Thursday, January 30, 2014

What is an Urban Forest?

Part of Washington, DC's urban forest as viewed from the National Cathedral
Nature doesn't stop at the boundaries of a city.  A web of living things weaves in and out of every human environment we have created; through city blocks, along railroad tracks, within farm fields and backyards, crisscrossing the boundaries of private and public property. Trees are the largest organisms living within the urban environment and create the biostructure below which all other layers of the urban forest fall. Some trees are planted intentionally while 'volunteers' spring up along fencelines, in abandoned lots and other places where seed get deposited by birds,animals, wind and water.

To understand why the urban forest is important, it's critical to understand the concept of Ecosystem Services.  Ecosystem services are benefits that humans receive from the surrounding environment. These benefits can be categorized into four types of services: supporting (such as formation of soil), regulating (filtering of water and air), provisioning (food or timber), and cultural (such as recreation). Trees are powerhouses of ecosystem services, improving our quality of life every day through functional processes.

Trees pull carbon from the air and produce oxygen, improving local air quality and reducing carbon in the global atmosphere.

Trees reduce the impact of rainfall in a community by actively absorbing water and by slowing runoff as it clings to the surface area of each leaf, stem, branch and trunk.
Rainwater clings to the leaves, branches, stems and bark of trees, slowing demand on infrastructure.

Trees improve the quality of our drinking water by filtering pollutants and material, reducing the need for pre-treatment of municipal supplies.

Trees reduce heating and cooling costs by shading homes in summer and blocking wind in winter.

Trees reduce heat island effect, a phenomenon which can raise local temperatures when the summer sun heats concrete and asphalt.

Trees increase property values: the American dream is lined with leafy, sun-dappled neighborhoods.

Tree plantings are an integral part of the streetscape in downtown Shirlington, Virginia
A grove of established trees in a neighborhood park in Rock Island, Illinois

Trees reduce crime by introducing a neighborhood watch effect: people spend more time outside, so there is more visibility and sense of ownership of one's community.

Trees promote biodiversity: birds, mammals, insects, fungi and microbes form a distinct web that increases quality of life for humans, from harvesting aspirin from willow bark to housing birds and bats that eat mosquitoes.

Trees provide food security by offering habitat to pollinators of crops.

Trees feed us: the harvesting of edible fruits, nuts and berries for consumption is called permaculture.

'Trees are the answer' is a phrase borrowed from a professor to indicate the myriad ways that our communities benefit from a healthy urban forest. Trees are the single biggest investment cities can make in themselves.  But it has to be a real commitment to investment, willing to provide the space and resources trees need to thrive and produce reliable benefits we can enjoy.

The urban forest grows powerful through economies of scale.  Yes, a tree in front of a home can create a shady spot, hold some rainwater that clings to its surfaces, uptake some water and remove some carbon from the air. But the impact is massive when one thousand, ten thousand trees or more grow together.  If you look down from above onto a city that is 20% covered by tree canopy, that is 1/5 of the city that is reducing demand on infrastructure while enriching the lives of its residents at the same time. A strong canopy is money in the bank for a city and the taxpayers who fund it in terms of utility management, property values and human health.

Future posts will point out challenges to maintaining a healthy urban forest by discussing the limitations of trees. Limitations include failing to thrive under stress or resource deprivation, and being unable to break up with us when we treat them poorly or move when they don't like their neighbors.

Summertime at the National Arboretum in Washington, DC

Friday, January 24, 2014

Tree Boxes Should Not Be a Thing

I think a lot about how to change the way our culture, specifically in cities, views open space in the built environment.  This means clients and developers, public and private land holders, designers, occupants, and visitors.  The single best argument for improving the functionality of open space is to grow and improve the urban forest. Many hallmark components of a healthy city fall either wholly or tangentially under the canopy of the urban forest. A healthy canopy contributes positively to municipal utility and quality of life demands- stormwater management, heat island effect, biodiversity (including pollination and pest control), property value and emotional well-being. And it's a true investment- plant a relatively small tree in the right place and it will grow faster every year, compounding return on investment.  It's a similar business model to Homer Simpson's plan to buy a tiny lobster for cheap and grow it into a larger lobster for eating (his plan failed when he bonded with Pinchy and fed him risotto).

But too often what ends up in the ground is a contractor's afterthought, or a remnant of value engineering after mitigating project-wide budget overruns. Landscape architects know that the last construction component in the ground is the first budget cut.  In the urban environment, the result is usually a small caliper tree that gets plunked into a 4' square pit, with no soil amendments or room to grow. Yet somehow we are surprised when street trees fail to grow into leafy cathedrals such as those that lined the streets of earlier generations.

