I'm writing a section for my next book about climate change predictions for the US by region. Wanna know what those predictions are? Look out the window. 2018 has been a real preview of the future, with above-average temperatures everywhere, soaking rains in the East, and drought and fire in the West. What matters is the long-term trend, not any individual year, but still, 2018 gives us a chance to see which everyday systems are not going to work for the warmer world. Ordinary things we take for granted. Like what happens in your yard when it rains.

Although I started my career as a landscape architect, full disclosure: I have always found stormwater management a little dull. These days precipitation of all kinds has become way more exciting, in the worst way, due to the increasing frequency of seriously scary storms. I write this with one eye on updates about Hurricane Florence inundating the Carolinas. My house up here in Connecticut has weathered nearly 50 years of coastal storms, including Hurricane Irene, in 2011, and Superstorm Sandy  just a year after that. Average annual precipitation here is about 47”. In recent decades, the Northeast as a whole has seen a marked increase - more than 70% - in the amount of rain falling during storms. This is a surprise/not a surprise, because these more frequent, rainier storms are part of climate change predictions for the region. And climate change, as you know, is a show already in progress. 

My house is in the woods between two seasonal creeks, with a walkout basement.  The whole property is sandy soil full of New England rocks, so drainage would seem to be a no-brainer. The previous owners of the house certainly thought so, since this house came to us with its sole drainage strategy as standard gutters and downspouts. This utterly predictable set-up is supposed to catch the water as it runs down the roof, funnel it through to eight points around the base of the house, and dump it out on the ground there, at the end of the downspouts. Those downspouts? They end 8” from the foundation of the house. A few have splash blocks that carry the water 24” from the foundation, if they don’t overflow. An absolutely typical setup, found on countless houses, maybe even yours.

What’s wrong with this? It works as intended, which means all the water captured by the gutters is dumped right next to the foundation, at the end of those downspouts. There the water can infiltrate into that rocky, sandy soil and go on its way through the hydrologic cycle and out of my life, and that works fine - most of the time. The walls of our basement testify that it didn’t work fine once, maybe twice, in the life of the house, when a flooding event marked the walls a few inches above the floor. Hmm. 

So we extend the downspouts, which is ugly, easy, and temporary. We need something more permanent, which would, in the past, have meant running those downspouts into a set of pipes to take that water, underground, to one of our creeks. The easiest way to route those pipes is across the driveway, which a landscaper suggested we do. You don’t really know what’s under a 50-year-old gravel driveway, but it’s probably not solid bedrock, a distinct possibility anywhere else in the yard. 

But wait: think about that tried-and-true set of underground pipes and the gutters in 10” (Irene) or 20” of rain? (Sure, 20” is a lot of rain, but Hurricane Harvey (2017) dumped up to 60” of rain on Texas, so…) Simply: everything overflows, and everything backs up. Only so much water can fit through those pipes at once, then water starts to pool. Water coming from the house and backing up means way too much water around the house’s foundation, and that means way too much (ie any) water inside the house. 

If you don’t want a lake in your basement, you need drainage meant to handle a deluge-worth of water. Yet it’s overkill to run the LA River through your yard. It’s hideous, and it’s right outside your house, and also: groundwater recharge is a thing. Sure, Connecticut’s had two badass storms in the last seven years, but it’s also just emerged from a two-year drought, because climate change is about weirder weather, not just warmer weather. Who wants to spend the next drought staring at a yard built for floods? 

A layered system seems to be the answer: a normal rainy day system to work all the time, with a gullywasher system for the next epic storm. The gullywasher layer doesn’t have to work very often, but when it’s needed, it really has to work, because it’ll be that epic storm. When the deluge comes, you’ll need to get in and out. Maybe that’s the classic supermarket run for bread and milk, but it could be for emergency services to rescue you. It could even be for you to evacuate. It’s important, that rare thing in home landscaping that actually is life or death. So nope, keep that pipe away from the driveway, aka the sole route in and out. Look around and imagine a foot or two of rain, and give it somewhere to flood that isn’t where you’ll be or how you’ll get out. 

