Hedges are both ecologically and culturally important and are a distinctive feature of the British landscape. However the overall length of hedges across Great Britain is decreasing. Current challenges in studying hedges relate to the dominance of research on rural, as opposed to urban, hedges, and their variability and geographical breadth. To help address these challenges and to educate the public on the importance of hedge habitats for wildlife, in 2010 the Open Air Laboratories (OPAL) programme coordinated a hedge-focused citizen science survey.
Results
Results from 2891 surveys were analysed. Woody plant species differed significantly between urban and rural areas. Beech, Holly, Ivy, Laurel, Privet and Yew were more commonly recorded in urban hedges whereas Blackthorn, Bramble, Dog Rose, Elder and Hawthorn were recorded more often in rural hedges. Urban and rural differences were shown for some groups of invertebrates. Ants, earwigs and shieldbugs were recorded more frequently in urban hedges whereas blowflies, caterpillars, harvestmen, other beetles, spiders and weevils were recorded more frequently in rural hedges. Spiders were the most frequently recorded invertebrate across all surveys. The presence of hard surfaces adjacent to the hedge was influential on hedge structure, number and diversity of plant species, amount of food available for wildlife and invertebrate number and diversity. In urban hedges with one adjacent hard surface, the food available for wildlife was significantly reduced and in rural hedges, one adjacent hard surface affected the diversity of invertebrates.
Conclusions
This research highlights that urban hedges may be important habitats for wildlife and that hard surfaces may have an impact on both the number and diversity of plant species and the number and diversity of invertebrates. This study demonstrates that citizen science programmes that focus on hedge surveillance can work and have the added benefit of educating the public on the importance of hedgerow habitats.
Hedges are familiar structures in the British landscape. They are a boundary or linear feature of shrubs and/or trees that is subject to some degree of management [1, 2] and are a distinct part of British cultural heritage [3].
The archetypal British landscape of a patchwork of small fields surrounded by hedges may be a feature of the period that follows the Great Enclosure (1750–1850) when 200,000 miles of hedges were planted [4]. However, there is clear evidence that the overall amount of hedges in Great Britain has decreased over the past 70 years [5–7]. Modernisation of agriculture after World War II led to considerable hedge removal and changes to management practices. Recognition of this led to a spate of research into the role of hedges in the countryside and the publication of a book specifically on hedges in the new naturalist series [6]. Another significant loss of hedges occurred in the latter part of the 20th century [8]. The 1990 Countryside Survey [9] reported that the length of hedges in Britain had decreased by 23 % between 1984 and 1990. This alarming discovery led to hedges being designated as a priority habitat for conservation in the 1994 UK Biodiversity Action Plan (now superseded by the UK post-2010 Biodiversity Framework [10]). However, despite no discernible change in hedge length between 1990 and 1998 [11], the 2007 Countryside Survey reported a further decrease in hedges, estimating a 1.7 % reduction in the total length of woody linear features in Great Britain since 1998 [5]. A reduction of 6.2 % in the same time frame was recorded for managed hedges, representing a loss of 31,000 km of hedge. Reasons for this are largely related to changes in cultural functions [2] and the over- and under-management of hedges [5, 12].
Hedges are largely man-made, often as a result of boundary delineation, agricultural practices such as stock control, or for provision of resources [2, 13]. They are aesthetically pleasing landscape features in both rural and urban areas and offer soft functions such as colours, smells and patterns [3]. Particularly in urban areas they may also provide privacy [3], function as noise barriers [14] and, broadly, vegetation in cities may help to mitigate air pollution [15].
Hedges are important ecologically and are highly valued for their ability to provide food and shelter for a wide range of vertebrates and invertebrates [2, 16–18]. Their structure and composition has an important influence on wildlife presence and abundance. Modelled relationships between the different structural components of a hedge and the animals that use them have shown that each component (e.g. trees, shrub layer) has value for different animal species throughout the year [19]. Other studies have focussed on particular species. For example, trees in hedges provide habitats for bats [20] and large moth species [21], and gaps in hedge structure influences bank vole abundance [22] and beetle populations [23]. The plants that make up a hedge also affects animal diversity with both herbivorous and detritivorous invertebrates and their associated predators and parasites being affected by floral composition [24]. They are also considered to be ‘corridors’ between areas such as woodlands, although it is noted that their function in this respect is lacking in empirical evidence [25–27]. Furthermore, hedges provide significant ecosystem services. They provide a regulating service through controlling water flow and preventing soil erosion [2, 28]. They provide a supporting service through soil nutrient retention [28] and provide habitats for pollinating insects, essential for arable farming [29]. They also provide an important cultural service through their heritage value as part of the British landscape. Hedge biodiversity is influenced inter alia by the management regime used: cutting frequency and timing can affect the diversity of hedge flora [30] and fauna [31, 32] and the food (flowers and berries) available for wildlife [12], while land use adjacent to the hedge also affects the diversity of both flora and fauna [28].
One of the significant challenges for current research on hedges is that there is considerable geographical breadth and variability in hedges. Furthermore, many of the studies highlighted thus far refer to hedges in rural areas, and in particular to farmland hedges. However, very few studies focus on urban hedges, although studies on urban ecology and biodiversity may cover hedges implicitly. The countryside survey, one of the most in-depth studies of hedges in the UK [8], does not cover urban areas and therefore the biodiversity value of urban hedges is not well known. Faiers and Bailey [33] examined canalside hedges and noted that urban hedges scored poorly for biodiversity and structure compared with rural hedges along the same 20 km stretch of canal. Other studies which have looked at the ecological differences between urban and rural environments noted the importance of landscape features and green space in providing valuable habitats in increasingly urbanised landscapes (e.g. [34, 35]) but did not necessarily look at hedge habitats.
