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Citation: Salih, K.; Saeed, Z.O.;
Almukhtar, A. Lessons from New
York High Line Green Roof:
Conserving Biodiversity and
Reconnecting with Nature. Urban Sci.
2022,6, 2. https://doi.org/
10.3390/urbansci6010002
Academic Editors:
Raúl Romero-Calcerrada,
Javier Cabello,
Manuel Pacheco-Romero and
Koldo Trapaga Monchet
Received: 11 November 2021
Accepted: 24 December 2021
Published: 28 December 2021
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Attribution (CC BY) license (https://
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4.0/).
Case Report
Lessons from New York High Line Green Roof: Conserving
Biodiversity and Reconnecting with Nature
Kawar Salih 1, *, Zaid O. Saeed 2, * and Avar Almukhtar 3
1Research Center, Duhok Polytechnic University, Duhok 42001, Iraq
2School of Design and the Built Environment, Curtin University, Bentley, WA 6102, Australia
3School of the Built Environment, Oxford Brookes University, Oxford OX3 0BP, UK;
a.almukhtar@brookes.ac.uk
*Correspondence: kawar.salih@dpu.edu.krd (K.S.); z.alawadi@postgrad.curtin.edu.au or
zaidosama94cpm@gmail.com (Z.O.S.)
Abstract:
The concept of sustainable urban design has appeared in different perspectives to minimize
and reduce the negative impacts of urban expansion in terms of climatic and environmental draw-
backs. One of the undeniable approaches of sustainable urban design is the adoption of green urban
roofs. Green roofs are seen to have a substantial role in addressing and resolving environmental
issues in the context of climate change. Research investigations have indicated that green roofs have
a remarkable impact on decreasing rainwater runoff, reducing the heat island effect in urban spaces,
and increasing biodiversity. Nevertheless, green roofs in urban spaces as a competent alternative to
nature remains a standing question. To what extent can green roofs mimic the biodiversity that is seen
in nature? Moreover, to what level is this approach practical for achieving a tangible reconnection
with nature, or so-called biophilia? This study attempts to discuss the essence and impact of green
roofs in urban spaces based on a case study approach. The study reflected lessons from the New York
High Line Green Roof regarding biophilia and biodiversity in this case study. It concludes with key
lessons that can be transferred to other urban spaces with similar settings.
Keywords:
green roofs; biodiversity; biophilia; the high line; reconnection with nature; green urbanism
1. Introduction
Over the last several decades, climate change has become one of the major issues for
the contemporary world. Transforming thousands of square miles to urban grey spaces
has influenced the ecosystem, wildlife existence and nature in the urban areas [
1
]. In
2018, the amount of CO
2
emission reached 33.5 Gt, driven by urbanization factors such
as buildings, transportation, industry, electricity and heat generation [
2
]. Considerable
research has been conducted regarding the climate change phenomenon; yet, most of this
research is limited to the presentation of theoretical frameworks for conserving biodiversity
in urban spaces [
3
–
5
]. The idea of sustainable urban design has appeared in different
perspectives, all aiming to minimize and reduce the negative impacts of urban expansion
on the biodiversity of urban spaces. One of the key approaches of sustainable urban design
is the adoption of green urban roofs [6–8].
Green roofs are seen to have a substantial role in addressing and resolving environ-
mental issues in the context of climate change. For instance, research investigations have
indicated that green roofs have a significant impact on decreasing rainwater runoff, re-
ducing the heat island effect in urban spaces, and conserving the ecosystem [
9
,
10
]. Green
roofs are highly effective in reducing the carbon footprint and the heat island effect in
urban spaces [
11
–
13
]. Additionally, green roofs positively enhance urban air quality by
mitigating air pollution and purifying the urban atmosphere through their features and
characteristics [
14
–
16
]. Large-scale green roofs provide an interactive ecological setting that
is recognised as a source of relief for the urban scheme and a preserver of its biodiversity.
Urban Sci. 2022,6, 2. https://doi.org/10.3390/urbansci6010002 https://www.mdpi.com/journal/urbansci
Urban Sci. 2022,6, 2 2 of 13
Moreover, these roofs are seen as a replacement for the existence of wildlife within urban
contexts. Having such features in urban spaces not only preserves the natural biodiver-
sity of the ecological system; it is a substantial element for reconnecting human beings
with nature as well [
17
,
18
]. The human reconnection with nature has been addressed as
a challenging aspect in the urban context due to the complexity of achieving a tangible
connection as well as the nature of urban expansion, which tends towards building rather
than preserving. However, green urbanism in general is seen to be a promising alternative
for reconnecting the urban space with the nature while preserving eco-diversity within the
urban context [19,20].
Nevertheless, the adoption of green roofs in urban spaces as a competent alternative
for nature in the urban areas remains a standing question. To what extent can green roofs
mimic the biodiversity that is seen in nature? Moreover, to what level is this approach
practical for achieving a tangible reconnection with nature, so-called biophilia? Accordingly,
this study attempts to discuss the essence and impact of green roofs in urban spaces based
on a case study approach. The study will analyse the New York High Line Green Roof
regarding biophilia and biodiversity aspects in urban areas. The study will conclude with
key lessons that can be applied to other urban spaces with similar settings.
