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Shades of green – “wildflowers” and biodiversity urban planting considerations

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Noeleen Ann Smyth at University College Dublin
Noeleen Ann Smyth
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Acta Hortic. 1374. ISHS 2023. DOI 10.17660/ActaHortic.2023.1374.28
Proc. II IS. on Greener Cities: Improving Ecosystem Services in a Climate-Changing World
(GreenCities2022)
Eds.: V. Loges and F.L. Cuquel
221

a

Abstract
Today more than half of the world’s population live in cities. Urban greenspace
has become an import habitat for native species biodiversity. The potential exists for
cities to provide refuges for native flora and threatened plants. Urban spaces are not
devoid of native species and native wildflowers. Urban areas are also often the point of
origin of many exotic invasive species, which can spread into adjacent landscapes along
transport corridors such as railways and roads, in many cases eventually invading
natural areas. There are many instances of horticultural planting of exotic wildflower
mixes into road verges in Dublin City the capital of Ireland. Some common horticultural
“wildflower” mixes which are labelled as biodiversity, woodland, meadow mixes
contain species which are exotic to Ireland and Europe and planting these into the
wider landscape poses a threat to native species biodiversity. Seed mixes for sale in
Ireland from the major retail stores were investigated, noting this is a small sample of
the wide variety of these unregulated seed mixes that are currently on the European
market. A total of 56 species were contained in the packets investigated. Forty four or
over 70 per cent (78.5%) are considered native to the European region, the concern is
that there is no provenance given for the seed on any of the packets. Twelve species or
one fifth (21.4%) of the species found in these packets are species not found in the wild
in the European region they occur naturally in parts of Asia, Africa, USA and Mexico.
Introducing these species to our wider natural environment and especially along road
verges in urban areas in these times of climate change is a concern. Only one quarter
(25%) or 14 species found in the packets are species considered native to Ireland
where the study was carried out. The contents of these wildflower seed packets are not
regulated within the EU and planting these exotic seed mixes have the potential to
negatively affect our local biodiversity. The remaining biodiversity in Ireland and
Europe is becoming increasingly marginalized and road verges where these species are
being sown into are considered an important refuge for native wildflower species.
Keywords:         

INTRODUCTION
             

           





           



a
E-mail: noeleen.smyth@ucd.ie
222









   


           

           
              
             
            
           
     



              

             


             





MATERIALS AND METHODS


               





            
           

RESULTS
           





223
 
          

Species distribution
Biodiversity impact when
planted into landscape
Seed
packet
SE. & E. Europe to N. Irana
Erosion of genetic diversity
4, 5
Europe to Central Siberia and W. Pakistan, N.W.
Africaa
Erosion of genetic diversity
5
N. Africa to Chad, Iran to Arabian Peninsula
Exotic/potential invasive
5
Macaronesia, Europe to Medit. and Irana
Erosion of genetic diversity
5
Subarctic & Temp. Northern Hemisphere to
Guatemalab
Erosion of genetic diversity
5
S. Central Europe to W. & Central Medit.a
Erosion of genetic diversity
5
Canada to N.W. & N. Central USA
Exotic/potential invasive
2
Macaronesia, Europe to Afghanistan, N.W.
Africab
Erosion of genetic diversity
5
Temp. Northern Hemisphereb
Erosion of genetic diversity
2
E. Central Europe to N.W. & N. Iran
Erosion of genetic diversity
5
W. & Central Medit.a
Erosion of genetic diversity
2,4, 5
West Medit.
Erosion of genetic diversity
4, 5, 6
Europe to W. Siberia, Türkiye to N. Caucasus
Erosion of genetic diversity
1, 2
Temp. Eurasia, N. Africab
Erosion of genetic diversity
5
Temp. Eurasiaa
Erosion of genetic diversity
5
Central & E. Medit. b
Erosion of genetic diversity
3,4,5,6,
7
Europe to Siberia and Central Asiab
Erosion of genetic diversity
5
Azores, W. Europe to N.W. Africab
Erosion of genetic diversity
4
Naturalised hybrid parents originating in W.
Europea
Exotic/invasive
5
Europe, C. Asia, W. Himalaya, Macaronesia to
N. Africaa
Erosion of genetic diversity
5
E. Medit. to Pakistan
Erosion of genetic diversity
5
Mexico to Central America
Exotic/potential invasive
5
Europea
Erosion of genetic diversity
5
Europe to Siberia and Caucasus
Erosion of genetic diversity
5
W. & S.W. Europe to N. Moroccob
Erosion of genetic diversity
1
Central and Eastern USA
Exotic/potential invasive
5
Europe to Xinjiangb
Erosion of genetic diversity
4, 5
W. & S. Central USA to N. Mexico
Exotic/potential invasive
5
Medit. to Ethiopia and W. Nepala
Erosion of genetic diversity
5
Europe to W. Siberia and Medit
Erosion of genetic diversity
5, 2, 7
Europe to Medit and Central Asia
Erosion of genetic diversity
2,3,5
S.W. USA to Mexico.
Exotic/potential invasive
5
S. France to Slovakia and Caucasusa
Erosion of genetic diversity
5
Europe to Central Siberiab
Erosion of genetic diversity
5
Europe, Medit. to Iran
Erosion of genetic diversity
5
S. Europe
Erosion of genetic diversity
5
Morocco
Exotic
/potential invasive
5
Europe to N.W. Africab
Erosion of genetic diversity
1
S. Iran to Afghanistan
Exotic/potential invasive
5
Europe to Russian Far East and Caucasusb
Erosion of genetic diversity
5
E. Central Europe to Siberia and China
Erosion of genetic diversity
4
SE. Canada to N. Central & E. USA
Exotic/invasive
5
Algeria to Tunisia
Exotic/potential invasive
6, 7
E. Central Europe to Siberia and China
Erosion of genetic diversity
4, 5
aIntroduced to Ireland, bNative to Ireland.
224
 
