Portland, Oregon, is adding residents faster than it almost ever has. Multnomah County has seen only two decades in its history with bigger booms: the 1900s and the 1940s.
But this time, something is almost certainly different: Portland is adding trees, too.
As noted last week by my colleague Dan Bertolet, there’s nothing inconsistent about a city adding more homes and more trees. Here in the Pacific Northwest, housing and tree growth can entwine—and in Portland, according to data Dan shared (and Willamette Week re-shared) it has been.
Portland parks bureau data show the share of the city covered by tree canopy steadily rising from 27 percent in 2000 to 31 percent in 2015. And the bureau noted that this growth is happening in the zones away from the parks, where the population boom is.
In response to Willamette Week‘s post, Iain MacKenzie, an associate at TVA Architects who moonlights as the publisher of development news site NextPortland.com, compiled a series of before-and-after Google Street View photos to show parts of the budding urban treescape that will continue to drive this trend in Portland over the decades to come.
Northwest Pettygrove Street, in 2012 and 2017:
Southwest River Parkway and Gaines, in 2009 and 2017:
Southwest 12th and Clay, in 2014 and 2017:
North Williams and Failing, in 2009 and 2016:
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Northeast 99th and Glisan, in 2011 and 2014:
Northeast 41st and Tillamook, in 2011 and 2016:
Is this mostly because Portland developers are really into trees? Of course not. It’s because decades ago, Portland passed laws. There’s currently one requiring street trees alongside new buildings (one for every 25 continuous feet of street frontage) and one requiring a certain minimum density of tree canopy (old or new) on the site of new developments.
This adds costs, no question, and every dollar reduces the probability that much-needed housing is going to be created. (Part of Portland’s law is that a project can only be required to spend up to 10 percent of its budget on trees.) As always, it’s worth weighing the benefits of rules like these against the damage to rural forests and habitats if they unintentionally push new development to the urban fringe instead.
As Dan noted in his piece, focusing specifically on better street tree policies is a good way to get more trees without simultaneously limiting the number of people who can enjoy them. Portland is working on this.
Here is the bottom line: Trees are awesome. And if tree-friendly mandates and incentives make new development more politically popular, then everyone can win. The happy result of Portland’s current laws is that a population boom has, probably for the first time in its history, correlated with more trees, not fewer.
Using photos of trees planted in COMMERCIAL zones to infer that RESIDENTIAL infill will somehow add to instead of greatly diminish the urban canopy is clumsy slight of hand at best. For the real truth on the ground, let’s look to Seattle’s experience since they voted for Residential Infill in their city.
50% of Seattle was zoned single family, and 62% of Seattle’s tree canopy was located in single family zones. From 2001- 2007, single family lots undergoing redevelopment lost 41% of their tree canopy, while multi-unit lots lost 69%.
Here’s a list of all the exemptions to Portland’s Tree Code for development situations.
Keep in mind that the tree code is split between Urban Forestry and the Bureau of Development Services – a little like sharing the protection of the henhouse with the fox if you ask me. For example, if a developer demolishes a home and splits the lot, any lot under 5,000 feet isn’t subject to the tree code and they can cut down several giant coastal cedars without a permit and without paying into the tree fund. If a parcel is zoned
I agree, this is a post about the lots that have been adding meaningful numbers of homes (the commercial zones), not a post about the low-density residential zones where the change has been mostly people getting displaced, rather than physical changes to the buildings.
What residential infill are you talking about in Seattle? They haven’t approved anything like the duplex/triplex re-legalization you oppose in Portland. My suspicion would be that most of that detached-lot housing undergoing redevelopment is either in a higher-density zone or being redeveloped for one giant house … which is, yes, obviously incompatible with whatever trees are there.
As for Portland’s proposal to re-legalize small triplexes, my understanding is that the new FAR limit would effectively reduce the maximum footprint that new buildings have on residential lots. Coupled with the canopy-coverage requirements, seems to me as if that’ll be a pretty big improvement to tree protection rules. Am I missing something on that front?