This paper takes a qualitative approach to discussing the concept of biophilia and
biodiversity in urban spaces from previous studies in Section 2, then links the two main
concepts to the application of green roofs in Section 3. Section 4provides background about
the High Line Green Roof, while Sections 5and 6reflect on the conceptual aspects of the
project through visual analysis of pictures as well as through previous data and references.
The study also derives key aspects learned from the High Line regarding the biodiversity
and biophilia achieved in this case. Lastly, Section 7concludes the study and suggests
further research into the scope of sustainability in urban spaces.
2. Biophilia, Biodiversity and Urban Spaces
2.1. Biophilia
Biophilia is a hypothesis that emerged in the late 20th century. Wilson defined biophilia
in 1984 as the preference and the pursuit of nature by humans, which is considered a
genetic root inherited millions of years ago when humans were highly associated with the
natural environment [
21
]. This old association might have influenced human behavior
toward nature, and it has remarkable effects on human health in general. Kellert (2008)
demonstrated that nature can significantly improve healing and recovery from illness,
social problems, motivation, physiological problems, and the human brain [
22
]. Research
associated with the impact of nature on the human species started with the beginning
of the biophilia concept. Old research as far back as 1984 suggested that patients with a
natural view can heal more quickly than those without [
23
]. Later research pointed out
that walking in nature improves self-esteem by 90% [
24
]. This indicates that the human
connection with nature has psychological benefits. This was deeply studied later on, and
many scholars noticed that this connection leads to numerous health benefits and better
quality of life [
22
]. Therefore, Beatley (2011) stressed that ‘we need nature in our lives; it
is not optional but essential’ [
25
]. Moreover, it has been mentioned that as the world is
becoming more urban, the human connection to nature is becoming more difficult [
25
].
Accordingly, human contact with nature is a basic need that should be reflected widely in
urban environments, which probably has been neglected or less-considered for many years.
The benefits of biophilia can be achieved in urban spaces if cities are designed based on
integrating nature into man-made environments. To adapt this Kellert, in 2011, suggested
biophilic design; this was then promoted and applied by Beatley and Newman in 2011
and 2014 respectively, which means it is not an old concept compared to other design con-
cepts [
22
,
25
,
26
]. Kellert and Calabrese (2015), in their Practice of Biophilic Design, suggested
fundamental rules for the effective practice of such design [
27
]. They highlighted that
biophilic design should sustain engagement with nature, encourage emotional attachment
to place and setting, and promote an expanded sense of relationship and responsibility for
Urban Sci. 2022,6, 2 3 of 13
both human and natural communities. This, in the end, requires integrated architectural
and urban solutions. Such ideas could be implemented, for example, through the fourteen
“patterns of biophilic design” [
28
]. These patterns are fundamentally categorised under the
headings of Nature in the Spaces, Natural Analogues, and Nature of the Space, as shown
in Figure 1[
28
]. Regarding Nature in the space, this approach emphasizes adding seven
design patterns that connect humans with nature through scenes or feelings from nature,
such as visual/non-visual connections, the presence of water, and the variability of nature
in terms of lighting, thermal and airflow. On the other hand, patterns regarding Natural
Analogues are added through biomorphic forms by using natural materials or mimicking
nature’s complexity and order. Biophilic design pattern can complexify to further ideas and
include Nature of the Space, such as the mystery of space, refuge, prospect, risk, and peril.
Urban Sci. 2022, 5, x FOR PEER REVIEW 3 of 14
in 2011 and 2014 respectively, which means it is not an old concept compared to other
design concepts [22,25,26]. Kellert and Calabrese (2015), in their Practice of Biophilic Design,
suggested fundamental rules for the effective practice of such design [27]. They
highlighted that biophilic design should sustain engagement with nature, encourage
emotional attachment to place and setting, and promote an expanded sense of relationship
and responsibility for both human and natural communities. This, in the end, requires
integrated architectural and urban solutions. Such ideas could be implemented, for
example, through the fourteen “patterns of biophilic design” [28]. These patterns are
fundamentally categorised under the headings of Nature in the Spaces, Natural
Analogues, and Nature of the Space, as shown in Figure 1 [28]. Regarding Nature in the
space, this approach emphasizes adding seven design patterns that connect humans with
nature through scenes or feelings from nature, such as visual/non-visual connections, the
presence of water, and the variability of nature in terms of lighting, thermal and airflow.
On the other hand, patterns regarding Natural Analogues are added through biomorphic
forms by using natural materials or mimicking nature’s complexity and order. Biophilic
design pattern can complexify to further ideas and include Nature of the Space, such as
the mystery of space, refuge, prospect, risk, and peril.
Figure 1. 14 Patterns of Biophilic design. Data from source: [28].
Urbanization has not only affected the connection between nature and human beings;
it has affected the existence of wildlife features in urban areas, cities and living places as
well. Thus, urbanization has impacted the biodiversity of the ecological system in urban
spaces.
2.2. Biodiversity in Urban Spaces
Ecosystem and wildlife features are some of the significant environmental challenges
that urban design confronts when designing urban areas. The ecosystem refers to a unique
interaction between the living species and the physical environment that enables those
species to sustain their lifecycle and maintain balance in nature [29]. Accordingly, any
defect in the ecosystem will impact the lifecycle of living species [29]. On the other hand,
urbanization has been seen as an extensive threat when it comes to breaking the ecological
balance of the environment. Several studies [30–32] have clearly demonstrated the
negative impact of transforming natural green areas into grey urban developments where
the biodiversity of the ecosystem is adversely affected. Generally, urbanization has been
pictured as in contrast with biodiversity; where the former increases, the latter decreases
Figure 1. 14 Patterns of Biophilic design. Data from source: [28].
