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The effectiveness of flower strips and hedgerows on pest control, pollination services and crop yield: a quantitative synthesis

Authors:
  • Agroscope, Zurich, Switzerland

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Floral plantings are promoted to foster ecological intensification of agriculture through provision-ing of ecosystem services. However, a comprehensive assessment of the effectiveness of different floral plantings, their characteristics and consequences for crop yield is lacking. Here we quantified the impacts of flower strips and hedgerows on pest control (18 studies) and pollination services (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips, but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However, effects on crop pollination and yield were more variable. Our synthesis identifies several important drivers of variability in effectiveness of plantings: pollination services declined exponentially with distance from plantings, and perennial and older flower strips with higher flowering plant diversity enhanced pollination more effectively. These findings provide promising pathways to optimise floral plantings to more effectively contribute to ecosystem service delivery and ecological intensifica-tion of agriculture in the future.ecolo
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LETTERS The effectiveness of flower strips and hedgerows on pest
control, pollination services and crop yield: a quantitative
synthesis
Matthias Albrecht,
1
* David
Kleijn,
2
Neal M. Williams,
3
Matthias
Tschumi,
1
Brett R. Blaauw,
4
Riccardo Bommarco,
5
Alistair
J. Campbell,
6
Matteo Dainese,
7
Francis A. Drummond,
8
Martin H.
Entling,
9
Dominik Ganser,
1,10
G. Arjen de Groot,
11
Dave
Goulson,
12
Heather Grab,
13
Hannah Hamilton,
12
Felix Herzog,
1
Rufus Isaacs,
14
Katja Jacot,
1
Philippe Jeanneret,
1
Mattias
Jonsson,
5
Eva Knop,
1,10
Claire
Kremen,
15
Douglas A. Landis,
16
Gregory M. Loeb,
13
Lorenzo
Marini,
17
Megan McKerchar,
18
Lora
Morandin,
19
Sonja C. Pfister,
9
Simon G. Potts,
20
Maj
Rundl
of,
21
Hillary Sardi~
nas,
22
Amber Sciligo,
22
Carsten Thies,
23
Teja Tscharntke,
23
Eric
Venturini,
24
Eve Veromann,
25
Ines M.G. Vollhardt,
23
Felix
W
ackers,
26
Kimiora Ward,
3
Duncan
B. Westbury,
18
Andrew Wilby,
26
Megan Woltz,
16
Steve Wratten
27
and Louis Sutter
1
Abstract
Floral plantings are promoted to foster ecological intensification of agriculture through provision-
ing of ecosystem services. However, a comprehensive assessment of the effectiveness of different
floral plantings, their characteristics and consequences for crop yield is lacking. Here we quanti-
fied the impacts of flower strips and hedgerows on pest control (18 studies) and pollination ser-
vices (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips,
but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However,
effects on crop pollination and yield were more variable. Our synthesis identifies several important
drivers of variability in effectiveness of plantings: pollination services declined exponentially with
distance from plantings, and perennial and older flower strips with higher flowering plant diversity
enhanced pollination more effectively. These findings provide promising pathways to optimise flo-
ral plantings to more effectively contribute to ecosystem service delivery and ecological intensifica-
tion of agriculture in the future.
Keywords
Agroecology, agri-environment schemes, bee pollinators, conservation biological control, ecologi-
cal intensification, farmland biodiversity, floral enhancements, natural pest regulation, pollination
reservoirs, sustainable agriculture, wildflower strips.
Ecology Letters (2021) 23: 1488–1498
[Correction added on 1 June 2021 after first online publication: Duncan B. Westbury has been added
as a co-author, and the Acknowledgments have been updated to reflect the associated funding informa-
tion, in this version.]
1
Agroecology and Environment, Agroscope, Reckenholzstrasse 191, Zurich
CH-8046, Switzerland
2
Plant Ecology and Nature Conservation Group, Wageningen University,
Droevendaalsesteeg 3a, Wageningen 6708PB, The Netherlands
3
Department of Entomology and Nematology and Graduate Group in
Ecology, University of California, Davis, One Shields Ave, Davis, CA 95616,
USA
4
Department of Entomology, University of Georgia, Athens, Georgia 30602,
USA
5
Department of Ecology, Swedish University of Agricultural Sciences, PO
Box 7044, Uppsala 75007, Sweden
6
Laborat
orio de Entomologia, Embrapa Amaz^
onia Oriental, Bel
em, Par
a CEP
66095-903, Brazil
7
Institute for Alpine Environment, Eurac Research, Viale Druso 1, Bozen/Bol-
zano 39100, Italy
8
School of Biology And Ecology, University of Maine, Orono, ME 04469, USA
9
iES Landau, Institute for Environmental Sciences, University of Koblenz-Lan-
dau, Fortstr. 7, Landau D-76829, Germany
10
University of Bern, Institute of Ecology and Evolution, Baltzerstrasse 6, Bern
3012, Switzerland
11
Wageningen Environmental Research, Wageningen University & Research,
P.O. Box 47, Wageningen 6700 AA, The Netherlands
12
School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK
13
Department of Entomology, Cornell University, Geneva, NY 14456, USA
14
Department of Entomology and EEBB Program, Michigan State University,
East Lansing, MI 48824, USA
15
Institute for Resources, Environment and Sustainability, & Department of
Zoology, University of British Columbia, Vancouver V6T 1Z4, Canada
16
Department of Entomology and Great Lakes Bioenergy Research Center,
Michigan State University, East Lansing, MI 48824, USA
17
DAFNAE, University of Padova, viale dell’Universit
a 16, Padova 35020, Italy
18
School of Science & the Environment, University of Worcester, Worcester, WR2
6AJ, UK
19
Pollinator Partnership, 475 Sansome Street, 17th Floor, San Francisco, CA
94111, USA
20
Centre for Agri-Environmental Research, School of Agriculture, Policy and
Development, Reading University, Reading RG6 6AR, UK
21
Department of Biology, Lund University, Lund 223 62, Sweden
22
Department of Environmental Science, Policy, and Management, University
of California, 130 Mulford Hall, Berkeley, CA 94720, USA
23
Agroecology, Department of Crop Sciences, University of G
ottingen, G
ottin-
gen, Germany
24
Wild Blueberry Commission of Maine, 5784 York Complex, Suite 52, Orono,
Maine 04469, USA
25
Estonian University of Life Sciences, Kreutzwaldi 1, Tartu 51006, Estonia
26
Lancaster Environnent Centre, Lancaster University, LA1 4YQ, UK
27
Bio-Protection Research Centre, Lincoln University, Lincoln, New Zealand
*Correspondence:E-mail: matthias.albrecht@agroscope.admin.ch
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.
Ecology Letters, (2021) 23: 1488–1498 doi: 10.1111/ele.13576
INTRODUCTION
Meeting the increasing demands for agricultural products
while minimising negative impacts on biodiversity and ecosys-
tem health is among the greatest global challenges (Godfray
et al., 2010). Intensive agricultural production and the simpli-
fication of agroecosystems threaten farmland biodiversity and
associated ecosystem services worldwide (Foley et al., 2005;
IPBES, 2016; IPBES, 2018). Concerns over loss of biodiversity
and associated impairment of ecosystem services have helped
strengthen the implementation of agri-environmental schemes
and other measures to mitigate such negative consequences
(IPBES, 2016). Beyond restoration of farmland biodiversity in
general, an implicit or explicit goal of such measures is to fos-
ter sustainable agricultural production through ecological
intensification by harnessing biodiversity-based ecosystem
services, such as crop pollination and natural pest control
services (Bommarco et al., 2013; Pywell et al., 2015; Kov
acs-
Hosty
anszki et al., 2017). In intensively managed agroecosys-
tems, the establishment of strips or other areas of flowering
herbaceous plants, hereafter ‘flower strips’, and hedgerows are
among the most commonly applied measures to achieve these
goals (Scheper et al., 2015; Tschumi et al., 2015; Williams
et al., 2015; Dainese et al., 2017; Kremen et al., 2019). For
example, the establishment of flower strips or hedgerows is
supported by the Common Agricultural Policy (CAP) in the
European Union and by the Farm Bill (e.g. programs of the
Natural Resources Conservation Service of the United States
Department of Agriculture) in the United States (IPBES,
2016; Kov
acs-Hosty
anszki et al., 2017; Venturini et al.,
2017a). Typically established along field edges, flower strips
and hedgerows offer resources for pollinators and natural ene-
mies of crop pests such as shelter, oviposition sites, overwin-
tering opportunities and food resources (Tschumi et al., 2015;
Holland et al., 2016; Kremen et al., 2019) and can locally
increase their abundance and diversity (Haaland et al., 2011;
Scheper et al., 2013; M’Gonigle et al., 2015; Williams et al.,
2015; Tschumi et al., 2016; Sutter et al., 2017, 2018; Kremen
et al., 2019). It is less well understood whether enhanced spe-
cies diversity translates to ex situ provisioning of pollination,
pest control and increased yield. The ‘exporter’ hypothesis
(Morandin and Kremen, 2013; Kremen et al., 2019) predicts
enhanced delivery of ecosystem services through functional
spillover from floral plantings (sensu Blitzer et al., 2012;
Albrecht et al., 2007; Morandin and Kremen, 2013; Pywell
et al., 2015; Tschumi et al., 2015, 2016; Sutter et al., 2017).
