plant and invertebrate diversity in grassland field margins

Plant and invertebrate diversity in grassland field margins

H. Sheridan a,*, J.A. Finn b, N. Culleton b, G. O’Donovan c

a School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Irelandb Teagasc Environment Research Centre, Johnstown Castle, Co. Wexford, Ireland

c Just Ecology Ltd., Woodend House, Woodend, Wotton under Edge, Gloucestershire, GL12 8AA, United Kingdom

Received 20 September 2006; received in revised form 1 July 2007; accepted 9 July 2007

Available online 7 September 2007

Abstract

This study investigates three treatment methods to establish field margins of high botanical and invertebrate diversity within an intensively

managed grassland system. Field margin treatments were: fenced only, rotavated and allowed to regenerate naturally, reseeded with a grass

and wildflower seed mixture. Control plots were unfenced and grazed. Field margin widths were established at 1.5, 2.5 and 3.5 m. The

botanical composition of the plots was examined on four occasions between 2002 and 2004 using permanent nested quadrats. Emergence

traps were installed in each of the treatments to investigate invertebrate abundance response to treatment. Results showed that (1) reseeding

had a positive effect on resultant botanical diversity when compared with other establishment treatments investigated, (2) natural regeneration

after rotavation could not be recommended as an effective means of restoring diversity under these environmental conditions, due to the

abundance of undesirable weed species, (3) exclusion of fertiliser inputs alone resulted in a very slow change in the botanical composition, (4)

width of plot did not have a significant influence on plant species richness and (5) treatment and time of sampling had highly significant

impacts on overall invertebrate abundance.

# 2007 Elsevier B.V. All rights reserved.

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Agriculture, Ecosystems and Environment 123 (2008) 225–232

Keywords: Field margin; Botanical diversity; Invertebrate; Grassland; Wild flower; Seed mixture

1. Introduction

The benefits for biodiversity gained through the retention

of field margin habitats within arable production systems

have been well documented (see Critchley et al., 2006;

Marshall et al., 2006). However, the increased soil fertility

status associated with pasture improvement may lead to the

exclusion of most indigenous grasses, herbs and wildflowers

which cannot compete with aggressive, sown grasses

(Frame, 2000). The resultant loss of botanical and structural

diversity coupled with intensive sward management

practices such as silage cutting, may also have profoundly

negative effects on arthropod populations (Rushton et al.,

1989; Purvis and Curry, 1981). For example, Foster et al.

(1997) found that the carabid faunal diversity of intensively

managed grassland was similar to that of arable systems.

* Corresponding author. Tel.: +353 1 716 7119.

E-mail address: [email protected] (H. Sheridan).

0167-8809/$ – see front matter # 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.agee.2007.07.001

Despite this, little attention has been afforded to the potential

benefits which may be derived from the establishment and

protection of field margins within grass-based agricultural

systems.

The Rural Environment Protection Scheme (REPS) was

initiated in Ireland in 1994 as the Irish government’s

response to the EU Agri-environmental Regulation (92/

2078/EEC). Details of the scheme are provided in Sheridan

(2005). The REPS includes management prescriptions for

the protection of biodiversity within grassland field margins,

through the exclusion of agricultural inputs from a 1.5 m

wide strip adjacent to hedgerows, watercourses and other

ecological infrastructural features. However, to date,

adoption of this measure appears not to have produced

significant benefits for the flora and Carabidae fauna of field

margins on participating farms when compared with non-

participating farms (Feehan et al., 2005).

