The thing about fall leaves is that they fall, sometimes from one person's tree onto a neighbor's yard.

	Matt Freed, Post-Gazette The stump of a city-owned red maple that was cut down by a Brighton Heights homeowner stands between feuding neighbors' homes in this 1998 photo. The two neighbors are still angry at each other over the tree issue. Click photo for larger image.

That can make normally reasonable people get irrational, especially if the mounds of leaves come on the heels of root-buckled sidewalks or overhanging branches from the same taunting, just-over-the-property-line tree.

William F. Elmendorf has heard from them.

"I get the calls: 'I came home and my neighbor cut down my tree.' Or, 'My neighbor dug a trench to the property line and took out all the roots of my tree,' " said Elmendorf, assistant professor of urban and community forestry at Penn State University's School of Forest Resources. "There's screaming and yelling. The police might become involved."

Mike Rudman, director of public works in Mt. Lebanon, has heard from them, too. So have Evans City arborist George A. Pegher and Gale McGloin, executive director of the Pittsburgh Mediation Center.

"We as a culture don't teach interpersonal skills," said McGloin. "Folks don't know how to bring up uncomfortable topics, or how to deal with someone's anger, or know if they blow up, they can still de-escalate the situation."

She said she has talked to City Council aides who take calls on neighbor disputes, including ones between tree huggers and haters. "They say that when they suggest mediation, the caller says, 'I don't want to talk to the person. That's why I'm calling you!' "

Rudman finds the same thing in Mt. Lebanon.

"Most people when they call, they want us to fight their battles for them. Some neighbors can be rather difficult. But we tell them it's out of our control," said Rudman. The municipality gets involved if the tree poses a danger, but not if it's a nuisance.

One person's nuisance, of course, is another's mighty oak, and the emotions run high on both sides.

"Absolutely, people become passionate about trees. Trees are objects that are enduring and they ground people in the places they live," said Elmendorf. "They help people cope with change because of their enduring nature. People become fundamentally attached to trees."

And sometimes quite aggravated by them.

"There are people who hate trees, because they're messy, or heave the sidewalk, or block the view," said Elmendorf. "And there are neighbors who drink too much on a Saturday and whack down a neighbor's tree."

Pegher said his firm deals with tree disputes on a regular basis. Last week, it was the neighbor of one of his clients who said that the toxicity of the roots of his client's black walnut tree made it impossible for her to grow anything in her yard.

"You can get into real tough situations, especially with invasive roots," he said. He also has to be aware of potential hazards -- a branch overhanging a children's play area in an adjoining yard, for example.

Sometimes, though, he said that the disputes have more to do with humans than trees: "It's just a neighbor thing, and the tree is an innocent bystander. If it wasn't that, it would be something else."

Pittsburgh attorney Ken Yarsky said that some cases do go to court, but more often they end up in arguments between the parties.

"Usually it just creates animosity between neighbors," Yarsky said, "and people all of the sudden are not speaking to each other anymore."

A tree dispute that started in 1998 has lost none of its fury for Brighton Heights neighbors Art Victor and Russ Dippel. After Victor bought a house on Orchlee Street, but before he moved in, Dippel took a chain saw to the city-owned red maple in front of Victor's property that Victor says was a main attraction of the house for him.

Dippel said the tree had caused $10,000 of damage to his property because its roots were entangled in his sewer system.

Victor was furious -- is still furious -- with both Dippel and the city, which he says did nothing to punish the lawbreaker next door.

"If I started cutting down trees on Grant Street, I would be arrested," Victor said. "This guy cut down a tree worth $25,000. The city did nothing, took no action. They offered to plant a sapling. I declined. It was a pathetic replacement. It's outrageous to me that they allow a guy to do something like this."

Dippel thinks Victor is the unreasonable one.

"It was resolved," he said. "Three lawyers from the Allegheny County Bar Association heard the case at the Allegheny County Courthouse. I made restitution with the city -- the city owned the tree. Mr. Victor thought I owed him restitution too. That was the whole thing in the first place. That animosity still goes on. We don't speak two words to each other."

Those who deal with disputes said they try to convince people to talk it out.

"We suggest the Mr. Nice policy," said Rudman. "We suggest they confer with the neighbor."

If the conference doesn't work, however, here are some rules of more active engagement.

Though it's against the law to chop down your neighbor's nuisance tree, it's perfectly legal to cut the branches and roots all the way to the property line. Even if your cutting kills the tree, you're within your rights in Pennsylvania

"I think people think, 'That's my tree, you can't do anything with it,' but that's not what the law says," said Yarsky. "The law says that overhang constitutes a trespass. I have the right to use my property up to the sky. It would be no different if someone built an awning overhanging onto a neighbor's property."

That goes for roots as well.

"The roots of a neighbor's tree can ruin the yard, create a nuisance, create a tripping hazard, damage lawn mowers," said Yarsky.

Tree ownership is determined by the trunk: Even if most of the tree occupies space on one property, if they trunk falls within the neighbor's property line, it's his or her tree. In cases where the trunk straddles the line, ownership is joint and nothing can be done to the tree without consent of both owners.

"It's quite clear that property owners have the right to trim trees that come on their property under law in Pennsylvania," said Pittsburgh attorney Andrea Geraghty.

You can't trespass in the process, though.

"If a neighbor comes onto my property and damages or removes a tree without permission, I can sue," said Elmendorf. "It happens in America all the time, every day."

Elmendorf had his own neighbor tree dispute, but found a way to resolve it.

"I have all these walnut trees on a joint property line. My neighbor hates them. I love them. What we've done is split the cost of pruning trees on her side. I get a good arborist, because I know what I'm doing, and so there's a reconciliation."