However, according the ‘concentrator’ hypothesis (Kremen
et al., 2019; also referred to as the ‘aggregation’ hypothesis
(Venturini et al., 2017a) or the ‘Circe principle’ (Lander et al.,
2011)), resource-rich floral plantings temporarily compete with
flowering crops and concentrate pollinators and natural ene-
mies from the surrounding agriculture into the floral plant-
ings, potentially resulting in (transiently) reduced crop
pollination and pest control services (Nicholson et al., 2019).
This may explain why plantings fail to enhance crop pollina-
tion or pest control services, even if they successfully promote
local pollinator or natural enemy abundance in restored habi-
tats (e.g. Phillips and Gardiner, 2015; Tscharntke et al., 2016;
Karp et al., 2018).
The lack of clarity about effects of flower plantings on
ecosystem service provisioning and crop yield scattered in
numerous case studies is a barrier to farmer adoption of such
measures (Garbach and Long, 2017; Kleijn et al., 2019). A
quantitative synthesis of such demonstrated broad evidence
may assist farmers in making the decision to adopt these mea-
sures (Garbach and Long, 2017; Kleijn et al., 2019). More-
over, it is important to gain a general understanding of
whether such effects are restricted to the area of the crop near
to the adjacent planting (Ganser et al., 2018) or be detectable
over larger distances (Tschumi et al., 2015). Such knowledge
should be considered when designing schemes with optimal
spatial arrangement of plantings across agricultural landscapes
(Ricketts et al., 2008; Garibaldi et al., 2011), and to facilitate
cost-benefit assessments (Blaauw and Isaacs, 2014; Morandin
et al., 2016; Dainese et al., 2017; Williams et al., 2019; Haan
et al., 2020).
To improve the effectiveness of flower strip and hedgerow
plantings in promoting crop pollination, natural pest control,
and potentially crop production, we need to better understand
what determines their failure or success. We hypothesise that
at least three factors influence the effectiveness of floral plant-
ings in enhancing crop pollination and pest control services:
plant diversity, time since establishment and landscape con-
text. First, theory predicts that higher plant species richness,
and associated trait diversity, promotes diverse pollinator and
natural enemy communities due to positive selection and com-
plementarity effects across space and time (e.g. Campbell
et al., 2012; Scheper et al., 2013; Sutter et al., 2017;
M’Gonigle et al., 2017). However, the role of plant diversity
driving effects of floral plantings on pollination and natural
pest control services benefits to nearby crops is poorly under-
stood. Second, time since the establishment of floral plantings
is likely to play a key role for the local delivery of crop polli-
nation and pest control services (Thies and Tscharntke, 1999).
This is of particular relevance for sown flower strips that may
range from short-lived annual plantings to longer-lived peren-
nial plantings. Perennial plantings should offer better overwin-
tering and nesting opportunities for pollinators and natural
enemies (Ganser et al., 2019; Kremen et al., 2019) and may
foster local population growth over time (e.g. Blaauw and
Isaacs, 2014; Venturini et al., 2017b). Third, the effectiveness
of floral plantings could depend on the agricultural landscape
context. Highly simplified landscapes likely have depleted
source populations of pollinators and natural enemies. In
complex landscapes, however, the ecological contrast intro-
duced by floral plantings may not be great enough to result in
strong effects (Scheper et al., 2013). Strongest effects are
therefore expected at intermediate landscape complexity (in-
termediate landscape complexity hypothesis; Tscharntke et al.,
2005; Kleijn et al., 2011). Although support for this hypothe-
sis has been found with respect to biodiversity restoration
(e.g. B
atary et al., 2011; Scheper et al., 2013, 2015; but see
e.g. Hoffmann et al., 2020), its validity for ecological intensifi-
cation and the local delivery of crop pollination and pest con-
trol services has only just begun to be explored (Jonsson
et al., 2015; Grab et al., 2018; Rundl
of et al., 2018).
Here we use data from 35 studies including 868 service-
site-year combinations across 529 sites in North American,
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
Letters Floral plantings for ecological intensification 1489
European and New Zealand agroecosystems to quantitatively
assess the effectiveness of two of the most commonly imple-
mented ecological intensification measures, flower strips and
hedgerows, in promoting crop pollination, pest control ser-
vices and crop production. Moreover, we aim to better under-
stand the key factors driving failure or success of these
measures to suggest improvement of their design and imple-
mentation. Specifically, we address: (1) the extent to which
flower strips and hedgerows enhance pollination and pest con-
trol services in adjacent crops; (2) how service provisioning
changes with distance from floral plantings; (3) the role of
plant diversity and time since establishment of floral plantings
in promoting pollination and pest control services; (4) whether
simplification of the surrounding landscape modifies the
responses; and (5) whether floral plantings enhance crop yield
in adjacent fields.
Our synthesis reveals general positive effects of flower strips
but not hedgerows on pest control services in adjacent crop
fields. Effects on crop pollination, however, depended on
flowering plant diversity and age since establishment, with
more species-rich and older plantings being more effective.
However, no consistent impacts of flower strips on crop yield
could be detected, highlighting the need for further optimisa-
tions of plantings as measures for ecological intensification.
MATERIALS AND METHODS
Data collection
To identify data sets suitable to address our research ques-
tions, we performed a search in the ISI Web of Science and
SCOPUS (records published until 31.12.2017 were consid-
ered). To minimise potential publication bias (i.e. the file
drawer problem, Rosenthal 1979) and to maximise the num-
ber of relevant data sets we also searched for unpublished
data by contacting potential data holders through researcher
networks. Data sets had to meet the following requirements
to be included in the analysis: (1) pollination and/or pest con-
trol services in crops were measured in both crop fields adja-
cent to floral plantings and control fields without planting; (2)
the replication at the field level was six fields per study
(three fields with plantings and three without; i.e. disqualify-
ing small-scaled plot treatment comparisons within fields). We
contacted data holders fulfilling these requirements and
requested primary data on plant species richness of plantings,
time since establishment, landscape context and crop yield
(see below) in addition to measured pollination and pest con-
trol services. Overall, we analysed data from 35 studies. We
here define a study as a dataset collected by the same group
of researchers for a particular crop species and ecosystem ser-
vice (pest control or pollination) in a particular region during
one or several sampling years. We collected 18 pest control
service and 17 pollination service studies, representing a total
of 868 service-site-year combinations across 529 sites (fields
with or without adjacent floral planting; see Fig. S1 for a map
showing the distribution of sites and Table S1 for detailed
information about studies). In eight of these studies (122 sites)
both crop pollination and pest control services were measured
(Table S1).