Urbanization has not only affected the connection between nature and human beings;
it has affected the existence of wildlife features in urban areas, cities and living places
as well. Thus, urbanization has impacted the biodiversity of the ecological system in
urban spaces.
2.2. Biodiversity in Urban Spaces
Ecosystem and wildlife features are some of the significant environmental challenges
that urban design confronts when designing urban areas. The ecosystem refers to a unique
interaction between the living species and the physical environment that enables those
species to sustain their lifecycle and maintain balance in nature [
29
]. Accordingly, any
defect in the ecosystem will impact the lifecycle of living species [
29
]. On the other hand,
urbanization has been seen as an extensive threat when it comes to breaking the ecological
balance of the environment. Several studies [
30
–
32
] have clearly demonstrated the negative
impact of transforming natural green areas into grey urban developments where the biodi-
versity of the ecosystem is adversely affected. Generally, urbanization has been pictured
as in contrast with biodiversity; where the former increases, the latter
decreases [30–32]
.
Therefore, architects, urban planners, and decision-makers have been seeking practical and
innovative solutions that could preserve biodiversity in urban areas and lead to healthier
and sustainable urbanization. These urban solutions are a key aspect in planning and
designing urban areas while preserving the ecological diversity in these areas through a set
of features and practices.
Urban Sci. 2022,6, 2 4 of 13
3. Green Roofs in Urban Spaces
Green roofs, also referred to as “Planted Roofs,” “Living Roofs,” “Eco-roofs,” or “Gar-
den Roofs”, are roofs with vegetation on their final layers which are applied in urbanized
spaces [
33
]. They are classified as extensive, intensive, and semi-intensive based on their
depths [
34
]. Their depth starts with extensive types with a depth of less than 200 mm
of growing media and grows to semi-intensive and intensive with more than 200 mm of
growing substrate [
34
]. As the environmental outcomes of green roofs have been identified
in the existing literature, this study investigates the contribution of green roofs in linking
humans with nature and bio-diversification of the urbanized areas.
3.1. Green Roofs and Biophila
Green roofs can play a substantial role in reconnecting humans with nature. As
expanding urban areas translate to demolition of natural spaces, architects and urban
designers recommend increasing garden roofs to compensate for those natural views
removed by urban expansions. Biophilic Urbanism (BU) can be a solution when dense
cities fail to increase green land, and Green Infrastructure (GI) can be used as an alternative
approach including green walls, roofs, and balconies [
35
]. This is widely seen in Singapore,
which has founded the SkyRise Greening Initiative (SRGI) to assess the quality of planted
roofs in the early phases of building designs [
26
]. Therefore, green roofs are presented as
a considerable dimension of Biophilic Urbanism, or BU [
17
]. The governments of Japan,
Singapore, Belgium, and Germany highly encourage the use of green roofs in urban areas
because of these benefits [
36
]. Moreover, studies have noticed a relationship between
rooftop forests and psychological illness improvements in cities [
37
]. However, the studies
which have investigated the contribution of a green roof for human reconnection with
nature and well-being are limited [
38
], and further research is required as green roofs
could be a notable method for increasing green space and reconnecting with nature in
urbanized areas.
3.2. Green Roofs and Biodiversity
Studying the ability of green roofs to providing a suitable environment for wildlife
existence appears to be controversial. The scholarly debate has focused on the possibility
of including wildlife in urban spaces through the adoption of green roofs [
9
,
39
,
40
]. Some
early investigations in Germany doubted the ability of green roofs to provide a rich biotic
diversity paradigm [
41
,
42
]. The study questioned the possible depth of the substrate
layers of the artificial roof, as the thinner the substrate layers are, the lower the cost of
green roof construction. At the same time, this can negatively affect the opportunity to
achieve an interconnected biodiverse paradigm. Nevertheless, later studies [
7
,
40
,
43
,
44
]
have demonstrated that a wide spectrum of living species can thrive in green roofs when
these roofs are properly designed with suitable substrate layers, landscape features, plants
and natural elements. For instance, the green roof of Chicago City Hall has the capacity
of accommodating nearly 20,000 plants and more than 150 different types of birds and
invertebrate species living in an area of 2000 m
2
[
45
]. Accordingly, green roofs have been
proposed as an appropriate alternative for adopting wildlife features in urbanized areas.
The scholarly debate has considered the adoption of green roofs in urban spaces as an
alternative to the existence of wildlife in these spaces; yet, more case studies need to be
discussed in order to better understand the practicality and functionality of green roofs as
a valid alternative for wildlife in urban areas.
For better understanding of the impact of green roofs on preserving biodiversity and
achieving biophilia in urban spaces, the case of the High Line Green Roof will be discussed
in this study to derive lessons on the adoption of large-scale green roofs in urban spaces.
Due to the proper scale and the urban value of the High Line, this case has been selected
for thorough investigation in this study.
