On Urban Forests and Urban Complexity
Urbanity as the most important and yet still unfinished invention of humanity is not a new concept[1]. This notion continues to remain both obtuse and true. Urbanity is not a singular concept, its complexity leads to a range of interpretations; its dynamism to possibilities. How urban space is understood dictates strongly how its components, such as urban forests are developed and stewarded. Importantly, it is how urbanity is understood that will dictate the type of impact that the urban forest has on the city and its communities. We must improve the narrative around cities and the ecosystem services provided by their essential systems such as urban forests.
The city exists as the ultimate representation of urbanity, though it is ever changing and incomplete. This completely dynamic nature lends itself easily to the consideration of the city through an ecological lens; an amalgamation of interdependent essential systems. This characterization is one that could as easily be applied to our most un-urban spaces, which we would more typically consider under a ecological paradigm.
Considering that urbanity is ecological in nature, the tools we use to attempt understanding should reflect this. Design as thoughtful decision making represented as physical or graphical is a key component of perception and action. Yet design presents a duality that is still both generally be odds with complexity-urbanity and yet oddly aligned with ecology-order. We must therefore dig deeper into these concepts. It is a very specific type of complexity we are talking about; complexity that is generated though the density and diversity of systems. This is a core of urbanity.
Urbanity should therefore not be defined by natural or unnatural, as these distinctions are semantic, but rather defined by complexity. It is along this continuum that urban is an extreme to traditional ecologies, which themselves are perhaps more complex than heavily designed human spaces such as sterile suburbs (Figure 1). The number of actors and possible decisions, the number of systems, and their complexity are all extremely high within the city.
fig 1
Complexity may be defined in this sense as the paired partners of diversity and density; a range of systems and a lot of them in a relatively small space. It is this intensity of activity that generates benefits: social (economic and cultural) and bio-physical. Here in lies the brilliance of the urban paradigm and the necessity of an urban forest. The ability to embrace and manage conflict, as opposed to avoiding it. Embracing the complexity allows for realization of ecosystem services (the benefit provision).
Urban forest, the trees and their supporting systems that exist in the places where people encounter them regularly, is a premiere both distillation and representation of natural system interface and natural ecosystem service generation. The resource is positioned best to be of use. The truest form of forest, that which is most ‘natural’, not mimicry but actuality, is also important. What is natural, or more ecologically in tune, however does depend heavily on context. And that is the consideration for harnessing complexity: where are the resources and how are the perceived and engaged by the larger system?
Components of urban space are complex. More complex perhaps than traditional ecosystems, in that another inherency of urbanism is multifunctionality of its components. The elements of a city overlap and have multiple uses, they provide ‘spillover impacts’[2]. This notion is eloquently presented by Alexander in ‘A city is not a tree’[3]. Each object, or process, in a city serves more than one structured use, it is not linear (it could be interpreted resilient, sustainable). This idea is represented by a network with a series of nodes and connections, as opposed to a hierarchy with single pathway sets (Figure 2A). A high complexity urbanity has components that are networked, not linear and ‘tree-like’.
fig 2
A beautiful illustration of this representation of urbanity is in fact, biological trees. A tree along the street can exist as an impediment to travel, a destructive force for pavement, habitat for birds, a sink for carbon dioxide, provider of clean air, source of cooling shade, a wonder for children, a capture of storm water, a calmer of traffic, and a million other roles in a range of system types. As the level of urbanity increases the number of networks this tree is associated with also increases. Generally, it could be assumed that its impacts, positive and negative also increase. This is the high complexity that develops in tandem with urbanity.
The collection of trees, operating in a efficient system, provide a services set greater than the some of its components. This is a forest. It could be argued that due to increased complexity, diversity and density of use and impact types, an urban forest provides an even greater set of services, impacts, uses, than one in a completely non-urban setting.
Importantly we need to understand this complexity. Comprehension of this range of values and impacts allows us to reap benefits and also provide for the sustainable provision of our resources. Additionally, it is through increased true understanding of complex systems such as urban forests that we can capitalize on the values of density and diversity, those that drive connection and passion.
If done correctly understanding will lead to valuation, which will direct the ability for us to capitalize on the benefits, and build a system that feedbacks as to sustain itself in a ecological manner. It is for this reason that consideration of value and benefits is necessary. In an urban ecological context benefits must be received to place the resource into ecological harmony through positive feedback. Before any of this can proceed in a meaningful and effective way however, we must improve the narrative and thus understanding and eventually the management of urban forests; it currently extremely illegible.