To gain geographical coverage in environmental research, scientists are increasingly using citizen science as a tool to gather data [36–38]. This is demonstrated by a large array of research in which members of the public and non-experts collect data on a range of topics and submit these data for further interrogation [36]. This method has the core benefits of enabling scientists to collect data from areas they cannot normally access and on a large geographical scale [39], although issues of data quality should be addressed [36, 40]. Nevertheless, citizen science can be used to provide a broad overview of phenomena and, furthermore, it can be used to engage people in science and environmental monitoring, creating a legacy for future conservation.
This paper looks at the results from a citizen science hedge survey, coordinated by the Open Air Laboratories (OPAL) programme and specifically, compares urban and rural hedges.
Methods
OPAL began in December 2007 with a grant from the UK Big Lottery Fund. OPAL aims to meet dual ambitions of encouraging more people to explore their local natural environment while also providing useful data which can be used for research [41].
With OPAL, participants of all ages and abilities carry out surveys on a range of environmental topics. The surveys have clear instructions and are designed to be self-explanatory [42] and simple to complete. In September 2010, OPAL launched the OPAL Biodiversity Survey, which asked participants to examine hedges and the biodiversity found in them. Although there are many examples of hedge surveys being organised at a local level, often using the methodologies outlined in the Hedgerow Survey Handbook [1] this OPAL survey was the first England-wide citizen science survey to address the wildlife value of hedges.
The survey was undertaken through four activities: an activity to describe the hedge’s features and components; an activity to note down how much food (berries, nuts) was present in the hedge; an activity to note any evidence of animals living there; and an activity to determine what invertebrates were found in the hedge.
Surveys were organised and often overseen by locally recruited staff (Community Scientists, see [42] and biodiversity mentors, see [43]), group leaders and school teachers. Participants in the surveys included volunteers affiliated to a community or voluntary organisation, youth groups, school groups, and groups of families and friends. Survey participants could also download a survey pack from the OPAL website [44] and take part in the survey independently of organised groups. Participants were provided with survey packs and were guided to find suitable local hedges to monitor. The survey pack included a field guide, a recording booklet and information on how to identify common hedge plants and invertebrates to varying taxonomic levels. Taxa included in the survey were selected on the basis that they were likely to be encountered and were reasonably distinctive for easy identification by untrained surveyors. For additional species identification support, participants were also guided to use the iSpot website [45], an OPAL website developed by The Open University to help people develop their interest in wildlife.
Survey participants were asked to select a three-metre stretch of hedge that was “typical of the whole hedge” [46] and to record the information listed in Table 1. The majority of surveys were entered online by the participants; a small number were entered by OPAL staff. Some responses were entered in the form of free text and these required a certain amount of editing for consistency and spelling. Participants identified the location of their hedge by pinpointing on an online map and these locations were recorded in the database in the form of latitude and longitude. ArcMap [47] and its ‘clip’ tool were used to extract surveys conducted in England only. Then the ‘selection’ tool was used to identify sites as urban or non-urban (rural) according to the 2001 census by the Office of National Statistics. The number of woody species, the number of invertebrate groups, and the total number of recorded individual invertebrates were also determined.
Table 1
Summarised recorded variables in the survey
Question category
Answer variables
Type of recording group
School, volunteer group, family or friends
Weather
Sunny, cloudy but no rain, raining
Location
Surrounding area
Urban, garden, park, school, farmland, grassland, wood or forest, other
Land use on both sides of the hedge
Crops, grassland, hard surface (unspecified), garden, woodland, waterway, cannot see (other side)
Presence/absence of 12 woody species, (see Table 3)
Numbers of berries, nuts or flowers
In four categories from <10 to >1000
Invertebrates
Counts of invertebrates in 24 named groups (see Table 4)
Size of any holes in the ground
In five categories from <2 cm to >30 cm
Other wildlife seen
Free text
Hedge scoring system
As part of the survey, a scoring system was created that would enable an assessment to be made of the potential that each hedge had for supporting a range of biodiversity (i.e. a quality score), and to provide meaningful feedback to survey participants. A number of systems have previously been developed to generate numerical scores for particular habitats. These may be based on the measured traits of particular species (e.g. [48]) or may assign values to particular habitat characteristics in order to compare different sites and assess their quality or condition (e.g. [49]). There have also been studies on how to classify hedges (e.g. [50, 51]) but only a few attempted to score hedges, such as Hedgelink’s (a partnership of 19 government, conservation and countryside organisations) management decision score [52], or to develop criteria for determining hedge importance ([53] cited in [54]). The OPAL Biodiversity Survey allowed for three scores to be created for: hedge structure/shape; provision of food for wildlife (plant species present, potential for flowers and fruits); and animal diversity based on the species found by the surveyors. Details on how scores were derived are listed in Table 2. This method has some parallels with the condition assessment approach, exemplified for grasslands by Robertson and Jefferson [49]. The method was tested using hypothetical data and then refined with data from field trials which confirmed that higher scores were generated for the better “quality” hedges. Since the three test scores were not highly positively correlated, and since each score may independently indicate a feature of benefit to wildlife, the three separate scores were retained, rather than combined into a single amalgamated score.