This research attempts to address the current lack of

knowledge surrounding the floral and invertebrate faunal

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http://dx.doi.org/10.1016/j.agee.2007.07.001

H. Sheridan et al. / Agriculture, Ecosystems and Environment 123 (2008) 225–232226

Table 1

Percentage germination from herb species included within the seed mixture

Species Germination

%

Species Germination

%

Achillea millefolium 61 Holcus lanatus *

Agrostis capillaries * Phleum pretense *

* *

ecology of field margin habitats within grass-based farming

systems. Three distinct methods of field margin establish-

ment were investigated and their ability to produce a diverse,

persistent flora compared. In addition, the ability of the

various establishment methods to promote and sustain

invertebrate faunal populations was explored.
Agrostis stolonifera Leontodon hispidus
Alliaria petiolata 0 Leucanthemum vulgare 32

Alopecurus pratensis * Lychnis flos-cuculi 0

Angelica sylvestris 0 Lythrum salicaria 31

Anthyllis vulneraria 1 Medicago lupulina 30

Anthoxanthum

odoratum

* Origanum vulgare 1

Arctium minus 38 Pedicularis palustris 0

Arrhenatherum

elatius

* Plantago lanceolata *

Capsella

bursa-pastoris

2 Primula veris 0

Centaurea nigra 4 Prunella vulgaris 0

Cynosurus cristatus * Pulicaria dysenterica 2

Dactylis glomerata * Ranunculus acris 8

Daucus carota 20 Rhinanthus minor 0

Digitalis purpurea 18 Rumex acetosa 6

Dipsacus fullonum 9 Silene vulgaris *

Eupatorium

cannabinum

* Succisa pratensis 0

Festuca rubra * Taraxacum off. agg. 0

Filipendula ulmaria 4 Vicia cracca 60

Galium verum 1

* indicates ‘‘no data available’’.

2. Materials and methods

The experimental site was located on the dairy farm of the

Teagasc Research Centre at Johnstown Castle, Co. Wexford,

Ireland (grid reference T026166). All internal hedgerows

were removed from the site during the 1970s. Paddocks were

separated by electric fences. Swards principally consisted of

a mid-season yielding variety of Lolium perenne. Prior to

this experiment, paddocks were grazed by a Friesian dairy

herd at a stocking rate of 2.5 livestock units/ha�1 on a 21-

day rotation and cut for silage in alternate years.

Approximately 300 kg ha�1 of nitrogen, half of which

was in the form of urea and half as chemical applied nitrogen

(CAN) was applied to swards during 2002 and 2003. Swards

also received 12 and 25 kg ha�1 of phosphorus and 24 and

50 kg ha�1 of potassium in 2002 and 2003, respectively.

Approximately 66 m�3 ha�1 of slurry was applied to swards

during 2002 with no further application made in 2003. The

first cut of silage was taken between the last week of May

and the first week of June in both years, while a second cut

was taken during the third week of August in 2002 only.

A stratified randomised split-plot field margin experiment

was established in spring 2002. Nine 90 m long strips of

grass sward along existing fences were fenced off from the

surrounding paddocks. One of three field margin widths (1.5,

2.5 and 3.5 m) was randomly assigned to each strip.

Three field margin establishment methods, each 30 m in

length, were randomly arranged across each of the 90 m long

strips. The establishment methods were: (1) fenced only; (2)

rotavated and allowed to regenerate naturally; (3) rotavated

and reseeded with a grass and herb seed mixture (hereafter

referred to as ‘fenced’, ‘rotavated’ and ‘reseeded’,

respectively). ‘Rotavated’ and ‘reseeded’ plots were treated

with a glyphosate herbicide at recommended application

rates to remove the existing vegetation prior to rotavation.

Three 90 m long and 1.5, 2.5 or 3.5 m wide unfenced strips

of existing grass sward acted as paired controls. These were

fertilised, grazed and cut for silage in a similar manner to the

remainder of the paddock.

Three replicates of each combination of width and

establishment method were made, resulting in 27 plots.

Grazing animals were excluded from treatment plots

between February 2002 and June 2003. Vegetation was

cut from all plots and clippings removed in September 2002.

To investigate persistence of the newly established flora

under grazing conditions, fencing was removed from half

the length (i.e. 15 m) of each experimental plot in June 2003.

