The Significance Of Hedgerows For Biodiversity Biology Essay
Hedgerows are an important part of the landscape that defines the UK and Ireland, traditionally planted to determine land boundaries; in the 1700s it became obligatory that landowners erect permanent boundaries around their properties. The boundaries from the farmer's point of view needed to be stock proof meaning that their stock could not escape and therefore were erected without gaps and tall. Sometimes these hedgerows determined parish boundaries; hedgerows dating back to the 1700s are now known as ancient hedgerows and are classed as being of significant ecological importance.
Hedgerows provide both food and shelter for eighty percent of woodland birds and thirty percent of mammals and thirty percent of butterflies in the UK also associated are ditches and river banks which also support frogs, newts and toads (RSPB, 2009)
Intensification in agriculture over the past 50 years has had a major impact on changes in field patterns, resulting in hedgerows being discarded in favour of larger field to promote higher production on the land. The removal of hedgerows has had a direct effect on the habitats that were supported by their existence as they provided the basis for a varied food chain and the report will outline some of the species that would be adversely affected if there was further reduction in the network of hedgerows in the UK.
The methods used in compiling the information was to determine if the species lived or visited the hedgerow in their lifetime and then to determine if their survival was based on the hedgerow existence. The report is theory based and as there was no fieldwork or data collection involved the methods and results are reflective of this. The information was gathered by searching for organisations that are directly or indirectly involved in the management and protection of hedgerows and collating information from the relative organisations and from books available to produce results that show the importance of the hedgerow to certain species in terms of their feeding.
The UK Biodiversity Action Plan (BAP) recognises certain species in the UK for their importance to the biodiversity that exists and define biological diversity as the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems (BAP, 2009).
Webb et al (2009) cited in Wolton (2009) observed that many of the widespread species associated with hedgerows require landscape – scale habitat mosaics of different habitats and that conserving any one habitat will be unlikely to reverse the fortunes of these species, attributing to the vital importance of the hedgerow as a whole. It was also noted that individual species often use several parts of the hedgerow, an example of this is the bird species, Yellowhammers, they feed in the margins, nest in the base, hide from predators in the shrubby parts and use the trees as song posts, thus cementing the basis for the report that the biological diversity of the hedgerows is dependent on more than individual species but a combination of species that make up the many small ecosystems within it.
Associated number of priority species (n = 79)
Percentage of priority species associated with the hedge component
Table 1. Numbers of priority species associated with the different structural components of hedges (Wolton, 2009)
Wolton (2009) reports that
- 45 of 79 of all priority species are dependant or partially dependant on hedgerow trees
- 33 of 79 species use the shrubby component of hedgerows for feeding, breeding or shelter and protection from weather and predators.
- The base of the hedgerow, beneath the canopy is important for 32 of 79 priority species
- The margins associated with the hedgerows are important for 27 of 79 priority species
Note: figures do not add up to 100% as some species require multiple habitats.
Hedgerows provide essential resources for mammals, birds and insects and are themselves an important habitat in their own right (unknown 2008) The results show that hedgerows are extremely important in the maintaining the biodiversity in Britain and there are many priority listed species that are in decline or on the verge of being and therefore need to be protected. Hedgerows are important in terms of their biodiversity function; the food web that is associated within a hedgerow is complex and very interactive. If the hedgerow was to be removed it would adversely affect many types of species. The hedgerow supports a varied food chain and food chains and webs are not simplistic and are further complicated as animals that are easily adaptable to changes in their environment will succeed and will involve competition for their survival with their own and other species and will for some inevitably be food for severable different animals and many birds and mammals will turn to other foods away from their normal diets as a supplement for their main diet. Different features in the hedgerows will appeal to different species as are shown in the results and the more diverse in composition a hedgerow is the more species it will support. Native hedge plants such as the Blackthorn, Hawthorn, Dogwood and Field Maple will support more species than non native plants (Unknown, 2008) To show the diversity in the hedgerow (Muir et al, 1987) have categorised hedgerow feeders into vegetarian, insect eating and carnivores, this classification will aim to highlight the diversity of feeders that a hedgerow supports with description given by the authors in their publication Hedgerows, Their history and wildlife.
A significant number of invertebrates, aphids, mammals and birds are among the hedgerows vegetarian feeders, with the invertebrates being in the highest population. Muir et al (1987) note that the most common hedge tree and hedge shrub are the oak and hazel and support the highest number of species.
