Marie FOURDRIGNIEZ & Jean-Yves MEYER Délégation à la Recherche, Government of French Polynesia

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1 The positive effects of a biocontrol pathogen agent introduced against the invasive tree Miconia calvescens on a threatened endemic plant (Ophiorrhiza subumbellata) in Tahiti, French Polynesia Marie FOURDRIGNIEZ & Jean-Yves MEYER Délégation à la Recherche, Government of French Polynesia marie.fourdrigniez@recherche.gov.pf

2 INTRODUCTION Assessment of biological control success? Most studies on the impacts of biocontrol agents have focused on the invasive target species populations plant growth and/or reproduction (Smith & DeBach 1942, Myers & Bazely 2003) Few studies on the replacement/recovery of invasive species by natives (Fowler et al. 2000, Austral Ecology 25; Barton et al. 2007, Biological Control 40) Very few studies on the positive effects of biocontrol agents on native species populations, plant growth and/or reproduction

3 INTRODUCTION Miconia invasion in Tahiti Miconia first introduction sites Miconia current distribution Polyscias tahitensis Miconia (Miconia calvescens, Melastomataceae) a small tree 6-12 m tall Occurs between 0 and 1400 m elev invades native rainforests and cloudforests Forms dense monospecific stands light in the understorey ca. 50% of the endemic plant species of Tahiti are directly threatened (Meyer and Florence 1996, Journal of Biogeography 23)

4 INTRODUCTION Miconia biocontrol program Fungal pathogen Collelotrichum gloeosporioides forma specialis Miconiae (Deuteromycotina) Highly specific to Miconia, from its native habitat (Brazil) First released in Tahiti in 2000 C.g.m. causes leaf anthracnose and necrosis (partial and premature defoliation) Miconia canopy opening Light in the understorey (Meyer, Taputuarai & Killgore Proceedings of the XII International Symposium of Biological Control of Weeds)

5 Objectives To assess : Direct impact of the C.g.m. on Miconia canopy cover Indirect effects of this partial defoliation on the recovery of endemic plant species

6 METHODS Ophiorrhiza Genus (Rubiaceae) 50 species in the South Pacific 8 endemic species to Tahiti Ophiorrhiza subumbellata Forst. (Rubiaceae) Flowers Endemic to Tahiti Understory sub-shrub (up to 1.80 m) Fruits Inflorescence: a cyme of 5-18 flowers Dehiscent dry fruits Tiny seeds (0.5 mm), dispersed by gravity

7 METHODS O. subumbellata distribution map Miconia distribution Miconia distribution O. subumbellata Ophiorrhiza distribution distribution Small isolated populations (1-67 individuals), patchy distribution Occurs in rainforest and cloudforest between 700-1,200 m O. subumbellata distribution is included in Miconia s distribution

8 METHODS Study sites and plots Col Hamuta SITE NAME PIC VERT COL HAMUTA Elevation (m) 1, N plots 6 7 Miconia invasion (Mean basal area cm²/m²) Miconia canopy leaf defoliation High (40%) Low (29%)

9 METHODS Measurements on Ophiorrhiza STUDY PLOT: Circle (25m²) centered on the highest plant SPECIES Density (indiv./m²) - seedlings (<5 cm tall) - juveniles and adults (>5 cm tall) Max. height Fertility (reproductive adults) - Number of cymes - Number of flowers and/or fruits

10 METHODS Measurements on Miconia DIRECT : % C.g.m. leaf damage - 3 Miconia canopy trees, 30 leaves/tree - Frame grid with a mesh of 4 cm² squares % C.g.m. damages = Number of squares with C.g.m. leaf spots Leaf area (estimated number of squares) x 100 INDIRECT : % Miconia canopy cover Canopy cover (vegetation image) Canopy opening (sky image) Spherical densiometer (Lemmon, 1956): a convex surface of 24 squares containing 4 points (96 points) % Canopy cover = (a/96) x 1.04 x 100 a is the number of canopy opening points

11 RESULTS C.g.m. defoliation and Miconia canopy cover 85 R² = *** 80 Miconia canopy cover (%) C.g.m. damages (%) C.g.m. leaf damages, Miconia canopy cover

12 RESULTS Effect of C.g.m. on Ophiorrhiza density Mean number of Ophiorrhiza/m² Low Defoliation n.s. High Defoliation Mann-Witney U Test on mean density n.s : not significant ** : p<0.01 Mean number of Ophiorrhiza/m² n.s. n.s. Low Defoliation High Defoliation Seedling (<5 cm) Juvenile or non reproductive plants Reproductive plants ** Positive effect on the density of reproductive plants only

13 RESULTS Effect of C.g.m. on Ophiorrhiza fertility Mean number of flow er and fruit per cyme Low Defoliation *** High Defoliation Mann-Whitney U Test on mean fertility/height classes ** : p<0.01 *** : p<0.001 Mean number of flower and fruit per cyme *** ** ** *** Low Defoliation High Defoliation ]5;75] ]75;100] Height class (cm) ]100;125] ]125;185] Positive effect on fertility for all height classes

14 RESULTS Effect of C.g.m. on Ophiorrhiza recruitment and survival T o tal n u m b er o f Op h io rrh iza x N=4 plots Pearson Chi-square test : Chi² = 35,8 ; ddl = 2 ; p<0,001 Total number of Ophiorrhiza Better germination Better survival ]0-5] ]5-50] ]50-200] Height class (cm) Positive effects on seedling recruitment and plant survival

15 CONCLUSIONS Assessment of biocontrol success 1. Direct impact of C.g.m. on Miconia partial defoliation of Miconia canopy trees 2. Indirect effects of C.g.m. on O. subumbellata density of reproductive plants fertility recruitment and survival of seedlings total density in the near future?

16 FUTURE PROSPECTS Perspectives for research & conservation The Miconia biological control agent has contributed to the recovery of endemic threatened plants in Tahiti e.g. Seedling recruitment of Lepinia taitensis and Myrsine longifolia after the C.g.m. introduction (Meyer et al Rev. Ecol.) Myrsine longifolia Cyrtandra vairiae Psychotria franchetiana Calanthe tahitensis Positive effects on other endemic species threatened by Miconia Effect on more shade-tolerant endemic species? Psychotria speciosa Reinvasion by other alien species? Sclerotheca arborea Long-term monitoring on the native and alien understorey species: evolution of species diversity and % plant cover (2005-on going)

17 Acknowledgements Research Program «Lutte Biologique contre le Miconia» funded by the «Contrat de Développement Etat-Pays» The Délégation à la Recherche (Priscille Tea FROGIER): Contract as «Corps des volontaires au développement» (Mai 2007-Avril 2009) Ravahere TAPUTUARAI and Sylvain MARTINEZ for their precious help on the field