Thus, unfenced portions of the plots became part of the

existing paddock, and were grazed by the dairy herd on an

approximate 21-day rotational basis. Vegetation from the

ungrazed section of each plot was cut and clippings were

removed in September 2003 and 2004. External inputs were

excluded from all but control plots for the duration of the

experiment.

Soil samples were taken from all experimental plots in

February 2002 and September 2004. These were analysed to

determine residual levels of phosphorus (P), potassium (K)

and magnesium (Mg).

The species contained within the seed mixture are listed

in Table 1. Herb seeds contained within the mixture were of

Irish origin, and were sown in equal quantities to a seeding

rate of 1.5 g m�2. Due to an absence of native grass seed

producers, grass seed was imported from the UK. Individual

grass species were sown in equal quantities to a seeding rate

of 1.0 g m�2. Plots were sown with a total seed weight of

2.5 g m�2 in early May 2002. Samples of herb seed were

sent to the Department of Agriculture and Food seed-testing

laboratory to ascertain percentage germination from

individual species contained within the mixture.

2.1. Sampling

Botanical data were collected using permanent, nested

quadrats. Four 3 m � 1 m quadrats were systematically

placed at 3 m intervals along the long axis of each plot 0.5 m

away from the fence. Additional parallel quadrats were also

H. Sheridan et al. / Agriculture, Ecosystems and Environment 123 (2008) 225–232 227

placed in the 2.5 and 3.5 m wide plots, respectively.

Presence/absence data were collected from 3 m � 1 m

quadrats. Abundance values using the Braun–Blanquet

scale were assigned to species rooted within the central 1 m2

of each quadrat. To exclude edge effects between treatments,

4.5 m at the end of each plot were not sampled. Data were

collected on four sampling occasions i.e. July 2002, May and

July 2003 and May 2004. Species were identified using

Farragher (1996).

Emergence traps were used to investigate the effect of field

margin establishment method on the number and type of

invertebrates present within treatment plots. The traps consis-

ted of a metal frame covered with 2 mm gauge nylon netting.

The steel base of each trap was inserted to a depth of appro-

ximately 1 cm into the soil. Four 7 cm metal spikes extended

beyond the base to stabilise the trap. Invertebrates were

collected in a plastic collecting head containing 70% ethanol.

Six emergence traps were randomly located within each

of the field margin establishment treatments i.e. ‘control’,

‘fenced’, ‘rotavated’, and ‘reseeded’. Trap heads were

changed at 28-day intervals on five collection dates during

this period i.e. (1) 30/05/03, (2) 27/06/03, (3) 25/07/03, (4)

22/08/03 and (5) 20/09/03. Because few invertebrate

specimens were observed within the collection heads by

the end of the first collection period, a 12 V hand held

suction sampler was used to suction the ground area

contained within each trap for a period of 90 s. Suction

samples were added to the normal sample to provide a total

catch for each trap. Following suctioning, traps were moved

to another randomly chosen position within the treatment

plots and a collecting head attached.

Invertebrate samples were sorted and specimens identi-

fied to order. In particular cases specimens were further

identified to family e.g. within the order Coleoptera,

members of the Chrysomelidae, Staphylinidae, Coccinelli-

dae and Curculionidae were recorded separately. All other

beetle families were recorded under the general title of

Coleoptera. Aphids were recorded separately from the

remainder of the Homopterans as the super family

Aphidoidea. The Collembola were divided into the

Anthropleona and the Symphyleona.

