- Lead scientist
- Helen Bostock (RHS) and Andrew Salisbury (RHS)
- Wildlife Gardening Forum,Roehampton University, Joe Perry and Mark Tatchell
- Start date
- End date
Biodiversity, native plants, non-native plants, exotic 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, worse 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, however approximately 70% of plants in the ‘average’ garden are non-native (Loram et al. 2008) and are therefore often considered to be of less benefit to biodiversity. In contrast, studies of urban gardens suggest they are rich in biodiversity (Smith et al. 2006). Therefore it is possible that native plants, which 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 valuable resource for biodiversity.
We are testing the effect of selected assemblages of native and non-native plants on invertebrate abundance and diversity. This will test the hypothesis that there is no difference in invertebrate diversity associated with assemblages of native, near-native and exotic garden border plants. Findings from this study will only begin to answer these questions and this will stimulate further research.
The effect of the different plant assemblages on invertebrate abundance and diversity is being tested with a field experiment, designed to be representative of a garden border. Some attempt has been made to match flowering time and habit across native and non-native plant assemblages. The design and treatment is as follows:
There are three plant treatments (assemblages):
- Native plants (naturally occurring in Britain and of British provenance where possible)
- Near-native plants (not native to Britain, but originating in the Northern hemisphere.
- Exotic plants (not native to Britain, but originating in the Southern hemisphere.
The experiment is made up of two replicate sites, Howard's Field, Wisley Gardens and at Deers Farm, Wisley Village.
The layout follows a randomized split-plot design with six replicates of each treatment at each site (12 replicates in total). Each replicate consists of a 14 plant species 3x3 m plot. Timber-edged wood-chip guard rows of 1 m wide separate the plots.
A minimum of 14 (from a total of 24) plant species were selected for each treatment. The plant assemblages were designed to appear as similar as possible in terms of plant height, density and position in the plots.
Other considerations for the experimental design include:
- The plots are treated as ‘garden-like’ as possible, e.g. visually appealing and weed free.
- Weed control is carried out to prevent flowering and competition with the plant assemblages
- Individual plant needs, e.g. sun or shade requirements, were taken into account
- The plots are rabbit-proofed with wire fencing
- Irrigation has been carried out during plant establishment as necessary
- Wherever possible, plants were clonally propagated to ensure uniformity.
- The Howard’s Field plots are accessible to garden visitors.
Data collection and analysis
Protocols for collection and identification of invertebrates were established during the pilot year (2009). Where possible, collected invertebrates are identified to species and classified to guild (e.g. predators, herbivores, detritivores). The invertebrates will be sampled on at least five occasions each year using the methods below.
Pitfall trapping and baited refuge traps for ground fauna
Suction sampling for invertebrates found on plants
Direct observation of flying insect visitors to the plots
Soil fauna and function monitoring. This involves taking soil cores from the plots and extracting invertebrates using Tullgren funnels and soil function is assessed using litter bags. This is part of a PhD project in collaboration with Roehampton University.
At the end of 2011 approximately 34000 invertebrates had been counted and identified, including 40 species of ground beetle from the pitfall traps, 27 species of spider from the suction sampler and 13 species of butterfly observed visiting the plots. Sampling will continue in 2012 and 2013, and data analysis will be completed at the end of the experiment.
Measurements of additional factors that may affect invertebrate abundance and diversity are made on each plot. This includes photographic records of the plots and assessments of canopy and ground cover, soil moisture, flower number, seed counts, plant height and structure.
- Further information
Plants for bugs blog
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 Management42:361-376
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 Conservation15:2415-2438.
Andrew Halstead - Entomological consultant
Andrew Salisbury – Assistant project manager
James Armitage - Botanical consultant
Joe Perry - External consultant on statistics and plot design
Helen Bostock – Project manager
Mark Tatchell - External consultant on science aspects
Roger Williams - Chair
The project is also supported by the Wisley Trials and Woody Ornamental teams and the Plants for Bugs volunteers