When Gov. Jerry Brown pronounced an end to the drought emergency last month — but not to the possibility of another drought — it would have been just like him to quote another eminent Californian, the naturalist John Muir, who said that “we all travel the Milky Way together, trees and men.”

Not enough trees, though, which is why making “urban forests” come true truly matters.

That’s where Igor Lacan can help out. He’s an expert tree advisor with the University of California’s cooperative extension, a kind of Johnny Appleseed of urban forestry, planting the seeds of knowledge about what trees can do for us. And it’s high time for us to ask what we can do for our trees.

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What is your reaction when people say, ‘Yay, the drought is over’?

My reaction is to say, yay, the drought is over. We now need to get back to maintaining our urban trees, which I think we’ve neglected a bit during the drought. We’re witnessing the end of the old paradigm where we’re just trying to remove the water from our urban surfaces, and we are slowly beginning to transition into the new paradigm where we try to use that storm water as a resource.

Trees are regarded as a luxury by some who say, ‘Well, trees, after all, don’t grow in the desert.’

No. 1, trees are not a luxury. Urban trees are an absolute necessity. Trees improve lives in cities, from improvement in health to reduction in crime to increases in property values. All of these things are dependent on living healthy urban trees. Now, I’ve lived in Southern California for a few years myself, and Los Angeles is not actually a desert. There is a small but important difference between not a desert and a desert. Not only that, Los Angeles is an artificial ecosystem at this point, so we really should think very hard about what we want an artificial ecosystem to look like.

When you talk about the benefits of trees, you cite many things, first of all trees as a benefit to public health.

There was a famous study that showed that patients who were coming from surgery and had a view of trees required less painkiller than those who had a view of just a brick wall. And this act influenced hospital design to a certain degree. But, unfortunately, it hasn’t trickled into the broader field of architectural design quite yet.

Humans have a preference for a view or nature in general. Having trees as part of your landscape, as something you look out on when you lift your gaze from the computer, makes a pretty substantial difference.


I also wonder whether it has to do with the fact that our forebears of many hundreds of thousands of years past lived in trees as a safety measure, and trees give you a sense of security.

There are theories in landscape architecture, and one of them is this thing called the prospect refuge theory, that says we prefer these landscapes that have some open space and some trees. It perhaps reminds of us of our very, very, very distant ancestors. It’s not surprising when you look at a lot of classically designed landscape: It’s not just a dense forest but also not plain open spaces — it’s a mix of trees, open space and paths leading somewhere.

There’s another study about how having trees around a house influences babies’ birth weights.

Babies are less likely to be underweight if the mother lived in a place surrounded by trees. That’s very important when you talk about support funding for urban forestry, because if we think of urban forestry as part of our health infrastructure — even as a very small part of our health infrastructure — it suddenly becomes very cost-effective to have healthy, living urban trees.

What kind of numbers are we talking about with low-birth weight babies and women who live surrounded by trees?

The actual number in the problematical birth weight was very small, but when you think about how difficult it is not only for a single family but also an entire society to care for those babies, suddenly that very small effect becomes very important.

If you want to be cold-blooded about it, you can say, ‘Plant trees to save healthcare costs.’

To be honest with you, I do want to be cold-blooded and say that, because we know our ability to influence some of these public health outcomes is quite limited, and trees are one of those things that provide so many different benefits that having this public health benefit on top of all the other things makes the case for trees that much more compelling.


There were also findings about trees increasing housing value, resale value and cutting crime.

When you have trees — and these were specifically street trees or frontyard trees — the price of houses goes up. And the benefit of a tree leaks out to the neighboring houses. In other words, if you have a tree in front of your house and I’m your neighbor, my house also appreciates in value because of your street tree.

Former Los Angeles Mayor Antonio Villaraigosa pledged to plant 1 million trees. When we talk about public trees, I think of tree abuse — trees that are planted and neglected, trees that are put in the wrong places.

We really need to do a better job of planting the trees properly, and then, once they are planted, caring for them. One thing that’s come out of the large-scale tree plantings that were popular in the last decade is exactly that realization: that it’s not so much how many trees are given away at an event, but it’s more how many trees actually survive to grow to reasonable size, provide benefits and then not cause too many problems.