2.2. Statistical analysis

To illustrate plant species richness, relative abundance

and how this changed over time, species were ranked in

descending order of abundance in terms of their mean cover

value (Braun–Blanquet) (Table 2). Species richness in

response to method of field margin establishment, time,

grazing and width of plot, was investigated using GLM

(SPSS 12.0). Species distributions relative to explanatory

variables were ascertained using Canonical Correspondence

Analysis (CCA) CANOCO 4.5. All species (both sown and

unsown) recorded within the treatment plots were included

in the analysis and rare species down-weighted. Field

margin establishment treatments were assigned nominal

values and entered as ‘dummy’ variables. The significance

of each variable was tested using Monte Carlo permutation

tests (full model, 199 permutations). Effects of field margin

establishment method and time of sampling on subsequent

invertebrate abundance were investigated using GLM.

3. Results

A total of 77 higher plant species including 15 grass

species, 60 herb species and 2 species of rush were recorded

within treatment plots over the four sampling periods. Each

of the 10 grass species included within the seed mixture

established successfully. However, only 16 of the 31 herb

species included within the mixture were subsequently

recorded within treatment plots. Germination tests revealed

very low percentage germination from most of the species

contained within the mixture (Table 1).

Analysis of botanical data using GLM revealed that the

influence of field margin establishment treatment and time

on subsequent species richness was highly significant

(Table 3). The interaction between these two factors was

also highly significant with species richness initially high in

‘rotavated’ and ‘reseeded’ plots but decreasing significantly

over time, while remaining unchanged within ‘fenced’ and

‘control’ plots over the duration of the experiment (Fig. 1).

Grazing did not affect species richness and neither of the

remaining interactions were significant (Table 3).

Comparison of all quadrats located between 0.5 and

1.5 m from the wire separating the paddocks (‘A’ quadrats),

revealed that both treatment and time had highly significant

influences on subsequent species richness (P < 0.001)

(Table 3). However, the effect of the extended buffer

available in the 2.5 and 3.5 m margins as opposed to the

1.5 m margins was not significant (P > 0.05). The interac-

tion between treatment and width of plot was significant

(P = 0.028). The remaining interactions between, treatment,

time and width were not significant (Table 3).

Similar comparison of botanical species richness in

quadrats located between 0.5 and 2.5 m from the wire fence

separating the paddocks (‘A’ and ‘B’ quadrats), revealed that

both time and treatment effects on species richness were

highly significant. However, the extended plot width

available in the 3.5 m wide margins did not significantly

alter species richness. Comparison of species richness in

inner, middle and outer quadrats (‘A’, ‘B’ and ‘C’ quadrats)

within 3.5 m wide margins showed similar species richness

across quadrat locations (Table 3).

CCA ordination of botanical data from 2002 (Fig. 2) and

2004 (Fig. 3) (species names abbreviated to six letters)

showed strongest separation of species along axis 1 with

‘control’ and ‘fenced’ treatments lying opposite the

‘reseeded’ treatment. Species associated with the ‘rotavated’

treatment lay orthogonal along axis 2. All of the analysed

variables (with the exception of ‘fenced’) were statistically

significant in terms of explaining variation in species


Table 2

Species recorded in reseeded, rotavated, fenced and control plots in 2002 and 2004 ranked in order of mean abundance (Braun–Blanquet)

Abundance

ranking

2002 2004

Reseeded Rotavated Fenced Control Reseeded Rotavated Fenced Control

76–100% (5) L. perenne L. perenne Agrostis spp. Agrostis spp. L. perenne

51–75% (4) Agrostis spp. Agrostis spp. Agrostis spp.

H. lanatus

R. acetosa

26–50% (3) Holcus lanatus R. obtusifolius Agrostis spp. Agrostis spp. H. lanatus H. lanatus Agrostis spp.

