How can forest fragments support protected areas connectivity in an urban landscape in Brazil? (2022)

Como fragmentos florestais podem sustentar a conectividade de áreas protegidas em uma paisagem urbana no Brasil?

Marina Pannunzio Ribeiro, Kaline de Mello e Roberta Averna Valente 

ABSTRACT

Cities continue to grow worldwide, and the highly modified urban landscape becomes an inhospitable environment for many species because the natural vegetation cover is commonly fragmented, and the remnants are often isolated. Protected Areas (PAs) located surrounding or within urban areas may not achieve their goal of protecting local or regional biodiversity. Thus, an urban ecological network is essential to support their PAs.

Thus, this study aimed at assessing the PAs connectivity in an urban landscape in Brazil and understanding whether urban forest fragments can support an urban ecological network. Besides spatial models based on functional connectivity and graph theory, we used participatory techniques to design the resistance surface and the least-cost paths (LCPs) for Atlantic Forest birds. The results showed critical paths (LCPs), important areas for restoration programs for improving PAs connectivity, and essential forest fragments for conservation and restoration.

Although the landscape has a forest structure with 1873 forest fragments and 516 links through which the LCPs were structured, most forest fragments and LCPs cannot provide the necessary support for the PAs connectivity. The current ecological network is dependent on forest fragments neighboring (outside PAs) and the flux dispersions occurred mainly in the peri-urban areas. Riparian zones and anthropic grasslands also showed importance for the PAs connectivity.

We identified only 28 forest fragments spatially connected, presenting several sizes, and located near large forest areas, relevant PAs, and riparian zones. Six of these forest fragments, smaller than ten hectares and strategically located in the urban matrix, were indicated for restoration actions. The current low connectivity among PAs brings the importance of native vegetation restoration in the riparian zone and anthropic grassland and the importance of the periurban areas to promote biodiversity connectivity in the urban landscape. 

Keywords: Landscape connectivity, Atlantic Forest, Urban ecological network, Forest fragmentation, Urban planning, Graph theory

RESUMO

As cidades continuam a crescer em todo o mundo, e a paisagem urbana altamente modificada torna-se um ambiente inóspito para muitas espécies, pois a cobertura vegetal natural é comumente fragmentada e os remanescentes são frequentemente isolados. 

Áreas Protegidas (APs) localizadas ao redor ou dentro de áreas urbanas podem não atingir seu objetivo de proteger a biodiversidade local ou regional. Assim, uma rede ecológica urbana é essencial para dar suporte a suas APs. Assim, este estudo teve como objetivo avaliar a conectividade das APs em uma paisagem urbana no Brasil e entender se fragmentos florestais urbanos podem suportar uma rede ecológica urbana.

Além de modelos espaciais baseados em conectividade funcional e teoria dos grafos, utilizamos técnicas participativas para projetar a superfície de resistência e as trilhas de menor custo (LCPs) para aves da Mata Atlânticaaves. Os resultados mostraram caminhos críticos (LCPs), áreas importantes para programas de restauração visando melhorar a conectividade com as APs, e fragmentos florestais essenciais para conservação e restauração.

Embora a paisagem apresente uma estrutura florestal com 1.873 fragmentos florestais e 516 ligações por meio das quais os LCPs foram estruturados, a maioria dos fragmentos florestais e LCPs não consegue fornecer o suporte necessário para a conectividade das APs. A rede ecológica atual depende de fragmentos florestais vizinhos (fora das APs) e as dispersões de fluxo ocorreram principalmente nas áreas periurbanas. Zonas ripárias e campos antrópicos também mostraram importância para a conectividade das APs.

Identificamos apenas 28 fragmentos florestais espacialmente conectados, apresentando diversos tamanhos e localizados próximos a grandes áreas florestais, APs relevantes e zonas ripárias. Seis desses fragmentos florestais, menores que dez hectares e estrategicamente localizados na matriz urbana, foram indicados para ações de restauração. A baixa conectividade atual entre as APs ressalta a importância da restauração da vegetação nativa na zona ripária e nos campos antrópicos e a importância das áreas periurbanas para promover a conectividade da biodiversidade na paisagem urbana.

Palavras-chave: Landscape connectivity, Atlantic Forest, Urban ecological network, Forest fragmentation, Urban planning, Graph theory

Introduction

The population is growing, and its continuous demand for space and infrastructure causes pressure on natural areas due to urban sprawl (Tannier et al., 2016; Habitat UN, 2021). Urbanization leads to forest loss and fragmentation, converting natural ecosystems into small fragments with complex shapes and isolated from other forest fragments scattered in an inhospitable matrix for native species (Haddad et al., 2015, Liu et al., 2017). It affects landscape connectivity, i.e., species movement and flow of the natural process landscape (CMS, 2020), causing biodiversity losses (Hernández et al., 2015). As cities continue to grow, the pressures of urbanization cannot lead to neglect for the protection of natural areas within the urban landscape (Trzyna, 2014).