Macaronesia, Europe to Central Asia and W.
Himalayaa
Erosion of genetic diversity
5. 7
Temp. Eurasia to Indo-China
Erosion of genetic diversity
3,5
E. Medit. to Central Asia and Arabian Peninsula
Erosion of genetic diversity
5
Macaronesia, Medit. to NW. Iran
Erosion of genetic diversity
5
S.E. USA
Exotic/invasive
5
Europe to W. Türkiyea
Erosion of genetic diversity
5
Macaronesia, Europe to Medit. and W.
Himalayab
Erosion of genetic diversity
3,4,5,7
Canary Islands, Medit. to Central Asia and
Arabian Peninsula, S. Africaa
Erosion of genetic diversity
2
Europe to Siberia and N. Caucasusb
Erosion of genetic diversity
5
Europe to Siberia, NW. India, Africa to E.
Tropical Africaa
Erosion of genetic diversity
5
Mexico to Guatemala
Exotic/potential invasive
2,5
Europe to Siberia and Xinjiangb
Erosion of genetic diversity
5
             

          
Centaurea cyanus
is

          
Agrostemma githago



Calendula officinalis),
r

Borago officinalis)

225
       
          


Lupinus 

DISCUSSION
  



            

 

            


            


       
  
     



               

              
         


            






         
   


             
           

      
             
 

  

diverse plant assemblages and provide plentiful resources for
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insect pollinators


          

Literature cited
               
   

            

33

31

17
               
            20 

              


 
  

              
   

               
164

      

180






  


s, No. 102

    
5
      


Centaurea cyanusChenopodium bonus-
henricus341
227
   Carpobrotus edulis

 

             