I don’t think there’s any question that the particular lots undergoing redevelopment are, on average, going to lose on-site tree canopy, especially because any new trees required by the tree code are going to start out pretty small. Seems to me that the relevant questions are:
– what is the aggregate long-term trend for the citywide canopy, thanks to trees in 30-year-old tree-lined redevelopments that upgraded 60-year-old treeless lots and so on? Are the lots pictured above in line to contribute to that trend when their turn comes 30 years from now?
– what can be done to maximize equitable distribution of that canopy around the city?
– how can we reduce the number of very-hard-to-replace big old trees that get cut down?
Unless we want to force all new development out to exurban farm and forest land, we’re going to have redevelopment of city lots one way or another. We can and should debate the details of the tree code exemptions you mention, but I think you and I probably agree it’s a good thing when we link redevelopment with new tree planting, one way or another.
Could you please provide the source of the Seattle data you cite in your comment?
Great article. Thanks for drawing attention to a some successes in Portland while also pointing out that much more work remains to integrate large healthy street trees into the public right-of-way. One of the “after” photos above shows where a private utility vault was placed in the public right-of-way precisely where a new tree well could have been located. Even though there are alternative locations for these vaults, the displacement of street tree planting sites happens all the time due to antiquated street design and the prioritization of space in the public right-of-way. While street tree planting standards look good on paper, exceptions that prioritize signage, utilities, parking, and other structures routinely displace street trees. In Portland, Bureau of Transportation only applies innovative practices to preserve or plant more street trees when neighbors yell loudly enough. Finally Portland unlike most other American Cities leaves the burden of street tree and sidewalk maintenance entirely to property owners. The cost of dealing with repairs can be a huge one-time cost. This provides a disincentive for street tree planting especially in low income neighborhoods.
I will add, that importance of urban trees and other green infrastructure in fostering walkable denser, healthier, and thus more affordable urban neighborhoods, politically and practically, is under-appreciated by urban planners, designers, and some housing advocates who fret, speculate, or fearmonger about the miniscule or non-existent impact of urban trees and tree codes on housing costs.
A large and growing body of research demonstrates clear link between human health and urban trees in cities. Time and again research that has been largely overlooked by urban planners demonstrates a robust association between healthy, mature trees and improved mental and physical health in urban neighborhoods. For example, a series of replicated studies in Europe and the United States (including one in Portland) controlled for a variety of factors to document the link between poor birth outcomes and urban trees and other vegetation. A recent study empirically documented the increase in lower respiratory and cardiovascular disease following the widespread loss of urban trees in counties afflicted by the Emerald Ash Borer epidemic in the Midwest, even after controlling for a wide range of compounding demographic factors including race, income, and education. An abundance of evidence links urban trees to mental health, especially along streets. Controlled studies have linked higher street tree densities to lower prescription rates of anti-depressants in London. In the Netherlands, overall quality of streetscape greenery was associated with lower stress levels and people’s self-reported health and social connection.
Street trees are particularly important to human health because they buffer urbanites from the major source of pollution and stress in cities: motor vehicles and roadways. The worst air and water pollution in cities comes from motor vehicles and the extensive paved surfaces they require. Noise and exhaust from vehicles are one thing, but extensive asphalt and concrete areas for roads and parking lots also trap heat creating urban heat island affect: an increase in air temperature extremes that worsens both summer heat waves and the health impacts of air pollution. Where tree canopy is thin or absent, exhaust, particulates, and pavement-induced heat waves compound each other to effectively create a toxic streetscape. The absence of street trees can also increases health impacts by increasing vehicle speeds and the severity of collisions as some studies suggest. Nevertheless all these health affects are certainly compounded further when the pedestrians and residents along stressful, toxic, treeless streets already face health risks or vulnerabilities. To the extent trees and other green infrastructure reduce the health impacts of urban living, they also reduce real health costs that impact the overall affordability.