The creation of Protected Areas (PAs) has been used as a global biodiversity conservation strategy to mitigate these losses (Wulder et al., 2018, Vieira et al., 2019) and as the primary strategy to protect these latest forest fragments in urban and peri-urban landscapes (Jenkins and Joppa, 2009, Leberger et al., 2019). If these areas are isolated from other forest fragments in the landscape, however, their ability to meet the conservation goal is hampered (Laurance et al., 2012, Saura et al., 2017, Hilty et al., 2020). This is the situation for many PAs in urban areas worldwide (Saura et al., 2017). Therefore, it is essential to ensure that these areas are connected to the landscape.

The connectivity between PAs and other forest remnants in anthropic landscapes has become essential to minimize the adverse effects of habitat fragmentation on biodiversity, ensuring the persistence of species on the landscape through the animals, seeds, and pollens dispersion (Saura et al., 2014; de la Fuente et al., 2018). Connecting these PAs with other natural elements in the urban and peri-urban landscapes, such as riparian corridors, small forest fragments, and green spaces, is crucial to the PAs’ ecological integrity (Trzyna, 2014).

In the tropical regions such as the Atlantic Forest in Brazil, some PAs located in urban landscapes protect native vegetation fragments that often represent the last forest fragments in metropolitan regions (Laurance et al., 2012, La Rosa and Privitera, 2013). These fragments are recognized as unique ecosystems, with the potential for biodiversity conservation and ecosystem service provision essential to urban populations (Tannier et al., 2012, Zhang and Muñoz Ramírez, 2019).

The Atlantic Forest is one of the most biodiverse biomes and one of the most threatened tropical ecosystems in the world (Laurance et al., 2014, Myers et al., 2000), considered a global biodiversity hotspot (Laurance, 2009). It covers approximately 15% of the entire Brazilian territory (SOS Mata Atlântica, 2016), and recent studies indicate that only 28% of its original coverage remains (Rezende et al., 2018).

For five centuries, urbanization, industrialization, and agricultural expansion were the drivers of intense changes in land use in this biome (Tabarelli et al., 2005, Joly et al., 2014). Currently, 60% of the Brazilian population lives in this biome’s domain (Scarano and Ceotto, 2015), where most of the country’s largest cities are located, including São Paulo, Rio de Janeiro, and Salvador. Therefore, it is crucial to discuss forest conservation in urban landscapes in the Atlantic Forest Biome and analyze if the PAs in these landscapes are connected.

Studies worldwide have focused on understanding and improving PAs connectivity as a global strategy for biodiversity conservation (Saura et al., 2017, Saura et al., 2018, Saura et al., 2019). Ecological corridors, stepping-stones, and permeable matrices are used as strategies to improve landscape connectivity (de la Fuente et al., 2018, Huang et al., 2018). Together, these natural landscape elements build an ecological network that will support species permanence and dispersion (Huang et al., 2021).

In Brazil, even though most of the Brazilian population (over 85%) lives in the cities (IBGE, 2010), there is a significant gap in research on PAs connectivity in urban landscapes. PAs connectivity studies are mainly conducted in the Atlantic Forest Biome; however, they are focused on the conservation of terrestrial mammal species in forested areas (Crouzeilles et al., 2011, Castilho et al., 2015, Diniz et al., 2017), and studies in agricultural landscapes (Moraes et al., 2017) or at a state level (Saraiva et al., 2018).

It is critical to identify priority urban forest fragments and other natural elements (i.e., semi-natural green spaces) that promote urban ecological network among PAs. The PA connectivity can ensure the landscape’s critical ecological functions, promoting conditions to support biodiversity and the provision of ecosystem services in urban areas.

This urban ecological network is composed by paths that connect ecological sources (natural and semi-natural), such as UCs, green areas (public or private), riparian zones, parks, squares, gardens, and cemeteries, among others, that integrate the urban environment (Boulton et al., 2018).

Thus, building an urban ecological network to ensure biodiversity conservation while improving ecosystem services provision is one of the current significant challenges for decision-makers in urban planning (Xun et al., 2017, IUCN-WCPA, 2019).

Models based on graph theory, which has been widely applied to assess landscape connectivity in forest and agricultural landscapes (Urban et al., 2009, Foltête and Vuidel, 2017, Sahraoui et al., 2017), can also be applied in studies of urban ecological networks (Urban and Keitt, 2001, LaPoint et al., 2015, Tannier et al., 2016, Huang et al., 2021). Graph theory models can transform the anthropic matrix complexity and biological flows into a vector-based approach (Urban and Keitt, 2001, Etherington and Penelope Holland, 2013), allowing functional connectivity modeling.