My strategy is something like this: some of those underground pipes attaching to the downspouts, but with the ground surface sloped to form swales that will move the water away from the house and into the creeks when all hell breaks loose. An old idea, the dry well, may come into play here, too, as a way to provide a place for water to pile up, so to speak, in the epic storm, and a place for water to infiltrate the rest of the time. Circling back to that recent drought, this also could be a good place to install a cistern, if the next drought or the one after that is worse. 

If climate change affects simple home landscaping to this extent, it really does affect everything. The strategy of layering everyday systems with ones for catastrophic events is a good one, and maybe one that can work elsewhere. Your yard seems ridiculously trivial, but aren’t you likely to shelter at home if/when the big one hits? A little planning can create a lot of resilience, or at least more than you’ve got now, exactly where you’ll need it when the storm comes. 

This post is a preview of a sidebar in my upcoming book about the neglected city, Design by Deficit. Also posted on Medium. 

​Syracuse, New York, the city where I used to live, is a shrubby place. By that I mean that unmaintained land within the city quickly becomes colonized by woody vegetation above waist height, but below the height of shade or canopy trees. This is the ecological process of succession, but it’s succession with a twist: it’s being done by what Peter del Tredici calls, “cosmopolitan urban vegetation.” This mix of natives and exotic invasives includes several of the Most Wanted on the list of invasives in the US: shrubby honeysuckles, autumn olive, Japanese knotweed, and of course, public enemy #1, buckthorn. This paper called out Syracuse as one of the only cities in the US where overall tree canopy is increasing, probably because of the buckthorn. That’s a lot of buckthorn. At least it’s too cold here for kudzu ...so far.

Syracuse isn’t alone. Cities in the eastern US, particularly those that have lost industry and population, have shrubby places in part because of this collection of large invasive shrubs, and the rainfall to support them. Numerous other trends converge in shrubbiness: vacant land, abandoned properties, tight municipal budgets that restrict mowing, but also an increased value placed on wildlife habitat and natural-looking landscapes. 

Urban shrubbiness sits at the junction between two established findings about human behavior and vegetation. In this research, tree canopy is the panacea, or nearly so. Tree canopy does it all - we think better, behave better, feel better, and like places and communities better when there are shade trees, to paint this research very broadly. Yes, these are largely studies finding association, not causation, and experiments are hard to design on this topic, but the association is consistent across many studies by many people, and in the end, there’s not much downside to planting trees, as we argue here. But on the other hand, there’s cues to care and loose space, research and theory that argues that we generally perceive apparently unmaintained land (such as that covered with successional vegetation) as out of control and outside the rules, fit for transgressive activities like vandalism. Tall dense vegetation - shrubbiness, again - has been shown in numerous studies to be a less preferred environment that makes us feel insecure, perhaps because we doubt our ability to navigate through it or discern threats within it. 

So shrubbiness is both good and bad, from a human behavior standpoint. Which wins out- the positive or negative impacts, or is it a draw? For that matter, invasives, or the cosmopolitan cocktail of urban vegetation, are a mixed bag ecologically as well. Invasives (like buckthorn) are demonized because they damage biodiversity and don’t do all the good things that their less-competitive native counterparts do, but sometimes, well, a tree’s a tree. They all photosynthesize, and mitigate heat island, and help slow stormwater runoff - or do they? There’s an implied balance sheet here, weighing the good and bad impacts of unmaintained urban understory vegetation in terms of social, economic, and ecological good. 

A tree isn’t a tree when it’s buckthorn vs. white oak, but many of our best and most sophisticated ways to measure urban vegetation in quantity (meaning on more sites that you can visit in person) sees those as the same.

In the lack of distinction lies the mystery; this devil’s in that detail.

What’s the impact of the shrubby city, and how do we find out? What about drier cities or ones without a Syracuse-caliber winter? Is the impact different there? If the environment matters, shouldn’t these differences matter, too? As climate change makes some places wetter as it dessicates others, and we all get hotter and hotter, we may find we want to know whether shrubbiness is working for or against us. Invasive large shrubs aren’t going away. We might as well understand what they’re doing to us.