S. media R. obtusifolius L. perenne

6–25% (2) Dacus carota E. montanum H. lanatus H. lanatus A. pratensis L. perenne H. lanatus

Leucanthemum

vulgare

H. lanatus A. odoratum R. repens

Phleum pretense J. bufonius C. cristatus

Poa annua P. annua P. pretense

Rumex obtusifolius P. lanceolata

R. obtusifolius

1–5% (1) Achillea millefolium C. arvense C. arvense H. mollis A. elatius H. mollis D. glomerata H. mollis

Arrhenatherum

elatius

C. fontanum H. mollis D. glomerata H. mollis

Cerastium fontanum H. mollis P. trivialis D. carota

Cirsium vulgare L. perenne Festuca rubra

Digitalis purpurea P. trivialis H. mollis

Epilobium montanum R. repens L. vulgare

Holcus mollis L. perenne

Juncus bufonius R. repens

Lolium perenne

Lotus corniculatus

Medicago lupulina

Plantago lanceolata

Poa trivialis

Rumex acetosa

Sonchus asper

Stellaria media

Trifolium pratense

<1% (+) Agrostemma githago A. arvensis A. elatius Alopecurus

geniculatus

A. millefolium A. geniculatus A. geniculatus A. geniculatus

Alopecurus pratensis A. elatius C. fontanum A. pretense A. geniculatus A. elatius C. fontanum A. pratensis

Anagallis arvensis C. vulgare C. vulgare C. fontanum Angelica sylvestris C. flexuosa C. arvense C. fontanum

Anthoxanthum

odoratum

D. glomerata D. glomerata C. arvense A. minus C. fontanum R. repens C. arvense

Arctium minus D. carota E. montanum D. glomerata C. nigra C. arvense R. obtusifolius D. glomerata

Capsella

bursa-pastoris

E. hirsutum J. bufonius E. montanum C. fontanum C. cristatus S. jacobaea D. carota

Chenopodium album G. uliginosum P. pratense P. trivialis C. arvense D. glomerata E. montanum

Cirsium arvense M. recutita Quercus robur R. repens D. purpurea E. montanum P. trivialis

Cynosurus cristatus Persicaria

maculosa

R. repens R. obtusifolius E. montanum F. rubra R. acetosa

Dactylis glomerata P. pretense R. obtusifolius Taraxacum

off. agg.

F. ulmaria

Juncus effusus

J. effusus R. obtusifolius

Epilobium hirsutum P. aviculare R. repens T. repens Lychnis flos-cuculi P. pretense S. jacobaea

Gnaphalium

uliginosum

Plantago major V. serpyllifolia P. vulgare R. acetosa S. media

Matricaria discoidea Poa pratensis R. acris R. acetosella Taraxacum

off. agg.

Matricaria recutita Rubus fruticosus S. jacobaea S. jacobaea

Papaver rhoeas R. acetosella S. media S. media

Polygonum aviculare S. jacobaea Taraxacum off. agg. Taraxacum off. agg.

Ranunculus repens S. asper T. pretense T. repens

Senecio jacobaea S. vulgare T. repens U. dioica

Senecio vulgare S. arvensis V. serpyllifolia V. serpyllifolia

Silene vulgaris S. oleraceus

Sonchus oleraceus Taraxacum off. agg.

Spergula arvensis T. repens

Trifolium repens U. dioica

Urtica dioica V. serpyllifolia

Veronica serpyllifolia


Table 3

Effects of treatment, time, grazing and width and the interactions of these

factors, on the botanical species richness of the experimental plots over four

sampling periods (July 2002, May and July 2003 and May 2004)

All quadrats d.f. F-value P-value Significance

Treatment 3, 1130 1104.89 <0.001 ***

Time 3, 1130 113.24 <0.001 ***

Grazing 1, 1130 0.24 0.623 ns

Treatment � time 8, 1130 22.85 <0.001 ***

Treatment � grazing 2, 1130 0.67 0.517 ns

Treatment � grazing � time 2, 1130 0.43 0.65 ns

‘A’ quadrats (all plots)

Time 3, 544 10.53 <0.001 ***

Treatment 3, 544 80.97 <0.001 ***

Width 1, 544 1.37 0.242 ns

Time � treatment 9, 544 1.15 0.325 ns

Time � width 3, 544 0.5 0.682 ns

Treatment � width 3, 544 3.06 0.028 *

Time � treatment � width 9, 544 0.14 0.999 ns

‘A’ and ‘B’ quadrats (2.5 and 3.5 m plots)