Pollination services, pest control services and crop yield
As different studies used different methods and measures to
quantify pollination services, pest control services and crop
yield, we standardised data prior to statistical analysis using
z-scores (e.g. Garibaldi et al., 2013; Dainese et al., 2019). The
use of z-scores has clear advantages compared with other
transformations or standardisation approaches (such as the
division by the absolute value of the maximum observed level
of the measured response) because (1) average z-scores follow
a normal distribution, and (2) the variability present in the
raw data is not constrained as in other indices that are bound
between 0 and 1 (Garibaldi et al., 2013). Pollination services
were measured as seed set (number of seeds per fruit), fruit
set (proportion of flowers setting fruit), pollen deposition rate
(number of pollen grains deposited on stigmas within a cer-
tain time period) and, in one study, flower visitation rate
(number of visits per flower within a certain time period). If
available, differences in pollination service measures of open-
pollinated flowers and flowers from which pollinators were
excluded were analysed. Measures of pest control services
were quantified as pest parasitism (proportion of parasitised
pests), pest predation (proportion of predated pests), popula-
tion growth (see below) or crop damage by pests or pest den-
sities (see Table S2 for an overview of pollination and pest
control service measures across studies). Whenever possible,
the pest control index based on population growth proposed
by Gardiner et al. (2009) was calculated and analysed
(Table S2). Note that standardised values of pest density and
crop damage were multiplied by 1 because lower values of
these measures reflect an increased pest control service (e.g.
Karp et al., 2018). Crop yield was only considered for the
analysis if a direct measure of final crop yield was available.
Too few studies assessed crop quality which was therefore not
considered further. Yield was measured as crop mass or num-
ber of fruits produced per unit area. Due to a lack of studies
measuring crop yield in fields with and without adjacent
hedgerows, the analysis of crop yield focused on effects of
flower strips. Crop yield measures were available from a total
of 11 flower strip studies and 194 fields (see Tables S1 and S2
for a detailed description of study systems, crop yield mea-
sures and methods used across studies).
Descriptors of floral plantings and landscape context
Flower strips are here defined as strips or other areas of
planted wild native and/or non-native flowering herbaceous
plants. Hedgerows are defined as areas of linear shape planted
with native and/or non-native at least partly flowering woody
plants and typically also herbaceous flowering plants. For
hedgerows, information about the exact time since establish-
ment and number of plant species was not available for most
studies. The analyses of these drivers (question 3) therefore
focus on flower strip effects on pollination and pest control
services. Information on plant species richness was available
in 12 out of 18 pest control studies and 10 out of 17 pollina-
tion studies. Whenever available, the species richness of flow-
ering plants was used. Otherwise, for some flower strip
studies, the number of sown, potentially flowering plant
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
1490 M. Albrecht et al. Letters
species (excluding grasses) was used. Time since establishment
of flower strips, that is the time span between seeding or
planting and data sampling, was available for all studies rang-
ing from 3 to 122 months.
The proportional cover of arable crops was available and
analysed as a proxy for landscape simplification (e.g. Tscharn-
tke et al., 2005; Dainese et al., 2019) in 11 pest control and 12
pollination studies. Proportional cover of arable crops was
calculated in circular sectors of 1 km radius around focal
crops, or 750 m or 500 m radius (two studies for which data
on a 1 km radius were not available; see Table S1; results
remained qualitatively identical when only considering the
1 km radius datasets).
Statistical analysis
We used a mixed effect-modelling approach to address our
research questions. In all models, study was included as a ran-
dom intercept to account for the hierarchical structure of the
data with field measures nested within study. To assess
whether flower strips and hedgerows enhanced pollination and
pest control services in adjacent crops (question 1) linear
mixed-effect models with planting (field with or without plant-
ing) were separately fitted for flower strips and hedgerows for
the response variables pollination service and pest control ser-
vice. To test how the effects on service provisioning change
with distance (continuous variable; meters) from plantings
(question 2) and with landscape simplification (question 4)
these explanatory variables and their interactions with the
fixed effects described earlier were included in the models.
Exploratory analyses showed that neither distance nor land-
scape simplification effects differed between flower strips and
hedgerows; that is no significant interactive effects of planting
type with any of the tested fixed effects. We therefore pooled
flower strip and hedgerow data in the final models, excluding
planting type and its two or three-way interactions as fixed
effects. In addition to linear relationships we tested for an
exponential decline of measured response variables from the
border of the field by fitting log10(distance) in the linear
mixed-effect models described earlier. In this case, field nested
within study was included as a random effect. To test the
intermediate landscape complexity hypothesis, we tested for
linear as well as hump-shaped relationships between landscape
context, and its interaction with local floral plantings by fit-
ting landscape variables as a quadratic fixed predictor in the
models described earlier (second degree polynomial functions).
To present the ranges covered by the agricultural landscape
gradients, we did not standardise measures of landscape sim-
plification within studies (e.g. Martin et al., 2019). To examine
how pollination and pest control service provisioning relates
to flower strip plant diversity and time since establishment
(question 3) plant species richness and log10(number of
months since establishment) were included as fixed effects in
models with study as a random effect. Using log(months since
establishment) predicted the data better than establishment
time as linear predictor. Plant species richness and time since
establishment of flower strips were not correlated (r=0.22).
Only 10 studies measured services in several years since estab-
lishment (Table S1), and we included only data from the last
sampling year. To assess how the presence of plantings
affected the agronomic yield of adjacent crops (question 5),
we fitted a linear mixed-effect model with the same fixed and
random structure as described for question 1, but with crop
yield as the response variable. Statistical analyses for different
models and response variables differed in sample sizes as not
all studies measured crop yield in addition to pollination or
pest control services (Tables 1, Table S1). In all models we
initially included planting area as a co-variate in an explo-
rative analysis, but removed it in the final models, as it did
not explain variation in any of the models and did not
improve model fit (not shown).
Effect sizes provided in the text and figures are model esti-
mates of z-transformed response variables. For statistical
inference of fixed effects we used log-likelihood ratio tests
(LRT) recommended for testing significant effects of a priori
selected parameters relevant to the hypotheses (Bolker et al.,
2009). For all models, assumptions were checked according to
the graphical validation procedures recommended by Zuur
et al. (2009). All statistical analyses were performed in Rver-
sion 3.5.2 (R Core Team, 2017) using the R-package lme4
(Bates et al., 2015).
RESULTS
Effects of floral plantings on pest control and pollination services
The provisioning of pest control services in crop fields adja-
cent to flower strips was enhanced by 16% on average com-
pared to fields without flower strips. On average, pest control
services were also increased in crops adjacent to hedgerows,
but effects were more variable and overall not statistically sig-
nificant (Fig. 1; Table 1). Pest control services declined expo-
nentially with distance from the field edge, but the slopes of
the distance functions between fields with and without adja-
cent floral plantings did not differ (Fig. 2a; Table 1).
Crop pollination effects were more variable across studies
and overall not significantly different between crops with or
without adjacent floral planting across all studies and within-
field distances (Fig 1; Table 1). However, effects of distance
to field edge differed for fields with floral plantings compared
with control fields (significant interaction between presence of
planting and distance from field border; Table 1). Pollination
services were increased near floral plantings and decreased
exponentially with increasing distance from plantings, while
no such effect of distance to field edge was detected for con-
trol fields (Fig. 2b). The fitted distance curves for fields with
or without floral plantings intersected at 43 m (Fig. 2b).
The role of flowering plant diversity and time since establishment of
flower strips
Crop pollination services, but not pest control services, tended
to increase with flowering plant species richness of the adja-
cent flower strip (52% predicted increase in crop pollination
from 1 to 25 plant species in adjacent flower strip; Fig. 3a;
Table 1). Crop pollination services also tended to increase
with time since establishment of the adjacent flower strip, but
showed a positive saturating relationship (Fig. 3b; Table 1).
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
Letters Floral plantings for ecological intensification 1491
Pollination services increased by 27% in 2 year old strips
compared with the youngest plantings (roughly 3 months
old), while the additional predicted increase from 2 to 4 years
or older strips was approximately 5% on average (Fig. 3b;
only few strips were older than four years, see Fig. 3b and
explanations in figure caption). Pest control services in crops
adjacent to flower strips did not increase with flower strip age
(Table 1).
Effects of landscape simplification
The model testing for a linear relationship between service
provision and landscape simplification and its interaction with
local flower presence fitted the data better than a model test-
ing for hump-shaped relationships (Table S3). Pollination, but
not pest control services, decreased linearly with landscape
simplification (12% decrease from 50 to 100% crops in the
surrounding landscape), irrespective of the presence of a floral
planting (no significant floral planting 9landscape simplifica-
tion interaction; Fig 4; Table 1).
