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Avian use of hedgerows and adjacent crops in Central California agricultural landscapes

Authors:
  • Colorado Chapter of The Nature Conservancy

Abstract and Figures

Background/Question/Methods Hedgerows provide valuable ecosystem services including air and water quality protection, soil erosion control, promotion of pollinators and other beneficial insects, and biodiversity. Planting hedgerows at field margins is an increasingly common conservation measure in heavily transformed agricultural regions of California. Hedgerows may also provide critical habitat for numerous avian species that utilize the small, linear, wooded patches for resting, foraging, wintering and breeding. However, avian usage of hedgerows in Central California has not been well studied and farmers fear they may attract undesirable bird species. More complex vegetation structure and composition attract numerous songbirds that frequent field edges, but there is little information about the degree to which hedgerows are used by wintering and breeding birds. We used a paired study design to 1) evaluate the degree to which hedgerows are used by birds relative to nearby unenhanced field margins; 2) evaluate bird use of adjacent crops (standardized by crop type) to determine if hedgerows attract bird species considered crop pests, 3) determine if hedgerows in agricultural landscapes increase avian diversity and abundance relative to landscapes without hedgerows and 4) quantify and determine key habitat structures that are influencing the avian community on our sites. Results/Conclusions The pilot phase of our study was conducted during winter (Nov-Jan 2011) and spring (Apr-Jun 2012) to determine wintering and breeding bird use on paired hedgerow and reference plots in Yolo County, CA. We quantified vegetation diversity, composition, structure, and noted fruiting and flowering events to include in avian-habitat relationship models. Analysis of pilot data indicate that more than twice as many bird species and nearly four times as many individual birds use habitat created by native-planted hedgerows as opposed to unenhanced field margins. Our results also show that species richness, abundance, and bird use in adjacent crops was not significantly different when hedgerows were present, indicating that hedgerows are not attracting pest bird species. Additionally, results indicate that planting hedgerows with native species may act as refugia for wintering songbirds without attracting species considered to be crop pests. These results may help act as an incentive for farmers and landowners to replace non-native field margins with native species, which in turn, provide valuable ecosystem services. We anticipate that survey efforts will continue and expand to further understand the role that hedgerow vegetation structure and composition plays in structuring avian communities in agricultural landscapes.
Content may be subject to copyright.
1
Agriculture and Natural
Resources, UC Cooperative
Extension, Woodland, CA.
2
Audubon California, Landowner
Stewardship Program,
Sacramento, CA.
3
Department of
Plant Sciences, UC Davis, CA.
4
College of Biological Sciences,
UC Davis, CA.
www.sercal.org 5 Ecesis
Introduction
Wildlife conservation in agro-ecosystems is especially challenging
due to habitat loss and fragmentation, intensive human land use,
and the need to balance conservation goals with agricultural
production. Hedgerows are often incorporated into agro-ecosystem
conservation planning since they offer disproportionate
enhancement of valuable ecosystem goods and services (e.g., air and
water quality protection, weed control, soil erosion control,
promotion of pollinators and other beneficial insects, and
biodiversity) in exchange for minimal reductions in production
(Earnshaw 2004, Long and Anderson 2010, Morandin and Kremen
2012). Hedgerows consist of trees, shrubs, perennial grasses, forbs
and other species planted in narrow strips along field margins
(Long and Anderson 2010), with the use of native species advocated
for in recent years (Long and Anderson 2010, Morandin and
Kremen 2012).
Hedgerows are an increasingly common conservation measure in
heavily transformed agricultural regions of Central California, in
part because of their perceived potential to provide critical habitat
for numerous avian species that may utilize the small, linear,
wooded patches for resting, foraging, wintering and breeding
(Hinsley and Bellamy 2000; Earnshaw 2004). However, avian usage
of hedgerows in Central California has not been well-studied, and
data is lacking in regard to hedgerow effects on avian abundance
and diversity and how these effects differ across wintering and
breeding seasons. Understanding these effects will be critical to the
promotion of hedgerows as agro-ecological conservation measures
in Central California and beyond. In addition, the perception that
hedgerows may attract
undesirable bird species into
agricultural fields (Earnshaw
2004) cannot be addressed
without quantitative data on
avian use of hedgerows and
adjacent fields.