All this is to point out that fretting about the extremely marginal costs of preserving and planting trees on housing costs is penny wise and pound foolish. It is also deaf to people’s real and valid concerns about urban tree loss. Finally it is a divisive distraction from the many threats to both urban trees and housing that thwart progress toward healthier, denser, and more affordable urban communities.
“Portland, Bureau of Transportation only applies innovative practices to preserve or plant more street trees when neighbors yell loudly enough.”
Maybe that is being a bit too categorical. PBOT has collaborated on some innovative projects with Urban Forestry and Bureau of Environmental Services. They have shown some leadership in installing green streets. But simple solutions like meandering sidewalks to avoid tree removal are rare and mostly in more affluent neighborhoods where the neighbors demand them. Also as far as I know Portland has yet to install a rubber sidewalk to save a large healthy street tree. Thanks for the rant.
Whoa… Might have to retract my categorical kudos for this article… I missed this flawed Bertoletian reasoning that seems to be fogging Sightline’s vision these days: “As always, it’s worth weighing the benefits of rules like these against the damage to rural forests and habitats if they unintentionally push new development to the urban fringe instead.”
Here’s a few reasons why I think this reasoning is flawed:
1.) First, tree codes (Portland’s especially) rarely if ever require trees to be preserved and in Oregon they can’t reduce allowed density. For example, Portland’s tree code doesn’t require any tree to be preserved; it merely encourages smarter site design to avoid 1/3 of the highest value trees (non-nuisance, healthy, >12″ DBH). 2/3rds of the healthy non-nuisance trees on site can be cut. Only 1/3 of healthy, non-nuisance trees that the developer doesn’t want to preserve are subject to fees in-lieu of preservation to replant trees elsewhere (prioritized to the public ROW). And, as pointed out in Nerdletta’s comment above, there are numerous exemptions that partially or fully exempt sites including residential sites under 5,000 feet. The code more strongly discourages removal a portion of the largest healthiest trees with higher fees in lieu of preservation. If any of those 1/3 of healthy, non-nuisance trees on site are exceptionally large ( > 35″ dbh) and healthy then there is a higher fee-in-lieu of preservation to replant more trees. But the number of sites where there are 3 or more trees >35″ dbh and that can’t be avoided to meet allowed densities is a very very, very small. Finally, where fees in lieu of preservation do apply they are based on the cost of replacing the trees elsewhere not the cost of development, so they are effectively shrinking as time goes by. For more detail on the myths about the tree code and how it and where it applies see Eight myths about Portland’s new tree code .
2.) Second, the region has an extreme surplus up buildable land inside the UGB and not all of this land is forested on the edge or in particularly good condition. In fact in the Metro now prioritizes future urbanization on the edge partially to avoid the highest value habitat that is hardest to preserve with urbanization. Given that there is a at least a 20 year supply of land inside the UGB and another 50 in urban reserves it is really hard to timid tree regulations in 2018 are going to lead to new urbanization sooner after 70 years. Moreover, it is possible through good planning and policy *(including smart regulations), that development on the edge could actually facilitate the restoration and enhancement of forests on the edge. For example Pleasant Valley which was brought into the UGB in 1998 was planned and is now being developed to preserve, restore, and enhance Johnson Creek’s the Kelly Creek subwatershed.
Because of 1 and 2, the argument that the code would “push new development to the urban fringe and threaten urban forest and habitats” is infinitesimal to the point of being spurious even before you consider all the other factors that might drive people and development to the edge (including the poor access to nature). The impact is so insignificant on the regional housing market and urbanization on the edge, it really isn’t “worth weighing.”
