Review of Literature Relating to the Development of Biodiversity Networks

Review of Literature relating to the development of Biodiversity Networks

Richard Knight

Overview

There is a lot of debate about the value of biological corridors and nodes, and over 200 research articles have been written on the topic. A quick review of the application of biodiversity networks at the global scale has revealed that almost each application has taken a unique approach to the planning of the framework, and it is consequently very difficult to synthesise. This is made more difficult since there is inconsistency in the use of various terms such as nodes and hubs. The European approach has thought of hubs from a conservation perspective, whereas in North America they are considered to be issues of development.

Another area of confusion is the difference either explicit or inferred between a biodiversity and an ecological network. Although often used interchangeably the biodiversity network attempts to conserve as many species as possible with as few risks of extinction, whereas ecological network seeks to conserve processes such as geomorphological and geohydrological. Other terms used include the “conservation network”; this terminology is particularly ambiguous since it can include species approach, the ecological process approach, and even a socio- economic approach.

In reviewing biodiversity networks it has also become clear that there is an initial dichotomy between species criteria, versus existing habitat criteria that have been used for building conservation networks. Intuitively one would consider species to be the better units for planning biodiversity networks. However, the problem is that we have never had enough information on species presence/absence for an effective conservation planning process to be implemented. The more analytical the technique applied, the more difficult it is to use species as units for conservation planning.

Role of systematic conservation planning

Systematic conservation planning requires that each species distribution is known to a similar accuracy. Without this certainty, species that have better known distribution records will influence the network at the expense of those species where the distribution is poorly recorded. In contrast to the species-based conservation approach to develop a biodiversity network, the use of habitat as the units for developing criteria is usually favoured. The habitat approach is based on securing ecological processes and services, and is essentially a surrogate for a species-based planning approach. Habitats are considered to buffer against the process of extinction and to include both immigration and emigration processes. One concept that is important in conservation biology is the minimum viable population, which essentially is the smallest number of individuals that is required to sustain a species add infinitum (i.e.sutainably). Virtually none of the studies reviewed included the concept of minimum viable population, probably because it is difficult to truly establish what an absolute number for a particular target species would be.

In cases where a species approach was adopted to develop the biodiversity network, this was achieved by using one or a few target species; that were either identified as a keystone or flagship species. In this case the distribution of the target species was modelled based on a GAP analysis. Essentially if you intend to use species distribution in conservation planning a modelling approach for identifying distributional envelopes is critical.

In applying the habitat approach, it is important that a reconstruction of the ecosystem, habitats and/or vegetation cover is first developed to represent the landscape features of ecosystems; prior to development and transformation by humans.

Concept of rarity that is critical for systematic conservation

Rarity, or endemism, is usually considered to be the best option to follow since it ensures that you maintain sufficient biodiversity by concentrating on those species that have are restricted to a narrow habitat range. Endemism is essentially a refinement of the concept of rarity that focuses on species that have restricted distributions and habitat requirements. When using either rarity or endemism an important concept is that of “complementarity”. Essentially complementarity reflects that areas that conserve a habitat or ecosystem, with either rare or endemic species, has a complementary component of common species that coexisted with the rare species. Since many common species are likely to coexist with each rare or endemic species, at many rather than few sites, these common species are easier to account for in the final biodiversity network because they are less impacted by the effects of fragmentation.

Although species biodiversity, endemism and habitat criteria for biodiversity networks share a similar approach, of establishing representivity, they also have a similar problem of integrating the initial planning domain of the study in question with adjacent conservation plans and biodiversity network planning at a larger regional and national scales. The issue here is that what is rare at local scales may become more common at a larger regional or national scale, and adversely affects the final biodiversity network solution. While many reviews recognised this problem of scale, virtually none have identified mechanisms to address it. In developing the biodiversity network the City of Cape Town would need to work within the larger planning domain of the Cape Floristic Region, which was undertaken in the C.A.P.E. project and used the concept of Broad Habitat Units.

Planning using keystone species

Essentially a biodiversity species approach is most appropriate where one wishes to conserved a keystone species such as the Brown Bear or the Spotted Owl. Usually keystone species are a top carnival in the ecosystem, or species that has established a number of mutualistic benefits to other species in the community and requires extensive habitat for its survival. In this case the keystone species are essentially surrogates for other species which have smaller habitat requirements, fewer mutualistic interactions with other species, and are lower down in the food chain. The use of the keystone species for identifying the biodiversity network is usually more appropriate where the environment has less biodiversity and less complex ecosystems. Consequently it is often applied to northern temperate systems. In tropical ecosystems, where biodiversity is high, it is less useful to use keystone species because tropical systems may have many keystone species, and their mutualistic relationships with other species are less clear. The use of the keystone species nevertheless has value since we can use modelling techniques which can predict where the species occurs and where it does not occur. This concept is captured in the GAP analysis. Essentially a GAP analysis identifies potential areas where a species can occur, and where we do not have distributional data.

Planning for fragmentation and habitat loss

The problem of habitat loss and consequent fragmentation requires that the ecology of the landscape is understood, together with biological parameters and interactions. The initial questions to be raised are how connected are the landscapes in nature with respect to distance, directness and degree of connectedness? Also needed is an understanding of how the spatial elements within the landscapes are maintained in the current state, and in any changed future state (as a result of climate change or some natural disaster). Various mathematical models have proved to be useful to identify the connectivity between various patches, and include the landscape graph analysis where the location of important individual habitats, patches and nodes, relative to the ecological corridors, is quantified (Jordan 2003).

