Marshall Agroecology Limited
Overwintering macro-invertebrates in the bases of six East Mendip hedgerows
E J P Marshall
Marshall Agroecology Ltd
2 Nut Tree Cottages, Barton, Winscombe, Somerset BS25 1DU
Tel/Fax: 01934 844844; jon.marshall@agroecol.co.uk
URL: http://www.agroecol.co.uk
March 2005
Executive summary 1
1. Introduction 2
2. Methods 2
3. Results 6
4. Discussion 11
5. Conclusions 12
6. References 13
Appendix 1 14
Appendix 2 27
Executive Summary
Six hedgerows in the East Mendip area, representing mature or untrimmed hedges with a woody species component that was either species-rich, species-poor or gappy, were selected for sampling. The aim of the study was to characterise the diversity of overwintering fauna in the hedgerow bases. These hedges represent the main hedgerow types identified by extensive surveys as part of the East Mendip Hedge Project. Each hedge was divided into three lengths and the macroinvertebrate fauna sampled at three locations in each length. Samples were bulked for sorting and identification. A Vortis vacuum sampler was first used to catch surface invertebrates in a 10cm diameter area, which was then soil cored to a depth of approximately 10cm. Samples were stored and then sorted. Vortis samples were sorted under a binocular microscope, while soil samples were washed through brass sieves and material retained by 420µm mesh was sorted by eye. Animals were identified to major groups under a binocular microscope and the data analysed using formal Analysis of Variance and Principal Component Analysis.
The results show that all the hedges supported significant numbers of invertebrates in the winter. Hedgerows are therefore significant winter habitats. Analyses demonstrated significant adverse effects of trimming on the abundances of a number of faunal groups, notably adult beetles and beetle and fly larvae. Diversity of invertebrates was greatest, on average, in hedges rich in woody species and lowest in gappy hedges. Faunal communities were very similar in all trimmed hedges and in the gappy, untrimmed hedge. Structure and management of these hedges may combine to create similar invertebrate communities. Nevertheless, the impacts of local management on the herbaceous component of hedges should not be overlooked, as invertebrate diversity is reported as being closely linked to herbaceous flora diversity. As part of a strategy for developing farm wildlife conservation, gappy hedges should be avoided and mature, stock-proof hedges that are rich in woody species should be encouraged.
1. Introduction
Field margins provide a key non-crop habitat in much of the agricultural land of north-western Europe (Burel, 1996; Marshall & Moonen, 2002). Hedges are the commonest boundary feature in lowland England and are an important part of the landscape of the Mendip Hills area. The East Mendip Hedgerow Project has surveyed over 2000 hedgerows for structure, management, woody species richness and associated historic and environmental features (Colborne & Lemon, 2004). A classification of the hedges identified those in favourable condition, those declining and some in a very poor state. A subsequent detailed survey of the herbaceous flora of 100 hedges has been conducted. This current report details an assessment of the macro-invertebrates in six representative hedgerows.
Aim:
To compare the fauna over-wintering in the litter and soil of six different hedges that represent the range of hedge types present in East Mendip
2. Methods
Sites
Six hedges identified as representative of the East Mendip hedgerow project area were selected. The hedges had a range of structures, woody species richness and management stages (Table 1).
Table 1. Descriptions of the six sampled hedgerows
|
Hedge number |
NGR |
Species richness |
Management |
|
7 |
652454 |
Gappy |
Mature |
|
28 |
630487 |
Poor |
Mature |
|
46 |
665477 |
Rich |
Mature |
|
76 |
698480 |
Gappy |
Trimmed |
|
53 |
678463 |
Poor |
Trimmed |
|
54 |
671484 |
Rich |
Trimmed |
The six sites are illustrated in Fig. 1. The impact of trimming on hedge size is obvious. Sites 7 and 76 clearly have a number of gaps along the hedgerow, whereas the other hedges have a contiguous shrub component. The herbaceous ground flora is variable between the hedges, with site 76 having the lowest ground cover.
The hedges were assessed according to the approved Hedgerow Survey Handbook – a standard procedure for local surveys in the UK (available at: http://www.english-nature.org.uk/pubs/publication/pub_results.asp?C=0&K=Hedge&K2=&I=&A=&Submit1=Search). This English Nature publication is associated with the BAP for species-rich and/or ancient hedgerows and outlines the assessment protocols for adjacent land use and structure of hedges. A summary of the resulting hedge structures for the sampled hedges is given in Table 2 and the detailed data, including site sketches are given in Appendix 1.
Site 7: Mature, gappy Site 76: Trimmed, gappy
Site 28: Mature, species-poor Site 53: Trimmed, species-poor
Site 46: Mature, species-rich Site 54: Trimmed, species-rich
Fig.1. Views of each of the six study hedges.
Table 2. Structural and land use attributes of the six hedges studied in detail.