Table 2
Derivation of hedge structure score, food for wildlife score and animal diversity score
Question category
Answer variables
Score
Hedge structure score—sum of the following seven elements
1. Structure of hedge
Line of bushes
4
Line of trees
3
Bushes and trees
5
2. Gaps in hedge
No gaps
5
A few gaps
3
More gaps than hedge
1
3. Shape of hedge: average of all that were recorded
Neatly trimmed
2
Untrimmed
4
Heavily cut
1
Leggy
1
Laid or coppiced
5
4. Other features: sum of all features recorded
Wall
1
Fence
0
Ditch
1
Bank
1
Undisturbed strip
2
5. Height of hedge
<1 m
1
1–2 m
3
2–3 m
5
>3 m
4
6. Width of hedge
<1 m
1
1–2 m
3
>2 m
5
7. Length of hedge
<5 m
2
5–20 m
3
20–50 m
4
>50 m
5
Food for wildlife score—sum of the following two elements
1. Hedge food species: sum of all recorded species. Sum multiplied by 2 if hedge shape recorded as “untrimmed”, or by 1.5 if shape recorded as “neatly trimmed” (providing “untrimmed” was not recorded)
Beech
1
Bramble
5
Blackthorn
5
Dog Rose
5
Elder
3
Hawthorn
5
Hazel
2
Holly
4
Ivy
4
Laurel
1
Privet
2
Yew
2
2. Numbers of flowers/berries
<10
1
10–100
4
100–1000
7
>1000
10
Animal diversity score—sum of the following two elements
1. Numbers of different types (see Table 4) of invertebrate: sum scores for all invertebrate types recorded.
Recorded as present
2
1–2
2
3–5
2.5
6–10
3
11–50
3.5
51–500
4
>500
5
2. Presence of holes
<2 cm
5
2–5 cm
10
5–10 cm
15
10–30 cm
20
>30 cm
25
Statistical analysis
Differences between urban and rural hedges in: (i) the proportions containing specific woody species and invertebrate groups were compared using Chi squared contingency tables, and (ii) the mean number of woody species, mean number of invertebrates, mean hedge structure score, mean wildlife food score and mean animal diversity score by independent samples t tests. A comparison between the number of invertebrate groups and the number of woody hedge species was made using Spearman rank correlation.
Hedge structure score, wildlife food score, animal diversity score, numbers of invertebrate groups and numbers of woody hedge species were further examined using analysis of variance (ANOVA). For each of the five variables an ANOVA was undertaken examining differences in urban and rural hedges, hard surface types adjacent to the hedge, and the interaction between urban/rural and hard surfaces. Hard surfaces were categorised as 0, 1 or 2 depending on how many sides of the hedge were hard surfaces. All analyses and graphs were generated in SPSS version 22 [55].
Results
Between September 2010 and August 2012, 2949 completed OPAL Biodiversity Surveys were returned, 82 % were recorded between April and October (83 % rural, 81 % urban). Figure 1 shows the distribution of survey returns across England. A total of 2891 responses that included both hedgerow and invertebrate data were included in the following analyses. Of these 46.6 % were on urban hedges with the remainder (53.4 %) on rural hedges. The majority of returns were from school groups (79.9 % urban, 60.5 % rural).
Fig. 1
Map showing the distribution of completed OPAL Biodiversity Surveys across England between September 2010 and August 2012. Solid grey circles indicate surveys from urban areas; open circles indicate surveys from rural areas
Recorded urban hedges were dominated by those in schools (55.3 %) and in gardens and parks (23.9 %), while rural hedges were dominated by those from farmland (30.8 %), schools (28.3 %) and grassland (22.3 %). Approximately one third of recorded hedges had no gaps (39.0 % urban, 34.2 % rural). In the entire sample, 69.5 % of hedges were recorded as untrimmed. In respect of other features of the boundary, 53.4 % also contained fences, 17.0 % ditches, 15.6 % earth banks, 27.2 % undisturbed strips and 11.7 % walls. 63.2 % of hedges were taller than 2 m and 43.8 % of hedges were wider than 2 m. Holes at the base of the hedge were reported in half of the returns (49.2 %).
Woody species
Table 3 summarises the percentage of urban and rural hedges containing each recorded woody species and the mean number of woody species recorded at each site. All species, except Hazel, differed significantly between urban and rural sites. Beech, Holly, Ivy, Laurel, Privet and Yew were recorded more often in urban hedges, while Blackthorn, Bramble, Dog Rose, Elder and Hawthorn were recorded more often in rural hedges. There was no significant difference in the mean number of woody species recorded in urban and rural hedges.
Table 3
The percentage of urban and rural hedges containing the 12 recorded woody species
Urban
Rural
χ2
P
Beech
23.1
13.9
38.13
<0.001
Blackthorn
25.9
31.7
10.90
0.001
Bramble
48.4
64.3
68.31
<0.001
Dog Rose
19.2
26.1
17.39
<0.001
Elder
15.6
19.3
6.35
0.012
Hawthorn
46.2
63.5
79.99
<0.001
Hazel
19.0
18.4
0.17
0.676
Holly
29.7
17.2
59.25
<0.001
Ivy
42.0
37.9
4.58
0.032
Laurel
17.1
6.1
82.56
<0.001
Privet
21.0
7.4
105.54
<0.001
Yew
8.9
4.1
26.73
<0.001
Mean number of woody species
3.16
3.10
0.92a
0.358
Significance is tested by Chi squared contingency tables, except mean number of species tested by independent samples t test
a t statistic
Invertebrates
Spiders were the most frequently recorded invertebrate, present in over half of all hedges surveyed. Table 4 summarises the percentage of urban and rural hedges that contained each invertebrate group, and the mean numbers of invertebrate groups and of the three calculated scores. Nine of the 24 invertebrate groups differed significantly between urban and rural hedges. Ants, earwigs and shieldbugs were recorded more often in urban hedges and blowflies, caterpillars, harvestmen, other beetles, spiders and weevils were recorded more often in rural hedges. There was no significant difference in the mean number of invertebrate groups recorded in urban and rural hedges.
