Ornamental or detrimental: can we benefit from horticulture without the cost of invasive garden escapes?

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Ethelbert McBride
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1 Ornamental or detrimental: can we benefit from horticulture without the cost of invasive garden escapes? Professor Philip Hulme Lincoln University, New Zealand 11 th May 2016

2 Beauty is in the eye of the beholder

3 Cumulative number of species Pressure from weeds is increasing Invasive plants in New Zealand show both a change in the rate at which species have been introduced over time and an increase in ornamentals Unknown Ornamental Not-ornamental Species / year Unknown Ornamental Not-ornamental Year of naturalisation

4 How big is the problem of ornamental species in plant invasions?

5 How important are ornamentals as invaders? Compendium of 450 plant species: Drawn from a global assessment Alien species that invade natural areas Seriously problematic (invasive) species Also lists where species are not invasive Identifies source of introduction - Ornamental e.g. gardens, landscape - Not ornamental e.g. fodder, fuel

6 Number of species Global patterns of plant invasions Naturalised Invasive Region

7 Ornamental (%) Ornamentals, introductions and invasions Naturalised Invasive Region

naturalized what is the risk it becomes invasive? 0.

8 Probability of becoming invasive Ornamentals more likely to become invasive Once a species has naturalized what is the risk it becomes invasive? P = Not-Ornamental Ornamental Source

9 Are popular garden plants often invasive? Examined >500 species awarded RHS Award of Garden Merit Checked species to see if any history of being invasive weeds

10 AGM plants are more likely invasive Number of species in each category Life-form Not invasive Invasive % Bamboos Bulbs, corms & tubers Cacti & other succulents Climbers Conifers Ferns Herbaceous perennials Trees and shrubs Total P = with cacti but P = without cacti Hulme PE (2011) Addressing the threat to biodiversity from botanic gardens. Trends in Ecology and Evolution, 26,

11 Are invasive plants often more popular? How do we assess popularity? Use BGCI Plant Search: 1,368,200 collection records 1,146 contributing institutions Examine frequency of AGM plants Frequency used as popularity index

12 Invasive plants more frequently cultivated Average number of botanic garden collections where species cultivated Life-form Not invasive Invasive P Bamboos ± 8.3 Bulbs, corms & tubers 32.4 ± ± 3.8 *** Cacti and other succulents 47.1 ± ± 8.0 Climbers 28.6 ± ± 4.3 Conifers 71.0 ± ± 14.0 Ferns 40.0 ± ± 7.5 * Herbaceous perennial 32.0 ± ± 2.8 *** Trees and shrubs 47.7 ± ± 7.1 *** Total 39.3 ± ± 2.0 *** Hulme PE (2011) Addressing the threat to biodiversity from botanic gardens. Trends in Ecology and Evolution, 26,

13 Why ornamentals are prone to be invasive Comparison of Award of Garden Merit winning ornamentals reveals: Most AGM species have a history of becoming invasive Not surprising given the criteria for Award of Garden Merit outstanding excellence for ordinary garden use good constitution not requiring specialist growing conditions not particularly susceptible to pests and diseases Invasive AGM species tend to be cultivated more frequently Challenge is that popularity and invasiveness may go together

14 How are industry, governments and the public responding to the risks of ornamental plant invasions?

15 Voluntary codes of conduct in horticulture 1. Dispose of plant waste responsibly 2. Know exactly what you are growing/buying. 3. Take advice on the best control techniques. 4. Control invasive non-native plants safely. 5. Be aware of relevant legislation. 6. Label plants clearly and accurately. 7. Provide substitutes for invasive plants. 8. Provide advice on disposal. 9. Beware of hitch-hiking pests on plants/soil.

16 Frequency of activity (%) Are voluntary codes of conduct followed? Frequency with which 846 botanic gardens address invasive species: Policy Monitoring Research Africa Asia Europe North America Oceania South America Continent Of 846 botanic gardens only a minority manage this risk Hulme PE (2015) Resolving whether botanic gardens are on the road to conservation or a pathway for plant invasions. Conservation Biology 29,

17 Encouraging alternatives to gardeners

18 Banning species from sale

19 Regulating international internet trade

20 What are the science and regulatory challenges in managing the risk of ornamental plant invasions?

Weed Risk Assessment Uses answers to 49 questions: Cultivation history Invasion history Climate matching Life-history and reproduction Undesirable traits Numerical

21 Weed Risk Assessment Uses answers to 49 questions: Cultivation history Invasion history Climate matching Life-history and reproduction Undesirable traits Numerical score rates species as: Invasive (Reject) Low risk (Accept) Requires further study Basis for screening alien plants in: Australia New Zealand USA Galapagos Islands

WRA Score Quantitative approaches are not perfect 16 90 14 12 WRA

(%) 2 10 0 Regenerating Naturalised Invasive 0 Invasion status

risk assessment as a conservation tool to identify invasive plant

22 WRA Score Quantitative approaches are not perfect WRA Score Rejection rate Rejection rate (%) Regenerating Naturalised Invasive 0 Invasion status Dawson W, Burslem DFRP & Hulme PE (2009) The suitability of weed risk assessment as a conservation tool to identify invasive plant threats in East African rainforests. Biological Conservation, 142,

23 Number of species naturalised Importance of introduction effort 1000 New Zealand Australia Number of species introduced Hulme PE (2012) Weed risk assessment: a way forward or a waste of time? Journal of Applied Ecology, 49, 10-19

24 Number of botanic gardens Is gardening increasingly popular globally? Use trend in new botanic gardens as an index of gardening popularity Africa S America Europe N America Asia Oceania Year of botanic garden establishment Hulme PE (2015) Resolving whether botanic gardens are on the road to conservation or a pathway for plant invasions. Conservation Biology 29,

25 Shifting trends in gardening fashion

26 Public perceptions and awareness matter

27 Conclusions 1. Ornamentals are a major source of alien plants that impact the environment. 2. This is partly due to the selection of plant traits that facilitate cultivation also assists subsequent invasion. 3. In addition, popular species are widely planted increasing their likelihood of escape and invasion. 4. The horticulture industry is aware of these risks and has been proactive in tackling this problem and banning high risk species. 5. Such initiatives help but are not a panacea, ornamental plant invasions continue to occur and a more effective approach to risk assessment of new and existing ornamental stock is needed. 6. The rapid change in horticultural fashion and globalisation of formal and informal plant trade pose significant future challenges.

28 Many Thanks Bio-Protection Research Centre PO Box Lincoln University Lincoln 7647, New Zealand P F

Building Weed Risk Assessments. Mindy Wilkinson Invasive Species Coordinator

Building Weed Risk Assessments Mindy Wilkinson Invasive Species Coordinator Is this plant a weed? Is this plant going to be worse than other weeds I manage? What impacts will this plant have? Is this plant