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How to invade an intact tropical rainforest
- 1. How to invade an intact tropical rainforest: a case study of Psidium cattleyanum a.k.a How to be a superweed David Tng, Susan Laurance Follow us on Twitter 2021 ESA Annual Meeting
- 2. Introduction • Disturbance is a major mechanism in the establishment of exotic plants • Most weeds are shade-intolerant • Closed forest understoreys are thought to be resistant to weeds • But there now wider recognition of a group of weeds that invade shaded areas (Martin et al. 2009)
- 3. Profile of Psidium cattleyanum • Shrub to small tree (up to ~ 8 m) • Flowers & fruits as a shrub • Originates from the Atlantic coast Southeast Brazil
- 4. Global distribution • Now pretty much everywhere in the tropics/subtropics & even some temperate areas • Problematic in Portugal, South Africa, La Réunion, the Seychelles, Mauritius, New Zealand, the USA, Hawaii, Micronesia and French Polynesia. iNaturalist query 4th July 2021
- 5. Current distribution in Australia Some areas of concern Wet Tropics World Heritage Area Gondwana Rainforests World Heritage Area Lord Howe Island World Heritage Area & also Norfolk Island Atlas of Living Australia Queried on 4th July 2021 Pers obs Cultivated in Hobart Botanical Gardens Probably introduced into Australia as a fruit tree
- 6. Research questions Question 1 What are the environmental drivers of P. cattleyanum invasion of closed forest? Question 2 Are there any functional differences between P. cattleyanum and understorey tree & shrubs?
- 7. Demography • Sampled forest sites in North Queensland • 33 successional forests 8 mature phase Preece et al. 2012 Q1: Environmental drivers of P. cattleyanum invasion of closed forest? Tng et al. 2015
- 8. Primary rainforest Secondary rainforest with P. cattleyanum Secondary rainforest w/o P. cattleyanum LEGEND CEC Q1: Environmental drivers of P. cattleyanum invasion of closed forest? • P. cattleyanum in 27 of the 41 sampled sites • Restricted to successional forests • Species ordination shows a floristic gradient Tng et al. 2015
- 9. Drivers of P. cattleyanum invasion West facing aspects Forest canopy height Soil CEC Soil pH Q1: Environmental drivers of P. cattleyanum invasion of closed forest? +ve -ve -ve +ve Tng et al. 2015
- 10. Traits SPECIES FAMILY Ardisia brevipedata Primulaceae Guioa acutifolia Sapindaceae Guioa lasioneura Sapindaceae Haplostichanthus submontanus Annonaceae Helicia nortoniana Proteaceae Macaranga inamoena Euphorbiaceae Pilidiostigma tropicum Myrtaceae Rhodamnia sessiliflora Myrtaceae Neolitsea dealbata Lauraceae Brackenridgea australiana Ochnaceae Myrsine porosa Primulaceae Tasmannia insipida Winteraceae Eupomatia laurina Eupomatiaceae Archirhodomyrtus beckleri Myrtaceae Psidium cattleianum Myrtaceae Macaranga involucrata Euphorbiaceae Wikstroemia indica Thymelaeaceae Rhodomyrtus pervagata Myrtaceae Mallotus mollissimus Euphorbiaceae Melastoma malabathricum Melastomataceae Rhodomyrtus canescens Myrtaceae Trema tomentosa Cannabaceae • Seed size • WD • Leaf mass per unit area • for a number of understorey shrubs and pioneer shrubs in the region Q2: Functional differences between P. cattleyanum and understorey shrubs? Shade-tolerant shrubs Shade-intolerant
- 11. Leaf mass per unit area Seed length Wood density Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 12. In multivariate space… • Scaled trait data 0-1 & ordinated species Stress: 0.117 Larger seeds Axis 2 Axis 1 Denser wood Higher leaf mass per unit area Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 13. Q2: Functional differences between P. cattleyanum and understorey shrubs? Tng et al. 2015
- 14. Regenerative ability • Frequent asexual regenerative ability Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 15. • Thicket forming ability Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 16. Very high propagule pressure • Large copious crop of sweet edible fruits • Attractive to native birds, bats, ?pigs • Signs of margin extensions, nucleations & irruptions across landscape Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 17. • Tolerance of both high and low light environments Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 18. • Resistance to Myrtle rust (Austropuccinia psidii) • Resistance to herbivory • Potentially allelopathic on surrounding plants (Antonelli et al. 2020) Q2: Functional differences between P. cattleyanum and understorey shrubs?
- 19. Conclusion • So far, Psidium cattleyanum has not been detected frequently in mature rainforest, but infestations in secondary forest may severely alter rainforest successional trajectories in certain landscape settings • Traits of a “super-invader”. Sleeper weed in many places • Eradication practically impossible. Management will require a combination of strategies. Physical, chemical ?biological • Monitoring needed
- 20. References Antonelli, L., Morelli, T. M., Yockey, K., Miyake, B., Talia, M., Sinclair, T., & Marahatta, S. P. (2020) Research Note Utilizing Psidium cattleianum leaves as a pre-emergent bio-herbicide: A study on its allelopathic effects on the in vitro germination of Lactuca sativa seeds. Pac. Agric. Nat. Resour. 10, 1-4 Martin P. H., Canham C. D., Marks P. L. (2009) Why forests appear resistant to exotic plant invasions: intentional introductions stand dynamics and the role of shade tolerance. Front. Ecol. Environ. 7, 142-149. Tng, D. Y., Goosem, M. W., Paz, C. P., Preece, N. D., Goosem, S., Fensham, R. J., & Laurance, S. G. (2016). Characteristics of the Psidium cattleianum invasion of secondary rainforests. Austral Ecol., 41, 344-354.