Are natives better than non natives for biodiversity?
Added on 24 January 2023
A four year Plants for Bugs project at RHS Wisley, using numerous trial beds between 2009 and 2013 aimed at identifying whether abundance and biodiversity of invertebrates is affected by the geographical origin of plants . It concluded that although there was a marginal preference towards natives it was not significant. The catalyst for the trials was the well documented decline in UK insects due to loss and fragmentation of their habitat for nesting, foraging and breeding due to changes in land use and climate change brought about by industrial practices both globally and at a local level such as using weed killers in gardens a practice which removes the food source of many insects.
Results found that although native trial beds where the most popular, they where only marginally better (10% greater abundance and diversity) than trial beds containing near natives. Trial beds containing exotics had around 20% fewer abundance and diversity of invertebrates than trial beds containing natives. Entomologists state that some insects are specialist feeders such as white admiral butterfly on honeysuckle whilst some are generalists. Most insects are a bit fussier focusing on plant families (Genuses). This is why natives are seen as only marginally favourable to near natives. For example our native Oxeye daisy, Leucanthemum vulgare has near native cousins such as the Shasta daisy , Leucanthemum x superbum spp. The latter N American species grown as an ornamental makes a more significant statement and is arguably appreciated as much. by pollinators as our own native species. Conclusions from the trial stated that in the garden setting a mix of natives and near natives with some exotics to for example extend the pollinator season for bees, butterflies, hoverflies etc was the most favourable for biodiversity. It was also suggested that if a garden owners particular preference is exotics, increased biodiversity can be achieved by denser planting and /or allowing plants to grow larger without restrictive pruning. The bottom line is one can grow a diverse range of the plants we like as long as we minimise interference with naturally developing wildlife biodiversity through constant ‘caring’ or maintenance.
Native v non native
As mentioned earlier non-native plants can enter the UK accidentally such as on soles of feet or purposely as ornamentals for gardens. When these escape from the garden into the wild accidentally or purposefully whether in seed form or dumped waste etc they can in the right conditions prove invasive certainly at local level as mentioned by David Wilkinson in Ecology and Natural History chapter 12. However as he goes on to state from research done at the University of York by Chris Thomas and Georgina Palmer (2015) on data from 479 sites between 1990 and 2007 for the British Countryside Commission that where non-natives where increasing so where natives showing that natives and non-natives where compatible with one another and goes on to say there are no firm examples on record of any UK species going extinct because of non native introductions. Dr Palmer stated ‘ Our research has shown that non-native plants are less widespread than native species, and are not increasing any more than native plants. It therefor seems likely that factors other than plant invasion are the main cause of vegetation change’.
The concern that non-natives escaping into the wild are a threat to native plant diversity is also repudiated by Chris Thomas. Of the 1800 naturalised garden escapees only around 100 are considered a nuisance and non have been evidenced as having contributed to the extinction of native species.