Effects of flower strips on crop yield
Overall, no significant effect of flower strips on yield in adja-
cent crops was detected (subset of 11 studies for which crop
yield data was available; Fig. 5; Table S4). Furthermore, no
effects of within-field distance, plant species richness, time
since establishment or landscape simplification, or their inter-
actions with flower strip presence on yield, were detected
(Table S4).
DISCUSSION
Our quantitative synthesis demonstrates a generally positive
effect of flower strips on pest control services but these effects
did not consistently translate into higher yields. Although in
most cases beneficial effects of plantings were also found for
crop pollination services, effects on crop pollination and final
Table 1 Summary of results of linear and generalised linear mixed-effects models testing the effects of presence and type of floral plantings (flower strips
and hedgerows) on crop pollination and natural pest control services, and how effects are influenced by in-field distance, local planting characteristics and
landscape context. Response variables, explanatory variables, estimates, numerator degrees of freedom and denominator degrees of freedom (Df), differ-
ences in log-likelihood for chi-squared tests (LRT) and Pvalues (P<0.05 in bold; P0.05 <0.10 in bold italic) are shown for each model. Note that
effects of local drivers (i.e. flowering plant species richness and time since establishment) considered only crops adjacent to flower strips
Response variable Explanatory variable Estimate Df LRT P-value
Effects of plantings
Natural pest control service Flower strip 0.254 1,316 7.26 0.007
Hedgerow 0.196 1,60 1.06 0.303
Crop pollination service Flower strip 0.032 1,170 0.06 0.808
Hedgerow 0.097 1,106 0.28 0.595
Distance effects
Natural pest control service Planting 9log(distance) 0.051 1,590.9 1.35 0.245
Planting 0.199 1,590.4 5.92 0.015
Log(distance) 0.052 1,618.5 5.62 0.018
Crop pollination service Planting 9log(distance) 0.082 1,445.3 5.73 0.017
Planting 0.315 1,420.8 2.40 0.121
Log(distance) 0.014 1,453.3 2.64 0.104
Effects of local drivers (flower strips)
Natural pest control service Flowering plant species richness 0.013 1,49.3 0.47 0.494
Log(time since establishment) 0.104 1,16.1 1.32 0.251
Crop pollination service Flowering plant species richness 0.036 1,49.8 3.39 0.066
Log(time since establishment) 0.276 1,10.9 3.47 0.062
Effects of landscape context
Natural pest control service Planting 9landscape simplification 0.004 1,274.2 0.10 0.754
Planting 0.171 1,286.2 1.28 0.257
Landscape simplification 0.007 1,181.9 1.81 0.179
Crop pollination service Planting 9landscape simplification 0.003 1,278.9 0.91 0.340
Planting 0.198 1,278.9 0.00 0.950
Landscape simplification 0.011 1,145.9 4.03 0.045
Figure 1 Forest plot showing effects of flower strips and hedgerows on
pollination and pest control service provisioning in adjacent crops
compared to control crops without adjacent floral plantings. Squares
illustrate predicted mean effects (z-score estimates), bars show 95%
confidence intervals (CIs). On average, pest control services were
enhanced by 16% (z-score: 0.25) in fields with adjacent flower strip
compared to control fields.
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
1492 M. Albrecht et al. Letters
crop yield were variable and overall not significant. The effect
of wildflower strips on pollination services increased with age
and species-richness suggesting that the quality of such plant-
ings plays a pivotal role in effective service provision. More-
over, crop pollination declined with increasing distance to
floral plantings (hedgerows and flower strips). These results
indicate that floral plantings have great potential to benefit
ecosystem service provision, but to do so will need to be care-
fully tailored for functioning at specific spatial scales. Flower
diversity and strip age are important drivers through which
this can be achieved and they should be considered integrally
before floral plantings can make a significant contribution to
the ecological intensification of agricultural production.
We found positive effects of flower strips on ecosystem ser-
vice provisioning in support of the ‘exporter’ hypothesis (sensu
Morandin and Kremen, 2013; Kremen et al., 2019), although
effects were generally variable and only significant for flower
strips enhancing pest control services by 16% on average.
This is an important finding as it provides general empirical
evidence that flower strips can reduce crop pest pressures
across various crops, landscape contexts and geographical
regions. One explanation for the more consistent positive
effects on pest control services of flower strips compared to
hedgerows may be that in many of the studied flower strips
the selection of flowering plants was tailored to the require-
ments of the target natural enemy taxa (Tschumi et al., 2015,
2016) while this was generally less the case in the studied
hedgerow plantings.
Wildflower plantings have been heralded as one of the
most effective measures to enhance the provision of ecosys-
tem service to crops (Kleijn et al., 2019) with many studies
showing positive effects on service provisioning (e.g. Blaauw
and Isaacs, 2014; Tschumi et al., 2015, 2016; included in this
quantitative synthesis). Our synthesis shows, however, that
although general significant effects of flower strips were
found for pest control service provisioning, effects of plant-
ings on crop pollination services were highly variable. This
highlights the need to better understand these conditions and
drivers of success or failure of floral plantings to promote
pollination services. Our synthesis identifies several drivers
explaining this variability in delivered services and therefore
offers pathways to enhance the effectiveness of these mea-
sures in the future.
First, the success of flower strips to promote crop pollina-
tion services increased with their age. The strongest increase
was detected up to roughly three years since the planting date.
Figure 2 Predicted relationships between (a) mean natural pest control
service and (b) mean crop pollination service (z-scores (solid lines) 95%
CI (dashed lines)) and in-field distance to field border for field with (red
lines; dots) or without adjacent floral planting (black lines, triangles).
Figure 3 Predicted relationships between mean crop pollination service (z-
scores (fat solid lines) 95% CI (fine solid lines)) and (a) flowering plant
species richness and (b) time since establishment of adjacent flower strips.
Predicted relationship and results of an analysis without the points
representing flower strips older than four years were qualitatively
identical.
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
Letters Floral plantings for ecological intensification 1493
Pollination services also appeared to continue to increase with
establishment time beyond three years. This trend needs to be
interpreted with caution as only three studies assessed four
years old or older flower strips highlighting that scarcity of
long-term data on the effects of floral plantings on services
provisioning and yield, which represents an important knowl-
edge gap. We found no evidence that this increase in effective-
ness with age is driven by floral abundance, as flower
abundance did not increase with flower strip age. Case studies
from Central and Northwestern Europe suggest that abun-
dance and species richness of flowering herbaceous plants in
sown flower strips on the highly fertilised soils in these agri-
cultural regions often even decline with age after the second
or third year as grasses take over (Steffan-Dewenter and
Tscharntke, 2001; Ganser et al., 2019). The observed positive
effect of flower strip age is, however, in agreement with the
expectation that the build-up and restoration of local crop
pollinator populations need time (Blaauw and Isaacs, 2014;
Buhk et al., 2018; Kremen et al., 2018). It may also be
explained by greater provision of nesting and overwintering
opportunities in older floral plantings (Kremen et al., 2019)
which are likely scarce in short-lived annual flower strips that
could even be ecological traps for overwintering arthropods
(Ganser et al., 2019). In fact, Kremen and M’Gonigle (2015)
found higher incidence of above-ground cavity nesting bees
compared to ground-nesting bees with hedgerow maturation;
Ganser et al. (2019) reported increased overwintering of
arthropod predators and pollinators of perennial compared to
annual flower strips.
