What is a habitat network?
A habitat network is a configuration of habitat that allows species to move and disperse through a landscape. Networks can be produced for a particular type of habitat. For example, a forest habitat network focuses on how woodland species utilise woodland habitat and disperse through this and other habitat types in the wider landscape.
What is classed as habitat?
Habitat is defined as the area of land cover where an organism or ecological community normally lives or occurs and is specific to each of the generic focal species being considered. For example, broadleaved woodland specialist habitat is derived from woodland data sets where the woodland type is broadleaved, within a minimum canopy cover. The woodland area classed as habitat may also be subject to a reduction in size due to the application of an internal buffer representing the edge effect.
What’s the difference between a forest habitat network and a habitat network for open ground species?
The principles for how forest species and open ground species use habitat networks are the same, but is defined by the type of habitat each is associated with. Hence an example of an open ground habitat network may be a heathland generalist, which uses heathland as habitat, rather than woodland.
The woodland network covers priority open ground habitat. Does this mean that the open ground has been changed/lost?
No, all networks represent the dispersal range of the generic focal species (GFS) being considered, rather than a physical change. Networks thus overlap a range of other habitats, and open ground networks are just as likely to overlap woodland habitat.
Why don’t broadleaved networks link to pine networks?
Broadleaved networks represent the functional connectivity of all types of broadleaved woodland and how species may move from one patch of broadleaved woodland to another. Although species specifically associated with broadleaved woodland may utilise some small elements of other land cover types, including pinewood, it is assumed they will find movement through these habitats more difficult. Consequently, broadleaved and pinewood networks are considered to operate independently and are not linked.
Why isn’t there a network around all the woodlands?
Woodlands that have little tree cover (less than 10% canopy cover), or are degraded or extensively managed (much farm and parkland woodland) are unlikely to possess the habitat attributes that many species require and were not considered as woodland habitat. Woodlands that are very narrow lack the ‘core woodland’ many species require, and this is represented in the modelling process by applying an internal buffer. Although these woodlands are not part of a network at present, they provide an excellent opportunity to improve the network by expanding their width.
Why isn’t a good (biodiversity) quality woodland I know about in a good (biodiversity) quality network?
The biodiversity quality of woodlands have been determined through interview (ancient pinewoods in Highland; mixed and broadleaved woodlands in the Borders, broadleaved woodlands in SW Scotland) or by using coincidence mapping (see Forest Habitat Networks Scotland - Borders and the Lothians report(PDF-2086K) for details). Both these approaches are reliant on knowledge or data being submitted for woodlands, so those that do not have this information have not been qualified as ‘good quality’. However, this does not mean an unqualified woodland is not good quality, we have highlighted those we know about. As more woodlands are qualified and the information gathered, we can begin to improve our data sets and help to use this information to help benefit woodland biodiversity.
Generic focal species
What are generic focal species (GFS)?
Conceptual or virtual species reflecting likely ecological requirements of a range of real species where species data are unavailable. This is similar to using an umbrella species except that the profile is not based on one actual species such as a slug, swallow or moth, but on a combination of most species needs. Further details on focal species.
What is a specialist / generalist generic focal species?
Specialists refer to species associated with particular habitat types, e.g. a pinewood specialist GFS is associated with pinewood; generalist GFS refer to species associated with a range of habitat types, e.g. a woodland generalist is associated with all types of woodland.
Why have certain generic focal species been used in some areas but not in others?
Regional variations have defined the important habitats that we have examined. Heathland generalists, woodland generalists, and broadleaved specialists have been used where the habitats are common across the regions, whilst pinewood specialists have been used in the extensive pinewoods of the highlands and western Grampian. There is little pinewood in the Borders, but broadleaved woodland is particularly important, so here we have focused on broadleaved and mixed woodland, particularly those of high biodiversity quality.
Why is an internal woodland buffer used?
An internal woodland buffer is used for woodland specialist analyses to represent how the woodland edge is not used by many woodland species who prefer to use the internal woodland. This may be due to differences in climatic conditions, light/shade, noise, predators, etc. The buffer represents up to two trees lengths (50 m), although this may be less where tree height is less or by riparian areas where the edge effect is less.
Networks and change
What about climate change – do the networks take this into account?
The networks demonstrate the current functional connectivity of the woodlands and heathland. Further analyses are being undertaken to determine how they may operate under future climate change scenarios and how they can be used to attempt to reduce the impact of climate change. A paper is currently being drafted to determine the robustness of the networks to deal with projected increases in temperature and the subsequent impact on site suitability for tree species.
How do the networks cope with land use change?
Changes in land use can affect the permeability of the habitat networks positively, through the addition of more semi-natural habitat, and negatively, if the change is to a more intensively managed land use. If the change in land use is not too extreme, e.g. if semi-natural land converted to buildings, then the networks are unlikely to change drastically. Larger area changes, such as intensification of farming practice on a large area of land within a habitat network is likely to reduce the permeability of the landcover matrix to many species. These larger changes in land use will require the datasets that represent the landcover to be updated periodically.
Who manages the data and how often is it updated?
The data are managed by Forest Research and are updated annually using improved data obtained from users and new data sets.
Using the networks
How can the networks be used?
The networks can be used to reduce the effects of habitat fragmentation and isolation using a number of approaches. For examples, refer to Evaluating biodiversity in fragmented landscapes: applications of landscape ecology tools - Forestry Commission Information Note 85.
What is BEETLE?
BEETLE is an acronym for ‘Biological and Environmental Evaluation Tools for Landscape Ecology’, a suite of tools developed by Forest Research to model and analyse landscape fragmentation and connectivity using GIS (Geographic Information Systems).
How does the modelling approach work?
The Habitat Network Tool analyses the land cover layer in relation to the habitat preferences and dispersal abilities of each generic focal species. It then calculates how far the generic focal species can move outside of it’s preferred habitat, through the wider landscape. This produces a buffer around each of the preferred habitat patches and where these buffers connect, they are designated as a functional network and the model joins them together. The model outputs are two GIS layers; one with the original preferred habitat, the other with the functional habitat networks.
Have the assumptions of how species move through the different land cover types been validated?
There are inherent assumptions within the modelling approach, such as habitat preference, area requirements, dispersal distance and matrix permeability. These assumptions are based on sound ecological theories and principles which have been developed through consultation with the steering groups working with each habitat network project and are explicit within the modelling approach. Although this approach is not intended to model and predict actual species dispersal and viability, it could undoubtedly be validated and refined with species-specific studies, improved species profiles and data, and improved habitat and land cover data. A study is planned to test the theory for an individual focal species on the Isle of Wight. Future work may focus on the use of genetic markers to verify that fragmented woodlands belong to the same network. Until then, the networks should be treated as fuzzy boundaries, and anyone using the networks should bear in mind the assumptions made in the analyses, and treat the networks as another tool, rather than using them as a definitive answer, e.g. this particular lichen will disperse 10 km. Differences in habitats, topography, and management practices will all add local variation and some dispersal may be site specific, but the general assumptions made will hold true.