        
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You Reap What You Sow: A Botanical and Economic Assessment of Wildflower Seed Mixes Available in Ireland
Article
Full-text available
  • Jan 2023
Planting wildflower seed mixes has become popular with individuals and community groups aiming to promote wildlife and enhance local biodiversity. Recently, however, these seed mixes have been criticized with respect to the origin of the seeds and the species they contain. There is a growing awareness that the unintended planting of exotic species may disrupt native ecological networks, introduce aggressive weeds, or facilitate the establishment of invasive species in new localities. In this study, we purchased two packets of twelve brands of wildflower seeds available in Ireland from stores or online suppliers. In total, the 24 packets contained 69,409 seeds weighing 304 g, and represented 92 plant species in 23 families. Only 25% of the seed packets purchased in Ireland originated from Ireland, and only 43% of the plant species we identified are considered native to Ireland. To reinforce this point, the most frequent species, Phacelia tanacetifolia, which occurred in nine of the twelve brands, is not a native Irish plant species. Multivariate analysis identified no obvious grouping of seed mixes based on their intended target group (e.g., bees, butterflies, wildlife), which might be expected had manufacturers followed scientific guidance describing which plants are preferred by which pollinator group. The creation of patches of diverse floral habitats in gardens and urban settings can significantly benefit wildlife and human wellbeing. Our results, however, reinforce the need for caution before using wildflower mixes in attempts to restore or recreate natural or semi-natural plant communities.
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Promoting wildflower biodiversity in dense and green cities: The important role of small vegetation patches
Article
Full-text available
  • Apr 2021
The conservation and promotion of biodiversity in urban spaces has become a core concern in urban greening. As cities continue to densify, however, urban green spaces are becoming smaller and more isolated. Many hope that wildflowers, and with them also faunistic biodiversity, can be maintained through networks of small informal green spaces. Currently, there are little data available for city planners to answer the questions of how patch size and ecological connectivity affect the population persistence of wildflowers in small vegetation patches. To address these concerns, we surveyed all vegetation patches greater than 1 m² in public spaces across seven 1 km² quadrats distributed across the city of Zurich, Switzerland. Our survey focused on a list of 166 herbaceous vascular plant species. We analyzed vegetation patch topologies (frequency distributions of size and connectivity) and related it to alpha and beta species diversity. Dispersal traits of investigated species were used to interpret connectivity patterns. Over 75% of patches were <20 m² in size, however, these small patches made up only 3.4% of total vegetation area. Species richness was significantly positively correlated with patch area. Nevertheless, taken together, small patches had similar species richness and higher beta diversity than larger patches. These small patches contribute far more than expected to overall wildflower species richness in the city – “punching above their weight”. This held true even for less common species. However, our research indicates that connecting these patches to one another and to larger green spaces is essential to unlocking their potential as habitats and potentially allowing for the natural colonization and reinforcement of existing populations. As cities densify, we must acknowledge that small vegetation patches such as tree discs or road margins are essential for the survival of wildflower populations and associated fauna, especially in highly urbanized areas.
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The monitoring and assessment of three EU Habitats Directive Annex I grassland habitats
Technical Report
Full-text available
  • Nov 2018
This report presents details of a monitoring survey conducted between 2015 and 2017 to assess the conservation status of three EU Annex I grassland habitats: Semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco-Brometalia) (6210) important orchid sites (*6210), Molinia meadows on calcareous, peaty or clayey-silt-laden soils (Molinion caeruleae) (6410), and Lowland hay meadows (Alopecurus pratensis, Sanguisorba officinalis) (6510).
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A systems approach reveals urban pollinator hotspots and conservation opportunities
Article
Full-text available
  • Mar 2019
  • Nat. Ecol. Evol.
Urban areas are often perceived to have lower biodiversity than the wider countryside, but a few small-scale studies suggest that some urban land uses can support substantial pollinator populations. We present a large-scale, well-replicated study of floral resources and pollinators in 360 sites incorporating all major land uses in four British cities. Using a systems approach, we developed Bayesian network models integrating pollinator dispersal and resource switching to estimate city-scale effects of management interventions on plant–pollinator community robustness to species loss. We show that residential gardens and allotments (community gardens) are pollinator ‘hotspots’: gardens due to their extensive area, and allotments due to their high pollinator diversity and leverage on city-scale plant–pollinator community robustness. Household income was positively associated with pollinator abundance in gardens, highlighting the influence of socioeconomic factors. Our results underpin urban planning recommendations to enhance pollinator conservation, using increasing city-scale community robustness as our measure of success.
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Plant species or flower colour diversity? Identifying the drivers of public and invertebrate response to designed annual meadows
Article
Full-text available
  • Sep 2018
  • LANDSCAPE URBAN PLAN