Second, our findings reveal that higher species richness of
flowering plants tends to enhance pollination service delivery
in adjacent crops. This is an important finding as it indicates
that restoring plant diversity can not only promote rare polli-
nator species and pollinator diversity (cf. Scheper et al., 2013;
Kremen and M’Gonigle, 2015; Sutter et al., 2017; Kremen
et al., 2018), but also crop pollination services. Flowering
plant diversity likely promotes complementary floral resources
for numerous pollinator taxa with different resource needs
and continuity of floral resource availability throughout the
season (Schellhorn et al., 2015; M’Gonigle et al., 2017). The
identification of species or traits contributing particularly
strongly to such effects is a promising area of research (Lun-
din et al., 2019). Moreover, appropriate management, such as
reducing the frequency of hedgerow cutting, is important to
ensuring high availability and diversity of floral resources
(Staley et al., 2012). Our synthesis reveals that floral plantings
enhance pollination services, but only in the part of adjacent
crops near to plantings, declining exponentially with distance
to plantings (Fig. 2). The exponential decline function predicts
pollination service provisioning of less than 50% at 10 m and
slightly more than 20% at 20 m compared to the level of ser-
vice provisioning directly adjacent to plantings, partially
explaining the overall non-significant benefits when consider-
ing all measured distances across the entire field (Fig. 2). This
may also explain part of the high variability observed across
studies and reconcile some of the contrasting findings with
Figure 4 Predicted relationship between mean (a) pest control and (b)
crop pollination service (z-scores (solid lines) 95% CI (dashed lines))
and landscape simplification (percentage of arable crops in the landscape)
in fields with adjacent floral planting (red line; red circles) or without
planting (black line; black triangles). Pollination services, but not pest
control services, declined with landscape simplification; the slight
differences in slopes for pollination-landscape simplification relationships
of fields with or without adjacent plantings were statistically not
significant.
Figure 5 Mean predicted crop yield (z-scores; 95% CI) of fields with
adjacent flower strips (red circles) and control fields without adjacent
flower strip (black triangles). The data set includes a subset of 11 studies.
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
1494 M. Albrecht et al. Letters
respect to pollination service provisioning in studies measuring
services relatively near plantings (e.g. up to 15 m; Blaauw and
Isaacs (2014), or up to larger distances, e.g. up to 200 m;
Morandin and Kremen (2013); Sardi~
nas et al, (2016)). We
found no indication that the degree of the dependency of a
crop on insect pollination significantly contributed the
observed variability in effects of plantings on crop pollination
services or yield (Table S5).
Consistent with previous studies (e.g. Dainese et al., 2019),
landscape simplification was associated with decreased polli-
nation services, irrespective of the presence of floral plantings.
In contrast, no such effects were detected for pest control ser-
vices, in agreement with recent studies (Karp et al., 2018; Dai-
nese et al., 2019; but see Veres et al., 2013; Rusch et al., 2016;
Martin et al., 2019). The effect of adding a flower strip or
hedgerow was, however, independent of landscape context.
Although individual case studies (Jonsson et al., 2015; Grab
et al., 2018; included in this synthesis) found support for the
intermediate landscape hypothesis, enhanced ecosystem ser-
vices associated with floral plantings were not generally lim-
ited to moderately complex landscape contexts, which should
encourage farmers to adopt these measures irrespective of the
type of landscape in which they are farming.
Crop yield is affected by a complex interplay of a multitude
of agricultural management practices such as fertilisation, level
of pesticide use, pest pressures, soil cultivation and other fac-
tors such as local soil and climatic conditions (e.g. Bartomeus
et al., 2015; Gagic et al., 2017), which can potentially mask
benefits from improved natural pest regulation or pollination
services (Sutter et al., 2018). Positive effects of floral plantings
have been shown by some case studies included in this synthe-
sis (e.g. Tschumi et al., 2016; see also Pywell et al., 2015),
although sometimes only several years after the establishment
of plantings (Blaauw and Isaacs, 2014; Morandin et al., 2016;
Venturini et al., 2017b), but we did not detect consistent effects
on crop yield associated with adjacent floral plantings. The
identified drivers of the effectiveness of floral plantings to
enhance crop pollination services, such as age and flowering
plant diversity, could provide promising pathways towards
optimising plantings as measures contributing to ecological
intensification. Future optimisations should also consider the
potential for synergistic interactions of enhanced pollination
and pest control services by ‘multi-service’ designs of plantings
(Sutter and Albrecht, 2016; Morandin et al., 2016), temporal
dynamics (Blaauw and Isaacs, 2014; M’Gonigle et al., 2015),
optimised ratios of floral planting (contributing to ecosystem
service supply) to crop area (affecting service demand; Kremen
et al., 2019; Williams et al., 2019), and the distance-depen-
dency of services quantified by this synthesis. However, floral
plantings are also established for other goals than yield
increase. From an environmental and health perspective, main-
taining crop yields through a replacement of insecticides by
enhanced natural pest control services, should be considered as
a great achievement (e.g. Tschumi et al., 2015). Moreover, flo-
ral plantings, of sufficient ecological quality, for example in
terms of native plant species diversity, contribute also to fur-
ther ecosystem services, especially biodiversity conservation
(e.g. Haaland et al., 2011; Scheper et al., 2013); but farmers
are often reluctant to adopt such measures due to concerns of
negative effects on crop yield, for example due to spillover of
pests. Our findings of similar crop yield in fields with and with-
out plantings can dispel such concerns.
Conclusions and implications
Our synthesis demonstrates enhanced natural pest control ser-
vices to crops adjacent flower strips plantings, across a broad
suite of regions, cropping systems and types of flower strips
studied. However, it also reveals inconsistent and highly vari-
able effects of flower strips and hedgerows on crop pollination
services and yield. This highlights a strong need to identify
the key factors driving this variability and the effectiveness of
different types of floral plantings in contributing to ecosystem
service delivery. Informed by such improved understanding,
the design, implementation and management of floral plant-
ings can increase their effectiveness as measures for ecological
intensification. This synthesis identifies several promising
pathways towards more effective floral plantings for the provi-
sion of ecosystem services and ecological intensification: the
modelled exponential distance-decay function of pollination
service provisioning by floral plantings into crop field helps to
predict service provision in crop fields; together with the lack
of a strong planting area effect, our findings suggest that a
dense spatial network of relatively small plantings will be
more effective than a few large ones to optimise pollination
service provisioning. Moreover, it identifies important drivers
of the effectiveness of floral plantings for delivery of crop pol-
lination services: flowering plant diversity and age. Based on
these findings we strongly encourage the establishment, ade-
quate management and restoration of existing perennial floral
plantings that ensure the availability of high floral diversity
across several years as promising pathways towards optimised
measures for ecological intensification.
ACKNOWLEDGEMENTS
We thank all farmers, field and technical assistants, research-
ers and funders who contributed to the studies made available
for this synthesis. We thank Matthias Suter, Lukas Pfiffner,
Henryk Luka, Mario Balzan, Michael Garratt and Emily
Martin for statistical advice and inspiring and valuable discus-
sions. We also thank Professor Irwin and two anonymous
reviewers for their thoughtful comments and excellent sugges-
tions that have clearly improved an earlier version of the
manuscript. Furthermore, we are grateful for funding by the
EU COST-Action FA1307 ‘SUPER-B’ that enable fruitful
discussions with members of the SUPER-B network during
the conceptual and analysis phase of this work. AJC was
funded by the Biotechnology and Biological Sciences Research
Council (BBSRC) and Syngenta UK as part of a case award
PhD (grant no. 1518739). DAL was supported by the Great
Lakes Bioenergy Research Center, U.S. Department of
Energy, Office of Science, Office of Biological and Environ-
mental Research (Award DE-SC0018409), by the National
Science Foundation Long-term Ecological Research Program
(DEB 1832042) at the Kellogg Biological Station, and by
Michigan State University AgBioResearch. RI and BB were
funded by the USDA Sustainable Agriculture Research and
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
Letters Floral plantings for ecological intensification 1495
Education program and by AgBioResearch. EV acknowledges
funding from Estonian Research Council Institutional Research
Funding project IUT36-2 and the QuESSA project funded by
the European Union (FB7, grant agreement no. 311879. EV and
FD were funded by The United States Department of Agricul-
ture National Institute of Food and Agriculture Specialty
Crops Research Initiative Grant 2011-51181-30673, and by the
University of Maine School of Biology and Ecology. MT was
funded by the Hauser and Sur-La-Croix foundations. SCP was
supported through the QuESSA project funded by the European
Union (FB7, grant agreement no. 311879). SGP was supported
through the Insect Pollinators Initiative UK Crop pollination
project funded by BBSRC, Defra, NERC, the Scottish Govern-
ment and the Wellcome Trust (BB/1000348/1), and SMOOPS
project funded by BBSRC, Worldwide Fruit Limited, Avalon
and Syngenta (BB/P003664/1). MJ acknowledges funding from
the Tertiary Education Commission through the Bio-Protection
Research Centre at Lincoln University, New Zealand and Centre
for Biological Control at Swedish University of Agricultural
Sciences. MMK and DBW acknowledge funding from Waitrose
& Partners, Fruition PO and the University of Worcester.