Of the two hundred and eighty four species it is considered that one hundred of these are moth species. Results from research undertaken in the optimisation of agri environment schemes show that hedgerow trees are the main reason for the beneficial effects on moth numbers and moth diversity. It was also reported that hedgerow trees create a micro climate for individual moth species and are used as wildlife corridors in enabling movement throughout open agricultural spaces (Merckx et al, 2009).
Beetles and bugs:
form an integral part as vegetarian feeders; these include leaf beetles, cockshaphers, weevils and the true bugs to include aphid hopper and scale insects. One of the most familiar of these bugs is the common frog hopper. Bug life an organisation involved in the protection of invertebrates state that the optimum hedges for biodiversity should be thick hedges with tussocks and accumulations of leaf litter, these sites are more likely to be preferred by invertebrates such as the ground beetle and that the lowest layer should be kept intact and not over managed as it is essential to invertebrate survival.
Slugs and snails also survive in hedgerows with their preference being for night-time feeding, but often damp weather forces them to feed during the day, where their liking is rotting leaves and fungi. Daytime feeding for snails allows them to become a potential source of food for their predator the song thrush.
Plants that flower at different times of the year are very important to the survival of many insects as prolonged flowering periods provides a source of nectar at different times and therefore supports more insects. The Royal Society for the Protection of Birds (RSPB) promote the value of hedgerows for wildlife and report that flowers on the hedgerows attract bees, wasps and spiders who then acquire nectar and pollen and in turn fertilise the flowers, cross interaction that benefits both parties.
Seeds and berries on a hedgerow support a number of invertebrate, the blackberry attract s wasps and the berries are a source of food for them near the hibernation season, when the berries become softer they are a source of food for the red admiral butterfly which feeds on the juices of the berry, birds and mammals are the main feeders on the seeds and fruits that are produced within hedgerows.
Rabbits and many other species directly and indirectly, ants then like the open spaces created by rabbits grazing and this positively affects the insectivorous feeders. Rabbits have also had negative interactions with other animals when a myxamatosis outbreak killed millions of rabbits in Britain, this affected predators such as stoats and buzzards where rabbits would have been the main source of their diet. Presently rabbit populations have increased and become abundant again.
such as bank vole, wood mouse and field vole are of the highest mammal's numbers to survive in hedgerows and survive on vegetation, seeds and nuts.
Descriptions and information obtained from Muir et al (1987)
The RSPB (2009) identified that hedgerows with a large number of woody species supports more birds and old trees with holes are extremely important for the blue tits, owls and kestrels when nesting. It is also noted in their information that hedges have the capacity to hold up to eighty percent of the woodland birds especially in areas where woodland is not sufficiently abundant and birds depend on the network of ancient hedgerows for their survival. The physical features of birds determine their diet and feeding techniques but in Muir et al (1987) it is also pointed out that birds have the ability to be opportunistic feeders and can adapt their diet as food becomes scarce.
Spiders: some of the spiders such as the garden spider spin their web to catch their prey and other species actively hunt for their prey. Spiders are of a carnivorous nature and are therefore always in danger of being prey to larger spiders.
Beetles: alongside leaf eating beetles are the insect eating community with ladybirds being the most widely known. They usually feed and scale insects, mealy bugs, mites and aphids. They are not usually seen as prey as they have brightly coloured hard shells warning potential predators of their poisonous nature.
Frogs: damp hedges are likely to reveal the common frog and toads, usually night feeder of insects. They are likely to become prey to omnivorous creatures such as rats, crows and hedgehogs.
Shrews: are consumers of mainly ground invertebrate food such as the earthworm, beetles, woodlice, spiders and flies. They need to consume oat least three quarters of their own body weight each day and a pregnant female needs to consume one and a half times her bodyweight in food is she is to survive. Shrews are mainly unpalatable reducing their number of predators but are still at risk as owls will feed on them.
