An image of landscape architecture project Central Green Forest Park , by design firm Hassell, in Beijing, China. Showing a wide pedestrian path adjacent a grove of trees, underplanted with a mass planting of white flowers.
Central Green Forest Park, Beijing, China, by design firm Hassell. Photo: Nancy Studio.

Resource Guide: Biodiversity

Articles + Resources

By Nicki Copley

Biodiversity Matters

Biodiversity (biological diversity) refers to the full diversity of life on earth, including people, animals, plants, fungi, and organisms, as well as genetic diversity. Biodiversity is essential to human health, economic prosperity, and well-being, yet it is alarmingly imperiled. Up to one million species are threatened by extinction, primarily resulting from the loss of habitat due to human development [1]. Climate change is also now a major driver for biodiversity loss and species will face greater threats with every degree of warming [1]. 

A 2016 study found that productive, sustainable ecosystems are not possible without maintaining biodiversity [2]. People need biodiversity, yet other non-human beings such as insects and plants also have an inherent right to healthy living conditions. 

Working to improve biodiversity is a critical action for landscape architects. In 2019 the International Federation of Landscape Architects (IFLA) declared a global climate and biodiversity emergency. They stated:

“Together with allied planning and design professionals, natural scientists, sociologists and economists, we will continue to advocate for innovative approaches to low carbon community development and management, and for the protection and enhancement of natural systems with emphasis on the integration of the natural environment into human communities through blue/green infrastructure projects and an enhanced urban canopy. We can and must do our part locally, nationally and internationally.”  [3]

[1] United Nations. (n.d.). Biodiversity – our strongest natural defense against climate change. United Nations. https://www.un.org/en/climatechange/science/climate-issues/biodiversity 

[2] Grace, J., Anderson, T., Seabloom, E. et al. (2016). Integrative modelling reveals mechanisms linking productivity and plant species richness. Nature 529, 390–393. https://doi.org/10.1038/nature16524

[3] International Federation of Landscape Architects. (2019). Global Climate and Biodiversity Emergency Declaration. https://static1.squarespace.com/static/5d16e42a3ae2ee0001a08d34/t/5d7fa3ebf7530f4d296dc970/1568646124158/Climate+Biodiversity+Emergency+Declaration_FINAL.pdf

Maropeng Stone Garden, Gauteng, South Africa. Design and photo by GREENinc Landscape Architecture and Urbanism. The planting palette makes use of locally indigenous forbs and trees which reflect and compliment the biodiverse Bankenveld vegetation type in which the site is situated.

Designing and specifying planting schemes to improve biodiversity must become the norm in our daily practice. The following sections cover several design considerations and outlines additional resources. 

Design considerations

Plant origin

The terms native or exotic are criticized by some as promoting xenophobic sentiments [1], and by others as lacking an appreciation of time – that plants grow indigenously in a location now doesn’t necessarily mean they grew in that same area hundreds of thousands of years ago [2]. Many people believe the use of exclusively native plants should be the rule, whereas others, such as Associate Professor of Urban & Regional Planning Nina-Marie Lister, believe non-natives offer many benefits such as habitat remediation and can be used in planting schemes in conjunction with native plants [1]. 

A compelling reason for using native or indigenous plants in projects lies in evolution. The vast majority (approximately 90% in the US [2]) of plant-feeding insects co-evolved with select plants that grew in a shared geographic area, leading to the development of ‘specialized’ relationships – where insects can meet their habitat or food needs from only a small number of plant species. This is opposed to ‘generalists’ who are less particular. A common generalist is the European Honey Bee. 

Projects with higher numbers of native plants will cater to a larger number of native insects [2]. For example, Eucalyptus supports 48 insect species in Australia where Eucaplypus is native, whereas in California where it was introduced in the 1850s, Eucalyptus supports only one insect species [2]. However, not all natives have equal weight – see keystone species below.

  • Identify the plants native to your region. Many agencies or organizations publish this information.
  • Identify local wildlife populations that might use your planting as a habitat.
  • Research their plant requirements i.e. food, nesting etc. Do they require specific plants or are they generalists? An example in California where this information is available is Calscape.
  • If a site is adjacent an area of existing indigenous vegetation, ensure appropriate species are selected to maintain the health and genetic diversity of the existing biodiversity i.e. use local eco-types instead of cultivars that could cross-pollinate with the local flora, avoid plants that could spread into the habitat and become invasive.