Table 4
The percentage of urban and rural hedges containing the 24 recorded invertebrate groups
Urban
Rural
χ2
P
Aphid
20.4
22.7
2.03
0.155
Ant
33.4
25.0
24.29
<0.001
Blowfly
9.2
13.1
10.33
0.001
Bee
13.4
13.3
0.01
0.912
Butterfly
10.4
10.1
0.08
0.779
Caterpillar
11.8
15.7
8.82
0.003
Centipede
6.7
5.6
1.52
0.218
Cranefly
7.1
8.6
2.14
0.143
Earwig
15.7
11.6
10.07
0.002
Froghopper
7.6
9.4
2.94
0.086
Harvestman
11.1
13.5
3.85
0.050
Hoverfly
9.8
9.9
0.01
0.936
Lacewing
4.8
4.6
0.08
0.773
Ladybird
23.2
23.4
0.02
0.889
Millipede
6.3
7.2
0.92
0.337
Moth
8.4
10.2
2.00
0.157
Other beetles
16.6
21.0
8.71
0.003
Shieldbug
9.1
6.3
7.83
0.005
Slug
12.5
11.6
0.47
0.492
Snail
25.2
25.9
0.18
0.675
Spider
54.5
58.8
5.17
0.023
Wasp
14.2
13.0
0.83
0.363
Weevil
6.3
9.5
9.72
0.002
Woodlouse
23.7
21.0
3.03
0.82
Mean number of invertebrate groups
3.61
3.71
−0.66a
0.513
Mean hedge structure score
23.1
24.4
−10.29a
<0.001
Mean wildlife food score
21.6
25.5
−7.16a
<0.001
Mean animal diversity score
17.6
19.1
−2.72a
0.007
Significance is tested by Chi squared contingency tables, except mean number of groups, and mean scores tested by independent samples t test
a t statistic
The Spearman rank correlation between the number of woody species and number of invertebrate groups was 0.146 (p < 0.001) suggesting that more botanically diverse hedges were also more diverse in invertebrates.
Hard surfaces
Only 5.3 % of the sample of 2891 hedges had hard surfaces on both sides. Hard surfaces were present on one or both sides for 45.2 % of urban hedges and 26.7 % of rural hedges.
Overall, rural hedges had a significantly higher structure score and wildlife food score than urban hedges (Table 5). Hedges with hard surfaces on both sides had significantly reduced scores for structure, wildlife food, and animal diversity, and much lower numbers of invertebrate groups and woody species (Table 5; Fig. 2). The interaction of hard surfaces and urban-rural was significant for two of these variables. For wildlife food score, mean values were lower in urban hedges with one hard surface compared to none, while in rural hedges there was little difference between these categories. However, for the animal diversity score, rural hedges with one hard surface had a lower mean than those with no hard surface, while in urban areas there was little difference between these two groups (Fig. 2).
Table 5
F statistics and p values from the ANOVAs to examine for urban-rural differences, the effects of adjacent hard surface, and their interaction on three scores and two measures of wildlife richness
Hedge structure score
Wildlife food score
Animal diversity score
Number of invertebrate groups
Number of woody species
df1
F
P
F
P
F
P
F
P
F
P
Urban/Rural (UR)
1
21.33
<0.001
14.96
<0.001
0.47
0.491
0.97
0.324
0.25
0.618
Hard surfaces (H)
2
16.04
<0.001
8.57
<0.001
19.47
<0.001
10.06
<0.001
8.04
<0.001
UR*H
2
1.31
0.269
1.85
0.158
7.19
0.001
0.76
0.469
2.26
0.104
Numerator degrees of freedom as shown (df1), denominator d.f. ranged from 2691 to 2885
Fig. 2
Mean ± SE scores displayed for hedge structure, wildlife food and animal diversity; and numbers of invertebrate groups and woody species for urban and rural hedges. White bars show data for hedges with no surrounding hard surfaces, grey bars for hedges with a hard surface on one side and black bars for hedges with a hard surface on both sides
Discussion
The results of this study have indicated that there are differences between urban and rural hedges and that adjacent hard surfaces may have an impact on hedge biodiversity.
The differences in woody species in urban and rural hedges (Table 3) are likely to reflect varying management practices. In urban areas, the likely preference for non-spiny shrubs in public areas such as parks and especially school grounds may determine the species commonly found. Not least, planted hedges found in urban areas are likely to contain shrubs that have dense foliage for privacy [3] and are easy to manage.
Bramble was less common in urban hedges; it tends to be more difficult to control and its sharp prickles are unpopular. Although only focusing on hedges in gardens in urban areas, Smith et al. showed that Privet was a dominant species [56]; in our study it was also recorded more often in urban hedges by survey participants. The higher wildlife food score found in rural hedges was clearly related to the plant species more commonly reported in rural areas, with four of the five species significantly more common in rural hedges scoring the highest possible value for wildlife food. Rural hedges also had a significantly higher structure score. The role that hedges perform—both now and historically—affects their structure [28]. Although the structure score was derived from a number of factors (Table 2), it could be assumed that rural hedges are longer, perhaps as field boundaries, and are more likely than urban hedges to be untrimmed, both of which generate higher scores.
