HOW DOES IRRIGATION MANAGEMENT AND WEED CONTROL INFLUENCE ON EXOTIC PLANT ASSEMBLAGES? Alejandro Juárez, Xavier Solé & Josep Antoni Conesa Departament d’Hortofructicultura, Botànica i Jardineria Escola Tècnica Superior d’Enginyeria Agrària. Universitat de Lleida

INTRODUCTION Catalan western plain: - Strongly contrasted temperatures - Low annual precipitation (380mm) - Summer water deficit The landscape consists on semiarid plant communities in mosaic with rainfed crops

Implementation and extension of irrigated crops, as fruit tree orchards, have transformed traditional landscape in recent decades These irrigated crops were established because of their larger productivity compared to traditional rainfed crops INTRODUCTION

Irrigated fruit tree orchards favor the entry and maintenance of exotic weed species: 1. Water facilitates diaspore entry 2. High disponibility of water and nutrients 3. Elevated temperatures in summer 4. Open structure of the orchards Consequences: Affect negatively to the crop yield and may develop invasive behaviour in surrounding natural habitats INTRODUCTION

Management of irrigated fruit tree orchards Irrigation system Flood irrigation Weed control Mecanically on inter- rows Herbicide application under the trees INTRODUCTION Drip irrigation

Hypothesis: Orchard management determines weed richness and diversity and could favor the presence of exotic flora Objectives: 1.Find relationships between irrigation system and richness and diversity of native and exotic flora 2.Analyze differences in richness and diversity of native and exotic flora between inter-rows and under the tree lines 3.Assess whether there is a synergistic effect between these two factors on richness and diversity of native and exotic flora INTRODUCTION

July-September fields with drip irrigation system 75 fields with flood irrigation system MATERIALS & METHODS

3 X Phytosociological surveys (Braun-Blanquet) 3 X 1m 10m 2m 5m MATERIALS & METHODS

DATA ANALYSIS Origin of species: Natives and exotics (Bolòs & Vigo, ) Richness -Total -By family -Depending on: irrigation system Plot position in field -By origin Shannon-Weaver diversity (from cover data for the same groups as richness) pi = Ri / R (Ri: relative cover of the i species; R: total cover of all species). Two-way ANOVA to evaluate the effect of irrigation system, plot position and the interaction between these two factors on richness and diversity MATERIALS & METHODS

Total: 179 species 40 families Flood irrigated: 104 species 32 families Drip irrigated: 157species 36 families Inter-rows: 86 species Under the tree: 92 species Inter-rows: 133 species Under the tree: 118 species RESULTS & DISCUSSION

Flood irrigated orchards Inter-rows % Freq Under tree %Freq Trifolium repens70,22Sonchus oleraceus60,70 Taraxacum officinale64,89Portulaca oleracea53,40 Bromus catharticus61,33Trifolium repens52,00 Setaria pumila46,67Echinochloa colona39,07 Rumex obtusifolius42,22Euphorbia prostrata36,57 Sorghum halepense38,22Setaria adhaerens36,06 Cyperus rotundus34,22Digitaria sanguinalis34,96 Echinochloa colona32,89Bromus catharticus28,49 Paspalum distichum28,00Taraxacum officinale24,63 Eleusine indica27,56Malva sylvestris24,36 In bold: exotic species Bromus catharticus Setaria pumila Sorghum halepense Eleusine indica Cyperus rotundusPaspalum distichumEuphorbia prostrata Setaria adhaerens Echinochloa colona RESULTS & DISCUSSION

In bold: exotic species Drip irrigated orchards Inter-rows % Freq Under tree %Freq Sonchus oleraceus45,54Sonchus oleraceus75,53 Aster squamatus39,79Setaria adhaerens34,36 Taraxacum officinale36,86Convolvulus arvensis27,61 Polygonum aviculare32,34Malva sylvestris25,66 Crepis bursifolia32,31Amaranthus albus21,21 Malva sylvestris28,74Chenopodium album20,71 Conyza bonariensis26,71Aster squamatus19,42 Plantago coronopus26,35Cynodon dactylon15,59 Kochia scoparia23,90Heliotropium europaeum14,75 Plantago lanceolata20,98Sonchus tenerrimus14,72 Conyza bonariensis Cynodon dactylon Amaranthus albus Aster squamatus Crepis bursifolia Setaria adhaerens RESULTS & DISCUSSION

Mean richness (number of species) in % Mean Shannon diversity index FI: flood irrigation DI: drip irrigation RESULTS & DISCUSSION

VariableDependent variableFPDirection effect irrigation system total 30,763<0,001 **F>D exotics 261,386<0,001 **F>D natives 40,763<0,001 **D>F Position total 80,164<0,001 **IR>TL exotics 56,716<0,001 **IR>TL natives 84,545<0,001 **IR>TL Irrigation x position total 2,6270,105 exotics 15,419<0,001 **IR>TL in D and F natives 17,590<0,001 **IR>TL in D and F TWO WAY ANOVA FOR RICHNESS/PLOT D: drip irrigation F: flood irrigation IR: inter-rows TL: tree line RESULTS & DISCUSSION

VariableDependent variableFPDirection effect irrigation system total 66,217<0,001 **F>D exotics 261,46<0,001 **F>D natives 11,182<0,001 **D>F position total 43,942<0,001 **IR>TL exotics 30,448<0,001 **IR>TL natives 12,299<0,001 **IR>TL Irrigation x position total 0,2840,594 exotics 18,730<0,001 **IR>TL in D and F natives 8,2960,004 *IR>TL in D and F D: drip irrigation F: flood irrigation IR: inter-rows TL: tree line TWO WAY ANOVA FOR SHANNON DIVERSITY INDEX RESULTS & DISCUSSION

Drip irrigated orchards have a larger total richness than flood irrigated orchads because they present different environments with contrasting conditions: irrigated under the tree and rainfed in the inter-rows Flood irrigated orchards have a higher Shannon diversity because cover of weeds is higher and more homogeneously distributed Flood irrigation favors both the presence and diversity of exotic flora to the detriment of native flora Exotic weeds presents in orchards are different depending on irrigation system CONCLUSIONS

Drip irrigation orchards shelter more native weeds because inter-rows maintain typical mediterranean stress conditions Below the tree rows in both irrigation systems, there are the lowest richness and diversity of species because the herbicide application ocurrs there There is a synergistic effect between irrigation system and weed management (plot position) over native and exotic weeds that favors exotic weeds in the inter- rows of flood irrigation and native weeds in the inter-rows of drip irrigation CONCLUSIONS

IMPLICATIONS FOR MANAGEMENT The choice of irrigation system becomes a crucial aspect in the design of a management system aimed to prevent the establishment of exotic flora in mediterranean areas

Thank you for your attention Acknowledgements: Financial support provided by AGAUR PhD grants Generalitat de Catalunya