Urban Sci. 2022,6, 2 5 of 13
4. The High Line
The High Line is a linear elevated urban park and greenway built on a former New
York Central Railroad spur on the west side of the Manhattan in New York city. It has
a length of 1.52 miles and an area of 27.499 m
2
. The structure is mainly steel frames
with reinforced concrete roof decking. The High Line is considered an iconic projects in
New York City. Scientifically, the High Line can be considered a green roof, following the
scientific definition that any top roof of a structure that contains vegetation on the final
layer is regarded as a green roof [33].
The history of the High Line elevated railway has a significant role in the success
of the project refurbishment. The structure was built in the 1930s, when the purpose
of its construction was to improve the urban economy and transportation in the Lower
Manhattan area of New York City [
46
]. The high line railway served to deliver and receive
products from the Meat Packing District [
47
]. The last train movement on this track was
in the 1980s, before a new generation of train were introduced [
48
]. The most significant
part of the High Line’s history starts in the year of 1980, when it stopped working until
1999. Throughout this 20-year timeframe, the High Line roof was abandoned and became
a place for the growth of different types of wildlife plants and other species, showing
the possibility of an emerging biodiverse environment where the required conditions are
available [
47
]. Over the years, some parts of the train tracks were demolished to provide
new areas for development on the site. However, in 1999, Robert Hammond created a
group called Friends of The High Line to preserve the abandoned structure from becoming
demolished [48].
In 2001, the New York City government decided to demolish the entire High Line
site in order to accommodate a new development. The Friends of the High Line strongly
opposed the demolition of the historic project, and provided remarkable financial support
through donation campaigns in order to preserve and redevelop the structure. In 2004, a
design competition was launched aiming to preserve and transform the High Line into a
public urban space. Ultimately, the landscape architect James Corner won the competition
in collaboration with the Field Operations Design Firm [
49
–
52
]. Figure 2illustrates the
main milestones in the history of the High Line.
Urban Sci. 2022, 5, x FOR PEER REVIEW 6 of 14
Figure 2. History of the High Line in different historical stages. Data from source: [49].
5. Lessons on Biophilia
The concept of the High Line green roof design was based on the principles of
biophilic design, seeking to engage people with nature while retaining the identity of the
place. The proposal involved the creation of a sustainable urban ecology park integrating
people with nature, and with the history of the site inspired by the years that the High
Line was abandoned, resulting in the site becoming obscured by natural vegetation [ibid].
The designers kept the original rails along some parts of the roof in order to preserve its
history. Trees and grass evoke the wildness of nature within the urban context of the New
York City. The pathways have been designed to take different directions and provide
various views of the location, as presented in Figure 3. The architect, James Corner, says
that ‘The High Line is a different place from the rest of New York. There is a sense of
slowness, distraction, and otherworldliness, and that is what we want to preserve’ [53].
Accordingly, the High Line renovation proposal has been designed based on the concept
of biophilia to revive an old construction into a living green roof project.
Figure 3. Design Proposal of the High Line. Reprinted from ref. [50].
Additionally, the High Line Project represents a successful example of green roofs
that engage people with nature. The total number of visitors to the park jumped from 4
Figure 2. History of the High Line in different historical stages. Data from source: [49].
Urban Sci. 2022,6, 2 6 of 13
5. Lessons on Biophilia
The concept of the High Line green roof design was based on the principles of biophilic
design, seeking to engage people with nature while retaining the identity of the place. The
proposal involved the creation of a sustainable urban ecology park integrating people
with nature, and with the history of the site inspired by the years that the High Line was
abandoned, resulting in the site becoming obscured by natural vegetation [ibid]. The
designers kept the original rails along some parts of the roof in order to preserve its history.
Trees and grass evoke the wildness of nature within the urban context of the New York City.
The pathways have been designed to take different directions and provide various views
of the location, as presented in Figure 3. The architect, James Corner, says that ‘The High
Line is a different place from the rest of New York. There is a sense of slowness, distraction,
and otherworldliness, and that is what we want to preserve’ [
53
]. Accordingly, the High
Line renovation proposal has been designed based on the concept of biophilia to revive an
old construction into a living green roof project.
Urban Sci. 2022, 5, x FOR PEER REVIEW 6 of 14
Figure 2. History of the High Line in different historical stages. Data from source: [49].
5. Lessons on Biophilia
The concept of the High Line green roof design was based on the principles of
biophilic design, seeking to engage people with nature while retaining the identity of the
place. The proposal involved the creation of a sustainable urban ecology park integrating
people with nature, and with the history of the site inspired by the years that the High
Line was abandoned, resulting in the site becoming obscured by natural vegetation [ibid].
The designers kept the original rails along some parts of the roof in order to preserve its
history. Trees and grass evoke the wildness of nature within the urban context of the New
York City. The pathways have been designed to take different directions and provide
various views of the location, as presented in Figure 3. The architect, James Corner, says
that ‘The High Line is a different place from the rest of New York. There is a sense of
slowness, distraction, and otherworldliness, and that is what we want to preserve’ [53].
Accordingly, the High Line renovation proposal has been designed based on the concept
of biophilia to revive an old construction into a living green roof project.
Figure 3. Design Proposal of the High Line. Reprinted from ref. [50].
Additionally, the High Line Project represents a successful example of green roofs
that engage people with nature. The total number of visitors to the park jumped from 4
Figure 3. Design Proposal of the High Line. Reprinted from ref. [50].
