The problem of fragmentation
Habitat fragmentation is a major problem across the Earth. A decrease in the overall area of wild places is bad enough. But combined with fragmentation, it can undermine the integrity of whole ecosystems. Roads, urbanisation and agriculture are some of the main activities that break up natural areas. This often has disastrous impacts on wildlife.
Imagine you are a red squirrel living in a large, healthy woodland. Humans then come along and put a major road right through the middle of those woods. The road becomes a serious barrier, and trying to cross it could be the last thing you do. The patch of woodland on the other side of the road might just as well be fifty miles away.
You can now only breed with those in your own limited patch. Your home is effectively an island, and the population is at risk of inbreeding. On top of this, if a disease, or some other natural catastrophe strikes, you and your kind could become locally extinct. The woods are now so cut off there’s little chance of squirrels making a comeback.
Other Caledonian Forest inhabitants that illustrate the importance of connectivity are wood ants. These ecologically important insects don’t travel very far. So again if they vanish in one area of woodland, the chances of them making a comeback on their own are virtually zero. This can also be the case with the capercaillie and crested tit.
Fragmentation can also lead to what is known as the ‘edge effect’. Some species, including certain mosses and lichens, like damp, shady conditions. As a patch of forest shrinks, they may get exposed to too much sun or drying wind, and disappear. (Note that there can be a positive natural edge effect where two habitats meet. This can be great for biodiversity, but this is a different effect to the one we’re looking at here.)
A healthy forest will be large enough to support those organisms with the largest home range. These are usually the top predators and they can be really vulnerable to fragmentation. Since they often play a vital role in regulating populations of other creatures, the ecosystem can be seriously upset if they disappear.
Thinking on this large scale, climate change is forcing certain species to migrate. If their natural habitat is too fragmented, many might not be able to move, and they will be at risk of extinction. This again highlights the importance of a connected landscape.
Conservationists use a range of techniques to help increase connectivity in fragmented landscapes. These include creating corridors, buffers and stepping stones to help wildlife move around.
A corridor can be anything from a hedgerow for dormice to a huge landscape-scale link. The basic idea is to create a direct connection between separate patches. Some artificial links can help particular species. Badger tunnels and aerial runways for squirrels are used to help these animals negotiate roads. In some countries, wide habitat bridges help larger animals cross motorways. Stepping stones are patches of habitat which ease movement through the landscape. Buffer zones around a woodland can help to reduce the edge effect. They can also protect the interior of the woods from activities such as fertiliser spraying on adjacent land.
Reconnecting habitats isn’t always straightforward, and we need to be careful not to create further problems. For example, by linking up two woodlands to help red squirrels we might accidentally help spread the invasive grey squirrel. Even so, these problems can be avoided with some careful planning. Re-establishing a more connected landscape should be seen as a conservation priority.
There are many projects worldwide aimed at addressing fragmentation. In Britain the concept of Forest Habitat Networks is helping create more connected habitats across the landscape. There are also a lot of conservation bodies and private landowners who are teaming up to make a difference on a large-scale. These rewilding projects are an exciting step forward in nature conservation.
Trees for Life’s work
The surviving patches of Scotland’s Caledonian Forest are a prime example of a severely fragmented habitat. What remains are small and scattered remnants. To counter this, we have already taken steps to create a more connected forest. For example in 1999 – 2000 we established the Allt na Muic forest corridor, as a north-south link between Glens Moriston and Affric. Over the decades, with the support of other landowners, we have also been helping expand tree cover further west in Glen Affric. Species such as black grouse are already benefiting from this expansion. Our East West Wild project seeks to build on this work by creating a large-scale corridor across this part of the Highlands.
Reversing fragmentation can take decades, or even centuries. In the meantime our Red Squirrel Reintroduction Project has helped these animals recolonise former haunts. In most cases it would have been a long time before they managed to do this on their own.
What can you do to help reverse fragmentation?
Supporting the work of organisations such as Trees for Life, and coming on a Conservation Week can really make a difference. So can speaking out to prevent further fragmentation. There are also ways in which you can increase connectivity in your local area. There are around 24 million gardens in the UK and they can be a vital refuge for wildlife. Leaving some patches to go wild is really helpful in our over-sanitised landscapes. There are also lots of available resources on wildlife gardening. It’s important to remember that we can all make a difference.
Sources and further reading
- Bennett, A. F. (1999) Linkages in the Landscape: the role of corridors and connectivity in wildlife conservation. IUCN: Gland, Switzerland and Cambridge.
- Bright, P.W. (1993) Habitat fragmentation – problems and predictions for British Mammals. Mammal Review. 23, 101-112.
- Chadwick, D.H. (1991) Introduction. In: Hudson, W.E. (ed.). Landscape Linkages and Biodiversity. Island Press: Washington D.C.
- Gilbert, O.L. & Anderson, P.A. (1998) Habitat Creation and Repair. Oxford University Press: Oxford.
- Harris, L.D. (1984). The Fragmented Forest: Island Biogeographical Theory and the Preservation of Biotic Diversity. University of Chicago Press: Chicago.
- Huxel, G.R. & Hastings, A. (1999) Habitat loss, fragmentation and restoration. Restoration Ecology. 7, 309-15.
- Kirby, K. (1995) Rebuilding the English Countryside: habitat fragmentation and wildlife corridors as issues in practical conservation. English Nature Science. No. 10. English Nature: Peterborough.
- MacArthur, R.H. & Wilson, E.O. (1967) The Theory of Island Biogeography. Princeton University Press: Princeton, NJ, USA.
- Macdonald, B. (2019). Rebirding. Pelagic Publishing: Exeter.
- Peterken, G.F., Baldock, D. and Hampson, A. (1995) A Forest Habitat Network for Scotland. Research, Survey and Monitoring Report No.44, Scottish Natural Heritage.
- Puplett, D.P. (2000) Assessment and amelioration of woodland fragmentation on the Menai Strait, using GIS. Unpublished MSc thesis. University of Wales: Bangor.
- Simberloff, D.S. & Cox, J. (1987) Consequences and costs of conservation corridors. Conservation Biology. 1, 63-71.
- Spellerberg, I.F. (1995) Biogeography and woodland design. In: Ferris-Kaan, R. (ed.). The Ecology of Woodland Creation. Wiley: Chichester, 49-62.
- Stewart, A.J.A. & Hutchings, M.J. (1996) Conservation of populations. In: Spellerberg, I.F. (ed.). Conservation Biology. Longman: Harlow, 122-140.
- Taylor, P.D., Fahrig, L., Henein, K. and Merriam, G. (1993) Connectivity as a vital element of landscape structure. Oikos 68, 571-73.
- Tree, I. (2018). Wilding – The return of nature to a British Farm. Picador: London
- Wickham, J.D., Jones, K.B., Riiters, K.H., Wade, T.G. & O’Neill, R.V. (1999) Transitions in forest fragmentation: implications for restoration opportunities at regional scales. Landscape Ecology. 14, 137-145.
- www.forestresearch.gov.uk/research/landscape-ecology/landscape-ecology-the-basics-of-landscape-ecology/ (Accessed September 2020)
- Forest Habitat Networks in Scotland (Accessed September 2020)
- Background to Forest Habitat Networks (Accessed September 2020)
- Scottish Forest Strategy (Accessed September 2020)
- Wildlife Trusts – Wildlife Gardening (Accessed September 2020)
- www.woodants.org.uk/ (Accessed September 2020)