Left: Andy Salisbury sampling insects with a Vortis vacuum sampler. Centre: Helen Bostock on the ladder measuring canopy cover using a camera. Right: sorting the Vortis samples.

Project results and interpretation

By the end of 2017 two scientific papers had been produced and interpreted: on the flying insect visitors (pollinators) and the invertebrates inhabiting the plants. The key messages are summarised below.

Pollinators:

In summary the key messages for planting for pollinators in gardens are:

• The best strategy for gardeners wanting to support pollinating insects in gardens is to plant a mix of flowering plants from different countries and regions.

• Emphasis should be given to plants native to the UK and the northern hemisphere, though exotic plants from the southern hemisphere can be used to extend the season (there are a greater proportion of exotic plants flowering later in the season compared to UK native and northern hemisphere plants) and provide nectar and pollen for some specific pollinators.

• Regardless of plant origin (native or non-native), the more flowers a garden can offer throughout the year, the greater the number of bees, hoverflies and other pollinating insects it will attract and support.

Invertebrates on the plants:

The second scientific paper from the project reports on the abundance of invertebrates that were found on the plants, including those feeding on living plant material, on decomposing organic matter, and all other invertebrates, excluding pollinators. It was published in Biodiversity and Conservation in July 2017

Interpretation of the data can be found in the RHS project interpretation bulletin 2

The key messages for gardeners wishing to provide habitat for invertebrates were

• To plant a predominance of plants native to the UK.

• Planting schemes that are based on plants originating from the Northern Hemisphere (near-natives) may support only marginally fewer (less than 10%) invertebrates in some functional groups (including herbivores and some predators) than UK native plant schemes. Plant schemes based on Southern Hemisphere (exotic) plants will still support a good number of invertebrates, albeit around 20% fewer than plants from the UK.

• Regardless of plant origin, the more densely a planting scheme is planted or allowed to grow, the more invertebrates of all kinds (herbivores, predators, detritivores and omnivores) it will support.

Soil surface invertebrates

The third paper of the series was published in November 2019 and described the findings of studies on the invertebrates using the soils surface - beetles, spiders, woodlice and millepedes among many others. There is an excellent resume available here . The key findings included:

• Overall, the denser the vegetation, the higher the ground-active invertebrate abundance regardless of plant origin. A notable exception is ground-active spiders, which were found in greater numbers among sparser plantings

• The best strategy for gardeners wanting to support ground-active invertebrates in gardens is to plant densely with more native and near-native plants than exotic plants.

• Planting schemes based on exotic plants may support relatively more ground-active invertebrates in winter than British native or near-native planting schemes. This is possibly related to the higher proportion of evergreens available in hardy exotic plantings

• Planting schemes based on native plants may support a greater abundance of ground-active herbivores than other planting schemes, but ground-active detritivores show no preference for plant origin.

• Species diversity appears to be reflected by invertebrate abundance: as invertebrate abundance increases so does the diversity of species.

Web links:

RHS Plants for Bugs information pages; https://www.rhs.org.uk/science/conservation-biodiversity/plants-for-bugs/plants-for-bugs-results

RHS Plants for Bugs results; https://www.rhs.org.uk/science/conservation-biodiversity/plants-for-bugs/plants-for-bugs-results

Plants for Bugs blog; http://mygarden.rhs.org.uk/blogs/science__advice/default.aspx

Salisbury, A., Armitage, J., Bostock, H., Perry, J., Tatchell, M., Thompson, K. (2015). Enhancing gardens as habitats for flower-visiting aerial insects (pollinators): should we plant native or exotic species? Journal of Applied Ecology 52:1156-1164.

Salisbury, A., Al-Beidh, S., Armitage, J., Bird, S. , Bostock, H., Platoni, A., Tatchell, M, Thompson, K. and Perry, J. (2017). Enhancing gardens as habitats for plant-associated invertebrates: should we plant native or exotic species? Biodiversity and Conservation

Salisbury, A., Al-Beidh, S., Armitage, J., Bird, S., Bostock, H., Platoni, A., Tatchell, M., Thompson, K. and Perry, J. (2019). Enhancing gardens as habitats for soil surface-active invertebrates: should we plant native or exotic species? Biodiversity and Conservation . (https://bit.ly/2sinFDA)

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