Focusing in, we need to better grasp what is meant by benefits or values of urban forests. Wolf’s, as yet unpublished, work on the shifting functionality of trees across a landscape gradient explores this phenomenon (Figure 3)[4]. Function in this case is based on ecosystem services, perhaps most aptly defined through the millennium ecosystem assessment[5]. This accounting identifies four basic sets of service types provided by natural systems, cultural, supporting, regulating, and provisioning systems. (There is not a distinction drawn between those provisioning services that increase with ecosystem health, such as fresh water, and those services that increase with ecosystem decline, such as timber or human food.) Presenting these services across a gradient of urbanity provides for an initial level of understanding of the complexity of the systems, and frames it in a way related to benefits. It is through this understanding and relation to benefits that we can integrate these services into systems.
Ecosystem services are the expression of some of the many complex systems that our urban forests and other natural infrastructure provide. Better understanding of these systems, and better policies, practice, and design around their role in our systems more broadly will lead to a more optimal use of the resource and allow for complexity driven conflict-impact to be embraced and managed. This will lead to self-sustaining urban ecological systems.
Two key approaches should be employed to harness the critical provisions from our urban complexity. First, build systems to identify and then capture of value of ecosystem services. This will lead to positive impacts from natural systems, and mechanisms for the natural, systemic preservation and expansion of our natural environment. Second, where possible integrate natural resources more seamlessly into the existing systems we have established. This will similarly allow for the capturing of their value, which due to systemic inclusion, will incentivize their preservation and restoration with positive feedback.
Both these approaches require embracing complexity and true urban ecological systems. Both approaches are also not necessarily discrete from one another. Additionally, these approaches are more likely to succeed in a true legible representation. Mimicry and replication manifested through highly designed or engineered systems are likely to be less efficient, less complex, and ultimately less sustainable. This reinforces the value of a self-sustaining and naturally occurring system, and importantly the reflection of such a system in the larger urban ecological context. Again, in an urban context the ecological system is necessarily a human system. Failing to incorporate this leads to reduced sustainability in the system.
What does building or integrating natural ecological complexity into systems look like? For urban forests, it largely means identifying the complexities; the understanding of the functions and the value of the functions associated with urban forests, then establishing recipients and incentives. This is mostly easily grasped by thinking in ecological-market terms; how do we gain from these benefits, and how can they be provided to ensure they continue to gain, sustainably?
An example would be developing urban forest carbon projects and selling the carbon sequestration into the California, or other established offset market. Gains are through the removal of carbon from the atmosphere, which are collectively received. Incentives are directed through regulation, as direct feedback is less available on such a large timescale as climate change. However, public perception and in the integration of ecosystem services into policy provide incentives for actions.
Another example would be identifying the property value increases[6] associated with trees and capture a portion of the tax receipt increment for the care and protection of more trees. This would establish a new system - capturing complexity benefits of the urban forest, and establishing a new component - payment towards the establishment of trees maintenance. The system capitalizes on complexity and feedback as to sustain the benefit. In this case the complexity is not full understood. Using market signals benefits are captured without needing full understanding of why property values increase.
A even more integrated approach would be the capitalization of the urban forest under accepted accounting principles. Such an approach would require the owner of the resource, public or private to take a financial loss at the urban forest’s decline, and a financial gain at its success; treating natural infrastructure like the urban forest just like it would other infrastructure such as a pipe system or bridge. This again would create an extremely legible connection between the resource and its value, providing an incentive to protect and restore our urban forests.
Each of these examples harness complexity by identifying ecosystem service value and does so in a way that reinforces the preservation and enhancement of the urban forest system sustainably. Developing mechanisms that capitalize on the complexity as opposed to ignoring or avoiding the complexity due to conflict concerns are the sustainable mechanisms. Sadly, attempts at capturing the value of our urban complexity and the ecosystem services it provides typically fails to integrate it into systems. We are weary of the complexity of the tree; is it destroying pavement, clogging drains, blocking views, or is it inviting pedestrians, capturing storm water, and a view itself? Only though adequately embracing this complexity, understanding it, and developing it into a human system (a sustaining ecology in a urban context), can we capture the benefits and solve the conflict.