Additionally, the High Line Project represents a successful example of green roofs
that engage people with nature. The total number of visitors to the park jumped from
4 million people in 2011 to 7 million in 2018 [
54
]. This has led the project to become one of
the most visited places in New York City and on the list of top New York City landmarks
[ibid]. According to online public reviews, it is a highly recommended destination for
visiting (www.tripadvisor.com) (accessed on 10 December 2021). According to the website,
there are more than 60,000 reviews on the project at present; more than 42,000 reviews
have given an excellent rating and 16.000 very good ratings. This amounts to 90% highly
positive reviews on the site. The most popular comments on the site are related to the green
spaces, pleasant walks, and elevated park, which shows the positive view of people about
the space and how they are connected to nature when they walk through it. Following are
samples of reviews of the highline project:
•
R1: “The walk along the High line is full of lush greenery intermingled with the “concrete
jungle” of high rise buildings. The walking path is well maintained, and is very accessible for
all types of walkers, runners and families with children. The gardens are diverse, with a good
selection of low lying, bush types and taller trees that provide lots of shade and fresh air and
plenty of benches are available for those looking to rest or take in the scenery.”
•
R2: “An urban green space built on an old railroad. You can still see the railroad structure
remnants. The walk is very peaceful and a great place to reflect on life or have a conversation
with a friend.”
•
R3: “Not sure what’s all the fuss. Without a doubt, great for the neighborhood to have this
green space in the middle of the city, but I’m not sure why a tourist would go out of their way
to walk along the High Line. Also very crowded and not a relaxing stroll along a relatively
narrow pathway.”
The public reviewers’ comments and the data provided lead to the conclusion that
the Highline successfully connects people with nature by bringing nature to urban areas
where minimal green regions exist. Transforming the old structure into an attractive green
destination is a testament to the project’s success in mimicking nature by having various
types of plants and providing fresh air and relaxation, as suggested by the reviewers.
Urban Sci. 2022,6, 2 7 of 13
To further investigate the project’s biophilic design aspect, a visual analysis of the
project design was undertaken. The analysis was based on measuring the High Line’s views
taking into account the biophilic design patterns discussed earlier in order to investigate
the aspects of biophilia in the project. Hence, photos of the project were collected from
the Friends of the High Line organization’s official website and the photos were visually
analyzed to find biophilic design patterns (https://www.thehighline.org/) (accessed on
10 March 2021). It was observed that the project is highly successful in touching and
applying all of the patterns from the three major categories, namely, Nature in Space,
Natural Analogues and Nature of the Spaces. Figure 4illustrates the visual analysis of
biophilic patterns.
Urban Sci. 2022, 5, x FOR PEER REVIEW 8 of 14
Figure 4. Biophilic patterns of the High Line. Diagram Source: Authors.
Visual observation of people’s interaction with the High Line, on the other hand,
provides further evidence of how green roofs manage to simulate a natural environment.
In [54] it was suggested that most of the visitors of the High Line come for walking and
relaxation purposes, and the study detected a high satisfaction among people visiting the
High Line. The reflections of visitors, as published online, demonstrates the success of the
High line in providing a tangible connection with nature in various forms, as
demonstrated by the remarkable number of visits to this distinguished urban roof. Figure
5 demonstrates the interaction between the visitors and the features and elements of the
High Line green roof.
Figure 4. Biophilic patterns of the High Line. Diagram Source: Authors.
Urban Sci. 2022,6, 2 8 of 13
In studying the aspects of Nature in Space, the High Line shows a high reflection
of visual and non-visual connection with nature, taking into account the wildness of the
views, smells, and sounds of nature. The project evidently encompasses diversity in its
selection of wild plants, the variability of the natural and artificial lights, the cycle of
nature, and seasonal alteration in order to touch human desires related to natural systems
and their variability. The project also incorporates water bodies and wild forms in its
design as important patterns of nature. In terms of its Natural Analogues aspects, the
project includes natural materials in the design of setting objects and excludes synthesized
materials wherever possible. It has also considered the use of organic forms and patterns
evocative of the biomorphic forms and its complicity and order at the same time. It can be
noticed that the Nature of Space has been well-studied in the design of the High line. The
visual analysis attracted the authors’ attention to the design of different activities that take
human attention in nature instinctively. This can be noticed in areas with risk-taking or
the use of mysterious objects and designs that attract visitors to discover, as well as areas
with sheltering and cover spaces to provide a feeling of inclusion to visitors, as presented
in Figure 4.
Visual observation of people’s interaction with the High Line, on the other hand,
provides further evidence of how green roofs manage to simulate a natural environment.
In [
54
] it was suggested that most of the visitors of the High Line come for walking and
relaxation purposes, and the study detected a high satisfaction among people visiting
the High Line. The reflections of visitors, as published online, demonstrates the success
of the High line in providing a tangible connection with nature in various forms, as
demonstrated by the remarkable number of visits to this distinguished urban roof. Figure 5
demonstrates the interaction between the visitors and the features and elements of the
High Line green roof.
Urban Sci. 2022, 5, x FOR PEER REVIEW 9 of 14
Figure 5. People engagement with nature on the top of the High Line. Data from source [49].
The case of the High Line has shown the importance of adopting green roofs as a
substantial alternative to increase greenery in urban spaces and to reconnect people with
nature. The project has shown the ability of green roofs in acting as a valid alternative to
nature in urban areas. The High Line has been successful in attracting visitors to spent
time for relaxation and walking to fulfill their instinctive desires for a connection with
nature, even in urban spaces.
