Institution: Harvard Graduate School of Design/ Harvard University Climate Change Solutions Fund (HCCSF)

Linear Urban Forests

Grant 2021-2024

Background

In 2017, Martha Schwartz and Markus Jatsch taught the Option Studio “Sequestropolis” at the Harvard Graduate School of Design. This worked on how to harvest space from city streets, so forests could be inserted that would create a green infrastructure that could combat the worst effects of climate change. Set in 2050, the studio assumed that automatic electric vehicles (AEV) would revolutionize the organization of the street space and provide the rationale to redesign streets to include this new concept, the Linear Urban Forest (LUF).

The studio produced metrics, revealing the cooling effect of the Urban heat Island Effect (UHIE) and its associated costs savings on energy. However, due to the limitations of a student led inquiry into a complex problem, there were many aspects that were underdeveloped and questions that remained unanswered. Still, the studio project showed the untapped potentials of linear urban afforestation, when applied at a large scale, could have pro-found city-wide benefits.

Key assumptions to the HCCSF

• Automatic electric vehicles (AEV) become future mode of transportation with corresponding changes to the street network.

• +2.7C. degrees temperature increase by end of the century based upon IPCC RCP 4.5 intermediate scenario. Emissions will peak in 2040 then start to decline. Net zero not reached by 2100.

• More intense storms-increased rainfall intensity.

• Precipitation increase.

• Increased heat and heatwaves.

“Making a city livable during extreme heat is the great urban engineering project of our time.”

(http://e360.yale.edu/features/paris-heat-wave-climate-change)

Cities need nature-based systems (NbS) to combat climate change impacts: particularly heat. 

While cities need nature-based solutions, open land in the city is at a premium - and often non-existent.  The automated electrical vehicle (AEV) evolution, this century, creates an opportunity that will free up the road space of the future. This projection that provides the space in combination with the rapid growing method Miyawaki, makes it possible to grow forest ecosystems fast. A Linear Urban Forest (LUF) can be produced throughout the future road network which will bring nature back into the city. It will create a better environment for all, with accrued climate benefits: urban cooling, improved health, energy reductions, storm water mitigation, biodiversity and economic uplifts and carbon sequestration.

(LUF) is a futuristic visionary proposal, to afforest the city at a hitherto unprecedented scale throughout the entire urban street network of the future.

This ‘design as research’ was undertaken with a grant from the Harvard Climate Change Solutions Fund, through the Graduate School of Design at Harvard. The project converts paved sections of roadways, transformed to accommodate the electric vehicle revolution, into an interconnected network of native forest ecosystems.

As urban mobility steadily shifts towards autonomous transportation, demand for traditional street surface requirements will gradually diminish. Automatic electric vehicles offer the possibility of freeing up a significant amount of public space. They will require fewer travel lanes, less on-street parking, and reduced width of travel lanes. All these road transformations will clear the path for the introduction of linear urban forests. These large, vegetated public spaces will confer many benefits in adapting to and mitigating climate change. Linear urban forests will be multi-layered native forest ecosystems modelled upon indigenous forests of the region, distributed linearly and continuously throughout the street network of the city. 

It is hypothesized that the benefits will far outweigh the costs in the creation of an equitable public forested urban landscape that will emerge throughout the transportation corridors. It is predicted to cool the city resulting in lower energy costs; mitigate stormwater flooding and reduce storm sewer loads, improve biodiversity, sequester CO2, and provide a myriad of other positive benefits for human health, welfare and economic uplifts.

The organizing principle is a pragmatic and phased approach. Over a period of 40 years, following three scenarios (2030, 2050, 2070), linear urban forests are implanted within the urban street network as it slowly is reconfigured to meet the autonomous vehicle evolution.

The pilot city chosen for this research was Springfield, MA: selected as a mid-size city with a population of about 155,000, that, like many cities, is predicted to experience increased heat and flooding from climate change impacts.

However, the LUF concept is intended for application to any city on the planet.

To map every street in the network of Springfield, geo-spatial modeling was employed using GIS data. The city was divided into four key land uses and five primary street classifications. Combining these parameters gave 19 distinct street typologies such as residential / local street, commercial/principal arterial etc. These typologies serve as the basis for designing the LUF in phased scenarios, and extrapolating quantitative and socio-economic metrics. Each street typology was assigned a corresponding prototypical civil engineered street section which showed the progression of the road transformation from 2030 to 2070. Prototypes of three most likely street sections were developed for the LUF: asymmetrical, symmetrical and middle median. Civil calculations for peak rate storm run-off and collection were used as the basis for determining the engineered design sections.

In each scenario, a cohort of native forest is planted using the rapid, mini forest Miyawaki method: a technique modeled on natural forest biomes, where a multi-layered mix of tree, shrub and grass species grow together as one ecosystem.

Because the inter-connected underground system of roots and mycorrhizal fungus leads to symbiotic sharing of nutrients, the emphasis is placed upon soil health and conditioning during the planting process. A variety of native trees plus understory vegetation are planted at unusual densities: 2 – 7 trees per square meter with a growing rate of 1 meter per year for temperate climates. As they grow, competing for the light, research suggests they sequester more carbon than conventional tree plantings. The forests require little maintenance and weeding after the first few years and provide new habitat for birds and insects. All plant species used in this project are based upon native forests around Springfield, identified from on-site reconnaissance. According to the Miyawaki method, within approximately 10 years a healthy, semi-mature forest will be established.

Findings

As the construction of the LUF takes place in three cohorts over a 40-year time period, each consecutive installation increases the size of the LUF and the benefits build up. Data analysis suggests that for every dollar spent to build LUF, at least $2 of benefits accrue. Cost/benefits that were analyzed include:

• Energy – direct and indirect energy savings

• Climate change – reduction in greenhouse gas emissions, and carbon sequestration and storage

• Pollution - trees absorb air pollutants with resultant benefits to human health

• Stormwater – mitigation of volume and quality as water is absorbed by the plants

• Health benefits from increasing urban tree canopy (UTC) are not included in the $2 of benefits. They include

  • Averting all-cause mortality

  • Number of averted strokes

  • Averted dementia cases

  • Air pollution reduction

  • Heat reduction

Studies suggest that heat wave hospitalizations for renal, respiratory and cardiovascular reasons increase with daily average air temperature, and that the city of Springfield is in the lowest quartile of air-conditioning prevalence among US cities.

Forward-looking conclusions

1.

For purposes of this in-depth study the grant took the application of LUF to the maximum - city-wide - which is how it would best be implemented. However, this concept may be applied strategically and proportionately in cities. In this regard, the study shows that LUF are highly efficacious for neighborhoods suffering the most from environmental injustice, where lack of vegetated, cooling green spaces is most pressing, and where water collection to avoid flooding is also needed. These are usually populations which are most vulnerable to urban heat, and the LUF health benefits would also be greatest.

2.

This study could also be resolved in greater urban design detail by integrating the LUF with other urban placemaking improvements such as:

• widened sidewalks and public space

• larger front yards

• neighborhood gardens

• outdoor picnicking

• jogging paths

• children’s play yards

• strategic street furniture resting places

• integration of outdoor gathering spots in widened walkways

• removal of traditional sidewalks and integrating walking paths through the LUF.

3.

This study began with the exploration of forest ecosystems into the future urban street network in a north-eastern US city. However, LUF can be applied to cities around the world in a variety of climates, from arid to temperate to tropical. This would merely require customizing the basic details outlined in this study with the pilot Springfield, MA.