air won’t be harmed, said Ernie Wintergerst, an arborist with the city’s forestry department.

Wintergerst is also a member of the ISA Rocky Mountain Chapter and helped land the competition for Longmont.

In fact, volunteers with ISA will climb the Thompson Park trees this week and prune away dead limbs so they aren’t accidentally dislodged during competition, Wintergerst said.

Wintergerst said he’s glad the Rocky Mountain ISA chapter was able to bring the competition to Longmont and the crowds streaming in to watch the event should help the local economy.

“It’s really exciting and rewarding to host an event of this caliber that travels around the country,” Wintergerst said. “Longmont will be the epicenter of the top talent of tree climbers, so it’s a big honor to have those guys showcasing their skills and working in our trees in Longmont.”

Rockett said he was grateful to both ISA volunteers and city employees for putting all the work into the upcoming event.

“It takes a lot of hours that they’re not getting paid for to put this all on and a lot of work to make it all go off without a hitch,” Rockett said.

Karen Antonacci: 303-684-5226, antonaccik@times-call.com or twitter.com/ktonacci