The example of the High Line can be replicated in other urban areas with a planned
Biophilic Urbanism strategy, and green roofs can be a proper alternative for nature when
dense cities fail to increase green land. In addition, the example of the High Line reflects
the essence of Biophilic design patterns as a key measure for the successful design of green
roofs. The more biophilic patterns are implemented, the more the connection with nature
is seen to be sensible. The impact of the High Line in the urban space of New York City is
not limited to reconnection with nature; the High Line has positively impacted the
existence of a more wild and biodiverse environment within the congested urban scheme
of New York City.
6. Lessons on Biodiversity
The emergence of a rich biodiverse environment on the abounded rail line serves as
a lesson on the possibility of the presence of natural wildlife features in a high-end urban
area. The features of wildlife appeared gradually on the surface of the rail line, with
increasing diversity over time. Looking at the timeline of the High Line, the elements of
biodiversity thrived on the surface of the abundant rail line. This was the spark of insight
for the High Line designers to preserve the emerging biodiverse elements and to redefine
them in a proper design scheme, that placed them within the redevelopment scheme.
Another lesson was the impact of strategic planning in preserving biodiversity in urban
spaces. The designers of the High Line embraced a temporal strategy for attracting
different forms of wildlife on the surface of the High Line, in different stages and with
different features; thus, a natural and biodiverse ecosystem thrived. Figure 6 illustrates
the emergence of wildlife features within specific timeframes. As demonstrated in the
diagram, the diversity and integrity of wildlife features increases over the time to include
a wider range of creatures. This process was exemplified in the case of the High Line.
Consequently, the biodiverse environment that has been emerging on the abandoned rail
line has inspired the community to preserve the structure and redesign the rail line in a
way that maintains the biodiversity of the place and presents an interactive urban space
for the citizens of New York City [49–51].
Figure 5. People engagement with nature on the top of the High Line. Data from source [49].
The case of the High Line has shown the importance of adopting green roofs as a
substantial alternative to increase greenery in urban spaces and to reconnect people with
nature. The project has shown the ability of green roofs in acting as a valid alternative to
nature in urban areas. The High Line has been successful in attracting visitors to spent time
for relaxation and walking to fulfill their instinctive desires for a connection with nature,
even in urban spaces.
The example of the High Line can be replicated in other urban areas with a planned
Biophilic Urbanism strategy, and green roofs can be a proper alternative for nature when
dense cities fail to increase green land. In addition, the example of the High Line reflects
the essence of Biophilic design patterns as a key measure for the successful design of green
roofs. The more biophilic patterns are implemented, the more the connection with nature is
seen to be sensible. The impact of the High Line in the urban space of New York City is not
limited to reconnection with nature; the High Line has positively impacted the existence
of a more wild and biodiverse environment within the congested urban scheme of New
York City.
Urban Sci. 2022,6, 2 9 of 13
6. Lessons on Biodiversity
The emergence of a rich biodiverse environment on the abounded rail line serves
as a lesson on the possibility of the presence of natural wildlife features in a high-end
urban area. The features of wildlife appeared gradually on the surface of the rail line, with
increasing diversity over time. Looking at the timeline of the High Line, the elements
of biodiversity thrived on the surface of the abundant rail line. This was the spark of
insight for the High Line designers to preserve the emerging biodiverse elements and
to redefine them in a proper design scheme, that placed them within the redevelopment
scheme. Another lesson was the impact of strategic planning in preserving biodiversity in
urban spaces. The designers of the High Line embraced a temporal strategy for attracting
different forms of wildlife on the surface of the High Line, in different stages and with
different features; thus, a natural and biodiverse ecosystem thrived. Figure 6illustrates the
emergence of wildlife features within specific timeframes. As demonstrated in the diagram,
the diversity and integrity of wildlife features increases over the time to include a wider
range of creatures. This process was exemplified in the case of the High Line. Consequently,
the biodiverse environment that has been emerging on the abandoned rail line has inspired
the community to preserve the structure and redesign the rail line in a way that maintains
the biodiversity of the place and presents an interactive urban space for the citizens of New
York City [49–51].
Urban Sci. 2022, 5, x FOR PEER REVIEW 10 of 14
Figure 6. The emergence of a wild and biodiverse ecological system over the time. Reprinted from
ref. [50].
One of the challenges in the redesign of the High Line was the ability to plant various
species within the limited earth layer of the rail line. The Dutch Garden Designer Piet
Oudolf addressed this problem by adopting specific plant types able grow and thrive
within the limited depth of the substrate layers. The average earth depth in the High Line
is 450 mm, and reaches 900 mm in particular locations to accommodate wild trees. Figure
7 illustrates cross-sections for the High Line Garden Roof and shows different substrate
layers from different locations on the roof [49–51].
Figure 7. The High Line: (A) cross-section of the main pathway; (B) cross-section of a multi-level
zone. Reprinted from ref. [50].