In order to address these gaps
in knowledge, we conducted a
pilot study of avian hedgerow
use in Yolo County from 2011-
2012. Our objectives were to
use a paired study design to quantify 1) hedgerow effects on avian
abundance, richness, and diversity in both wintering and breeding
seasons relative to unenhanced field margins (control sites); 2)
avian use of adjacent crop fields (standardized by crop type) to
determine if hedgerows attract avian crop pests; and 3) key habitat
characteristics that may be influencing avian use of hedgerows and
unenhanced field margins. In this article, we focus primarily on the
results of avian analyses while briefly describing vegetation in
hedgerow and control sites.
Methods
We selected four hedgerow sites in Yolo County that were similar in
age and structure and that were already being used in UC
Cooperative Extension research (Fig. 1). Nearby unenhanced field
margins served as control sites, and both hedgerow and control sites
were standardized by adjacent crop type. Six 20-min avian search
censuses were conducted at 2-week intervals along 0.25-mi stretches
of hedgerow and control habitat in both winter (Nov. 2011-Jan
2012) and breeding (Apr-June 2012) seasons. Vegetation surveys
were conducted in May 2012, and consisted of identification and
measurements of all trees and shrubs (hedgerows) and 1-m
2
percent
cover quadrats in understories of both hedgerow and control sites.
Statistical comparisons of means were conducted using program R,
and statistical significance was assessed at the P≤0.05 level.
Results
Avian abundance, richness, and diversity. Pooled across seasons, we
found that avian abundance was more than three times higher in
Figure 1 A native-planted hedgerow in Yolo County, California. Photograph courtesy H.M.White.
Avian Use of Hedgerows and Adjacent Crops in Central
California Agricultural Landscapes
by Hillary M. White
1
, Rachael F. Long
1
, Karen Velas
2
, Andrew P. Rayburn
3
, William L. Rockey
4
, and Rodd Kelsey
2
.
continued next page
Ecesis 6 Winter 2012 Volume 22, Issue 4
hedgerows (1689 individuals) compared to control sites (514
individuals). This difference in abundance persisted when the data
were analyzed separately for wintering (N
hedgerows
= 1314
individuals and N
control
= 331 individuals) and breeding seasons
(N
hedgerows
= 375 individuals and N
control
= 183 individuals).
Similar results were found for species richness. A total of 41 species
were detected at hedgerow sites, compared to 22 species at control
sites. Pooled across seasons, average avian richness was nearly
double in hedgerows (27.50 ± 1.55 spp.) compared to control sites
(15.25 ± 0.95 spp.). Analysis by season showed that average avian
richness was significantly higher in hedgerows in both wintering
(20.00 ± 1.96 spp. in hedgerows, 8.00 ± 0.41 spp. in control sites)
and breeding seasons (17.50 ± 1.32 spp. in hedgerows, 9.25 ± 0.25
spp. in control sites).
Results were less clear for species diversity, which we calculated
using the Shannon-Wiener index that accounts for species richness
and relative abundance. During the breeding season, avian species
diversity was significantly higher in hedgerow sites (9.94 ± 1.15)
compared to controls sites (5.70 ± 0.82). No other significant
differences in diversity between hedgerow and control sites were
detected.
Interestingly, our results showed that avian abundance and richness
in adjacent crop fields were not significantly different when
hedgerows were present, suggesting that hedgerows are not
attracting avian pest species into nearby crops. For example, for
three of the most common avian crop pests (American crow
[Corvus brachyrhynchos], red-winged blackbird [Agelaius
phoeniceus], and Brewer’s blackbird [Euphagus cyanocephalus]),
there were between five and ten times more birds detected during
the study in agricultural fields adjacent to unenhanced field margins
Our many thanks to our generous
2012 conference sponsors…
compared to crop fields adjacent to hedgerows. Analysis of flyover
data collected during the study suggested that these species tended
to pass over hedgerows entirely and may have been more focused
on crop fields as a landscape feature.