Time 3, 736 4.6 0.004 **

Treatment 3, 736 77.25 <0.001 ***

Width 1, 736 0.95 0.331 ns

Time � treatment 9, 736 0.34 0.960 ns

Time � width 3, 736 1.51 0.211 ns

Treatment � width 3, 736 3.37 0.018 *


‘A’, ‘B’ and ‘C’ quadrats (3.5 m plots)

Time 3, 544 9.83 <0.001 ***

Treatment 3, 544 147.61 <0.001 ***

Width 1, 544 2.91 0.089 ns

Time � treatment 9, 544 3.55 <0.001 ***

Time � width 3, 544 0.34 0.794 ns

Treatment � width 3, 544 1.63 0.18 ns


* P < 0.05.** P < 0.01.

*** P < 0.001.

Fig. 1. Mean plant species richness from 72 quadrats within each field

margin establishment treatment (control, fenced, rotavated and reseeded)

over each of four sampling periods (July 2002, May and July 2003, May

2004) (�S.E.M.).

Fig. 2. Species–environment biplot of field margin botanical abundance

data in 2002.

distribution in the experiment (P < 0.005). Collectively the

explanatory variables accounted for 30.75 and 31.85% of the

inertia present within the 2002 and 2004 data sets,

respectively. Eigenvalues and cumulative percentage var-

iance of the species–environment relationship for axes 1 and

2 and total inertia in 2002 and 2004 data sets are presented in

Table 4.

A total of 10 and 12 grass species and 20 and 38 herb

species were recorded within ‘rotavated’ and ‘reseeded’

plots, respectively during the 2002 sampling period. While

both of these treatments facilitated the presence of a group of

transient, annual species including for example, Stellaria

media, Juncus bufonius and Poa annua, a lower abundance

of these pioneer species was recorded within the ‘reseeded’

plots (Table 2, Fig. 2). Ground disturbance due to rotavation

was associated with another group of more persistent

agriculturally ‘undesirable’ weed species. This included

Rumex obtusifolius and Senecio jacobaea. However, these

were less abundant within plots which were reseeded

following rotavation (Table 2, Figs. 2 and 3).

While Agrostis spp. were dominant within both treat-

ments, they were less abundant within ‘reseeded’ plots. In

addition, reseeding gave rise to numerous species never

recorded within plots which were allowed to regenerate

naturally e.g. Arrhenatherum elatius, Anthoxanthum odor-

atum, Cynosurus cristatus, Phleum pratense, Plantago

lanceolata and Rumex acetosa (Table 2, Figs. 2 and 3).

The reduction in species richness recorded within both

treatment types by 2004 may be accounted for in part by the


Fig. 3. Species–environment biplot of field margin botanical abundance

data in 2004.

loss of the group of transient pioneer species which

disappeared following cutting and removal of the vegetation

from treatment plots in September 2002 (Table 2, Figs. 2 and

3). Additionally a number of species included within the

seed mixture germinated initially but subsequently failed to

establish.

The majority of species included within the seed

mixture were closely correlated with each other and with

the ‘reseeded’ eigenvector over the duration of the trial

(Figs. 2 and 3). In the absence of reseeding, therefore it

seems highly unlikely that these species would have been

present at the site. Automatic forward selection of

environmental variables using Monte Carlo permutation

tests (full model, 199 permutations) found that ‘reseeding’

was the most significant variable determining species

distribution, with a l1 value of 0.3 in 2002 and 0.4 in

2004, respectively.

