Plants for Bugs

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A project investigating invertebrate abundance and diversity in assemblages of native and non-native garden plant species

Lead scientist

Helen Bostock, RHS and Andrew Salisbury, RHS

Partners

Wildlife Gardening Forum, Joe Perry and Mark Tatchell

Start date

2009

End date

2012

Keywords

Biodiversity, native plants, non-native plants, garden wildlife, field trial, Plants for Bugs.

Benefits to gardeners

The study will give gardeners more confidence when deciding what to plant for wildlife. Surveys of urban gardens have indicated that non-native plant species are of benefit to garden biodiversity (BUGS project, see Gaston et al 2005 and references therein).

The experiment has been rigorously designed to provide scientific evidence of the value of native and non-native plant assemblages for wildlife diversity which is of relevance to the gardener.

The problem

It is generally accepted that some plants are better at supporting wildlife than others. However, planting guidance for gardeners is largely based on anecdotal evidence or, worst still assumptions that have been shown to be untrue (e.g. that nettles are required to attract butterflies see Gaston et al 2005). There is a widely held belief that native plants should be paramount in wildlife gardening.

Approximately 70% of plants in the ‘average’ garden are non-native (Loram et al 2008) and are therefore generally considered to be of little biodiversity benefit. In contrast, studies of urban gardens suggest they are rich in biodiversity (Smith et al 2006). Therefore it is possible that native plants that make up the minority of plants in the ‘average’ garden are having a significantly greater impact than their numbers suggest or that non-native plants also provide a resource for biodiversity.

We will therefore test the effect of selected assemblages of native and non-native plants on invertebrate abundance and diversity. Findings from this study will only begin to answer these questions and it is hoped will stimulate further research.

Approach

The effect of the different plant assemblages on invertebrate abundance and diversity will be tested with a field experiment, designed to be representative of a garden border.

Plot design and plant treatment

The experiment will consist of two 27x14m sites (one in Howards Field, RHS Garden Wisley, the other at the Deers Farm trials site, Wisley Village).

There will be three plant treatments (assemblages):

Natives (naturally occurring in Britain and of British provenance where possible)
Near-natives (not native to Britain, but originating in the Northern hemisphere. Some attempt to match flowering time and habit)
Exotics (not native to Britain, but originating in the Southern hemisphere. Some attempt to match flowering time and habit)

The experiment will follow a split plot design with six replicates of each treatment at each site (12 replicates in total). Each replicate will consist of a 3x3m plot. Timber-edged wood-chip guard rows of at least 1m will separate the plots.

Other considerations for the experimental design include;

(a) Staggered development – to be reviewed after Year one with a view to grubbing out and re-planting some plots in years two and three.

Other conditions of the experiment include:

Treatments will be as ‘garden-like’ as possible, e.g. visually appealing and weed free. Weed control as required to prevent flowering and competition to plant assemblages.
A minimum of 14 (from a total of 24) plant species will be selected for each treatment. The plant assemblages will appear as similar as possible in terms of plant height, density and position in the plots.
Individual plant needs, e.g. sun or shade requirements, will be taken into account.
Slug pellets may be used for a very limited period to enable plant establishment, mirroring common garden practice. The plots will be rabbit-proofed.
Irrigation needs during plant establishment will be considered.
Wherever possible, plants will be clonally propagated.
The Howard’s Field plot will be accessible to garden visitors.

Data collection and analysis

Invertebrates (variable):

Collection of invertebrates will begin in the pilot year and continue for at least a further two years. Where possible collected invertebrates will be identified to species and classified to guild (e.g. specialists, non specialists). Collection and analysis methods will be modified and developed in the pilot year and will initially be based on methodologies from those used in the Farm Scale Evaluations of GM crops (Firbank et al 1999) and will include;

Pitfall trapping and baited refuge traps for ground fauna
Suction sampling for invertebrates found on plants
Direct observation of flying insect visitors to plots

Factors other than plant assemblage:

Measurements of additional factors that may effect invertebrate abundance and diversity will be made on each plot at the time of invertebrate recording. This will include an assessment of ground cover, plant height and structure.

Further information

Download promotional poster

Download handout

References

Firbank L G, Dewar A M, Hill M O, May M J, Perry J N, Rothery S P, Squire G R and Woiwod I P (1999). Farm-scale evaluation of GM crops explained. Nature, 399:727-728.

Gaston K J, Warren P H, Thompson K & Smith R M (2005). Urban domestic gardens (IV): the extent of the resource and its associated features. Biodiversity and Conservation 14: 3327-3349

Loram A, Warren P H and Gaston K J (2008). Urban Domestic Gardens (XIV): The Characteristics of Gardens in Five Cities. Environmental Management, e-first.

Smith R M, Warren P H, Thompson K and Gaston K J (2006). Urban domestic gardens (VI): environmental correlates of invertebrate species richness. Biodiversity and Conservation, 15:2415-2438.

Advisory information

Link to staff profile