There is increasing evidence of the benefits of introducing urban meadows as an alternative to amenity mown grass in public greenspaces, both for biodiversity, and human wellbeing. Developing a better understanding of the meadow characteristics driving human and wildlife response is therefore critical. We addressed this by assessing public and invertebrate response to eight different annual meadow mixes defined by two levels of plant species diversity and two levels of colour diversity, sown in an urban park in Luton, UK, in April 2015. On-site questionnaires with the visiting public were conducted in July, August and September 2015. Invertebrate responses were assessed via contemporaneous visual surveys and one sweep net survey (August 2015). Flower colour diversity had effects on human aesthetic response and the response of pollinators such as bumblebees and hoverflies. Plant species diversity, however, was not a driver of human response with evidence that people used colour diversity as a cue to assessing species diversity. Plant species diversity did affect some invertebrates, with higher abundances of certain taxa in low species diversity meadows. Our findings indicate that if the priority for sown meadows is to maximise human aesthetic enjoyment and the abundance and diversity of observable invertebrates, particularly pollinators, managers of urban green infrastructure should prioritise high flower colour diversity mixes over those of high plant species diversity. Incorporating late-flowering non-native species such as Coreopsis tinctoria (plains coreopsis) can prolong the attractiveness of the meadows for people and availability of resources for pollinators and would therefore be beneficial.
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All about the ‘wow factor’? The relationships between aesthetics, restorative effect and perceived biodiversity in designed urban planting
Article
Full-text available
  • Aug 2017
  • LANDSCAPE URBAN PLAN
Urban populations experience the multiple health and well-being benefits of nature predominantly via urban green infrastructure. If this is to be designed and managed optimally for both nature and people, there is an urgent need for greater understanding of the complex relationships between human aesthetic experience, well-being and actual or perceived biodiversity. This integrative study assessed human aesthetic reaction, restorative effect and perceived biodiversity in relation to fine-grained categories of woodland, shrub and herbaceous planting. We surveyed 1411 members of the public who walked through planting of varying structure, species character and percentage flower cover whilst completing a site-based questionnaire. Semi-structured, in-depth interviews were then carried out with 34 questionnaire participants. Correlations between perceived attractiveness and perceived biodiversity were identified for three out of four biodiversity indicators. There was a correlation between perceived attractiveness and restorative effect yet this was not strong. Colourful planting with flower cover above a critical threshold (27%) was associated with the highest level of aesthetic preference. Subtle green ‘background’ planting afforded a restorative effect. These results are discussed with reference to the Circumplex Model of Affect. Our findings indicate that people appreciate colourful flowering public planting for the ‘wow factor’, but that green planting outside the narrow flowering season of most species is greatly valued. Planting moderately or most natural in structure was perceived as significantly more restorative than that least natural in structure suggesting that people in the UK may be increasingly accepting of a messier ‘ecological aesthetic’ in urban planting.
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Taxonomic and functional trait diversity of wild bees in different urban settings
Article
Full-text available
  • Mar 2017
Urbanization is one of the major anthropogenic processes contributing to local habitat loss and extirpation of numerous species, including wild bees, the most widespread pollinators. Little is known about the mechanisms through which urbanization impacts wild bee communities, or the types of urban green spaces that best promote their conservation in cities. The main objective of this study was to describe and compare wild bee community diversity, structure, and dynamics in two Canadian cities, Montreal and Quebec City. A second objective was to compare functional trait diversity among three habitat types (cemeteries, community gardens and urban parks) within each city. Bees were collected using pan traps and netting on the same 46 sites, multiple times, over the active season in 2012 and 2013. A total of 32,237 specimens were identified, representing 200 species and 6 families, including two new continental records, Hylaeus communis Nylander (1852) and Anthidium florentinum (Fabricius, 1775). Despite high community evenness, we found significant abundance of diverse species, including exotic ones. Spatio-temporal analysis showed higher stability in the most urbanized city (Montreal) but low nestedness of species assemblages among the three urban habitats in both cities. Our study demonstrates that cities are home to diverse communities of wild bees, but in turn affect bee community structure and dynamics. We also found that community gardens harbour high levels of functional trait diversity. Urban agriculture therefore contributes substantially to the provision of functionally diverse bee communities and possibly to urban pollination services.
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Wildflowers: From conserving biodiversity to urban greening—A review
Article
  • Oct 2016
Species-rich herbaceous communities, such as prairies, steppes, meadows and pastures, have a high biodiversity value. There is considerable interest in the loss of these complex ecosystems and the associated biodiversity, due to intensive agriculture, pasture abandonment, pollution, and climate change. These habitats can constitute models, in terms of landscape management and plant community composition, that can be successfully duplicated in anthropized areas in order to mitigate the adverse effects of human activities in the city and enhance the biotic component. The idea is to revegetate urban degraded soil with aesthetically pleasing wildflower meadows, while increasing biodiversity, creating a habitat and conserving the local flora, with low management cost. In urban sites seed mixtures containing a high percentage of native and exotic herbaceous flowering plants have been successfully used. We review the factors affecting the ecological aspects of species-rich herbaceous communities in disturbed environments and urban landscape design. The review addresses the use of these communities in urban green areas for recreation, socialization and environmental education.
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