Learn more:

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Keystone species

The term borrows the concept of an arch keystone – where the keystone at the top of the arch supports the arch. If the keystone is removed, the arch crumbles. In ecology, keystone species fulfill a similar role where they maintain an ecological community’s overall structure and integrity [1]. Keystone plant species support the food and shelter needs of many other species, i.e. caterpillars, bees, etc. For example in California, Quercus (Oak) species act as a host plant to 275 species of caterpillar [2].

“The research of entomologist, Dr. Doug Tallamy, and his team at the University of Delaware have identified 14% of native plants (the keystones) support 90% of butterfly and moth lepidoptera species. The research of horticulturist Jarrod Fowler has shown that 15% to 60% of North American native bee species are pollen specialists who only eat pollen from 40% of native plants.” [2]

  • Become familiar with your local area’s keystone plant species and incorporate them into landscape projects. In the USA, a helpful resource is the plant lists put out by The National Wildlife Federation. 

Learn more:

[1] Wagner, S. C. (2010) Keystone Species. Nature Education Knowledge 3(10):51. https://www.nature.com/scitable/knowledge/library/keystone-species-15786127/

[2] The National Wildlife Federation (USA) – Keystone Plants by Ecoregion

An image of landscape architecture project Central Green Forest Park , by design firm Hassell, in Beijing, China. Showing a wide pedestrian path adjacent a grove of trees, underplanted with a mass planting of white flowers.
Central Green Forest Park, Beijing, China, by design firm Hassell. Photo: Nancy Studio. Phenology helped guide the approach to planting and creating authentic seasonal journeys for visitors. For example, the behaviour of various species of birds influenced the planting design for the Minor Cold area – like geese flying north, magpies building nests and ring-necked pheasants beginning to crow.

Genetic diversity

Another aspect of biodiversity is genetic diversity. Maintaining genetic diversity within individual plant species supports greater resilience. A plant species is typically made up of multiple different genetic ecotypes. An ecotype is defined as “a group,… within a species, having unique physical characteristics genetically adapted to particular environmental conditions” – Collins Dictionary. 

As plants adapt themselves to local environmental conditions, their genetic makeup alters. Even within an ecotype, there can be significant genetic variation in terms of size, form, flowering, growth rate, pest resistance, etc. The U.S. Forest Service describes ensuring genetic diversity as important “because it can strongly influence the long term viability of plant populations, and their ability to adapt to changing climatic and environmental conditions. Plant materials that lack genetic diversity may be more susceptible to pathogens and other environmental stresses, and less competitive with exotic invasive species.” [1]

In a 2021 article  – Designing for change [2] – Eve Allen, Molly Bourne and Signe Nielsen discuss strategies and constraints in incoporating greater genetic diversity to projects – specifically to the planting design of Pier 42, a waterfront development in New York designed by MNLA. Read the full article here. The following strategies follow their recommendations:

  • Where possible specify a mix of local ecotypes. Many specialist native plant nurseries will list this information. 
  • Arrange for local seed collection and contract growing where feasible.
  • Where local ecotypes aren’t available use 2-4 varieties or cultivars of each species:
    • Select varieties or cultivars appropriate to your area’s growing conditions.
    • Select varieties or cultivars that flower at different times of the year.
    • Install varieties or cultivars together in tight groups rather than intermingling them, as this will help maintain distinctive genetic characteristics.

Learn more:

Plant diversity

Plant a mix of species – Landscapes with a higher diversity of plants will support a higher diversity of wildlife, making them more resilient habitats. The example Rick Darke and Doug Tallamy give in their 2014 book The Living Landscape [1] is of a Chickadee. This Chickadee lives in a landscape with only one tree species, making it food reliant on the one species of caterpillar that lives in that one type of tree. Whereas if four different species of tree were present, all hosting different caterpillar species, the Chickadee has greater food security if one of the caterpillar populations declines. 

Staggered seasonal interest – Incorporate a mix of species that will provide habitat or food throughout the year for your target species. There are many agencies or organizations that publish material on bloom timing or habitat needs. Two examples are below: 

Attract birds to your garden – New Zealand Department of Conversation

Plant lists – Xerces Society 

[1] Darke, R., & Tallamy, D. W. (2014). The living landscape: Designing for beauty and biodiversity in the home garden. Timber Press. 