AUTHORS’ CONTRIBUTIONS
MA and LS designed the study. MA, DK, MT, BRB, RB,
AJC, MD, FD, MHE, DG, ADG, DG, HG, HH, FH, RI,
KJ, PJ, MJ, EK, CK, DAL, GML, LM, MMK, LM, SCP,
SGP, MR, HS, AS, CT, TT, EV, EV, IMGV, AW, DBW,
FW, KW, NMW, MW, SW and LS contributed data. MA
compiled the dataset. LS and MA analysed the data. MA, LS,
DK, MG, SGP and MR interpreted results. MA wrote the
paper and all authors contributed to revision
DATA AVAILABILITY STATEMENT
Data available from the Dryad Digital Repository: https://
doi.org/10.5061/dryad.ns1rn8pq2.
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SUPPORTING INFORMATION
Additional supporting information may be found online in
the Supporting Information section at the end of the article.
Editor, Rebecca Irwin
Manuscript received 2 April 2020
First decision made 1 June 2020
Manuscript accepted 19 June 2020
©2020 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
1498 M. Albrecht et al. Letters
... Field margins sown with pollinator-friendly seed mixes have been found to increase pollinator abundance and diversity in the margin itself [13][14][15][16][17][18][19]. There are mixed findings with respect to spillover of pollinators into the crop and effects on yield [13,15,20,21]. The flower diversity within the margin and the heterogeneity of the surrounding landscape can both modify the impact on pollinators. ...
... Generally, more diverse flower strips support a more diverse pollinator community, and less benefit is seen in heterogenous landscapes [22][23][24]. Studies looking at the impacts of flower margins are often conducted only over 1-3 years [20] which is shorter than the typical lifetime of a flower margin on farmland. There is little data available on how flower margins perform over longer time periods or how best to manage them in the longer term to ensure the maintenance of floral resources for pollinators and wider biodiversity. ...
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Supporting biodiversity in agricultural landscapes is key from both a conservation and ecosystem services perspective. Planting flower margins along crop field edges is one of the most established approaches to try and improve habitat and resources for insect pollinators on farms. Whilst there is growing evidence that these margins can result in increased pollinator abundance and diversity on farms in the short-term, there is little data looking at how these margins perform over longer periods. This study looked at the utilization of pollinator-friendly margins over time in an agricultural landscape in Hungary. ‘Operation Pollinator’ seed mixes with 12 species, were used at 96 farms in Hungary from 2010 to 2018. Insect pollinators were recorded on the sown flower margins and control margins (with naturally occurring vegetation) using walked transects. Repeated sampling of the margins was done over several years so that data was collected on margins from 0 (planted that season) to 7 years old. The abundance of pollinators in the Operation Pollinator flower margins was greater than in control margins for all groups recorded (honey bees, bumble bees, mining bees, trap-nesting bees, hoverflies and Lepidoptera). The biggest relative increase in abundance was in honey bees (768% increase in average abundance in the flower margin compared to the control across all observations), with mining (566%) and bumble bees (414%) showing the next largest increases. The abundance of bumble bees, trap-nesting bees and Lepidoptera in the margins did not vary with the age of the margin. Honey bees, mining bees and hoverflies all decreased in abundance with increasing margin age, as did flower abundance. The results suggest that for some pollinator groups, regardless of age, flower margins provide important resources in the agricultural landscape. However, this is not universally true and for certain pollinator groups, some re-sowing of the margins may be needed to sustain longer-term benefits.
... In practice, schemes are offered as sets of interventions where participants have flexibility as to the type, quantity and location of interventions implemented. Individual interventions differ in their floral and/ or nesting value contributions (Cole et al. 2020) but the effect of an individual intervention depends on its placement relative to pollinator-dependent crops as well as its quantity and quality (Albrecht et al. 2020). The change in visitation achieved may also potentially depend on the interaction between intervention types: for example, one intervention that individually provides only good nesting resource, and a second intervention that provides only a good floral resource may be more effective if co-located. ...
... They may also be providing ecological connectivity from resource-limited cropping areas to resource-rich existing semi-natural habitat features (Sullivan et al. 2017). Maintaining this extent of hedgerow/woodland edge management in future schemes will therefore be important in supporting pollination services (Albrecht et al. 2020). In principle, the beneficial effect could be enhanced by planting new hedgerows to further extend the hedgerow network, though it may take over five years for these to provide resources of equivalent quality to mature hedgerows (Kremen et al. 2018). ...
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Context Agri-environment schemes support land management interventions that benefit biodiversity, environmental objectives, and other public goods. Process-based model simulations suggest the English scheme, as implemented in 2016, increased wild bee pollination services to pollinator-dependent crops and non-crop areas in a geographically heterogeneous manner. Objectives We investigated which interventions drove the scheme-wide predicted pollination service increase to oilseed rape, field beans and non-cropped areas. We determined whether the relative contribution of each intervention was related to floral and/or nesting resource quality of the intervention, area of uptake, or placement in the landscape. Methods We categorised interventions into functional groups and used linear regression to determine the relationship between predicted visitation rate increase and each category’s area within a 10 km grid tile. We compared the magnitude of the regression coefficients to measures of resource quality, area of uptake nationally, and placement to infer the factors underpinning this relationship. Results Hedgerow/woodland edge management had the largest positive effect on pollination service change, due to high resource quality. Fallow areas were also strong drivers, despite lower resource quality, implying effective placement. Floral margins had limited benefit due to later resource phenology. Interventions had stronger effects where there was less pre-existing semi-natural habitat. Conclusions Future schemes could support greater and more resilient pollination service in arable landscapes by promoting hedgerow/woodland edge management and fallow interventions. Including early-flowering species and increasing uptake would improve the effect of floral margins. Spatial targeting of interventions should consider landscape context and pairing complimentary interventions to maximise whole-scheme effectiveness.
... In response to the widespread and highly publicized declines in insect pollinators [1][2][3][4][5], people are increasingly interested in supporting them locally by providing foraging resources and habitats. Some of these enhancements are occurring at a landscape level [6][7][8][9][10][11][12], while other modifications are enacted at a smaller scale. For example, there is a growing movement for lawn mowing to be reduced or delayed, allowing flowers and nesting habitats to go undisturbed during critical insect foraging and reproductive phases [13][14][15][16]. ...
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Gardening for pollinators and other flower-visiting insects, where ornamental landscaping plants are added to provide habitats and foraging resources, may provide substantial benefits to declining insect populations. However, plant recommendations often lack empirical grounding or are limited geographically. Here, we created a pollinator garden, replicated across two sites, that contained 25 ornamental landscape plants that were either native or non-native to mid-Atlantic states and perennial or annual. Our objective was to determine the plants that would bring insect abundance and diversity to gardens. We surveyed the number and taxonomy of insects visiting the plants for two summers. We found a significant effect of plant species on both the abundance and diversity of flower-visiting insects. Insects were 42 times more abundant on our most visited plant (black-eyed Susan, Rudbeckia fulgida) versus our least visited plant (petunia, Petunia sp.). There was more than one diversity point difference in the Shannon index between the plant with the most (purple coneflower, Echinacea purpurea) and least (verbena, Verbena bonariensis) diverse visitors. Across our plants, honey bee (Apis mellifera) abundance positively correlated with other insect pollinators, although not specifically with wild bee abundance. Native perennials outperformed non-native perennials and non-native annuals in insect abundance, and both non-native and native perennials attracted more diversity than non-native annuals. Across plants, diversity scores quadratically related to insect abundance, where the highest diversity was seen on the plants with medium abundance. Lastly, we present the weighted sums of all insect visitors per plant, which will allow future gardeners to make informed landscaping decisions. Overall, we have shown that gardening schemes could benefit from a data-driven approach to better support abundant and diverse insect populations within ornamental landscape gardens.