This post is a preview of a sidebar in my upcoming book about the neglected city, Design by Deficit. Also posted on Medium. 

If you spend a lot of time outdoors, like I do, you’re more or less perpetually alarmed about Lyme disease. Even more alarming are the array of other tick-borne diseases  that are way scarier, but reported at much lower levels - SO FAR!! As always, it’s easy to panic, and difficult to know what to do. 

Those rare-but-scary other diseases make solutions that only work on Lyme, like vaccinations, only so promising. More promising are solutions targeting these diseases’ common factor: what people are doing, what ticks are doing, and where they meet each other. 

There’s some surprising tidbits to be found in this. Like this: most people are infected with Lyme in their own yards, during daily activities, not out in the woods on that hike or camping trip. Maybe this is because we think about ticks in the woods but we don’t at home. Or perhaps people who choose to be out in the woods are people more likely to know about ticks and take those precautions - you were wearing special hiking clothes anyway - while people doing daily activities in their yards are just people, without that self-selection effect. 

You can’t stay in the house forever, so can you de-tick your yard or de-Lyme your ticks? Another surprising fact: deer aren’t the main villains here. The tick in question is the deer tick (aka blacklegged tick), so white-tailed deer get blamed for this modern plague. But a closer look at the life cycle of Lyme-infected ticks reveals the key middleman is much smaller and more common: the white-footed mouse. As mice tend to be, they are around in large numbers, unnoticed, and closer than you think. You see deer, but not mice. This particular mouse likes woodsy areas and their edges. Your yard will do fine, especially if you live in a heavily wooded area like much of New England, ground zero for Lyme. 

It’s tough to exclude mice from your yard. You can fence out deer, but just try fencing out mice. What really works to suppress mice is eating them. Since you probably don’t want to try that yourself, it’s lucky that foxes are very happy to do that job. A 2017 study found that indeed, where there are more foxes (and some other European predators, where the study was set), there are lower numbers of Lyme-infected ticks and ticks in general. Surprising again, the key dynamic in play seemed to be that mice move around less when there are predators around, as the study’s authors speculated. There are still mice around, but they are kept under wraps by the foxes, so they encounter fewer ticks. 

Red foxes are champion mouse eaters, and where foxes are, there tend to be other creatures. Some of these, like opossums and possibly turkeys, eat a lot of ticks, which helps in a different way. Others could help in a less direct but effective way by serving as alternate hosts for ticks. This means the ticks bite other creatures, like squirrels, that are less likely to carry Lyme disease instead of disease-carrying white-footed mice, and therefore never become infected with Lyme. You may still get bitten, but you won’t get infected if the tick that bites you doesn’t carry Lyme. 

How do you get foxes on board in your backyard fight against tick-borne disease? You do it with landscape management, looking at your yard and neighborhood as habitat. This starts with trees. A landscape with very small patches of forest is good for mice, but not larger animals that prey on them or on ticks. A landscape with larger patches of forest has the potential to house foxes and possums and so on, thus keeping the lid on mice and ticks and Lyme.  In urban areas, tree canopy is often referred to as the critical factor in the presence of foxes and other larger wildlife. It stands to reason, though, that what’s under those trees matters, too, as well as what kind of trees they are. More diverse woodlands with greater diversity of plants at ground level, especially native plants, tend to be home to greater diversity of wildlife. 

What else makes up the low-Lyme landscape? At a more detailed level, it’s less obvious what’s good and bad. Leaf litter is the natural cover of the forest floor, but it’s also habitat for deer tick nymphs and larvae. Brush and tall grass create good wildlife cover, but they are also the preferred spots for adult ticks to lie in wait for someone to bite. Every creature needs a water source, but dampness and humidity are key to deer tick survival. Obviously there are a series of trade-offs here that merit more study to discover the right balance. Foxes in particular need den sites, hollow logs or buildings to dig under or similar. But these same denning sites can also make the fox’s larger cousin, the coyote, at home, which brings us to one last surprising fact.  