The design of the High Line demonstrates another lesson on the possibility of
accommodating various types of wild plants within a limited substrate layer. The rational
use of the available depth in the structure and the proper selection of wild plant types
enabled the generation of a thriving and livable biodiverse environment on the top of the
redesigned High Line. The design adopted seasonal plants of various types, with the aim
of accommodating different living species that find in the seasonal plants a place to
complete their lifecycle, even within a vibrant and crowded urban space. As a result, the
High Line has become a suitable site for different types of migratory and local birds to
grow, feed, and nest on the Green Roof. For instance, the American Kestrel, House
Sparrow, Mourning Dove, Northern Mockingbird and Peregrine Falcon are among the
types of birds living along the High Line. This demonstrates another lesson on the
importance of adopting various planting strategies that match with all the seasons in order
to achieve a rich ecological environment that accommodates different forms of wildlife in
the urban space.
James Corner, the design architect, and the design team have outlined the High Line
design to reflect different microclimatic conditions [52]. Along the linear landscape of the
High Line, multiple climatic zones have been presented, each with the features and
Figure 6.
The emergence of a wild and biodiverse ecological system over the time. Reprinted from
ref. [50].
One of the challenges in the redesign of the High Line was the ability to plant various
species within the limited earth layer of the rail line. The Dutch Garden Designer Piet
Oudolf addressed this problem by adopting specific plant types able grow and thrive
within the limited depth of the substrate layers. The average earth depth in the High Line
is 450 mm, and reaches 900 mm in particular locations to accommodate wild trees. Figure 7
illustrates cross-sections for the High Line Garden Roof and shows different substrate
layers from different locations on the roof [49–51].
Urban Sci. 2022,6, 2 10 of 13
Urban Sci. 2022, 5, x FOR PEER REVIEW 10 of 14
Figure 6. The emergence of a wild and biodiverse ecological system over the time. Reprinted from
ref. [50].
One of the challenges in the redesign of the High Line was the ability to plant various
species within the limited earth layer of the rail line. The Dutch Garden Designer Piet
Oudolf addressed this problem by adopting specific plant types able grow and thrive
within the limited depth of the substrate layers. The average earth depth in the High Line
is 450 mm, and reaches 900 mm in particular locations to accommodate wild trees. Figure
7 illustrates cross-sections for the High Line Garden Roof and shows different substrate
layers from different locations on the roof [49–51].
Figure 7. The High Line: (A) cross-section of the main pathway; (B) cross-section of a multi-level
zone. Reprinted from ref. [50].
The design of the High Line demonstrates another lesson on the possibility of
accommodating various types of wild plants within a limited substrate layer. The rational
use of the available depth in the structure and the proper selection of wild plant types
enabled the generation of a thriving and livable biodiverse environment on the top of the
redesigned High Line. The design adopted seasonal plants of various types, with the aim
of accommodating different living species that find in the seasonal plants a place to
complete their lifecycle, even within a vibrant and crowded urban space. As a result, the
High Line has become a suitable site for different types of migratory and local birds to
grow, feed, and nest on the Green Roof. For instance, the American Kestrel, House
Sparrow, Mourning Dove, Northern Mockingbird and Peregrine Falcon are among the
types of birds living along the High Line. This demonstrates another lesson on the
importance of adopting various planting strategies that match with all the seasons in order
to achieve a rich ecological environment that accommodates different forms of wildlife in
the urban space.
James Corner, the design architect, and the design team have outlined the High Line
design to reflect different microclimatic conditions [52]. Along the linear landscape of the
High Line, multiple climatic zones have been presented, each with the features and
Figure 7.
The High Line: (
A
) cross-section of the main pathway; (
B
) cross-section of a multi-level
zone. Reprinted from ref. [50].
The design of the High Line demonstrates another lesson on the possibility of accom-
modating various types of wild plants within a limited substrate layer. The rational use of
the available depth in the structure and the proper selection of wild plant types enabled the
generation of a thriving and livable biodiverse environment on the top of the redesigned
High Line. The design adopted seasonal plants of various types, with the aim of accom-
modating different living species that find in the seasonal plants a place to complete their
lifecycle, even within a vibrant and crowded urban space. As a result, the High Line has
become a suitable site for different types of migratory and local birds to grow, feed, and nest
on the Green Roof. For instance, the American Kestrel, House Sparrow, Mourning Dove,
Northern Mockingbird and Peregrine Falcon are among the types of birds living along
the High Line. This demonstrates another lesson on the importance of adopting various
planting strategies that match with all the seasons in order to achieve a rich ecological
environment that accommodates different forms of wildlife in the urban space.
James Corner, the design architect, and the design team have outlined the High Line
design to reflect different microclimatic conditions [
52
]. Along the linear landscape of
the High Line, multiple climatic zones have been presented, each with the features and
characteristics of that particular zone. For instance, the Falcone Flyover zone is a wet-shaded
climatic zone that accommodates wild forest trees, while the Sun lawn zone is a dry–sunny
climatic zone that accommodates wild high grasses and seasonal flowers, as shown in
Figure 8. The variety of climatic zones in the High Line reflects the essence of mimicking
different climatic conditions in the design of urban spaces to allow the flourishing of a
biodiverse environment. The High Line design has successfully reflected various climatic
conditions in the different zones of the design, presenting a holistic and comprehensive
picture of biodiversity [49–52].
Urban Sci. 2022, 5, x FOR PEER REVIEW 11 of 14
characteristics of that particular zone. For instance, the Falcone Flyover zone is a wet-
shaded climatic zone that accommodates wild forest trees, while the Sun lawn zone is a
dry–sunny climatic zone that accommodates wild high grasses and seasonal flowers, as
shown in Figure 8. The variety of climatic zones in the High Line reflects the essence of
mimicking different climatic conditions in the design of urban spaces to allow the
flourishing of a biodiverse environment. The High Line design has successfully reflected
various climatic conditions in the different zones of the design, presenting a holistic and
comprehensive picture of biodiversity [49–52].