... These attributes make semi-natural areas an important landscape component to preserve taxonomic and functional diversity of floral visitor insects. In fact, environmental legislation aiming to conserve farmland diversity by promoting set-aside areas in crops has proven successful (Albrecht et al., 2020). However, the potential of semi-natural areas to maintain diverse floral visitor communities is expected to be moderated by several factors such as landscape context, the intensity of farming management in the surrounding crop area and the quality of these areas (Bartual et al., 2019;Garratt et al., 2017;Larkin and Stanley, 2021). ...
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Small floral patches that coexist with crops in agricultural landscapes can function as biodiversity reservoirs. However, the influence of the landscape context and agricultural management on the capacity of these small green infrastructures to support diversity is poorly understood. Here, we evaluate the effect of landscape simplification, agricultural intensification in the neighbourhood, and quality of the floral habitats on the success of these patches to support flower-visiting insect communities as well as the pollination service they provide. To this aim, we sampled floral patches located in 18 paired olive farms with contrasting herb cover management (intensive vs. low-intensity), distributed along a wide gradient of landscape complexity at the regional scale of South Spain. We conducted surveys of flower-visiting insects in 36 multi-floral stands and 36 mono-floral stands of Sinapis alba Linnaeus (1753) within these floral patches. Mono-floral stands were used to evaluate variations in the pollination service through number of viable seeds and seed set. Results revealed that the abundance and diversity of flower-visiting insects respond to the quality of the floral patch (diversity of flowers) but not to landscape context nor agricultural management around it. Moreover, the pollination service was similar and high (seed set ca. 100 %) in all floral patches regardless of their context. Our findings highlight the importance of even small floral patches that function as reservoirs of diversity of flower-visiting insects and the pollination service. They also show the high resistance of these patches to agricultural intensification and simplification in olive grove landscapes.
... Local habitats should provide resources and conditions to ensure the movement of bees between natural and cropped areas in the landscape (Holzschuh et al. 2008;Winfree et al. 2008). Increasing the local floral resources within and around the cropped area by managing non-crop plants can serve this purpose (Albrecht et al. 2020;Hass et al. 2018). Non-crop plants (commonly known as weeds, hereafter referred to as noncrop plants) may increase local resource diversity and availability owing to their continuous flowering and varied floral morphology (Bretagnolle and Gaba 2015;Laha et al. 2020). ...
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Landscape structure and local floral resources can modulate bee diversity and ecological interactions in agroecosystems. Theory predicts that, at different spatial scales, both factors may interact and influence assemblage patterns and interactions simultaneously, ultimately affecting the provision of ecosystem services. We investigated how habitat heterogeneity at different spatial scales influenced the assemblage of tomato flower-visiting bees in organic cropped areas in the Cerrado biome, Brazil, from 2019 to 2020. We also evaluated the structure and stability of the interaction network among tomatoes, non-crop plants, and bees. We found that landscape heterogeneity can benefit and serve as a source of bee species when natural vegetation remnants are not highly fragmented in the landscape. Non-crop plants increase the permeability of agroecosystems to bees by providing additional and diverse floral resources. The interaction network between non-crop plants and bees was found to be modular and robust, suggesting spatial habitat partitioning among the bee species. The presence of non-crop plants plays a central role in preventing bee species loss in the cropped areas by locally maintaining the stability of the interaction network. Implications for insect conservation Factors operating at multiple spatial scales determine species occurrence in the landscape, but local interactions with non-crop plants dictate habitat permeability to species. Such factors should be considered when designing strategies to make tropical agroecosystems more permeable and functional to bee biodiversity and the pollination services they provide.
... Many studies have demonstrated the effectiveness of pest control by the enhancement of natural enemies via the establishment of flower strips compared with natural vegetation strips, or without border flower strips (Hatt et al. 2017, Tschumi et al. 2015, Zhao et al. 2016. However, few studies (but see e.g., Albrecht et al. 2020, Gurr et al. 2016) have compared the effectiveness of the pest control strategies relying on the establishment of flower strips versus chemical control, and how far into crop fields are border flower strips effective in promoting pest control efficacy. ...
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Manipulating border flower strips is an effective method of conservation biological control, and can promote natural enemies and boost biocontrol services in agroecosystems. However, few studies have compared the effectiveness of flower strip establishment versus chemical control, and how far from border strips into fields does pest control remain efficient. We conducted a two-year experiment in cotton plots to compare three pest management measures for cotton aphids in China: (1) sown borders of flower strips, (2) chemical control using imidacloprid with border flower strip replaced by a cotton strip, and (3) control treatment: no insecticide applications and border flower strip replaced by a cotton strip. We monitored the abundances of aphids and natural enemies in border strips and at different distances away from border strips into cotton plots. Abundances of cotton aphids' natural enemies including ladybeetles, predatory bugs, lacewings, and hoverflies were significantly higher in border flower strips than in border cotton strips. Importantly, aphid abundances were lower in cotton plots with flower strips than cotton plots treated chemically in 2020, and about similar in 2021. They were also lower by 57 % and 34 % compared to the control plots in 2020 and 2021, respectively. Moreover, efficient pest suppression in cotton plots with flower strips was achieved as far as 10.5-14.6 m away from the strip into the plots (the maximum distance sampled). Our study demonstrates a high degree of effectiveness of flower strips in promoting natural enemy abundances and aphid suppression, and reducing the need for insecticide use in cotton crops.
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The rice stem borer (RSB), Chilo suppressalis (Walker), is an economically important pest of rice in subtropical Asia. Up till present, it remains unknown how pest abundance and parasitoid-mediated biological control are modulated by landscape composition. In this study, 20 rice fields with varying proportion of non-crop habitat in (2000 m radius) landscape sectors were selected in China’s Jiangxi province. RSB infestation levels were highest in agriculture-dominated landscapes. Meanwhile, parasitism rate increased with pest pressure but was not related to landscape-level non-crop habitat cover. Landscape-level responses of parasitoids were species-specific and likely modulated by functional traits. The specialist parasitoid Cotesia chilonis (Munakata) responded negatively to non-crop habitat, while positive responses were recorded for the generalists Eriborus sinicus (Holmgren) and Microgaster russata (Haliday). Our work unveils the occurrence of a bottom-up cascade in which spatiotemporal rice cropping patterns shape pest pressure and parasitism dynamics, with more diverse landscapes experiencing lower RSB infestation levels. Non-crop habitats within the landscape matrix equally retained parasitoid species with varying feeding modes and attack strategies. Hence, despite its (globally) inconsistent impacts on biological control, agricultural landscape diversification can directly benefit pest suppression and thus remains a valuable component of the ecological intensification toolbox.
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Insect pollinators are declining globally as a result of the anthropogenic pressures that have destroyed native habitats and eroded ecosystems. These declines have been associated with agricultural productivity losses, threatening food security. Efforts to restore habitat for pollinators are underway, emphasizing large-scale habitat creation like wildflower strips, yet ignoring the impact of smaller or more isolated patch-creation. A meta-analysis of 31 independent published studies assessed the effect of scale of pollinator planting interventions (herbaceous strips, hedgerows, fertiliser/grazing/mowing control). We assessed pollinator species richness and abundance against size of intervention and type. Pollinator conservation interventions increased species richness and abundance in almost all of the studies examined, with the greatest increases in pollinator ecological metrics seen from hedgerows covering 40 m² and herbaceous interventions at 500 m². We then analysed results from a 5-year study that deployed small pollinator habitats (30 m²) at community gardens and farms (<150,000 m²) practicing organic methods in the Pacific Northwest US. Small additions to pollinator resources had a significant local impact on pollinator abundance, but this effect was lost when these relatively small additions were introduced to sites in larger landscapes (>150,000 m²). Together, we show that small interventions (∼500 m²) can significantly benefit pollinators, but only when sufficiently densely distributed at a landscape level. Though we understand the effects of single interventions at various scales, future research is needed to understand how these relatively small interventions act cumulatively at a landscape scale, and within this context whether larger areas are still needed for some species. Nonetheless, these preliminary data are promising, and may play an important role in convincing smaller landowners to act to preserve insect pollinators.