‘Fenced’ and ‘control’ plots were strongly co-correlated

in 2002 (Fig. 2), with L. perenne accounting for up to 75% of

the ground cover within these plots (Table 2). The

correlation between these treatments decreased by 2004,

reflected by the divergence of their respective eigenvectors

(Fig. 3). This was due primarily to replacement of L. perenne

with Agrostis spp. as the dominant species within ‘rotavated’

plots by this time (Table 2). With the exception of Agrostis

spp. and Holcus lanatus, other recorded species e.g. R.

obtusifolius and Cirsium arvense accounted for little of the

ground cover within these plots (Table 2).

Table 4

Eigenvalues, cumulative percentage variance of species–environment relation (CC

Sampling period Eigenvalues Percentag

species–en

Axis 1 Axis 2 Axis 1

2002 0.394 0.191 60.4

2004 0.38 0.129 64.8

While GLM analysis found that species richness did not

change in response to margin width (Table 3), the close

correlation of the ‘grazing’ and ‘control’ eigenvectors in Fig.

4 indicated that grazing at this level of intensity facilitated a

reduction in botanical diversity within the experimental

plots. Monte Carlo permutation tests (full model, 199

permutations) indicate that grazing had a significant

influence on overall species diversity with l1 values of

0.03 in 2002 and 0.02 in 2004, respectively.

GLM analysis revealed that both method of field margin

establishment (F3,100 = 20.34) and time of sampling

(F4,100 = 9.36) had highly significant influences on sub-

sequent invertebrate abundance (P < 0.001). The interaction

between these factors was also found to be significant

(F12,100 = 1.76, P = 0.021).

With regard to the Anthropleona (Collembola), treatment

(F3,100 = 27.74) and time of sampling (F4,100 = 13.94) had

significant effects on abundance recorded (P < 0.001). The

interaction between these factors (F12,100 = 3.76) was also

highly significant (P < 0.001). Higher abundance of

Anthropleona were recorded within ‘fenced’, ‘rotavated’

and ‘reseeded’ plots than within the ‘control’ plots over the

duration of the sampling period however, a significant

decrease in Anthropleona abundance observed across all

treatments from sampling period three onwards i.e. 20-07-03

to 18-10-03 inclusive.

The Araneae also showed a highly significant abundance

response to field margin treatment (F3,100 = 13.86,

P < 0.001). Significantly lower abundance of spiders was

recorded within ‘control’ plots when compared with all

other treatments (P < 0.001). Abundance responses

between other treatments were not significant (P > 0.05).

Abundance response to time of sampling was not significant

(F4,100 = 2.15, P 0.186). Aphid abundance response to time

of sampling was highly significant (F4,12 = 34.53,

P < 0.001), with highest numbers recorded during sampling

periods one and two. Lowest abundance was recorded during

the fourth sampling period i.e. 22/08/03 to 20/09/03

inclusive (P < 0.001). Treatment did not significantly

influence aphid abundance (F3,100 = 0.892, P = 0.448) and

the interaction between treatment and time was not

significant (F12,100 = 1.761, P = 0.65).

With regard to the Diptera, an interaction between time of

sampling and treatment was not observed (F12,100 = 1.43,

P = 0.17). A highly significant decrease in the abundance of

Diptera was recorded from the first sample period when

compared with each of the other sample periods (P < 0.001).

A) of axes 1 and 2, total and explained inertia in 2002 and 2004 data sets

e variance

vironment

Total inertia Percentage inertia

Axis 2

89.6 2.12 30.75

89.9 1.84 31.85


The difference between subsequent sample periods was not

significant (P > 0.05). Field margin treatment was also found

to influence abundance (F3,100 = 2.75, P = 0.047). Signifi-

cantly fewer Diptera were recorded within ‘control’ and

‘fenced’ plots than within those that had been ‘reseeded’

(P < 0.05). A difference was not found between the

abundance levels recorded within plots which were reseeded

and those which were ‘rotavated’ but not reseeded.

4. Discussion

Our results indicate that the use of wild flower and grass

seed mixtures was the most successful of the methods

investigated for establishing a diverse, perennial field

margin sward. Reseeding also reduced the abundance of

undesirable weed species, through their rapid exclusion by

the development of the sown perennial species (see also

Smith and MacDonald, 1992).

