Tree Windscreen, San Francisco

Many of the major pubic street spaces of San Francisco are currently wind tunnels, as the dynamic forces sweeping in from across the bay are funneled into tight, urban corridors. As the city continues to experience unparalleled urban and architectural growth, mostly vertically, the wind speeds and their force are only increasing in intensity, making it difficult, if not impossible for some tree types to grow at the street level—to take root—as part of the urban environment. Trees located at streets, parks and open spaces can literally buffer these dynamic wind forces, however they need to be able to be grow unhindered by strong wind forces. Currently, the city’s response to this issue is to pay to bring in mature trees—already grown—or, to literally tie them. As our natural, dynamic weather pattern systems continue to increasingly flux with global warming, it will become all the more important for our urban forests, particularly our street tree systems, to be intelligently positioned within the city, along with the certainty that individual trees will be able to grow vertically, unchallenged by the physical pressures applied to them throughout critical periods of their growth cycle.

As part of an effort to increase the number of plantings—of various tree species throughout the city—and maintain their well-being, especially when young, and growing, I propose an architectonic solution as a type of street tree management—a tree armoring as a windscreen—essentially, a shield erected for a small duration of the trees growth cycle to mitigate the dynamic wind forces enacted upon it. The screen also serves an additional purpose in that it will draw attention to this often times overlooked urban infrastructure.

(From The San Francisco Planning Department)

San Francisco was once a largely treeless landscape of expansive grasslands, sand dunes and wetlands. Today, almost 700,000 trees grow along the city’s streets, parks and private properties. From the Embarcadero’s stately Palms to the tall Cypresses of Golden Gate Park, trees are a beloved feature of the city and a critical piece of urban infrastructure.

Our urban forest creates a more walkable, livable and sustainable city. Trees and other vegetation clean our air and water, create greener neighborhoods, calm traffic and improve public health, provide wildlife habitat and absorb greenhouse gases. Annually, the benefits provided by trees in San Francisco are estimated at over $100 million.

Trees in San Francisco face a number of challenges. Historically underfunded and inadequately maintained, the city’s tree canopy is one of the smallest of any large United States city. Lack of funding has restricted the City’s ability to plant and care for its street trees. Maintenance responsibility is increasingly being transferred to property owners. Widely unpopular with the public, this approach puts trees at further risk for neglect and potential hazards.

Our urban forest is a valuable capital asset worth $1.7 billion, Like the public transit and sewer systems, it needs a long-term plan to ensure its health and longevity.

Trees transplantations from farm to sidewalk include the tree being specified, purchased--the London planetree being the most common--and shipped to the site, or nearby, where it will wait to be planted when scheduling permits.

Tree armoring recommendations from the Friends of the Urban Forest feature this image (above) of tree stakes that are crossbraced and made of wood. The City’s version of tree armoring against the wind is to use metal pipes that are driven, or staked into the ground, with a collar, or series of collars that wrap the tree and prevent it from bending too far in any one direction during sustained and / or high winds. These vertical pipes are often times used in conjunction with cyclindrical metal fence surrounds, or extruded collars, also driven into the soil or affixed to the sidewalk or tree planter area.

The London Plane tree type is specified as the go to tree type for urban sidewalk infrastructure, as it grows really quickly and is both hearty and resilient--it has an extremely accommodating temperature range and can grow almost anywhere. The shadows created from its leaf canopy are full of dappled sunlight.

The Laurel Fig and Chinese Banyon (as shown above), dense shade trees, were previously specified as the common sidewalk tree type, however, once mature, their canopy casts an almost impenetrable shadow, sometimes the entire width of the sidewalk, where neither artificial or natural light can penetrate through. This has become a problem for the City as per safety and lighting related issues.

The physical spacing of the trees along the length of the sidewalk is also a result of this shadow phenomena and related safety issues, however this linear separation of trees comes as a cost, as trees typically fare better when grown in clusters or within a grove. The more densely packed together trees are, the better chance they have to mature and increase their own resilience against sustained wind force pressures--when they are isolated, like every tree is when planted in a linear sidewalk configuration, they are on their own against the wind.

Architecture has and continues to have an entwined relationship with trees. All columnar structures owe a debt of gratitude to trees, and from our first additive structures, after we moved from subtractive spaces, like caves, to other types of shelter, like yurts and tepees, it was though the use of trees and their parts that we created protection from the elements.

Laugier's Essay on Architecture from 1753 features an illustration of trees as architecture and nature simultaneously, and which is formally and performatively interesting to compare to Viollet-le-Duc's illustration from 1875, where the engineering is authentic. Of note, le-Duc's interest with Gothic architecture and its formal translation to the new material of that age--cast-iron--echoes the textile arts reflection of the many complex, curvature-based geometries found within Gothic architecture. Illustrations of masonry--and, in particular, lenticular geometries--are shown as reflected in tree tying, or pleaching, essentially, the tying together of individual sapling limbs to create new geometries. This translatory act is of great interest to me, as well as the spatiality and formal complexity found within every example above, from Lancet to Ogee to Trefoil.

Here are a number of singular surface topological studies conducted in Autodesk Maya using deformation tools (twist, etc.) in an attempt to create a windscreen form that wraps around or "cloaks" the tree, while also mimicking its generic volume--wide at its base where the root system is located, slender along its length where the trunk is located, and voluminous at the top, where the leaf canopy and branches are located. Self-intersecting singular surface studies, essentially "blebs," were conducted in an attempt to create an immediate structure for a singular surface to be self-supportive and totally independent of the tree; see Rene Thom's Catastrophe Set. These mimetic trees were converted into triangulated frames, after converting the NURBS surface to a polygonal mesh with a dimensional thickness.

I next created a generic tile, similar perhaps to the leaf or bark element of a tree, and component populated that form to the nodes of the singular surfaces. This digital process led to me to think that a polygonalized frame derived from a self-intersecting singular surface--a "self-similar-structure"--could accrete a number of tiles, or cell components to control the amount of wind flow over and through the surfaces.

Next, a final series of "chalice" volumetric studies were conducted using McNeel's Rhino with both a singular tree form and a cluster organization, or copse formation, essentially, a small group of trees. The form was directly inspired by Karl Weierstrass's Maquette de la Function from 1952, with topological degrees of curvature that shift from 1-degree to 3-degree (and back again). The self-intersecting surface topologies were removed altogether during this latter study, which, as a design system, allows for multiple configurations--for each tree, there could be a four sided windscreen, or figure--the chalice--or a single-sided windscreen--essentially, one of the four sides from this figure, and each of those configurations (x1 or x4 sides, per), could repeat.

The cell in this case can be thought of materially as a tile--a ceramic tile.

For the city sidewalk sites most pressured by constant wind pressure coming in off of the bay water, I identified multiple sites along the Embarcadero and on Market Street between 4th & 11th.