Sensitivity analyses and buffering

Of importance in the proposed biodiversity network is some form of “sensitivity analysis” and “buffering”, to reduce the impacts of natural disasters or adjacent uncomplimentary land-use practices. It is important that various corridors are analysed on an individual basis to determine how critical they are to the entire network if they were compromised. Also the use of buffers to either restrict certain developments that have potential threat to biodiversity and ecosystem integrity, or protect especially sensitive core sites, should be addressed - but virtually no attempt has been offered to quantify what constitutes an effective buffer.

Prioritisation-linked implementation

Surprising very few studies have undertaken prioritisation within the network to assess higher and lower quality corridors and nodes. Yet this is an essential process in order to implement the biodiversity network. What prioritisation has been suggested revolves around simple categorisation based on the degree of threat, cross-linked to representatives at local and regional levels. Serious attention needs to given to assessing the quality of the resulting biodiversity network designs; with respect to defensible prioritisation techniques so that the implementation of the biodiversity network can be optimised with respect to minimimising loss of biodiversity and ecosystem integrity.

Global review of biodiversity networks

Pan-European Ecological Network

The pan-European Ecological Network was a request made by the Council of Europe and consisted of a panel of experts mandated to formulate a common approach to formulating a pan-European Network. The approach used was a review of national and international terminology, definitions, standards, conventions and criteria, to develop a vision of what is important for an integrated European ecological network.

One of the key issues was an exploration of the concept of naturalness in terms of processes operating within ecosystems and at different scales of landscapes, and the maintenance of biodiversity with respect to species distributions and threats. An important prerequisite was to develop a “shared vision” on nature conservation within government and non-government groups.

The aim of the pan-European biological and landscape diversity were

The following aims were identified

1.  To reduce substantially existing threats to the continent’s biological and landscape diversity, to a point where they are almost entirely contained.

2.  To increase the resilience of the continent’s biological and landscape diversity.

3.  To strengthen the ecological coherence of the entire continent.

4.  To promote full public involvement in the conservation and protection of various aspects of biological and landscape diversity.

The following objectives were formulated

1.  To conserve and restore key ecosystems habitats, species and features of landscape through the development and management of a pan-European Ecological Network

2.  To ensure the sustainable management of Europe's biological and landscape diversity; by taking full opportunities of economic and social opportunities that will facilitate the development of this network at national and local levels.

3.  To integrate “diversity conservation” with “sustainable use” objectives.

4.  To improve the information base and the dissemination of it to the public and decision makers.

5.  To improve the understanding of the state of biological and landscape diversity in Europe and the underlying ecological processes that render it sustainable.

The following action plan for 1996 to 2000 was formulated

1.  Establish a pan-European ecological network

2.  Integration of biological and landscape diversity considerations

3.  Raising awareness and support among policy makers and the public

4.  Initiate conservation of landscapes

5.  Initiate coastal and marine system conservation

6.  Initiate river ecosystems and related wetland conservation

7.  Initiate inland wetland conservation

8.  Initiate Grassland ecosystems conservation

9.  Initiate forest ecosystem conservation

10. Initiate mountain ecosystem conservation

11. Take action on threatened species

Within the first 10 years the following deliverable goals were identified

1) Protection of all natural ecosystems on the continent

2) Protection of semi-natural ecosystems on the continent that are endemic and/or characteristic

3) Protection of all multi-functional ecosystems on the continent that are endemic, characteristic and/or threatened

4) Protection of all characteristic species that occur on the continent

The following basic problems were identified for maintaining natural values

1) Urbanisation: which is to be addressed by increasing the amount and status of natural areas and by diminishing the fragmentation of natural areas as caused by draining, land reclamation and development

2) Decline in water quality and quantity and an increase in water pollution, drought and erosion

3) Intensification of agriculture and forestry

4) Abandonment of man-made semi-natural and multi-functional areas (this could be turned into a part solution)

Pan-European Ecological Network Philosophy

Since the pan-European Ecological Network acknowledged ecological coherence as a principle, it sought to provide a unifying framework for many nature conservation activities in the field, and represented a shift from a defensive approach to a proactive approach. This vision was approached through the creation of core areas in which primary conservation is practice and the identification of buffer zones; which would create the necessary spatial context for core areas to operate effectively within the ecological network. This approach was also followed through at both national and continental scales.

Protected areas were recognised as nodes within the network, and plans were made to link them by corridors. The nodes were not just representative of top site such as recognised by Ramsar. A great emphasis was placed on management that was directed at maintaining or improving ecological functioning of the continent in its entirety.

Consequently the following specific principles were identified

1.  To maintain and enrich the characteristic ecosystems and species across their natural ranges.

2.  To support ecological processes across the continent.

3.  To restore in a sufficient degree natural ecosystems and processes.

4.  To conserve semi-natural and other ecosystems, especially where they are indispensable as substitutes for natural habitat,

5.  To adopt sustainability as the guiding principle for decisions and actions.

This ecological network will comprise the following components

a)  Core areas, comprising a particular ecosystems, group of ecosystems, habitats and/or biotypes

b) Corridors comprising continuous linear structures, or discontinuous stepping stones, which facilitate the dispersal, or migration of species and/or genetic information between various core areas

c) Development areas and natural restoration areas, which increase the area

of the network, and provide new habitats or facilitate dispersal and

migration

d)  Buffer zones which serve to protect the network from the intrusive effects

of nearby economic activities

Structure of the network

Core areas

Core areas were designated to conserve ecosystems and species that were representative of biological diversity and reflect natural areas of the continent. Core areas are essential for abiotic and biotic processes together with the maintenance of ecological functioning. Ecological functioning includes water regimes (surface and ground), biogeochemical cycles, etc., and the provision for restoration to fulfil these requirements. The core areas will cover considerable areas and have high species richness that contributes value to the landscape. Core areas may include some semi-natural areas with characteristic species of the ecosystems, and may include localised areas of high scenic value.