Where there are coyotes, there are fewer foxes, because the bigger, stronger coyotes tend to kill the foxes. So if more foxes means less Lyme, do more coyotes mean fewer foxes and therefore more Lyme? That’s exactly the suspicion of a few researchers studying the matter, who note that the key factor in the outbreak of Lyme in New England may have been the arrival and establishment of coyotes in the region. 

So stay tuned, but consider what a low-Lyme landscape might be. Maybe also consider what the fox is worth to you that keeps you from getting Lyme disease, and what the forest that nurtures that fox is worth, too. The assortment of creatures living around us and the web of their interactions with each other plays a surprisingly key role here. You can surround yourself entirely with pavement and buildings. You can do the vegetated version of that with closely mown, chemical-soaked lawn. Or you can have a diverse, intact woodland edge ecosystem that works just well enough to allow predators like foxes to keep the mice and their ticks in balance, without making coyotes too much at home. Wild, but not too wild; just wild enough.

Quick, how do you build a huge wall without anyone to build it? Consider: as the US edges closer to building a border wall, a newly released report from the home building industry reports that about one in four workers in construction are immigrants. This isn’t all people from Mexico, of course. It includes both people who emigrated via official channels and those here without documentation. Anyway you parse it, though, one-quarter is a lot. Imagine a construction site with one in four of the workers gone. And a project on the immense scale of the Republicans’ border wall will need a tremendous number of workers, should it ever be funded.

It’s not just gigantic border walls, of course, but all kinds of construction in the US that’s built by immigrant hands. Spanish on the job site has been common for at least 20 years, and that’s from my experience working as a landscape architect in the Midwest — not California, not Florida, but the middle of the country a thousand miles from Mexico. Why? The National Association of Home Builders points at the slow return of native-born workers to construction trades when building picked up again after the Great Recession (2007–2009 or so). They also point at the aging of the US population, especially when we only look at native-born residents. A construction site is a tough place for an aging back, and that may what we’re see in these figures, too.

It’s not just construction. Agriculture, facilities maintenance, personal care and service, health care support and more — all are at least 20% immigrant workers. You can’t dig far into immigration without finding this: jobs, the people who come here for them and the people who hire them. It’s this broad reach into the US economy and our everyday lives that makes immigration reform so tricky.

Strip mall in Indianapolis (author photo)What these figures don’t include is also construction, in a sense — rebuilding the threadbare parts of American towns and cities. In 2001, I was inspired by Mike Davis’s description of “All of Latin America is now a dynamo turning the lights back on in the dead spaces of North American cities.” I looked around the Midwestern city where I lived, and asked whether what he saw in California was also happening there.

Short answer: yes. I went on to write my own book about this immigrant revitalization, happening in the very same small Rustbelt communities that we’ve heard so much about since the 2016 election. Long answer: my recent book, Immigrant Pastoral: Midwestern Landscapes and Mexican-American Neighborhoods, which says:

​Now that America’s great again, the Clean Power Plan  is in limbo, we’ve got a brand-new tariff on solar panels, and clean coal will save us all. Or something like that. When policy and regulation aren’t your friend, there’s still the market, erstwhile darling of conservatives. The story goes like this: If your product is any good, people should want to buy it, and government should get out of the way of that. 

Since unfettered capitalism also produced child labor and sweatshops, the market is less panacea and more unreliable ally. Nonetheless, plenty of people are discovering that resilient power - renewables and distributed systems - can in fact outcompete conventional systems, in US markets and elsewhere. 

The market is supposed to be rational decisions based on cost and benefits, but I bet you can look around your house and see things you bought even though they weren’t the most benefit for the least money. Why do we buy these things? Two big reasons are status and style, to look good or to impress the cool kids. We don’t outgrow this. We just buy bigger cool things.

