Ecological connectivity & Green Infrastructures: it's all about NETWORKS

Green Infrastructures, GI, can be defined as ecological NETWORKS composed of species' CORE AREAS and CORRIDORS to move between them (Fig 1). These networks of high quality natural areas maintain functioning ecosystems and deliver Ecosystem Services, ES (biodiversity, pollination, carbon sequestration, recreation) in the long term[1].  

To protect biodiversity and ES it is necessary to preserve ecological netwoks for a large number of species. Because different species have different requirements, there are often trade-offs between prioritizing one species / groups of species vs. another. Both science and management play a role in identifying ensamble of species of relevance for conservation and society, and in setting adequate goals for weighing their importance (guidelines under development). Understanding the mechanisms supporting multi-species' Green Infrastructure Networks is the first step towards really sustainable land planning strategies ensuring functioning ecosystem to future generations.

Sustainable Land Planning: it's all about PRIORITIES

Land use is the major driver for habitat loss and fragmentation globally[2]. The piecemeal development of infrastructure severes ecological networks and caused an unprecedented nature decline worldwide[3]. Climate change acts on top of this, and often exacerbates this trend . 

It has become clear that protecting isolated nature patches (core areas) is useful, but far not sufficient: to preserve the funcionality of ecosystems we must maintain entire GI networks, composed by both CORE AREAS and CORRIDORS. 

It has also become clear that nature is not an "ON-and-OFF" concept: there are no such things as clearly defined "core areas", "corridors". Species perceive the landscape as a CONTINUUM of areas of that are more or less functional as living areas and / or for movements, often in multiuse landscapes, coexisting with humans. In other words, each area unit has some degree of potential for a species, but its real importance can be understood only by taking a bird-eye-view and understanding the species' full ecological network. Areas that to us may look "natural" might be irrelevant for the species, if they cannot be reached due to barriers (e.g. fences). On the other side, areas that to us may look "unsuitable" (e.g. cement bridge over a highway, or parking lot) might serve as corridors and be crucial for a species' survival. 

This has critical implications for land planning. Obviously, the only way to protect all existing GI for all species and ES is not to change the landscape. Because this is not realistic, it is crucial for management to correctly identify and prioritize for conservation the most critical areas ensuring the functionality of the entire ecological network, and whose perturbation would risk having disproportionate impact for the species' survival in the long term. It is also crucial to identify areas whose restoration would be most efficient to re-establish lost corridors. 

Fig 1. Illustration of the 2 main components of an Ecological Network/Green Infrastructure for an hypothetical forest-dwelling species: (1) Funcional Areas (core areas), and (2) Movement Corridors. Note that the most funcional areas are at the same time highly suitable (provide adequate resources, and little human disturbance) and well connected to other suitable areas. Isolated small areas are little funcional, even if they provide suitable resources. Similarly, larger and continuous corridors are in general more functional than discontinuous ones (however, note that even corridors providing suboptimal habitat - e.g. road overpassages - can be crucial to maintain connectivity, depending on the spatial configuration of the funcional areas). Highly fragmented and little suitable habitat are not funcional. In the example, land development in the middle of the hihgly funcional area, or in the main corridor would have the highest impact on the species.  

REFERENCES

[1] https://biodiversity.europa.eu/green-infrastructure

[2] Dirzo R, Young et al (2014). Defaunation in the Anthropocene. Science, 345, 401-6

[3] IPBES (2019). Global assessment report on biodiversity and ecosystem services.... IPBES secretariat, Bonn, Germany.