The average number of woody species for urban hedges was 3.16. In contrast, Smith et al. found that 82 % of urban garden hedges contained only one plant species [56], although that figure covers hedges of varying lengths and some may have been shorter than 3 m.
The urban and rural differences in hedge plant composition highlighted by the survey have ecological implications, particularly for urban areas. The lower score for wildlife food in urban areas suggests that urban hedges provide fewer resources (flowers, seeds, fruits) for animals than their rural counterparts. A more heterogeneous hedge planting regime by residents and authorities may encourage more animals to make use of hedge habitats for food and shelter.
The difference between the presence of urban and rural invertebrates is more difficult to explain, partly because, despite the plethora of research on urbanisation and varying invertebrate assemblages (e.g. [57, 58]), the overall results are inconclusive. Urbanisation appears to have a positive or negative effect on invertebrates depending on the species. The OPAL Biodiversity Survey looked at invertebrates in broader taxonomic groups and therefore the results from this study are unlikely to provide insights into individual species preference for an urban or rural environment. In a review of research on the effect of urbanisation on flora and fauna, 29.8 % of studies that looked at the effects on invertebrates demonstrated an increase in species richness with increasing urbanisation, with 63.8 % showing a decrease and the remainder showing no change [59]. More investigation is needed and perhaps an alteration to the Biodiversity Survey methodology that would identify key indicator species before these results can provide any interpretable information regarding invertebrate preferences for urban or rural environments.
It is noted that when asking non-experts to identify invertebrates, a likely bias will occur towards those that are visually distinctive, as evidenced by Ward [60] for Hymenoptera in a New Zealand-based citizen science project. Spiders were the most frequently recorded invertebrate and this may be due to the relative ease of identifying them since they are distinctive from the remaining groups in the survey and more people are familiar with them. Other groups may also be more camouflaged than spiders, so participants may miss their presence or the invertebrates are able to flee the surveyor quickly before identification and recording can occur. It is also noted that seasonal differences and daily weather conditions are likely to have affected species presence and abundance.
The weak but highly significant positive correlation between increasing numbers of woody species and an increase in invertebrate diversity is supported by a large volume of existing research (see [24], and references supplied therein for a summary).
Results from the OPAL Biodiversity Survey suggest that the presence of hard surfaces on both sides of the hedge can have a significant impact on the biodiversity it supports. Furthermore, results have shown that even just one side of the hedge being a hard surface can have some impact. This is an important result as it suggests that many of the hedges that we see alongside roads and in much of the urban landscape may not have as much wildlife value as the presence of the hedge itself alone would imply.
Existing research identifies the environmental impacts of hard surfaces, often focusing on the general loss of green space in urban areas (e.g. [61]), but few specifically discuss the impact of hard surfaces on hedge biodiversity. However, Faiers and Bailey [33] noted, in their study on canalside hedges, that surrounding amenity value (the potential of the site to accommodate visitors e.g. footpaths, car parks) were negatively correlated with the biodiversity and structure value of the hedge. Although it is not possible to ascertain the number of adjacent hard surfaces to the study hedges, the investigation by Faiers and Bailey does support the finding that a hard surface—whatever its use—may have a negative impact on hedges. Smith et al. [62], in their study of urban garden habitats, also found that the presence of hard surfaces was negatively correlated with the abundance of some invertebrates.
Other studies have shown that surrounding habitat types in general impact upon the invertebrate diversity within hedges. Dover and Sparks [16] demonstrated that butterflies were more abundant in hedges adjacent to woodland and areas where floral density was high. Croxton et al. [63] found that the inside of green lanes (tracks with hedges on both sides) had higher bumblebee abundance and richness, suggesting that “two hedges are better than one”. In addition, that study also demonstrated that plant assemblages differed, with the inside of tracks a better resource for wildlife. Although these studies did not specifically concern hard surfaces adjacent to the hedge, they demonstrated that habitat types surrounding hedges can have a significant impact on the diversity found within.
The topic of the impact of adjacent hard surfaces on hedges is one that may need further research, particularly for hedges in urban areas.
There are a number of factors that can affect the quality of data resulting from a large citizen science survey such as the OPAL Biodiversity Survey. While it is beyond the scope of the present paper to discuss these factors in detail they should nevertheless be acknowledged. The majority of surveys are carried out by untrained individuals in their own time and in their local area, therefore it is impossible for the results of the survey to be verified by experts. Bonney [64] states that ensuring participants have clear instructions, guidance and data forms are important for accurate data submission. Rigorous testing of the survey was carried out and shaped the final draft while provision of face-to-face training also helped to improve the quality of data submitted. These aspects do not guarantee data accuracy; however they are key elements to the OPAL Biodiversity Survey. Other studies involving OPAL surveys have been undertaken to test the validity of results from citizen scientists. Rose et al. [65] discussed these at length and described the verification tests used for data submitted for the OPAL Water Survey. They noted that when testing variability in sampled water invertebrate results from different experienced surveyors, there was a reasonably high level of variability, although this reduced when results were amalgamated for the whole pond. Furthermore, when comparing results from untrained participants with those from experts, they found that they matched reasonably well. A comparison between OPAL Soil and Earthworm Survey results and those obtained from national databases showed that there was a reasonable match [66]. Similarly, a study to assess the usefulness of results from the OPAL Air Survey demonstrated that the methodology employed by the survey could indicate presence of nitrogenous air pollution but not at low concentrations [67].