A counter example reflects what often the current complexity-avoiding approaches look like. A prime one is the absurdity of a million trees campaign[7]. While such an effort generates understanding, in a shallow sense, it contradictorily misses the holistic value of the urban forest, all the while attempt to restore it. It is a tree campaign, but not focused on the forest; the full socio-ecological system that supports it. Little true urban ecological consideration is given. The sustaining ecology in this sense is an urban one of human dominated systems, and these trees are not properly integrated into the ecology leading to lack of sustainability and reduced capture of benefits, the positive impacts.
One million trees or 200 trees, the goal is not a number but a function; if one million trees truly provides the necessary functionally sought, then perhaps it is a meaningful goal, but likely it is just a number. What is missing is the ecological support system. In the urban complexity context this is the socio-system that tracks, maintains, and captures the value of these trees. Far more valuable would perhaps be a million stewards campaign, where one million New Yorker’s commit to maintaining and monitoring a particular number of trees and their forest components. Additionally, a new system or insertion of this urban forest into an existing system would likely magnify the ability for the value or function of the trees, the real rationale behind their planting, to be gained.
Urban forest may seem like a small component of our natural environment, and therefore not critical in a broader sustainability scheme, but by many of the definitions outlined here all forests are urban and many truly natural systems operate in a similar manner. Wilderness is a creation of humanity, designated for particular geographies. Those forests are spaces that are designed and managed by people, but in a different set of systems and processes than ones in more densely urban space. All of our forests are collections of trees, but all are also the larger ecology which necessarily includes the actions, inactions, and unintended impacts of people.
Within the city, the ultimate urban space, this understanding of complexity of urban resource can be better utilized for benefit, and thus sustainability in an ecological context. The city provides us with the most complexity and thus the most opportunity for capturing values. We can easily identify a whole range of urban forest values and incentive pairs: air pollution - health care industry, storm water - utilities, property values - municipal finance, to name a few. This opportunity does not mean however that the highly urban forest is easier to capture these values. Space of lower complexity might have less opportunity, but increased legibility my simplify the process of systems development, such as water quality permit trading on rural agricultural and industrial lands.
With urbanity we have high complexity thus the premier presentation of density and diversity. The urban forest reflects this. We also have the forest and natural resource generally that is perhaps most in interface with people. The urban forest is the nature we interact with most. Building its legibility into our systems, and in turn developing and expanding the resource and collecting the associate benefits brings also advanced understanding and internalization of complexity. We have density and diversity that we can connect to.
Developing urban forests into fully ecological systems, where the major actors of the forest’s fate, people, are incentivized to perpetuate and support the forest system is how we reach sustainability. The benefits received from the urban forest moves us towards sustainability, and the processes and systems by which this happens helps moves us towards substantiality.
Taken in whole this line of thinking provides a range of principles that identify the value of reframing urban space and the complexity of the urban forest. Complexity is density and diversity. Complexity is high when urbanity is high. Complexity causes conflict, but contains more potential benefit. Building complexity into a system is how resources are sustained and how we best benefit from them.
{C}[1]{C} Lewis Mumford. The City in History: Its Origins, Its Transformations, and Its Prospects. New York: Hardcourt, Brace & World, Inc., 1961.
{C}[2]{C} Nikos A Salingaros. The Principles of Urban Space. Amsterdam: Techne, 2005.
{C}[3]{C} Christopher Alexander “A city is not a tree.” Design, London: Council of Industrial Design, 1966.
{C}[4]{C} Kathleen L. Wolf. “Urban Greening and Public Health as Ecosystem Services,” An Urban Research Agenda Decision Ready Science: Priorities and Opportunities. Wharton School, University of Pennsylvania, May 2013. www.naturewithin.info/talks/wharton.ecoservices.wolf.pdf.
{C}[5]{C} Millennium Ecosystem Assessment. 2005. Accessed October 2013. http://www.unep.org/.
{C}[6]{C} Geoffrey H. Donovan and David Butry. “The effect of urban trees on the rental price of single-family homes in Portland, Oregon.” Urban Forestry and Urban Greening 10(3) (2011): 163-168.
{C}[7]{C} MillionTreesNYC. Accessed October 2013. http://www.milliontreesnyc.org/html/home/home.shtml.