On this page: Why do we need connectivity? | How can we measure connectivity? | What causes hedge gappiness? | How do we improve connectivity?
Hedgerows criss-cross our agricultural landscape not only providing valuable habitat for our wildlife, but connecting other habitats. It's how a dormouse may travel from one patch of woodland to another; providing an important link between copses that are too small to support a viable dormouse population on their own.
Habitat fragmentation limits the distribution of some species and is through to be a threat to the survival of others in this country. Fragmentation is dangerous as isolated populations are more at risk of local extinction and without corridors the populations cannot recover, but also as
The wildlife corridors provided by hedgerows can alleviate negative impacts of this fragmentation by allowing movement between other areas of habitat.
- Flying insects like butterflies need sheltered conditions to be able to gain, and retain, the heat necessary to fly.
- Protected Species, such as dormouse, most species of bat and great-crested newt require well connected networks of hedgerows, rather than individual hedgerows, emphasising the importance of hedgerows at a landscape level.
- Bats use them to commute between roosting and feeding sites and the shelter hedges provide makes it easier for them, and importantly their insect prey, to fly on windy nights.
- The presence of continuous hedgerows close to maternity roosts is very important for Pipistrelle bats. Bats with limited range echo-location calls rely strongly on continuous landscape features such as hedges for orientation.
- Poor quality, gappy hedges are known to be detrimental to several farmland birds.
With hedgerows we can look at connectivity both on an individual hedge level, but we can also look at hedgerows as a network and assess how well they connect to the wider landscape.
In an individual hedge
Within each hedge we can look at a number of elements that may affect how useful it is at creating a safe passage for our wildlife. Most obviously, we can look at how gappy the hedge is. Even small gaps can be an obstacle for animals like dormice, which prefer to travel on the branches of bushes and on brambles rather than on the ground.
We also look at the number of large gaps (5m or more) which can often be indicative of poor hedgerow health.
In a hedgerow network
Hedgerows in the countryside form a network, with many hedges linked together. They provide both a physical home for our wildlife and connect up our landscape so animals can travel. How connected an individual hedge is to the other hedges in the network, as well as to the wider landscape affects how well they do both of these roles.
In this survey we measure connections at each end, to other hedges or woodland. For example, the hedge highlighted below is connected to a woodland at one end and to three other hedges at the other. The hedgerows in this image connect up the three fragments of woodland shown.
Gappiness in hedgerows is often a result of hedgerow management, and so must be the gapping up. Gappiness can happen through:
- over-trimming to the point where individual shrubs die,
- ploughing too close and killing off the roots of the hedge shrubs and trees,
- spray drift can hasten the demise of any shrubs that are already struggling with any of the above.
- and sometimes through under management where a hedge can gradually develop into a line of trees which will shade out the shrubby growth below and eventually
However you fill in these gaps, it is vital to protect young growth from livestock and browsing wild animals, good to control weeds until they are well established, and sensible to ensure there is an unploughed unsprayed margin large enough to protect your newly restored hedge from damage.
How do we improve connectivity?
Large gaps in hedgerows can be replanted to re-connect the woody shrub layer. This can be a great opportunity to increase the range of species in the hedge. The young plants will need to be protected whilst they establish, and cut on a different regimen to the rest of the hedge in order for them to develop the structural complexity desired in a hedge.
There are a number of ways you can gap up small gaps in your hedgerow.
- Planting new stems as long as they won't be shaded out. This can be an opportunity to increase the variety of shrub species present.
- Laying the hedge, if it is the appropriate condition can fill hedgerow gaps. You can also 'layer' stems into the gaps, (where a pleacher is bent over and dug into the ground) to establish new root stock in the gap.
- If the gaps are too large to be filled by laying, then this is still a good time to plant up the gaps with new stems as there will be less light competition from a newly layed hedge.
- Sometimes, a small hedge gap can provide a good opportunity to plant a hedgerow tree. This will need to be marked and care taken when the hedge is trimmed.
On the landscape level, increasing connectivity could mean planting new hedges, extending current hedges to re-form lost connections, or extending hedgerows to help them connect to other habitats in the wider landscape such as any patches of woodland.