Although covering different environmental topics, these studies suggest that while the survey methods employed by OPAL may not be suitable for measuring small-scale phenomena, when applied on a broad scale, they are of value. Furthermore, when coupled with the educative aims of the surveys, they offer considerable value.
Conclusions
This study has shown that urban and rural hedges are different in floral and faunal composition and that adjacent hard surfaces may have an impact on hedge biodiversity. The constraints of the survey methodology and associated data do not allow for detailed investigation, however, the findings have implications on how urban hedges in particular are managed, with suggestion that the surfaces immediately adjacent to the hedge need consideration if the wildlife value of an urban hedge is to be optimised. Overall, the study has highlighted the need for more research to be undertaken on the under-recorded topic of urban hedges and the effects that adjacent hard surfaces may have on their biodiversity. In addition, the OPAL Biodiversity Survey, as with other OPAL surveys, has shown that the public have enthusiasm for completing simple ecological surveys. Despite the limitations regarding data verification, the survey provides a basis for further research using citizen science methodology.
Utilising the manpower of the general public enables scientists some additional capacity to study hedge habitats. Furthermore, educating the public about hedges and the plants and animals that use them can help to protect their future. Encouraging people to develop a passion for the natural world and recording, monitoring and protecting it is perhaps one of the best future-proofing techniques against further habitat loss that scientists can provide.
Declarations
Authors’ contributions
LG and TS drafted the manuscript. TS conducted statistical testing. MH and JA provided additional information on the survey methodology, in particular on the survey scoring system. YA provided background information to hedge research. All authors read and approved the final manuscript.
Acknowledgements
We are grateful to the Big Lottery Fund for funding the OPAL project, and all of the people involved in developing the survey from the following organisations: The Open University (Graham Banwell, Jonathan Silvertown and Jenny Worthington), Imperial College London (Roger Fradera and Linda Davies), Field Studies Council (Simon Norman), Natural History Museum (Gill Stevens), HedgeLink (Rob Wolton) and Peoples Trust for Endangered Species (Jim Jones). We would also like to thank Poppy Lakeman Fraser, David Slawson and Kate Martin for their assistance in the preparation of the manuscript. We thank all of the OPAL Community Scientists and biodiversity mentors who championed the survey and encouraged participants from across England to take part. Finally, we are most grateful to the participants of the OPAL Biodiversity Survey.
Competing interests
The authors declare that they have no competing interests.
Declarations
This article has been published as part of BMC Ecology Volume 16 Supplement 1, 2016: Citizen science through the OPAL lens. The full contents of the supplement are available online at http://bmcecol.biomedcentral.com/articles/supplements/volume-16-supplement-1. Publication of this supplement was supported by Defra.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Authors’ Affiliations
(1)
Imperial College London
(2)
Coventry University
(3)
The Open University
(4)
Birkbeck, University of London
References
Defra. Hedgerow Survey Handbook: A Standard Procedure for Local Surveys in the UK. 2007.Google Scholar
Baudry J, Bunce RG, Burel F. Hedgerows: an international perspective on their origin, function and management. J Environ Manage. 2000;60:7–22.View ArticleGoogle Scholar
Oreszczyn S, Lane A: Hedgerows of different cultures: implications from a Canadian and English cross-cultural study. 2001.Google Scholar
Rackham O. The History of the Countryside. London: J.M. Dent and Sons Ltd.; 1984.Google Scholar
Carey PD, Wallis S, Chamberlain PM, Cooper A, Emmett BA, Maskell LC, McCann T, Murphy J, Norton LR, Reynolds B, Scott WA, Simpson IC, Smart SM, Ullyett JM. Boundary and linear features. In: Carey PD, Wallis S, Chamberlain PM, Cooper A, Emmett BA, Maskell LC, McCann T, Murphy J, Norton LR, Reynolds B, Scott WA, Simpson IC, Smart SM, Ullyett JM, editors. Countrys Surv UK Results from 2007. Centre for Ecology and Hydrology. 2008.Google Scholar
Pollard, E, Hooper, MD, Moore N. Hedges. Glasgow: William Collins Sons and Co Ltd;1974.Google Scholar
Westmacott R, Worthington T. Agricultural landscapes: 33 years of change. Countrys Agency;2006.Google Scholar
Barr CJ, Gillespie MK. Estimating hedgerow length and pattern characteristics in Great Britain using Countryside Survey data. J Environ Manage. 2000;60:23–32.View ArticleGoogle Scholar
