Dissertation

Urban green infrastructure for biodiversity and ecosystem services

Urbanisation is steadily increasing with estimates expecting that 68% of the global population will live in cities by 2050. To accommodate the rural to urban transition, large quantities of land are transformed from natural to urban lands.

Author: J. Morpurgo
Date: 03 June 2025
Links: Thesis in Leiden Repository

This transition is widely acknowledged to be one of the main drivers of global biodiversity loss. Simultaneously, cities also lack the capacity to provide a healthy living environment for its citizens. In order to solve both problems simultaneously, Green Infrastructure (GI) has been proposed as a way to enhance both biodiversity and create a safer and healthier living environment. Substantial evidence is emerging that GI benefits to humans (typically defined as Ecosystem Services (ES)), through e.g. regulating air temperature, air pollution and water, and enhancing biodiversity.

However, there is a lack of, or none at all, evidence explaining which GI features are responsible for the enhancement of biodiversity and generation of ES. This thesis contributes to this gap in knowledge by investigating how urban GI, and its different features, drive biodiversity and ES. To address this knowledge gap, I investigated the following:

How is the GI concept used across urban biodiversity and ES research, and is there a possibility to consolidate key-concepts from them?

How do GI, and its different features, drive urban biodiversity?

How do GI, and its different features, drive urban ES?
Do biodiversity and ES have synergies or trade-offs in GI?

First, I reviewed the literature focussing on research articles that covered urban GI and its relation to biodiversity and ES (Chapter 2). The results showed that many types of GI are uniquely studied in relation to either biodiversity or ES. Moreover, studies including GI types that are used near-universally, such as ‘forest’ or ‘park’, rarely use the same definition or method of quantification. Finally, I show that most studies are based on readily available Land-Use or Land-Cover (LULC) maps, lacking explanation on which GI features are causally driving biodiversity or ES. These results show that the literature on urban GI benefits to biodiversity and ES tends to be based on data-availability instead of theory. Furthermore, the lack of standardized methods to quantify GI and its features impedes our capacity to research and understand the causal mechanisms behind urban biodiversity and ES.

In light of these results, I created the Consolidated Urban Green Infrastructure Classification (CUGIC). The CUGIC accommodates interdisciplinary research on biodiversity and ES and allows for elucidating the complex interplay between urban GI, biodiversity and ES relationships. The standardized approach from CUGIC, using both satellite data and LULC maps, facilitates cross-comparisons and integrated assessments. Using CUGIC, I investigated both biodiversity and ES patterns in relation to GI and its features. In parallel, I also investigated minute features of GI, which cannot be capture well by the CUGIC, to understand which mechanisms may be important for biodiversity but are not captured by globally available data.

A considerable body of literature shows that urban biodiversity are driven by the design, quantity, spatial lay-out and quality of urban GI. However, there is lack of research explaining the distributions of individual species. This is important as species distributions are fundamental to community assembly and also directly relate to our capacity to protect species considered important. Using an city-wide field survey, results (Chapter 3) show that, in contrast to overall biodiversity patterns, species distributions are rarely predicted well by GI and features. Importantly, this suggest that we are missing key-elements to understand species their occupation in cities. Consequently, this limits our ability to design GI for the protection of species, with our remaining best option being —though limited in effectiveness— to add extra GI.

In contrast, using façade gardens survey on GI features and biodiversity results (Chapter 4) showed a different picture. In line with the city-wide study, it highlights GI quantity as most important for urban biodiversity. Yet, analysing different functional taxa highlighted the importance of functional ecological relationships between GI and the animal biodiversity it contains. For instance, pollinating insects, compared to herbivorous insects, tend to be found more often in gardens with high flower availability. The most common herbivorous insects found were specialists, solely found when their host-plant was present in the gardens. Most importantly, including GI features that relate to the life-history allowed for substantially improved explanatory power of the analysis. These results illustrate the complex interrelationships of urban GI and its biodiversity, while simultaneously explaining why large-scale remote sensing and LULC maps do not fully capture species distributions well.

Finally, I studied the generation of ES by GI and its features and simultaneously assessed if these correlate among themselves and to biodiversity (Chapter 5). Gathering city-wide ES data, results show that ES and biodiversity do no co-occur in GI, and that specific features of GI are responsible for the generation of ES and enhancement of biodiversity. This is against the current paradigm that urban GI is multifunctional —delivering multiple ES and enhancing biodiversity simultaneously— and instead suggests that finding the right combination of GI features is necessary to enable multifunctionality.

There are no signs that urbanisation is slowing down. With it comes loss of biodiversity and a worse living environment. Proposed solutions such as GI are praised for their multifunctionality, intending to partially remediate these problems simultaneously. Previous scientific research showed unambiguous evidence that urban GI has the capacity to provide benefits to biodiversity and ES. Yet, there is a lack of understanding which components of GI drive biodiversity and ES enhancement and a lack of evidence of them co-occurring in GI (i.e. multifunctionality). The results of this thesis show that the most frequently used indicators of GI lack explanatory power, indicating that we are missing large pieces of the GI multifunctionality puzzle.

To solve this puzzle, we need to start acknowledging that urban and natural ecosystems work differently, and change our research and understanding of the field accordingly. As a start, I proposed a theory of urban multifunctionality with urban ecology at the centre. Going forward, I suggest —instead of using readily available data— to find and empirically test novel indicators that are hypothesized to be mechanistically linked with urban GI multifunctionality.