3.) Third, and most importantly, it is the policy of our region to conserve natural resources deemed significant to the community regardless of whether they are on the edge or in the center because of the multiple social and environmental values they provide to urban communities. Urban trees are really integral to healthy and affordable cities determined by much more than just cheap housing. These benefits include the significant health benefits of trees and other green infrastructure in our densest neighborhoods (see my other comment) and most vulnerable communities translates directly to lower health care costs. And, again, a lack of access to nature in cities is also what has historically driven people and thus development to greenfields on the edge. Thus preserving a space for nature in cities needs to be part of the strategy for preventing sprawl on the edge. As Mike Houck has said for years, paraphrasing Thoreau, “In livable cities, is the preservation of the wild.”
In sum, there is no meaningful trade-off between preserving trees in the core vs. the edge. But even if there were, the premises that a tree on the edge is more valuable than tree in the core is simply false. It doesn’t fully appreciate the importance of trees and other green infrastructure to human health and well-being our densest urban neighborhoods.
Jim, weighing costs and benefits is very different from concluding the costs outweigh the benefits! I completely agree that urban trees have major benefits, and I think Portland’s tree code probably strikes a fine balance, for all the reasons you mention. The whole point of this post is to praise the code’s effects!
But a different tree code that (for example) forbade the cutting of any healthy tree would be a different matter … especially if it were in, say, a natively wooded area in a non-GMA county like Castle Rock WA instead of Portland OR. That’s why I wanted to include the caveat.
These images convey one important policy regarding requirements for tree planting – that street trees are required for new development. What they fail to show is that most sidewalks in Portland neighborhood main streets are 10 to 12 feet in width and new multi-story structures are being built to the property line leaving no space for healthy long lived trees.
That’s why the aggregate tree canopy figures cited here are so important.
Tanya Lyn March
Gary Moll, “The state of our urban forest,” American Forests 95 (1989): 61-64. This article is where the figure that urban street trees are expected to last seven years. The figure I hear the most from developers at NWDA Planning meetings.
Bob Skiera and Gary Moll, “The sad state of city trees,” American Forests (1992): 61-64. This article also dated gives urban street trees about 13 years.
I took an urban heritage tree walk lead by Martin Nicholson, Hoyt Arboretum Curator this month. As the tour progressed I was alarmed by the impact of our dry 2018 summer on many street trees (young and old). Many trees are not going to survive if we do not bump up our watering and mediated for compacted soils and hard surfaces. We lack longitudinal urban tree and many trees planted in Portland. Planted trees may not last to provide the ecosystem services that motivate our City’s tree codes.
Trees for Life Oregon
Something can be true and at the same time misleading. Trees for Life Oregon would like to respond to “Housing Infill and Tree Infill Go Together in Portland,” published by the Sightline Institute on September 14, 2018. We believe its author, Michael Anderson, paints too rosy a picture of the Rose City’s tree canopy.
Data does support Anderson’s contention that canopy has increased in Portland in the past decade or so. Are there more trees in the Pearl District now than when it was a district of old industrial warehouses? Almost certainly. Massive infill and high-rises went hand-in-hand with increased canopy because that area had few trees to begin with.
In fact, many plantable spaces in street right-of-ways had become vacant. One reason is that after the 1970s, the city stopped providing free city-planted trees for street tree spaces. As trees died out in many older neighborhoods, residents who had just paid to remove them were often disinclined to pay to plant new ones. This was due in part to the lack of help the city offered to prune, rake leaves, or repair tree-damaged sidewalks. By the 1990s, when the tree-planting organization Friends of Trees was getting underway, the nonprofit had ample opportunity to increase canopy just by filling vacant spots in the right-of-way. Trees for Life Oregon celebrates the private-public partnership that has led to this positive effect on returning trees to public right-of-ways.
If canopy is defined as a tree growing in a space, there are more trees in right-of-ways today than a few decades ago. What the Sightline article doesn’t raise is the age of those new trees and their size at maturity. For example, until rules tightened up in the 1980s, many large-form trees were planted in right-of-ways now considered too small for their root spread. Now, each time a large tree in a three- or four-foot-wide planting strip comes down because of old age or buckling sidewalks, by law it has to be replaced by a tree that will mature at no more than about 35 feet, overhead power lines or not. So canopy numbers can look unchanged or even appear to be expanding, while the structure of the canopy is shrinking.