Barr, CJ, Bunce RGH, Clarke RT, Fuller RM, Furse MT, Gillespie MK, Groom GB, Hallam CJ, Hornung M, Howard DC, Ness MJ: Countryside Survey 1990. Main Rep. 1993.Google Scholar
Haines-Young RH, Barr CJ, Black HIJ, Briggs DJ, Bunce RGH, Clarke RT, Cooper A, Dawson FH, Firbank LG, Fuller RM, Furse MT, Gillespie MK, Hill R, Hornung M, Howard DC, McCann T, Morecroft MD, Petit S, Sier ARJ, Smart SM, Smith GM, Stott AP, Stuart RC, Watkins JW. Accounting for Nature: Assessing Habitats in the UK Countryside. 2000.Google Scholar
Cherrill A. Landscapes, land covers and linear features in a river catchment in Northern England. Landsc Res. 1996;21:109–22.View ArticleGoogle Scholar
Van Renterghem T, Attenborough K, Maennel M, Defrance J, Horoshenkov K, Kang J, Bashir I, Taherzadeh S, Altreuther B, Khan A, Smyrnova Y, Yang H-S. Measured light vehicle noise reduction by hedges. Appl Acoust. 2014;78:19–27.View ArticleGoogle Scholar
Currie BA, Bass B. Estimates of air pollution mitigation with green plants and green roofs using the UFORE model. Urban Ecosyst. 2008;11:409–22.View ArticleGoogle Scholar
Dover J, Sparks T. A review of the ecology of butterflies in British hedgerows. J Environ Manage. 2000;60:51–63.View ArticleGoogle Scholar
Whittingham M, Krebs J, Swetnam R, Thewlis R, Wilson J, Freckleton R. Habitat associations of British breeding farmland birds. Bird Study. 2009;56:43–52.View ArticleGoogle Scholar
Jacobs JH, Clark SJ, Denholm I, Goulson D, Stoate C, Osborne JL. Pollination biology of fruit-bearing hedgerow plants and the role of flower-visiting insects in fruit-set. Ann Bot. 2009;104:1397–404.View ArticlePubMedPubMed CentralGoogle Scholar
Wolton R, Morris R, Pollard K, Dover J. Understanding the combined biodiversity benefits of the component features of hedges. 2013.Google Scholar
Boughey KL, Lake IR, Haysom KA, Dolman PM. Improving the biodiversity benefits of hedgerows: how physical characteristics and the proximity of foraging habitat affect the use of linear features by bats. Biol Conserv. 2011;144:1790–8.View ArticleGoogle Scholar
Merckx T, Marini L, Feber RE, Macdonald DW. Hedgerow trees and extended-width field margins enhance macro-moth diversity: implications for management. J Appl Ecol. 2012;49:1396–404.View ArticleGoogle Scholar
Gelling M, Macdonald DW, Mathews F. Are hedgerows the route to increased farmland small mammal density? Use of hedgerows in British pastoral habitats. Landsc Ecol. 2007;22:1019–32.View ArticleGoogle Scholar
Feehan J, Gillmor DA, Culleton N. Effects of an agri-environment scheme on farmland biodiversity in Ireland. Agric Ecosyst Environ. 2005;107:275–86.View ArticleGoogle Scholar
Maudsley MJ. A review of the ecology and conservation of hedgerow invertebrates in Britain. J Environ Manage. 2000;60:65–76.View ArticleGoogle Scholar
Dawson D. English nature research reports: are habitat corridors conduits for animals and plants in a fragmented landscape?. A review of the scientific evidence. 1994.Google Scholar
Smart S, Bunce R, Stuart R. An assessment of the potential of British hedges to act as corridors and refuges for Ancient Woodland indicator plants. In: Barr C, Petit S. Hedgerows World their Ecol Funct Differ landscapes. IALE (UK). 2001:137–146.Google Scholar
Davies ZG, Pullin AS. Are hedgerows effective corridors between fragments of woodland habitat? An evidence-based approach. Landsc Ecol. 2007;22:333–51.View ArticleGoogle Scholar
Baudry J, Bunce, RGH. An overview of the landscape ecology of hedgerows. In: Barr C, Petit S. Hedgerows World their Ecol Funct Differ landscapes Proc 2001 Annu IALE Conf. IALE (UK). 2001:3–15.Google Scholar
Wratten SD, Gillespie M, Decourtye A, Mader E, Desneux N. Pollinator habitat enhancement: benefits to other ecosystem services. Agric Ecosyst Environ. 2012;159:112–22.View ArticleGoogle Scholar
Staley JT, Bullock JM, Baldock KCR, Redhead JW, Hooftman DAP, Button N, Pywell RF. Changes in hedgerow floral diversity over 70 years in an English rural landscape, and the impacts of management. Biol Conserv. 2013;167:97–105.View ArticleGoogle Scholar
Facey SL, Botham MS, Heard MS, Pywell RF, Staley JT. Moth communities and agri-environment schemes: Examining the effects of hedgerow cutting regime on diversity, abundance, and parasitism. Insect Conserv Divers. 2014.Google Scholar
Wolton RJ. Hazel dormouse Muscardinus avellanarius (L.) nest site selection in hedgerows. Mammalia. 2009;73:7–12.View ArticleGoogle Scholar
Faiers A, Bailey A. Evaluating canalside hedgerows to determine future interventions. J Environ Manage. 2005;74:71–8.View ArticlePubMedGoogle Scholar
Smith RM, Warren PH, Thompson K, Gaston KJ. Urban domestic gardens (VI): environmental correlates of invertebrate species richness. Biodivers Conserv. 2005;15:2415–38.View ArticleGoogle Scholar
Goddard MA, Dougill AJ, Benton TG. Scaling up from gardens: biodiversity conservation in urban environments. Trends Ecol Evol. 2010;25:90–8.View ArticlePubMedGoogle Scholar