Habitat characteristics. Overstory vegetation in hedgerows was
dominated by Coyotebush (Baccharis pularis), Black elderberry
(Sambucus nigra), and California coffeeberry (Frangula californica).
Mean abundance, richness, and diversity of trees and shrubs in
hedgerows were 83 ± 6.50 individuals, 9.25 ± 0.58 spp., and 5.17 ±
0.63 respectively. Understory vegetation in both hedgerows and
control sites was characterized by both native and exotic grasses and
forbs, although native cover was significantly higher in hedgerows
(30.65 ± 8.36% ) versus control sites (8.05 ± 3.17%) and exotic cover
was significantly higher in control sites (64.90 ± 3.42%) versus
hedgerow sites (47.90 ± 6.29%). Hedgerow sites also had
significantly more litter, while control sites had significantly more
bare ground. No differences in native understory species richness
were found, but control sites did have significantly more exotic
understory species.
Conclusions and future research directions
We found that avian abundance and richness were significantly
higher in native hedgerows compared to unenhanced field margins,
especially during the wintering season. During the breeding season,
avian diversity was higher in hedgerows compared to unenhanced
field margins. Our results strongly suggest that native hedgerows in
Central California agricultural landscapes may act as both refugia
for wintering songbirds and as habitat for breeding songbirds
without attracting avian pests into adjacent crop fields. These
findings may serve as an incentive for producers to plant hedgerows
at field margins, since native-planted hedgerows positively influence
a broad suite of valuable ecosystem goods and services in addition
to providing wildlife habitat.
The results of this pilot study are being used to scale up research
efforts to include a larger set of study sites across the Sacramento
Valley in conjunction with native pollinator researchers at
UC Berkeley, enabling us to further understand the effects
of hedgerows on avian communities in agricultural
landscapes.
References
Earnshaw, S. 2004. Hedgerows for California agriculture. CAFF.
caff.org/wp-content/uploads/2010/07/Hedgerow_
manual.pdf
Hinsley, S.A. and P.E. Bellamy. 2000. The influence of hedge
structure, management and landscape context on the value of
hedgerows to birds: A review. Journal of Environmental
Management 60:33-49.
Long R.F., and J. Anderson. 2010. Establishing Hedgerows on
Field Crop Farms in Californias Central Valley. UC ANR Pub
8390. Oakland, CA. 7 p.
Morandin, L.A. and C. Kremen. 2012. Bee preference for native
versus exotic plants in restored agricultural hedgerows.
Restoration Ecology. doi: 10.1111/j.1526-100X.2012.00876.x
Avian use of hedgerows and adjacent crops
continued
... Despite the goal of providing habitat for birds, research on woody field margin habitats in California has focused on evaluating their benefits for pollinators and other agriculturally-beneficial insects (Morandin et al., 2014;Morandin and Kremen, 2013). Studies detailing the effects of hedgerows and other field margin habitats on birds in California have been preliminary (White et al., 2013), or have focused on single crop-types or seasons (Jedlicka et al., 2014;Kross et al., 2016). To inform and improve state and national policies and incentive programs, we evaluated the effects of different field margin habitat features on both breeding and winter season avian community structure in the context of several local and landscape scale habitat characteristics. ...
Article
Considerable funding has been allocated to conservation management of non-crop habitat in agricultural landscapes, particularly field margin habitat such as hedgerows. Evaluation of the biodiversity benefits of non-crop habitat has lagged behind implementation, however, especially in the United States where this habitat has the potential to supply important resources for both common and rare species of birds. We examined the effects of woody field margin vegetation on winter and breeding season avian communities at 103 fields, row crops, and orchards in California's Central Valley, one of the most intensively-farmed landscapes on Earth. We found that margins with hedgerows, treelines or remnant riparian habitat harbored 2–3 times as many bird species, significantly greater species evenness, and 3–6 times higher maximum total abundances of birds than bare or weedy margins. The effect of margin type on richness was modulated by water year, whereas the effect of margin type on maximum total abundance was modulated by adjacent crop type. At the landscape scale, hedgerow and riparian margins that were further from woodland harbored greater species richness; a result that supports our recommendation for targeted development of hedgerows in simplified agricultural landscapes. These results demonstrate that non-crop woody habitats, both planted and remnant native patches, increase the biodiversity value of farms, providing support for policies to preserve remaining habitat and incentivize installation of woody hedgerows.