In research terms, this involves peer effect. In terms of resilient energy, peer effect means that the more exposure a person has to renewable generation, the more likely s/he is to install his/her own system, specifically with photovoltaic (PV) systems. This produces clusters of PV installations. Peer effect can be one of the most influential factors in deciding to install a PV system. You think it’s weird, until you see it enough. You see it some more, and you start to want it. 

This implies a tipping point: eventually enough people live near solar panels to change the average perception of solar generation from oddball to normal. Same with home standby generators, seen and marketed as desirable in higher-end homes. This presents on-site power generation not just as normal, but  desirable. Higher-end homes that feature generators (or PV) make resilient power an aspirational home feature, advancing even farther from normal to trendy, a feature to covet. 

Fashions tend to start at the top of the income scale and spread downward; tastemaking trickles down. Fashion has the power to really increase adoption of energy systems. Only environmentalists (who can afford it) want eco-friendly systems, but everybody wants the next hot trend. Once it stops being weird, it can start being desirable, and once it’s cool, it’s a whole new landscape, energy-wise. 

Speaking of landscape, do these dynamics work just anywhere, or can the location stack the deck? I recently moved from upstate New York to Connecticut, one renewable-loving, overburdened grid blue state to another. Upstate New York is famously gloomy, but solar is still worthwhile there, and New York does a good job of making it worth your while with incentives and policies. You wouldn’t expect a difference, and yet there is: Connecticut loves rooftop PV. Property listings include an index of solar energy potential, with “Good!” in the description where appropriate. Connecticut home listings also feature home standby generators. Generator-ready homes are not at the bottom of the price range, either - this is a selling point to buyers with means.

Why? It could be Superstorm Sandy (2012) or her predecessor Irene (2011) or Connecticut’s pioneering Green Bank (also 2011). Power is no bargain in Connecticut, which makes alternatives appealing. But Connecticut also is ideal for peer effect’s effect. It’s dense, in number of people per square mile. It’s also dense with people with means, or enough means to be in the market for rooftop solar, whole house generators, and the like. It’s in constant competition with New York City and Boston for people and businesses. This tiny state with all the people and the coastal storms could be poised to cross the threshold into resilient power being… cool. 

Style has a price tag for places. A few years ago, every city wanted to lure the Creative Class. These days, that’s evolved into places for innovation. Amazon’s HQ2 competition is a new iteration of this same idea, with the criterion “potential to attract and retain strong technical talent.” Could resilient power belong on the list of magic factors that make a place cool? Obviously, it does a lot for your business to keep the lights on, but it’s much more than that for some energy-intensive businesses, like data centers. For them, the extra assurance of a microgrid can make the decision about where to locate.  

If you want to add cachet to practicality, installations have to be visible and recognizable, not just to the trained eye of an electrical engineer, but to the public - the  property-buying, disposable-income-spending public. People who don’t know a watt from an amp have to recognize resilient power installations to know they want one - peer effect can’t work if you can’t see what to want. Rooftop PV has the edge here, because it’s readily seen and recognized by the non-expert. Rooftop PV and on-site wind are like driving a Prius, an immediately recognizable statement of eco-consciousness, and the affluence that goes along with being able to spend to make that statement. Contrast that with geothermal, microgrids, or weatherization, all of which are legit green, but invisible to the layperson passing by. These are like driving a Hybrid Civic. Only you, your pocketbook, and your carbon footprint know for sure.

Other resilient power components need visual signatures as distinctive and universal as rooftop solar. As long as no one sees your geothermal, only environmentalists (and engineers) will buy it. Once everyone can see it, and see it as something the richer neighbors have, in the house, the subdivision, or the city next door, everyone who wants to impress someone will want one. And that’s all of us.


 

 Also posted on Medium.

(Based on my November 3, 2017, presentation at “Community Renewal and its Discontents,” a conference at Albany Law School’s Government Law Center) 

Picture a vacant lot. If nothing comes to mind, the one in the photo will do. What would you find there? Litter, probably. Rats, perhaps. Maybe an old tire or two. Your first answer is probably not “climate change mitigation” or “better mental health.” But expectations aside, you could be getting both from that vacant lot and other accidental urban natural areas.

