Scientific principles of landscape ecology at Forest Research

Fragmentation

Photo
Broadleaf woodland (very dark green) within a highly fragmented agricultural landscape

The fragmentation of woodland habitat into smaller isolated patches poses one of the key threats to forest biodiversity. Fragmentation:

  • Reduces the total amount of habitat area
  • Increases edge effects around habitat patches reducing core area
  • Increases patch isolation.

According to a number of scientific theories, such as island biogeography and metapopulation dynamics, the reduction in area may lead to increased local extinctions, while increased isolation may cause a reduction in the exchange of individuals between isolated patches, threatening their long-term viability.

Landscape structure and function

Land management activities which change landscapes have an impact on both the structure and function of the landscape.  It is predicted that such changes, which include fragmentation, will influence the ability of biodiversity to survive within, and move through, the landscape.  In terms of evaluating biodiversity, it is necessary to assess the impact of changes upon both structure and function.

The structural element refers to the spatial arrangement and organisation of distinct landscape elements.  Analysis is often focused towards the physical composition and configuration of particular habitat patches within a landscape.

Landscape function is concerned with the interactions between these structural elements, through ecological processes and the flow of energy.  In terms of biodiversity, landscape function is often related to the movement and viability of particular species within these structures.

Connectivity

Connectivity is a landscape characteristic that encompasses habitat amount and isolation. It is important to assess both the structural connectedness and the functional connectivity within a landscape. The latter occurs when individuals are able to move between habitat patches.

Functional connectivity depends upon both the arrangement of suitable sized patches (Figure 1) and the matrix (non-habitat landuse) in between them - more intensive landuses being resistant to movement for some species (Figure 2).

Diagram showing the roles of woodland isolation and surrounding land uses on woodland connectivity - Figure 1Diagram showing the roles of woodland isolation and surrouding land uses on woodland connectivity - Figure 2

Species - landscape interactions

Assessing landscape function requires some information about how biodiversity interacts with landscape structure. We can analyse landscapes for individual species of particular interest or set parameters which protect whole groups.

Individual focal species

We may analyse connectivity for a range of individual species for different reasons, e.g.

  • target species of intensive conservation effort such as the red squirrel
  • keystone species believed to support a large part of ecosystem function
  • umbrella species whose protection is believed to be adequate to protect a range of other species
  • flagship species which people are motivated to support.

The term ‘focal species’ is somewhat contentious. Lambeck’s (1997) definition uses ‘focal species’ to set parameters for reserves according to the most rigorous requirements of the suite of species present. For example, whilst the area requirement could be set by one species, the connectivity requirement could be set by another. For our work ‘focal species’ simply means the species we are concentrating upon in that particular analysis.

The ecological information needed to analyse connectivity and fragmentation in a landscape is quite complex, especially the variation in the resistance, or permeability, of different landscape elements in the matrix. Focussing on an individual species may have negative impacts for other important species with different needs.

Generic Focal Species

These are an alternative to using individual target species for landscape analysis and evaluation.

A Generic Focal Species is a combination of ecological requirements that the modeller, to the best of their knowledge, thinks will cover the requirements of all the species they wish to account for in their landscape plan or evaluation. This is like an extension of the umbrella species concept, but without using a particular real species. The use of generic focal species defined by fragmentation sensitivity is currently an integral part of our Habitat Network model. The approach is not limited to Forest Research, as eco-profiles, which are based on a similar set of characteristics, are used by ALTERRA, a Dutch agency.

Evaluating biodiversity in fragmented landscapes: principles (PDF-488K)
Forestry Commission Information Note 73

           

What's of interest

A metapopulation is a set of sub-populations which are dynamically connected by immigration and emigration.