Shirk JL, Ballard HL, Wilderman CC, Phillips T, Wiggins A, Jordan R. Public participation in scientific research : a framework for deliberate design. 2012;17.Google Scholar
Roy, HE., Pocock, MJO., Preston, CD., Roy, DB., Savage, J., Tweddle, JC., Robinson L: Understanding Citizen Science and Environmental Monitoring. Final Report on Behalf of UK-EOF. NERC Centre for Ecology and Hydrology and Natural History Museum. 2012.Google Scholar
Dickinson JL, Zuckerberg B, Bonter DN. Citizen science as an ecological research tool: challenges and benefits. Annu Rev Ecol Evol Syst. 2010;41:149–72.View ArticleGoogle Scholar
Crall AW, Newman GJ, Stohlgren TJ, Holfelder KA, Graham J, Waller DM. Assessing citizen science data quality: an invasive species case study. Conserv Lett. 2011;4:433–42.View ArticleGoogle Scholar
Davies L, Bell JNB, Bone J, Head M, Hill L, Howard C, Hobbs SJ, Jones DT, Power SA, Rose N, Ryder C, Seed L, Stevens G, Toumi R, Voulvoulis N, White PCL. Open Air Laboratories (OPAL): a community-driven research programme. Environ Pollut. 2011;159:2203–10.View ArticlePubMedGoogle Scholar
Davies L, Gosling L, Bachariou C, Eastwood J, Fradera R, Manomaiudom N, Robins S. OPAL Community Environ Rep. 2013.Google Scholar
Ansine J. Reaching the public through iSpot: your place to share nature, Case Study 8.5. In: Bowater L, Yeoman K. Sci Commun a Pract Guid Sci. Oxford: Wiley Blackwell; 2013.Google Scholar
Ellenberg H, Weber HE, Düll R, Wirth V, Werner W. Paulissen D: zeigerwerte von Pflanzen in Mitteleuropa. Scr Geobot. 1991;18:1–248.Google Scholar
Robertson HJ, Jefferson RG. Monitoring the Condition of Lowland Grassland SSSIs. Part1-English nature’s rapid assessment method. Eng Nat Res Rep No. 315. Peterborough. 2000.Google Scholar
French DD, Cummins RP. Classification, composition, richness and diversity of British hedgerows. Appl Veg Sci. 2001;4:213–28.View ArticleGoogle Scholar
Critchley CNR, Wilson LA, Mole AC, Norton LR, Smart SM. A functional classification of herbaceous hedgerow vegetation for setting restoration objectives. Biodivers Conserv. 2013;22:701–17.View ArticleGoogle Scholar
Hedgelink. The hedgerow management cycle. 2014.Google Scholar
Grieves C, Lloyd D. Conservation of roadsides and roadside vegetation—technical report No. 11. Polish J Ecol. 1984.Google Scholar
Akbar KF, Hales WHG, Headley AD, Ashraf I. Evaluation of conservation status of roadside verges and their vegetation in north England. Polish J Ecol. 2010;58.Google Scholar
IBM Corp. SPSS statistics for windows: version 22.0. 2013.Google Scholar
Smith RM, Gaston KJ, Warren PH, Thompson K. Urban domestic gardens (V): relationships between landcover composition, housing and landscape. Landsc Ecol. 2005;20:235–53.View ArticleGoogle Scholar
Angold PG, Sadler JP, Hill MO, Pullin A, Rushton S, Austin K, Small E, Wood B, Wadsworth R, Sanderson R, Thompson K. Biodiversity in urban habitat patches. Sci Total Environ. 2006;360:196–204.View ArticlePubMedGoogle Scholar
Bates AJ, Sadler JP, Fairbrass AJ, Falk SJ, Hale JD, Matthews TJ. Changing bee and hoverfly pollinator assemblages along an urban-rural gradient. PLoS One. 2011;6:e23459.View ArticlePubMedPubMed CentralGoogle Scholar
McKinney ML. Effects of urbanization on species richness: a review of plants and animals. Urban Ecosyst. 2008;11:161–76.View ArticleGoogle Scholar
Ward DF. Understanding sampling and taxonomic biases recorded by citizen scientists. J Insect Conserv. 2014;18:753–6.View ArticleGoogle Scholar
Pauleit S, Ennos R, Golding Y. Modeling the environmental impacts of urban land use and land cover change—a study in Merseyside, UK. Landsc Urban Plan. 2005;71:295–310.View ArticleGoogle Scholar
Smith RM, Gaston KJ, Warren PH, Thompson K. Urban domestic gardens (VIII): environmental correlates of invertebrate abundance. Biodivers Conserv. 2006;15:2515–45.View ArticleGoogle Scholar
Croxton PJ, Carvell C, Mountford JO, Sparks TH. A comparison of green lanes and field margins as bumblebee habitat in an arable landscape. Biol Conserv. 2002;107:365–74.View ArticleGoogle Scholar
Bonney R, Cooper CB, Dickinson J, Kelling S, Phillips T, Rosenberg KV, Shirk J. Citizen science: a developing tool for expanding science knowledge and scientific literacy. Bioscience. 2009;59:977–84.View ArticleGoogle Scholar
Rose N, Turner S, Goldsmith B, Gosling L, Davidson T. Paper 3, this supplement. 2015.Google Scholar
Bone J, Archer M, Barraclough D, Eggleton P, Flight D, Head M, Jones DT, Scheib C, Voulvoulis N. Public participation in soil surveys: lessons from a pilot study in England. Environ Sci Technol. 2012;46:3687–96.View ArticlePubMedGoogle Scholar
Tregidgo DJ, West SE, Ashmore MR. Can citizen science produce good science? Testing the OPAL air survey methodology, using lichens as indicators of nitrogenous pollution. Environ Pollut. 2013;182:448–51.View ArticlePubMedGoogle Scholar