An image of landscape architecture project Stadium Park & Chevron Parkland, by design firm Hassell, in Perth, Australia. Showing an aerial view of a large park bordered on two sides by water. A series of pathways connect a playground, lawn and areas of planting.
Stadium Park & Chevron Parkland in Perth, Western Australia, by design firm Hassell. Photo: Peter Bennetts. Thousands of native plants have been introduced, supporting a safe and sustainable public parkland. The capping of contaminants in latent soils, reduction of fertiliser use and bio-filtering of surface water has improved the micro-organisms found in both the soil and the water.

Habitat Fragmentation

Fragmentation is a process where portions of an area of habitat are destroyed, typically due to human development (farming, housing, roads etc.). This results in smaller areas, known as patches, of habitat that form islands within the matrix of developed land. Habitat fragmentation can restrict or eliminate the ability of a species to move across the wider landscape. It can also lead to a loss of genetic diversity within species which reduces species resilience. Each time a habitat patch is fragmented, the amount of habitat along the perimeter of the patch (the edge) increases and the amount of interior habitat decreases – threatening the plant and wildlife species that can only survive in the interior of a habitat patch. 

  • Landscape architects, particularly those who are working on large-scale projects where habitat protection or remediation is possible, can have an influential role in the design or decision-making about how a landscape is divided. Decisions on where to place a road or driveway, or locate a new building can have a significant impact on habitat fragmentation. Landscape architects should act as advocates for the plant and wildlife residing on their site.

Learn more: 

The USDA National Agroforestry Center provides useful diagrams and design considerations for patches and the implications of fragmentation.

Lighting

Lighting in the landscape can be detrimental to wildlife (bees, moths, bats etc.) as well as plants. A study in 2014 found that over 70% of the moths studied were drawn toward lights and away from the plants they would otherwise be pollinating [1]. Lighting can also affect a plant’s circadian rhythm by altering the daily and seasonal light levels the plant would normally experience. This can reduce the plant’s health and pollen output [1]. Light pollution can also negatively impact people and wastes energy.

  • Limit lighting to places where lighting is required for safety and use the minimum required.
  • Direct lights away from planting and avoid light spilling into planting areas.
  • Incorporate dimmers, sensors, and/or timers.
  • Specify lights that meet best practice recommendations for wildlife such as low-wattage lights of warm white or amber temperature.

Learn more: 

[1] Hirschlag, A. (2023). How light pollution disrupts plants’ senses. BBC Future. https://www.bbc.com/future/article/20230308-how-light-pollution-disrupts-plants-senses  

Demidova, I. (n.d.). Relighting and rewilding our environment. Arup. https://www.arup.com/perspectives/relighting-and-rewilding-our-environment

Lang, V. (n.d.). The birds and the bees – why wildlife needs nightlife. Schréder. https://www.schreder.com/en/blogs/schreder-designs-lighting-solutions-protect-people-and-wildlife-during-night

Albouy, X. (2018). Smarter lighting is good for biodiversity. The Agility Effect. https://www.theagilityeffect.com/en/opinions/smarter-lighting-is-good-for-biodiversity/

Soil

No-Till – Historically, conventional farming and gardening practice is to till – to turn over the soil with a plow or spade in preparation for planting. However, this can damage soil microbial biomass (fungi, bacteria, fine roots), cause erosion, deplete soil’s water-holding capacity, and release greenhouse gases stored within the soil. In contrast, no-till can improve soil health and enhance plant productivity [1]. 

  • Eliminate tilling and limit soil disturbance

Nesting bees – Honeybees are often what people conjure in their minds when thinking of bees. But there are thousands of other species of bee and the majority of these live alone in tunnels made in bare soil, wood, or hollow plant stems. 

  • Incorporate small sunny patches of bare soil, kept free from foot traffic or garden maintenance activities.

Learn more:

Conclusion

It is imperative that landscape architects act to protect and improve biodiversity.

As Kate Orff from SCAPE states: 

“Ecocide and the loss of the earth’s biodiversity, in all its immense texture, color, scale and intensity, is an aesthetic and moral question that dwarfs our more internal conversations about architecture. The act of unmaking the errors of the past, of gathering, and of recognising each other and the earth as worthy of deep care is one of the most profound design challenges before us.” 

– Wall, E., & Orff, K. (2020). What is Design Now? Unmaking the Landscape. In The landscapists: Redefining Landscape Relations. Architectural Design (pp. 95–99). essay, Wiley.

Check out more Biodiversity Enhancement projects here.

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