Weeds fight climate change? Well, yes, but not weeds especially - plants do. The list of ways urban trees mitigate climate change impacts is impressive, but they boil down to this: cleaner air, cleaner water and less flooding, cooler local temperatures, and better livability in the city generally. Trees aren’t weeds (except when they are), but any plant growing on that vacant lot shares some of the salient characteristics. They all photosynthesize. They all raise the relative humidity around them. They all sequester carbon within their structures. They all allow more rainwater to soak into the often-compacted urban soil. At core, “weeds” vs. “trees” is a distinction of human perception, and these climate benefits depend on what plants do and how they interact with the physical world, not how or whether we see those plants. True, some of the benefits of urban trees depend on the larger overall size of the trees to cast shade, but then again, some weedy species, like tree of heaven (Ailanthus altissima) or buckthorn (Rhamnus spp.), can get pretty big. Bottom line: look at that vacant lot again, and take a deep breath.

While you breathe, relax, because that same urban wild is also benefiting your mental health. Again, the list of mental health benefits from urban trees is lengthy, and again, it’s mostly about trees. In summary, humans evolved in natural environments, and therefore, we do better in some important ways when we can see natural environments. We think better, we feel better, and we treat each other better. Research on these effects usually shows a small benefit, but a (statistically) significant one, and these are easy benefits to get, with little downside. The research on benefits to mental health falls into three categories: benefits related to getting more exercise, benefits related to better social cohesion, and benefits related to stress reduction. Do you get these benefits from weeds as well as from trees? Yes, at least some of the time, but what matters here is how we see the weeds. Is that vacant lot a danger or an oasis? Are those weeds wildflowers or a home for vermin? Is that a deer or an assailant hiding in the underbrush?

That ambiguity makes it essential that we know whose health we’re trying to improve with these urban wilds and their benefits. Who you are makes a difference in how you see a given wild, and who you are also often makes a difference in where you live within a particular city. The demographic group, particularly race/ethnicity and gender, of the viewer can make a difference in how s/he views unmaintained vegetation, particularly whether it is threatening or desirable. The level of environmental education a person has, as well as how urban or rural a place s/he grew up in, can also matter.

More useful than sweeping statements about perception and demographic groups: it matters where you are in proximity to the wild area in question. You might enjoy the view from your 10th floor office while I worry about the overgrown lot across the street, but we could be looking at the same vegetated land. Each health benefit of urban wilds has its own geography. Some benefits, like heat island reduction, are best experienced by those closest to the wild site. Some costs, like depression of property values, are, too. Other benefits, like vegetated views and downstream reduction in flooding, may be gained by people too far away from the wild site to be affected by nearby burdens like increased pollen count or disease-carrying ticks. The same urban wild can simultaneously provide benefits to some and burdens to others, or some benefits and burdens to the same people at the same time. It’s not simply good or bad. It’s…both. 

The question that matters, then, is how to manage wilds in your city for the most benefit and least burden to those most in need. What parcels are more valuable as wilds than as redevelopment, and why? What neighborhoods have the greatest health needs and the fewest resources with which to meet them? For parcels that remain wild, how best can they be managed to be healthy for nearby residents and positively viewed by the general public?

Climate change and healthcare share an urgent need for on-the-ground action that transcends contentious debate. Both are complex problems poorly suited to soundbite solutions. Both are negatively affecting the health of countless people, right now, today. If you had something that could make a difference in both areas without the need for political will or legislative action, wouldn’t you use it, even if the difference it made was small? Look out your window. That small difference may be closer than you think.

If you're going to be in Albany (New York) on November 3, stop by and say hello! I'm speaking about the health aspects of urban wilds on the panel on Shrinking Spaces and Community Development. Keynote looks great, and... it's free! For a bonus point, City Wild Seminar alum Jordyn Conway is helping plan the conference in her current position with Albany Law's Government Law Center. How can you resist? See you there!