Article
Habitat restoration to promote wild pollinator populations is becoming increasingly common in agricultural lands. Yet, little is known about how wild bees, globally the most important wild pollinators, use resources in restored habitats. We compared bee use of native and exotic plants in two types of restored native plant hedgerows: mature hedgerows (>10 years from establishment) designed for natural enemy enhancement and new hedgerows (≤2 years from establishment) designed to enhance bee populations. Bees were collected from flowers using timed aerial netting and flowering plant cover was estimated by species using cover classes. At mature hedgerow sites, wild bee abundance, richness, and diversity were greater on native plants than exotic plants. At new sites, where native plants were small and had limited floral display, abundance of bees was greater on native plants than exotic plants; but, controlling for floral cover, there was no difference in bee diversity and richness between the two plant types. At both mature and new hedgerows, wild bees preferred to forage from native plants than exotic plants. Honey bees, which were from managed colonies, also preferred native plants at mature hedgerow sites but exhibited no preference at new sites. Our study shows that wild bees, and managed bees in some cases, prefer to forage on native plants in hedgerows over co‐occurring weedy, exotic plants. Semi‐quantitative ranking identified which native plants were most preferred. Hedgerow restoration with native plants may help enhance wild bee abundance and diversity, and maintain honey bee health, in agricultural areas.
Article
In this review, we discuss the value of hedgerows as bird habitat in lowland-farming landscapes to provide a background against which decisions concerning hedgerow management might be evaluated. The two most important factors positively associated with species richness and abundance of breeding birds in hedgerows are hedge size (height/width/volume) and the presence/abundance of trees. The provision of cover and the botanical and structural complexity of the vegetation are also important. However, large hedges do not suit all species; birds tend to prefer hedgerow types which most closely resemble their usual non-hedgerow breeding habitat. The value of hedgerows to birds can be increased by combining them with other features such as headlands (for game birds), verges, wildflower strips, game and wild-bird cover and well-vegetated banks and ditches. The presence of well-grown, dead or decaying trees is beneficial to many species, providing nest holes, foraging sites and perches. Increasing the structural complexity of a hedgerow and its associated habitat may also reduce the incidence of predation. Hedgerows also provide physical shelter and roost sites and are an important source of winter food supplies, especially berries and other fruits. Some bird species, usually those whose primary habitat is woodland, live mainly within the hedgerow itself, whereas others are more dependent on the surrounding landscape to a greater or lesser extent. However, even the presence of woodland bird species is influenced by the availability and characteristics of alternative habitats in the surroundings and therefore hedgerows and their bird populations do not function as isolated patches. As linear landscape elements, hedgerows also provide safe cover for both local and larger-scale movements and may facilitate access to resources or habitat which might otherwise be too risky or too remote for birds to use or colonise. A number of recommendations for improving hedgerow habitat for birds are reiterated from an extensive literature and include combining hedgerows with other semi-natural habitat, providing a variety of structural types, maintaining good cover in the hedge-base, e.g. by excluding stock and herbicide, and avoiding excessive cutting. However, good hedgerow management has costs and is unlikely to be applied widely in the absence of national policy and funding.
Hedgerows for California agriculture
  • S Earnshaw
Earnshaw, S. 2004. Hedgerows for California agriculture. CAFF. caff.org/wp-content/uploads/2010/07/Hedgerow_ manual.pdf
Establishing Hedgerows on Field Crop Farms in California's Central Valley
  • R F Long
  • J Anderson
Long R.F., and J. Anderson. 2010. Establishing Hedgerows on Field Crop Farms in California's Central Valley. UC ANR Pub 8390. Oakland, CA. 7 p.
Bee preference for native versus exotic plants in restored agricultural hedgerows. Restoration Ecology
  • L A Morandin
  • C Kremen
Morandin, L.A. and C. Kremen. 2012. Bee preference for native versus exotic plants in restored agricultural hedgerows. Restoration Ecology. doi: 10.1111/j.1526-100X.2012.00876.x Avian use of hedgerows and adjacent crops continued