Note: Site 54 was defined as two hedges according to the Hedgerow Survey Handbook (see Appendix 1 for details and sketches)
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East Mendip Hedge Project: Detailed study hedge structure
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A = sampled side: B = other side of hedge |
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Hedge Number |
7 |
76 |
28 |
53 |
46 |
54 - A |
54 - B |
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Hedgerow tree number |
1-5 |
0 |
1-5 |
0 |
1-5 |
1 |
0 |
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Bank height |
1.1-1.5 |
<0.5 |
0.5-1.0 |
0.5-1.0 |
0.5-1.0 |
<0.5 |
<0.5 |
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Bank management |
Grazed |
0 |
Fenced off |
Cut |
Fenced off |
0 |
Grazed |
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Ditch |
0 |
0 |
0 |
0 |
0 |
0 |
B: 0.5-1.0 |
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Verge width |
<1 |
<1 |
<1 |
<1 |
1-2 |
<1 |
<1 |
|
Verge management (A) |
Grazed |
Uncut |
Cut |
Cut |
Cut |
Uncut |
Grazed |
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Fence (side) |
None |
Wire B |
Wire A & B |
Wire A |
Wire A & B |
Wire A |
Wire A |
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Hedge height |
>4.1 |
1 |
>4.1 |
1.1-2.0 |
>4.1 |
1.1-2.0 |
1.1-2.0 |
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Hedge width at base |
1.1-2.0 |
1.1-2.0 |
2.1-4.0 |
1.1-2.0 |
1.1-2.0 |
1.1-2.0 |
1.1-2.0 |
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Hedge integrity |
Sign. Gaps |
Minor gaps |
Sign. Leggy |
Stockproof |
Mostly stockproof |
Stockproof |
Stockproof |
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Recent management |
Sides trimmed |
Flailed |
Sides trimmed |
Flailed |
Trimmed |
Flailed |
Flailed |
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Older management |
Laid in places |
Coppice |
Coppice |
Laid in places |
Coppice and laid |
Coppice |
Coppice |
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Adjacent land use A |
Semi-improved grass |
Cereal |
Maize |
Improved grass |
OSR |
Semi-improved grass |
Semi-improved grass |
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Adjacent land use B |
Semi-improved grass |
Cereal |
Semi-improved grass |
Improved grass |
Cereal |
Metalled road |
Metalled road |
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Other features |
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A: 6m grass margin |
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Sampling
Each hedge was divided into three equal lengths and samples of litter and soil from each length was bulked to give three samples per site. Samples were taken in the hedge base (Fig.2). Sampling included two methods: 1) a surface vacuum sample using a Vortis suction sampler (Burkard Engineering) and 2) soil cores in the same location. Soils cores were 100mm wide and taken to a similar depth. The Vortis aperture was also 100mm, though the suction effect may have included fauna from a slightly wider area than the nominal 78.5 cm2. Thus each site generated six samples for processing. Vortis samples were frozen and soil core samples kept in an unheated store, before processing.
Fig. 2. Vortis suction samples and soil cores were taken at the edge of the hedge.
Sample processing
Vortis samples were defrosted and then sorted under a binocular microscope. All fauna were preserved in 70% alcohol. Soil samples were washed through brass sieves and material retained by a 420μm mesh was sorted by eye. Preserved material was then examined under a binocular microscope and all animals were identified to major groups.
Analysis
Data from the samples were either examined on a sample-by-sample basis, or totalled for the six hedgerows. A comparison of the number of faunal groups, total numbers of individuals recorded, Shannon diversity index and evenness score from the six sites was made using Analysis of Variance. One test between sites was made using the samples to give a measure of variation. A second analysis was structured to test for the effects of management (mature v. trimmed) and species richness (rich v. poor v. gappy), using sites as replicates. In addition, the data were subjected to a principal component analysis, in order to give an ordination of the faunal communities. A linear analysis was appropriate to examine the similarity or otherwise of the fauna from the 18 samples.
3. Results
The data from the Vortis samples were combined with the soil samples for comparisons between the sites. The full data set is presented in Appendix 1, with information for each of the three samples per site for the 31 groups identified. Total numbers of animals found per site and the number of groups represented are given in Table 2.
Table 2. The overall total numbers of individuals
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Hedge |
7 |
28 |
46 |
76 |
53 |
54 |
|
Hedge type |
M G |
M P |
M R |
T G |
T P |
T R |
|
Number of individuals |
729 |
758 |
676 |
493 |
597 |
374 |
|
No. groups |
28 |
29 |
23 |
24 |
25 |
28 |
Hedge types: M = mature; T = trimmed; G = gappy; P = species poor; R = species rich
Diversity
Average numbers of animals, groups and diversity scores per sample for each hedge are shown in Table 3. Significantly more animals per sample were recorded from mature hedges, compared with trimmed hedges (240 v. 167; P=0.001), but there was no overall significant effect of woody species richness on total abundances.
