Biodiversity, native plants, non-native plants, exotic plants, garden wildlife, field trial, Plants for Bugs.
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):
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 3x3m plot. Timber-edged wood-chip guard rows of 1m 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:
Data collection and analysis
Invertebrate diversity: 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 and detritivores). The invertebrates will be sampled on at least five occasions each year using the methods below:
At the end of 2013 approximately 80,000 invertebrates had been counted and identified, including more than 40 species of ground beetle from the pitfall traps, 30 species of spider from the suction sampler and 16 species of butterfly observed visiting the plots. Other factors:
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.
Project team
Helen Bostock - Project manager Andrew Salisbury - Lead Entomologist James Armitage - Botanical consultant Joe Perry - External consultant on statistics and plot design Mark Tatchell - External consultant Anna Platoni - Entomologist The project is also supported by several RHS volunteers University of Roehampton Plants for Bugs study Plants for Bugs handout Plants for Bugs blog Plants for Bugs first paper on pollinators Interpretation Bulletin one
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 42: 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 Conservation 15: 2415-2438.
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