Figure 8. The High Line: (A) Sun Lawn Zone; (B) Falcone Flyover Zone. Data from source [49].
Today, the High Line Green Roof is seen as a successful paradigm for bringing
wildlife into urban spaces. The artificial alternative greenspace has reflected an effective
and practical approach for the emergence and thriving of a biodiverse environment within
the urban scheme. Having adequate conditions and proper design elements, green roofs
can substantially enhance the biodiversity of public urban spaces. The lessons reflected in
this study on biophilia and biodiversity demonstrate the success factors behind the High
Line Green Roof. These lessons can be transferred to and implemented in other urban
areas where the aim is to reconnect with the nature and conserve biodiversity in the urban
area.
7. Conclusions
Urbanization has notably impacted the connection of human beings with nature, as
well as the existence of wildlife and biodiversity in urban spaces. The adoption of green
roofs in urban areas is seen to be one of the substantial aspects of sustainable urban design
that could significantly answer the call for tangible reconnection with nature as well as
tackle the challenges of climate changes caused by urbanization. This study has attempted
to reflect lessons on the implementation of green roofs in urban spaces based on a case
study. The study has yielded the conclusions drawn below.
First, green roofs have proven to be a substantial alternative method for increasing
greenery in urban spaces and reconnecting people with nature. The case study presented
a successful project that is able to attract visitors to spent time in relaxation and walking
and fulfill their instinctive desires for the natural environment in an urban space.
Second, the example of the High Line can be replicated through Biophilic Urbanism
(BU) when dense cities fail to increase green land, by using alternative GIs such as green
walls, roofs, and balconies. However, pre-planning is essential before any applications for
the success of this strategy.
Third, biophilic design patterns can be used as a key measure to design green roofs,
and should take the maximum number of biophilic patterns into design consideration,
Figure 8. The High Line: (A) Sun Lawn Zone; (B) Falcone Flyover Zone. Data from source [49].
Urban Sci. 2022,6, 2 11 of 13
Today, the High Line Green Roof is seen as a successful paradigm for bringing wildlife
into urban spaces. The artificial alternative greenspace has reflected an effective and
practical approach for the emergence and thriving of a biodiverse environment within the
urban scheme. Having adequate conditions and proper design elements, green roofs can
substantially enhance the biodiversity of public urban spaces. The lessons reflected in this
study on biophilia and biodiversity demonstrate the success factors behind the High Line
Green Roof. These lessons can be transferred to and implemented in other urban areas
where the aim is to reconnect with the nature and conserve biodiversity in the urban area.
7. Conclusions
Urbanization has notably impacted the connection of human beings with nature, as
well as the existence of wildlife and biodiversity in urban spaces. The adoption of green
roofs in urban areas is seen to be one of the substantial aspects of sustainable urban design
that could significantly answer the call for tangible reconnection with nature as well as
tackle the challenges of climate changes caused by urbanization. This study has attempted
to reflect lessons on the implementation of green roofs in urban spaces based on a case
study. The study has yielded the conclusions drawn below.
First, green roofs have proven to be a substantial alternative method for increasing
greenery in urban spaces and reconnecting people with nature. The case study presented a
successful project that is able to attract visitors to spent time in relaxation and walking and
fulfill their instinctive desires for the natural environment in an urban space.
Second, the example of the High Line can be replicated through Biophilic Urbanism
(BU) when dense cities fail to increase green land, by using alternative GIs such as green
walls, roofs, and balconies. However, pre-planning is essential before any applications for
the success of this strategy.
Third, biophilic design patterns can be used as a key measure to design green roofs,
and should take the maximum number of biophilic patterns into design consideration,
namely, Nature in Space, Natural Analogues, and Nature of Space. This, in return, will aid
in reconnection with nature in urban areas.
Fourth, with a proper design strategy and adequate conditions green roofs can ac-
commodate a thriving and biodiverse environment within urban areas. The variety of soil
depth and different microclimate conditions in green roofs can help accommodate different
types of plants, insects, birds, and other animals accordingly. Such design strategies are
critical for the creation of a rich ecological area.
Fifth, although green roofs are human-made structures, these structures have shown
the ability to mimic the features and characteristics of wild areas. The diversity of planting
in the different site zones and the existence of living species actively depict the features
of wildlife.
Finally, the adoption of green roofs in the design of urban areas can be a competent
alternative to the existence of nature in the urban scheme. However, further research is rec-
ommended in order to investigate and discuss the challenges and barriers in transforming
this approach to other urban areas.
Author Contributions:
Conceptualization, K.S.; methodology, K.S., software, K.S. and Z.O.S.; valida-
tion, K.S., Z.O.S. and A.A.; formal analysis, K.S. and Z.O.S.; investigation, K.S. and Z.O.S.; resources,
K.S. and Z.O.S.; data curation, K.S. and Z.O.S.; writing—original draft preparation, K.S.; writing—
review and editing, K.S., Z.O.S. and A.A.; visualization, K.S. and Z.O.S.; supervision, K.S.; project
administration, K.S. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
Urban Sci. 2022,6, 2 12 of 13
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