The least-cost path (LCP) model, based on graph theory, is used to identify paths (i.e., ecological corridors) among PAs where the probability of species movements is higher (or less costly) (Pinto and Keitt, 2009, Etherington and Penelope Holland, 2013). Thus, functional connectivity combined with graph theory have been used to identify priority forest fragments conservation (Crouzeilles et al., 2013, Diniz et al., 2017).

Together, these methods can support the design of ecological corridors, setting priority forest fragments, fragments that play the function of stepping-stones, and indicate areas of restoration or management practices to improve matrix permeability (Saura et al., 2017, Thompson and Gonzalez, 2017).

Our study brings a unique application of these methods to an urban landscape in the Atlantic Forest, presenting new and important information about urban forest conservation, restoration, and environmental management in the cities to promote an urban ecological network. This information is essential to making cities more resilient to current and future climate change (Elmqvist et al., 2019).

In 2021, the State of São Paulo created the Climate Action Plan (Decree n. 65.881/2021) to achieve the goals of the “Race to Zero” and “Race to Resilience” campaigns of the United Nations. For urban regions, the goal of the Race to Resilience campaign is to promote a healthy, safe, and thriving space that supports resilient livelihoods and allows for green recovery.

In this context, this study aimed to assess the PAs’ connectivity in an urban landscape in Brazil and understand whether urban forest fragments can support an urban ecological network, generating important information for biodiversity conservation and urban planning.

The specific objectives were to identify: (1) the least-cost paths for endemic forest birds among PAs in the urban landscape; (2) the essential urban forest fragments for landscape connectivity; (3) the forest fragments that work as stepping-stones between PAs, and (4) to identify the necessary actions to improve the urban ecological network. For this purpose, we used functional connectivity based on graph theory and least-cost paths (LCPs).

This research supported the design of the Sorocaba ecological corridor, which will soon become a municipal Decree (Municipal Process No. 2020/013463–3). With this study, we can create ecological corridors and set priority areas for conservation and restoration in the urban matrix to support the decision-making in Sorocaba.

As the method can be applied to other urban areas, this study is also important to other cities in the Atlantic Forest biome and tropical urban landscapes worldwide.

Section snippets

Study area

The study area is the Sorocaba city and its surroundings (a five km-buffer), representing a typical urban landscape in the Atlantic Forest context, wherein the major challenge is the maintenance of functional connectivity among its PAs (Fig. 1). The five km-buffer was used to include the riparian vegetation along the rivers in the municipality boundary and critical forest fragments, such as the Ipanema National Forest, located in the town of Iperó, and the Itupararanga Environmental

The resistance surface and the least-cost paths for Atlantic Forest birds in an urban matrix

The resistance surface of the Sorocaba city and its surroundings showed a minimum resistance value (equal to one) for the ideal forest bird habitat, i.e., the native forest within PAs. Conversely, when the birds’ movements occurred outside the ideal habitat, we observed an increase in the values (Supplementary Material, Table S2).

The maximum value observed for the resistance surface was 100 for urbanized and mining areas, representing barriers to species movement. Temporary and permanent crops

Discussion

Graph theory and functional connectivity models supported the analysis of PAs connectivity for Sorocaba and its surroundings. We identified essential paths for bird dispersal in the urban matrix, such as forest fragments, riparian zones, and anthropic grasslands composing an urban ecological network. Furthermore, we found significant connectivity gaps among PAs in this urban landscape. Our study in Sorocaba brings a new view of urban forests that can compose an urban ecological network. The

Conclusion

The multidisciplinary approach applied to an urban landscape in Brazil allowed the understanding of urban PAs connectivity. We identified critical paths (LCPs), important areas for restoration programs for improving PAs connectivity, and essential forest fragments for conservation and restoration through functional landscape connectivity and graph theory.

Our findings suggest significant connectivity gaps among PAs and the current PAs network in Sorocaba and the surrounding forest fragments.

Funding

The present work was supported by Coordination for the Improvement of Higher Education Personnel – Brazil (CAPES) – Financing Code 001 (Process: 88887.603853/2021-00), São Paulo Research Foundation – FAPESP (Process: 2021/04421-7) and the Program in Planning and Use of Renewable Resources – PPGPUR, Federal University of São Carlos, Sorocaba Campus.

CRediT authorship contribution statement

Marina Pannunzio Ribeiro: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Visualization. Kaline de Mello: Conceptualization, Methodology, Validation, Resources, Writing – original draft, Writing – review & editing, Visualization. Roberta Averna Valente: Conceptualization, Methodology, Validation, Resources, Writing – original draft, Writing – review & editing, Visualization, Supervision, Funding

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the Coordination for the Improvement of Higher Education Personnel (CAPES), the São Paulo Research Foundation (FAPESP), and the Program in Planning and Use of Renewable Resources – PPGPUR, Federal University of São Carlos (UFSCar) for supporting this research. We also thank the Secretariat for the Environment of the City of Sorocaba for the support and data supply and all participants who helped improve our methodological approach; the University of São Carlos, Sorocaba campus, for

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