Full conference info here.

Also posted on Medium.

​Call it biking the urban wild. Portland, Oregon, is developing a citywide off-road trail network, called the Portland Off-road Cycling Master Plan. Conventional planning processes will produce a network of single-track trails through natural areas, instead of the much more common paved bike/pedestrian trails. Portland is reported to be inspired in this effort by the broad popularity of mountain biking within the area, but the advantages of “wild” urban trails over conventional multi-use paths are worth considering anywhere. A network of single-track through the city is a network of urban wilds, with a built-in community of people to use them. 

What are these advantages? First, there’s the array of benefits to physical and mental health that come with exposure to everyday nature, particularly vegetation. Key to this list are lower perceived stress, greater time spent exercising, and improved mental focus. These three benefits lead to a host of secondary effects, from lower blood pressure to better mood and social relationships. Research on this nature-health connection generally finds that benefits are significant, but small, meaning that the ideal way to benefit from them is through activities done on an everyday basis. Thus, the trail through the natural area across the street is potentially much better for your health than the trail at the state park twenty miles away. It’s the everyday that makes the difference. 

Key to the the mental health benefits is mindfulness, or the necessity of being present and focused on the moment. The more rugged surface of unpaved trails promotes this, as does the narrowness of single-track. The limited views through trees and shrubs promote the feeling of being away from the city, even in locations well within city limits. This feeling of being away, or “extent,” is also key to achieving health benefits from nature, as is the feeling that a landscape can’t be understood completely at a glance, that it contains scope for exploration. 

Biking or running on a trail is obviously good for the trail user’s health, but it’s also good for everyone else’s health, in terms of the climate change mitigation benefits of urban wilds. The abundant vegetation of natural areas in cities sequesters carbon, which aids in offsetting climate change. These same natural areas also help cities adapt to the impacts of a warmer, more volatile climate, through lowering the temperature of adjacent areas and creating more area for rainwater from storms to infiltrate.  

Urban trail networks of any kind fight climate change by promoting human-powered transportation over cars, but an urban off-road network in an outdoorsy town like Portland goes further. If many people - Portland found 12% of county residents - are already doing single-track recreation, they are likely driving to those trails. Trails in the city eliminate at least some of those trips. This is not to say that trail users will never drive out of town, but as with everything having to do with lowering our impact on climate change, it is what you do routinely that matters, not the special occasion. It's the Tuesday night ride, not what you do one Saturday each summer.

An urban wild network promises major advantages to local wildlife and its ability to withstand the disruption of climate change. A substantial challenge for wildlife of warming temperatures and changing precipitation levels is the ability to move fast enough to keep pace with a livable climate. For some creatures, this means moving up in elevation or farther north to stay with cooler temperatures, while for others it means moving to stay with adequate moisture levels. Cities and many suburbs are obstacles to this movement, because they interrupt the habitat necessary to allow wildlife to travel. This fragmentation of habitat is offset by urban wilds, especially those that occur in a connected network, because the wild areas provide wildlife corridors, a kind of safe route for creatures to move through the city. Even manicured lawn, like in the top photo, is inhospitable to many organisms. Even though it’s green, it lacks sufficient shelter and may well lack adequate food and water sources as well. 

There are more benefits - reduced maintenance, improved views from adjacent properties - but this short list illustrates the advantages of a wild trail network like this in an urban area, that are not available with a more conventional trail network. Intriguingly, a wild trail network may be much less expensive, and therefore far more feasible, to build in urban areas that already have ample amounts of vacant lots, brownfields, and other urban wild spaces. Traditional trails are surprisingly expensive to build, so the cost difference between simply adding single-track to existing wild areas and clearing those areas,  establishing lawn, and constructing an asphalt trail, could be quite substantial. Since urban wild spaces are usually seen as waste space, using these spaces more or less as they are to get a desirable recreation and health benefit is well worth considering, for many places other than Portland. Maybe your town needs some killer in-town single-track, too.