Bats: Linear landscapes features such as hedgerows are favourable to bats as they are used as a flight path from roosting sites and feeding areas. It is important that hedgerows do not contain gaps as this can deter bats from foraging and nesting there. Hedgerows allow bats to use them as connections throughout the countryside. Some species of bats such as the greater and lesser horseshoe, brown long eared and Natters Bat can feeds on insects directly from foliage and prefer being in close proximity to vegetation cover. Bats generally do not compete with birds for insects as they feed at dusk and at night when birds are the least active and bats such as the pipstrell can catch up to three thousand insects a night in flight, (Unknown, 2008)
Birds: Many birds feed on insect's species along with being vegetarians, including many woodland species of birds and those who have had their origins in the woodland habitat and have developed preferences for the hedgerow such as the thrush family, whitethroat and the dunnock. The population of birds in one hedgerow depend on their ability to establish a territory and also their diet preferences, by holding a territory birds avoid competition for food.
Descriptions and information obtained from Muir et al (1987)
Carnivores and Carrions
Fox: Foxes tend to be very opportunistic in their feeding habits and often will kill more than what is needed for food if the need arises; they also have the liking for insects and berries.
Badgers: are also opportunistic feeders and preference is given to what is available rather than a specific diet, this includes insects, voles, mice, amphibians and rabbits. As they at the top of the ground food pyramid their predators as with the fox are humans, not for food but as a control issue.
Weasels and Stoats: these creatures mainly have a diet of rodent prey and both kill their prey with a bite to the back of the neck. Weasels being the smaller of the two feed on smaller mammals and therefore do not go into direct competition with the stoat for food. The stoat usually preys on rabbits and this is the main part of their dies, the myxomatosis outbreak in 1954 severely impacted on the stoat population and it has been recovering slowly since.
Descriptions and information obtained from Muir et al (1987)
The above descriptions of the food pyramids involved in a hedgerow network and how they evolve into complex food web reiterates the importance of the hedgerow to maintaining biological and ecological diversity in Britain. Hedgerows have been key in adapting to changing environments as some have been around for almost a century. Maintenance and proper management can determine the future of these mini ecosystems, this has been recognised in legislation in both the EU and Britain in the Hedgerow regulation (1997) and reforms under Common Agricultural Policy in Europe further consideration have been taken in relation to hedgerows. Proper management and understanding of hedgerows can have major benefits and for the custodians a good knowledge of animal behaviour, patterns and habitats is necessary an example of bad management can result in the loss or decline of a single species. An example of this is the Brown Hairstreak Butterfly, due to its dependence on hedgerows; the butterfly is affected by hedge removal and frequency of cutting. The female lays its eggs on the projecting shoots of the blackthorn and hawthorn and there they lay dormant for the winter. If the hedgerows are cut during this period the result is potentially the loss of all eggs and this has been the reason for the near extinction of this species in recent years (Butterfly Conservation, 2009).
Butterfly Conservation (2009) Hedgerows for Hair Streaks [online] available from http://www.butterfly-conservation.org/uploads/hedgerows%20for%20hairstreaks.pdf. Accessed 07/12/2009
Merckx et al. Optimizing the biodiversity gain from agri-environment schemes. Agriculture Ecosystems & Environment, 2009; 130 (3-4): 177 DOI: 10.1016/j.agee.2009.01.006
Muir, N. Muir, R. (1987) Hedgerows: Their History and Wildlife. Butler and Tanner Ltd, UK
RSPB (2009) Value of Hedgerows for Wildlife [online] available from http://www.rspb.org.uk/ourwork/conservation/advice/farmhedges/value.asp. Accessed 08/12/2009
UK Biodiversity Action Plan (2007) Definition [online] available from http://www.ukbap.org.uk/GenPageText.aspx?id=52. Accessed 05/12/2009
Unknown (2008) Wildlife and Hedgerows. [online] available from http://hedgelink.org.uk/index.php?id=26#Hedgerow_Features_Important_to_Wildlife_2. Accessed 03/12/2009
Wolton, R. (2009) UK Biodiversity Action Plan: Priority species linked to hedgerows – Final Version [online] available from http://www.hedgelink.org.uk/index.php?id=26. Accessed 01/12/2009
Barnes, G. Williamson, T (2006) Hedgerow history: Ecology, History and Landscape Character. Windgather Press, UK
Chapman, L (2001) The living history of our hedgerows. Orchard Publications, UK
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Putman, R.J. (1994) Community Ecology. Chapman and Hall, UK
Unknown (2006) A strategy for the renewal of hedgerow trees throughout the UK [online] available from http://www.ukagriculture.com/pdfs/hedgerowtrees.pdf. Accessed 07/12/2009
1 Student ID: 200497332 09/12/2009
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