Jim Urban (full disclosure: Jim Urban is my professional crush) estimates that a properly planted street tree costs ten thousand dollars to install, the budgetary equivalent of a decorative light pole.  How many project managers balk at the true expense of one tree but not the light pole?  Trees offer heat mitigation, storm mitigation, emission reduction and a neighborhood feel. The light pole demands electricity (outdoor lighting is a major power hog), but provides the notion of safety. Neither the tree nor the light pole are maintenance free or damage-proof.  A well planted tree will only get more productive with time- the same cannot be said for the light pole.  The light pole may feel more permanent, that it has more longevity and is deserving of the investment.

An oversimplified recommendation for improving the urban forest is this- plant trees everywhere! Except for where there are overhead lines... or buried utilities... or light poles... or bird-phobic airport traffic... or vehicular lines of sight... etc.  There is no silver bullet treatment for urban forestry- placement must be based on technical and contextual data. The right tree in the right place, as the arborists say. The backlash will be fiery if you plant a fruiting sweetgum (or female ginkgo) near a walkway! Wise placment is critical for every layer of the urban forest, from the overhead canopy of an oak to a scrappy planting of festuca next to a side door.  

The largest roadblocks to change are the excuses most often given.  As advocates for the urban forest, we should never accept these excuses if we really want to improve the way we conduct the business of development.  They are frequently intertwined and tough to overcome. 

#1. It's too expensive.

This might refer to materials, installation processes or maintenance.  Military installations, forever under pressure to trim budgets, can be the worst environment for progress.  To be fair, the separation of construction and maintenance budgets (a contract issue) is a huge hurdle facing development on federal land. One Request for Proposals listed all trees as a bid option, an option which was ultimately not accepted due to price.  An 8 acre site ended up treeless, a far cry from its native forested condition. The issue at hand is that in the construction industry's mind, trees cost money; trees are not necessary; trees have no value beyond aesthetics.  There is no question that grading, drainage and piping are necessary for stormwater management; these things are required by code and by law. Many contractors dislike spending the money to install the system, but there is no question that in today's world, stormwater management is necessary. What is still misunderstood is how trees and plants can play a role and ultimately defray the cost of infrastructure if planned early and well. Trees provide value; but without metrics to integrate that value into standard construction, new project s will continue to to be built using obsolete practice.

In the case of the tree-less 8 acre site, fingers crossed that squirrels get to work burying acorns.

 Departments of Transportation (DOT) can be resistant  as well, particularly to proven systems such as Silva Cells.  They refuse to consider them due to the initial cost of installation, never considering that those initial costs could defray the larger down-pipe cost of increased stormwater infrastructure.  Disparity in budget allocation between construction and maintenance is a broad, recurring topic; one to be addressed in a later post.

#2.  We've never done it that way.

Risk aversion, leeriness of liability, concern over replacement costs, unfamiliarity with maintenance requirements etc. all contribute to a reluctance to innovate.  Again with city DOTs- some would rather install a streetscape in the same obsolete manner that it has been done for 30 years, because estimators know how to estimate it and installers know how to install it.  There is no money in the razor-thin budget to design and test anything new; perhaps the city code doesn't explicitly include it.  Bureaucracy can present a huge hurdle to innovation.  In one city, designers are unable to select a tree species that does not appear on the existing list.  Not because an arborist takes great care with the list; rather it is because every construction component must have a unique line item code in order to be included in a project, and it's too difficult to get something added to the master list. On the approved species list is Bradford pear, simply because it already has an assigned line item code. (If you're unfamiliar with the shortcomings of the Bradford pear, send me and email and I'll bring you up to speed.) Where is the flexibility and willingness to invest in innovative methods to address infrastructure problems?  To be blunt, municipal governments aren't driven to turn a profit in the same way as the private firms performing the design and construction work. As a taxpayer, I'd like to see funds allocated to absorb the risk associated with testing innovation in urban forestry as a tool for improved city function. Take my taxes and lead the way in experimental new methods that can become the new and improved standard to beat.

There are many municipalities that are actively pursuing the benefits of the urban forest and they will be highlighted in later posts. There is nothing new that needs to be invented in order for us to tackle these problems; our culture is primed for multi-pronged investments in our cities.  Urban forestry, able to be implemented at any scale, is the low hanging fruit.