After all those new buildings go up, is there adequate space left for long-term healthy growth of a large tree–one maturing at more than 50 feet and living more than 75 years? These are the trees that give us the greatest climate benefits. It’s not hard to find lots where, once developed, builders added street trees that weren’t there to begin with. They now have to do this by law. But look closely at the photos the author presents as proof that the canopy is doing fine and that we have more of it: almost every tree is planted in cutouts. The lifespan of a tree in a four-foot-square cutout surrounded by concrete is not anywhere near that of a tree in a large yard. Trees planted this way are unlikely to reach their full size and longevity, limiting their health and environmental benefits.
Street trees have more legal protection than private yard trees do. Crucially, private trees are what the Sightline author does not address. The bulk of Portland’s large trees are on private residential lots. It is these large- and medium-form trees that are now at risk of being lost to development. How many have already been lost? We have few numbers because the city doesn’t track trees removed on sites 5,000 square feet or less or trees less than 12 inches in diameter.
Trees removed for development are most often replaced with small or, at best, medium trees, because city codes don’t require that space for large trees be preserved. They make it costlier than it once was for developers to cut down large trees on lots 5,000 square feet or larger. But developers can and do choose to simply pay fees to remove large trees rather than to design buildings that integrate space for decent-sized trees. And trees on smaller lots receive no protection.
We have numerous examples of this trend across the city, even before new infill laws become effective on August 1, 2021. After that, city code will require that triplexes and four-plexes have only half the outdoor area required for a single-family home or duplex. The little dogwoods or Japanese maples plopped next to new buildings may add up to the same number of trees removed, but they will never provide anywhere near the health and environmental benefits of the big trees we are letting slip away. More and more Portlanders are living in brand new buildings built over the stumps of big trees like Douglas-firs that might have lived through the rest of this century or beyond.
Not all of Portland’s residential lots will be bought and their trees and houses torn down and replaced in a single year. But the cumulative effect of a tree or grove lost here and then there will take its toll on the most valuable part of the canopy. The large yard trees that have adequate space to reach their full lifespan can do the most to help Portland meet its stated climate and environmental equity goals. We can’t shade the city adequately with street trees alone. Yard trees are an essential part of Portland’s urban forest.
So while overall canopy figures, at least for now, have moved in the right direction thanks to heroic street-tree planting efforts, Trees for Life Oregon believes the data are masking the unfolding deforestation of big trees in yards across the city and the loss of large-form street trees due to overhead wires and narrow planting strips.
We believe that housing infill and tree infill can go together. But let’s do infill without blithely destroying the legacy of large trees we’ve inherited.
Healthy housing across Portland requires that we consciously help large trees everywhere reach their full potential. Why? To foster the physical and emotional well-being of all Portlanders regardless of income or geography.
Trees for Life Oregon
Thanks for this thoughtful critique. I agree with its facts as I understand them. The street trees pictured here are definitely not as valuable as large off-street trees.
I am strongly in favor of urban trees. But every policy has tradeoffs. Mandating the lowest-density and most expensive housing type in most of Portland — or creating limits on lot coverage that essentially make the lowest-density and most expensive housing types inevitable — does not strike me as a net positive for the Pacific Northwest’s environment, for our planet as a whole, or for the people of Portland.
Like many tree advocates, I’m heartened by the fact that the reforms taking effect in August will make tree-killing driveways no longer mandatory. Even so, I expect that one net effect of the reforms will be to slightly reduce the number of large private trees in Portland over the long term. (Another effect is that they will slightly enlarge the tax base and flow of parks fees to the city and regional parks budgets, so I think they will probably also slightly increase the number of public trees in Portland.)