Table 3. A summary of the average numbers and diversity of the macroinvertebrate fauna of the hedgerows, derived from the three samples per site. Numbers with the same superscript letter are statistically similar. lsd = least significant difference at P=0.05 (means that differ by more than the lsd are statistically different)
|
Hedge |
7 |
28 |
46 |
76 |
53 |
54 |
lsd |
|
Hedge type |
M G |
M P |
M R |
T G |
T P |
T R |
|
|
Average numbers of individuals per sample |
243.0c |
252.7c |
225.3bc |
164.3ab |
199.0bc |
124.7a |
69.75 |
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Mean No. groups per sample |
23.3b |
24.0b |
20.0ab |
17.7a |
23.7b |
22.0ab |
4.17 |
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Shannon diversity |
2.67 a |
2.79 b |
2.84 bc |
2.87 c |
2.86 c |
2.86 c
|
0.0756
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Evenness |
0.488 a |
0.508 ab |
0.525 bc |
0.565d |
0.540cd |
0.593e |
0.0268 |
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Fisher’s alpha |
6.02 e |
5.54 d |
5.26 c |
4.71 a |
5.02 b |
4.86 ab |
0.1835 |
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Simpson’s index |
11.51 a |
12.89 b |
13.53 bc |
13.90 c |
13.69 c |
13.78 c |
0.786 |
Hedge types: M = mature; T = trimmed; G = gappy; P = species poor; R = species rich
There was no influence of trimming on numbers of taxa found, though there was a trend for species poor hedges (28 and 53) having the most groups present.
Surprisingly, the Shannon diversity index was higher on average in trimmed compared with mature hedges, but, as expected, species-rich hedges had the highest average diversity (2.85:2.82:2.77 in rich:poor:gappy hedges respectively). There was an interaction between management and species richness, because the gappy hedges had markedly different diversity indices. The mature gappy hedge had the lowest index of all six hedges, while the trimmed gappy hedge had the highest index. Evenness, a measure of the spread of species abundance or lack of dominance, was also higher in trimmed hedges and in species-rich hedges (0.559:0.524:0.526 in rich:poor:gappy hedges respectively). Other measures of diversity, Fisher’s Alpha index and the Simpson Index, showed different patterns. Fisher’s alpha showed effects of management, species richness and an interaction between these factors. The index was higher on mature hedges on average and highest in gappy hedges. However, the score was highest overall in the mature gappy hedge, but lowest in the trimmed gappy hedge. Simpson’s inverse index showed the opposite.
Faunal groups
Analyses of the 31 faunal groups individually showed a small number of significant effects of treatments. The totals for adult beetles, spiders, mites and all fly larvae was also analysed There were significant effects of trimming on nematodes, ticks, bugs, ground beetles, beetle larvae and fly larvae (Table 4).
Table 4. Faunal groups that were significantly affected by hedge trimming.
|
Faunal group |
Mean number of individuals |
|
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Mature hedges |
Trimmed hedges |
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Nematodes |
6.00 |
1.11 |
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Ticks |
25.40 |
9.40 |
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Bugs |
0.33 |
4.00 |
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Ground beetles |
13.00 |
6.20 |
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Beetle larvae |
6.44 |
2.56 |
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Fly larvae – type 1 |
9.20 |
1.40 |
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All fly larvae |
21.10 |
5.10 |
Generally, groups were negatively affected by trimming, though nematode numbers were apparently enhanced in trimmed hedges. Beetle and fly larvae were particularly reduced by trimming.
Woody species richness had effects on ticks, rove beetles and plant beetles (Table 5). Rove beetles were more numerous in gappy hedges (but see on for interaction effects), while plant beetles and ticks were favoured in species-poor hedges.
Table 5. Faunal groups that were significantly affected by woody species content of the hedges. Numbers with the same superscript letter are statistically similar. lsd = least significant difference at P=0.05 (means that differ by more than the lsd are statistically different)
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Faunal group |
Mean number of individuals |
lsd |
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Species- rich |
Species-poor |
Gappy |
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Ticks |
11.7a |
29.3b |
11.3 a |
15.50 |
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Rove beetles |
10.7 a |
11.8 a |
23.2 b |
8.27 |
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Plant beetles |
0.3 a |
2.3 b |
0.3 a |
1.779 |
There was evidence for statistical interactions between trimming and woody species richness for woodlice, rove beetles and all adult beetles (Table 6).
Table 6. Faunal groups that showed an interaction between trimming and woody species richness. Numbers with the same superscript letter are statistically similar. lsd = least significant difference at P=0.05 (means that differ by more than the lsd are statistically different)
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Hedge |
46 |
28 |
7 |
54 |
53 |
76 |
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Hedge type |
M R |
M P |
M G |
T R |
T P |
T G |
lsd |
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Woodlice 1 |
|
30.0ab |
25.0a |
53.3 b |
18.7 a |
31.3ab |
14.7 a |