Within the reseeded plots, P. lanceolata, R. acetosa,

Leucanthemum vulgare and Daucus carota were among the

herb species which established well. Other species such as

Lychnis flos-cuculi, Centaurea nigra, Achillea millefolium

and Prunella vulgaris, though not so abundant, were

frequently recorded. Successful establishment of some of

these species have also been reported by Hopkins et al.

(1999). The success of these species can largely be attributed

to their relatively non-specific ecological requirements

(Grime, 2001). Analogous reductions in species richness as

were found during this experiment have also been reported

by Bokenstrand et al. (2004) and Huusela-Veistola and

Vasarainen (2000).

Difficulties associated with reseeding treatment in

particular include the poor establishment rate of some herb

species (Asteraki et al., 2004; Bokenstrand et al., 2004;

Hopkins et al., 1999). Plant diversity is usually highest when

fertility levels are low (Schippers and Joenje, 2002; Hopkins

et al., 1999). Medium levels of P, K and Mg in the soil were

recorded across all plots in 2002 (Sheridan, 2005). However,

these samples were extracted prior to rotavation of the upper

layers of soil. According to Hopkins et al. (1999), rotavation

may increase the rate of nutrient mineralisation in the soil,

leading to a short-term increase in soil fertility levels which

can affect species establishment.

Cutting and removal of field margin vegetation has been

recommended as a means of retaining species diversity.

These may be of particular benefit to low-growing species

(Bokenstrand et al., 2004) due to factors such as reduced

competition for light and space. The removal of the cuttings

also has the desirable (though slow) effect of reducing soil

fertility (Berendse et al., 1992). However, our results show

that heterogeneity in field margin structure is necessary for

the retention of high levels of invertebrate abundance. This

implies that defoliation of these habitats through cutting and/

or grazing should be undertaken in stages rather than all at

once.

Grazing was associated with a reduction in species

diversity within the experimental plots. According to

Bullock and Marriott (2000) herb species respond positively

to grazing while the response of grasses is species-specific.

For example, species such as A. elatius do not survive heavy

grazing (Hubbard, 1984) and taller herb species would also

be expected to disappear from the sward over time.

It is likely that the time-span involved in this trial was

inadequate to allow the benefits of increased field margin

width on species diversity to be observed. An important role

of increased width of field margins is to provide a buffer

effect for the inner area of the margin against agricultural

disturbance in the adjacent agricultural area (Marshall et al.,

2006). In addition, the probability of persistence and

survival of species increases exponentially with increases in

population size (Opdam, 1990).

The reduced abundance of undesirable species recorded

within ‘reseeded’ when compared with ‘rotavated’ plots (see

also Bokenstrand et al., 2004; Baines et al., 1996) may be

influenced by the diversity of the mix, with highly diverse

mixtures more likely to suppress undesirable species than

low diversity mixtures (Van der Putten et al., 2000). The

change in species dominance from L. perenne to Agrostis

spp. recorded within ‘fenced’ plots is likely due to the

cessation of fertiliser application (Sheldrick et al., 1990).

Increased botanical diversity in field margin habitats

leads to higher faunal diversity (Pfiffner and Luka, 2000).

However, prior to this experiment much of such evidence has

been derived from margins in arable rather than in grassland

systems.

Acknowledgements

We thank Teagasc for funding the lead author of this

research through the Walsh Fellowship Scheme. We are also

grateful to Tony Farragher and Austin O’ Sullivan for their

help with plant identification and to Catherine Keena, John

Murphy, Frank and Rosaleen Sheridan for their technical

support and advice. Thanks to Annette Anderson, Bernard

Kaye, Tahar Kechadi and David Wilson for their help, and to

two anonymous referees for their comments on an earlier

draft.

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