To the credit of our policymakers, they recognize this. One thing we’ve learned is that trees do best in places and situations and during times when there’s good cooperation between residents, community benefit organizations and municipal governments. We are not only trying to plant trees that do well today, but we’re also trying to anticipate climate change and what kinds of conditions we might be facing 10 or 20 years from now.

This is a challenge for urban trees in general: They are a very, very long-term investment. So we are looking at the legacy of urban forestry programs from 50 to 100 years ago. That’s why our cities look like they do.


Did the city of Los Angeles pick the wrong trees to plant 40, 50, 60, 100 years ago?

You know, that’s a bit of a trick question. And I hesitate to say because it’s very easy to look at a single tree somewhere and say, ‘Wow what they were thinking?’ Certainly we can do better, let ‘s put it that way. And I think over time we’re gradually learning to do better.

Everyone’s familiar with the parkway strips of land between the street and the sidewalk. You’ve been working on ‘bio-swales,’ to turn those strips into places that can hold water and even nourish trees.

When you look at a typical residential street, especially in low-density neighborhoods, you have the roadway, then you have the curb and after that you have that green strip, that park strip, where trees are usually planted, and then the sidewalk and then the frontyard. We’re looking for opportunities to manage storm water without sending it into the storm drain. A place where we can do that are these green strips which can be excavated, the soil replaced with the special biotreatment soil mix, and then replanted with vegetation that’s suitable. I think we’re going to be seeing more and more of our green strips replaced with bio-swales.

I don’t know if you have been in California long enough to remember when Ronald Reagan talked about trees as creating pollution.

I do know that quote. It’s quite famous among plant biologists and foresters. The quote is technically correct but it’s highly misleading; in our urban environment, pollution from trees amounts to a vanishingly small fraction of the overall air pollution. Yes, there are some trees that emit more and there are some trees that emit less. But when you look at your urban air quality, biogenic emissions are not something we need to lose sleep over.

There is no such thing as a bad tree, but some trees are better than others. You speak about a tree-benefit calculator that cities can use, that individuals can use, to find out which tree is best.

The U.S. Forest Service has developed a whole set of tree benefit calculators. This is all online; there are calculators you can use if you’re an individual homeowner thinking of replacing your landscape, and the calculator will help you place your tree. There are also calculators that will help you calculate benefits for an entire neighborhood or an entire city.


These are all based on geographic information systems, and you can typically see your house on a satellite image, or see your neighborhood. You just click on the trees that you have or the trees that you’d like to have, and the computer does its magic. It tells you the benefits and it breaks it down for you, from energy to storm water reduction to carbon sequestration. In the next few years, I think we will have even more comprehensive tree-benefit calculators that will help us really make the best decisions.

What cities do this right?

The cities in California that have managed to preserve their legacy canopies. For example, Sacramento is famous for having a large canopy of old trees, and, through an integrated approach from their local community benefit organizations and their municipal government, they’ve managed to preserve a lot of that canopy.

A number of cities have started large-scale tree-planting programs that have morphed into large-scale tree care programs. I would actually point out Los Angeles as one of the cities that is successfully pivoting from a focus on tree-planting to a focus on tree care.

In 1769, in August, when the Portola expedition came through Los Angeles, it noted the water in the streams, and the foliage. Has the landscape changed that much? Have we altered it so much?

Unfortunately, we have. We have covered the ground that would have absorbed the rainfall. We’ve covered it with surfaces like asphalt pavement that don’t let the water infiltrate. So right there, you lose that entire ecosystem that surrounds streams. and that’s where you would have found a lot of trees originally in California. We also have made our environment much warmer, and this is the infamous urban heat island effect. So we have changed the environment quite drastically. The question now is, how do we make the necessary changes to allow those large old trees to survive?


Urban legend aside, it was actress Katharine Hepburn who raised the I-am-a-tree point to Barbara Walters, who responded, ‘What kind of tree are you, if you think you’re a tree?’ I won’t ask you that, but I will ask you what kind of tree you like.

I have no preference whatsoever. I walked down Market Street in San Francisco this morning, and I think it’s probably one of the toughest environments for trees anywhere in the world. And there are these very ordinary-looking London plane trees that are newly planted, and they’re absolutely beautiful, the contrast between a very urban scene and these very nice-looking trees. If you saw them in a forest, maybe you would say they’re quite ordinary, but when they’re in a place like downtown San Francisco, the financial district of San Francisco, they look really extraordinary.

So my favorite tree is any tree that is making it in a tough urban environment.

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