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Flower strips are a commonly used tool for improving agricultural landscapes for pollinators. The plant composition of the seed mixtures employed is based on logistic decisions, e.g. costs or seed availability, the literature and expert opinion, and only rarely on direct information about bee-plant interactions. We combined two datasets on bee-plant interactions involving 460 bee species. The first consisted of 23,864 bee-plant interactions, recorded in twenty locations in Germany from 2018 and 2019, whereas the second consisted of 86,509 bee-plant interactions sampled across multiple sites in southwest Germany over more than 30 years. We explored three objectives. (1) Which plant species attract the greatest number of wild bee species and individuals across plant communities within and across seasons of bee activity? (2) Do the most attractive plant species also support threatened and specialized wild bees? (3) Do seed mixtures contain attractive plant species? High attractiveness was defined as a consistently high interaction frequency and number of visiting bee species to a plant species across the sampled communities. Our results identified 34 herbaceous key plant species that were highly attractive for wild bees independently of plant abundance and across locations. Further, we identified a large number of plant species for which the attractiveness for wild bees depended on the sampled community. The identified key plant species attracted between 2% and 32% of oligolectic or red-listed bees present in our datasets. Although some of these plant species, such as Centaurea cyanus or C. jacea, are commonly found in seed mixtures, others, such as Stachys recta or Carduus nutans, are not. These large-scale and robust interaction data highlight key plant species that provide an attractive core for herbaceous floral strips aimed at supporting high numbers of wild bee species.
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The contribution of wild pollination service to global agriculture is increasingly recognized. Still, biotic pollination demand is mainly covered by managed species, whereas implementing ecological intensification practices to promote wild pollination service remain less common. In this study, we evaluated (i) the effect of wild and managed pollinators and the richness of pollinator functional groups (RPFG) on production quality (i.e., fruit size) and quantity (i.e., crop yield), of two southern highbush blueberry (Vaccinium corymbosum) cultivars, and (ii) how wild pollinator service and crop production correlate with farm’s land cover. We found that pollination service supply and the spatial context interact with the blueberry cultivar to determine yield and fruit size. The abundance of big-sized wild bees and hummingbirds positively affected fruit size and crop yield, but the relationship's significance was cultivar-dependent. In contrast, the increase in honeybees visitation rate was detrimental to the average fruit size of blueberries, but the effect was not generalizable between cultivars. The amount of forested area affected positively wild pollinator abundance and RPFG only in one cultivar, whereas grassland and hedgerow had adverse effects for pollinators in the other. Consistently, the relation between blueberry fruit size and the farm’s land cover was subordinate to the cultivar. That is, despite all significant relations had the same sign between cultivars, their coefficients were statistically different. Our results support the idea that wild pollinators contribute to producing higher yields and larger berries in blueberry crops. Moreover, we found that the retention of natural forest at a 200 m radius within the farm may increase pollination service supply. However, the significance of every effect was contingent on the blueberry cultivar. This cultivar-dependent response points out that a robust assessment of pollinator benefits not only should include multiple production metrics, but also must incorporate within-crop variation, particularly in systems where growers use a mosaic of cultivars with different pollination requirements.
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Arthropod predators and parasitoids attack crop pests, providing a valuable ecosystem service. The amount of noncrop habitat surrounding crop fields influences pest suppression, but synthesis of new studies suggests that the spatial configuration of crops and other habitats is similarly important. Natural enemies are often more abundant in fine-grained agricultural landscapes comprising smaller patches and can increase or decrease with the connectivity of crop fields to other habitats. Partitioning organisms by traits has emerged as a promising way to predict the strength and direction of these effects. Furthermore, our ability to predict configurational effects will depend on understanding the potential for indirect effects among trophic levels and the relationship between arthropod dispersal capability and the spatial scale of underlying landscape structure.
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Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and non-crop habitats, and species' dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7-and 1.4-fold respectively. Arable-dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield-enhancing ecosystem services.
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Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and non-crop habitats, and species' dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7-and 1.4-fold respectively. Arable-dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield-enhancing ecosystem services.
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Wildflower strips (WFS) are increasingly commonly adopted measures to promote biodiversity in agro-ecosystems. While their effectiveness in providing floral and other food resources for pollinators and natural enemies has been relatively well studied, much less is known about the value of different types of WFS as overwintering habitat for different functional arthropod groups. Here, we examined arthropod overwintering in WFS of different age compared to winter wheat fields. Moreover, we addressed the largely unexplored question to what extent non-permanent WFS may act as sink or ecological trap, if they attract high numbers of overwintering arthropods but only a low proportion of them survive and successfully emerge due to ploughing of strips during overwintering. Overwintering of all studied arthropod groups eincluding potential pest natural enemies spiders, carabid beetles, staphylinid beetles and different families of pollinating flies ewas higher in WFS compared to winter wheat crops. Overwintering increased in WFS compared to wheat fields irrespective of WFS age, except for 4 year old WFS in the case of carabid beetles and 1 year old WFS in the case of spiders. While WFS age positively affected spider overwintering, numbers of overwintering pollinating flies and staphylinid beetles did not change significantly with WFS age. Moreover, carabid beetles tended to decline in the four years old WFS compared to younger ones. Ploughing of annual WFS during overwintering significantly reduced the number of successfully emerging arthropods by 59% on average. Detrimental effects were strongest for carabid beetles and spiders (reductions by 67% and 69%, respectively) to their numbers in ploughed WFS being similar to winter wheat fields. Reductions were less severe for pollinating flies and staphylinid beetles (both 47%), with higher numbers emerging from annual WFS compared to winter wheat fields even after ploughing of WFS. We conclude that perennial WFS are valuable overwintering habitats for a range of arthropod taxa across functional groups in arable cropping systems. Distinct responses of different arthropod taxa to WFS age highlight the importance of managing perennial WFS of various successional stages in order to promote overwintering of a broad variety arthropods in agro-ecosystems. Our study raises concerns, however, that annual WFS ploughed during the overwintering period are poor overwintering habitats for arthropods and may even act as ecological traps.
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Enhancing floral resources is a widely accepted strategy for supporting wild bees and promoting crop pollination. Planning effective enhancements can be informed with pollination service models, but these models should capture the behavioural and spatial dynamics of service‐providing organisms. Model predictions, and hence management recommendations, are likely to be sensitive to these dynamics. We used two established models of pollinator foraging to investigate whether habitat enhancement improves crop visitation; whether this effect is influenced by pollinator foraging distance and landscape pattern; and whether behavioural detail improves model predictions. The more detailed central place foraging model better predicted variation in bee visitation observed between habitat types, because it includes optimized trade‐offs between patch quality and distance. Both models performed well when predicting visitation rates across broader scales. Using real agricultural landscapes and simulating habitat enhancements, we show that additional floral resources can have diverging effects on predicted crop visitation. When only co‐flowering resources were added, optimally foraging bees concentrated in enhancements to the detriment of crop pollination. For both models, adding nesting resources increased crop visitation. Finally, the marginal effect of enhancements was greater in simple landscapes. Synthesis and applications. Model results help to identify the conditions under which habitat enhancements are most likely to increase pollination services in agriculture. Three design principles for pollinator habitat enhancement emerge: (a) enhancing only flowers can diminish services by distracting pollinators away from crops, (b) providing nesting resources is more likely to increase bee populations and crop visitation and (c) the benefit of enhancements will be greatest in landscapes that do not already contain abundant habitat.
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There is worldwide concern about the environmental costs of conventional intensification of agriculture. Growing evidence suggests that ecological intensification of mainstream farming can safeguard food production, with accompanying environmental benefits; however, the approach is rarely adopted by farmers. Our review of the evidence for replacing external inputs with ecosystem services shows that scientists tend to focus on processes (e.g., pollination) rather than outcomes (e.g., profits), and express benefits at spatio-temporal scales that are not always relevant to farmers. This results in mismatches in perceived benefits of ecological intensification between scientists and farmers, which hinders its uptake. We provide recommendations for overcoming these mismatches and highlight important additional factors driving uptake of nature-based management practices, such as social acceptability of farming.