Yann Béliard

Tony Benn

Frank, Horner Stewart 'foreword'

Benn 'foreword'

Towards a people's history of British decolonisation

Our intention in convening the November 2013 conference in Paris was to make a double contribution, to imperial studies and to labour history, possibly to break down subdisciplinary boundaries and help those fields of research cross-fertilise each other. We were also hoping to overcome some of the weaknesses in the usual treatment of labour's role in British decolonisation: the artificial separation between the metropole and the colonies; the narrow focus on Labour Party headquarters on the one hand, and on nationalist elites on the other. In short we were determined to highlight the initiatives of transnational actors and the role of the workers themselves, both in Britain and in its imperial domain. We were fully aware that we were not the first to ask, as Bernard Porter had in 2004: 'What about the workers?'. 1 But whereas most studies have tended to scrutinise times of imperial expansion and consolidation, what we were seeking to do was analyse the role of workers and their organisations in a time of disruption and destabilisation. Besides, whereas British decolonisation had been so often presented as a relatively smooth transfer of power from London to new nation-states, we felt that top-down approach was not satisfactory, that the intervention of anti-colonial left-wing activists and of the labouring masses themselves in the process needed to be examined more seriously.

1 Bernard Porter, 'What about the workers?', chapter 9 in Absent-Minded Imperialists.

1

The need to push the efforts of our predecessors a little further stemmed partly from the frustration towards interpretations that painted too rosy a picture of British decolonisation, of the British Left, and also of its relationship with anti-imperial fighters in the coloniesmisgivings apparent for example in Tony Benn's foreword to Frank, Horner and Stewart's

The British Labour Movement and Imperialism. His preface unduly transformed what was so often a story of missed encounters between metropolitan and colonial anti-imperialists into a barely credible success story in which '(d)emocracy dissolved the British Empire'. 2 The claim that 'a relatively peaceful end to British imperialism' was made possible by 'the good will of influential socialists in the post-war government of Britain' was also problematic. 3 The vision of Britain as a 'smooth decoloniser' has been torn apart by so much recent research that there is no need to go into too much detail here. To summarise, in their very different narratives of the end of empire, Darwin, Hyam and Cain and Hopkins have all highlighted the messy character of Britain's retreat: the fact that it was imposed on all British governments, including the Labour governments, rather than planned; and that it resulted above all from changes in the international balance of forces and revolts in the colonies, but only marginally from the concerted action of British anti-colonialists and colonial freedom fighters. 4 Such observations have only been confirmed by the growing literature on the policing of the Empire and on the British art of counter-insurgency. Studies of the partition of the Indian Empire as well as histories of British disengagement from Palestine point in the same direction, that of a process that was no less bloody than in the French or the Portuguese ones, and that left a possibly greater number of time bombs behind.

number of established 'truths' and question the part played by working-class actors in those untidy transitions.

As for the role of the Left, it is true that, until Howe's pioneering work, it had been grossly under-estimated. But the risk is to overestimate the influence of the leftists inside the Labour Party, when the shift in Labour Party policy on colonial questions in the late 1950s had probably less to do with the left wing convincing the centre and the right wing than to the shift away from direct colonial rule inside the Establishment itself. 5 Here again, in the eyes of labour historians, one of the values in re-evaluating the impact of the metropolitan Left on colonial policies is that it could lead to a useful shift towards a so far neglected object of study: the working-class mobilisations in the colonies, which owed little to metropolitan influences and were probably more disturbing for the managers of the Empire than Stafford Cripps' or Aneurin Bevan's manoeuvres behind the curtains. 6 On top of this, the thesis that the links established by the metropolitan Left with colonial liberation movements were essential in making the liquidation of Empire smooth is also debatable. Such ties did exist -a point worth underlining, as Marie Terrier does in her chapter on Annie Besant, since it goes against those post-colonial readings that tend to reify or essentialise cultural barriers. But those convergences and alliances were in general fragile and temporary. Indeed, though the British Left could in theory have collaborated with colonised people on their road to independence, around the common objective of a socialist reorganisation of the world, several factors -clearly identified by Howe, and explored in 5 Several reviewers of Howe's book called for a qualification of the MCF's direct impact on the dismemberment of the Empire. See reviews by John Darwin (English Historical Review, 110 (1995), 429-32) and Andrew Porter (History Workshop Journal, 40 (1995), 261-3).

6

This was notable in Trinidad and Tobago. See Jerome Teelucksingh, Labour and the Decolonization Struggle in Trinidad and Tobago (Basingstoke, 2014). more depth by Owen and others after him -made that bonding of forces impossible. 7 All in all, neither the bourgeois nationalists nor the labouring classes in the colonies had reason to feel particularly confident in the metropolitan Left -which helps understand why, in the aftermath of the Second World War, colonial rebellions against the British Empire were led along nationalist lines and not under the flag of labour internationalism.

Diverse approaches and common assumptions

Many admitted visions of labour's part in British decolonisation therefore need to be discussed and qualified. The chapters collected here were produced by writers with distinct methodological and political outlooks. Yet they are united by a common refusal to hide any of the dark sides of British imperial rule and retreat; and a parallel refusal to obliterate any of the many ambiguities or contradictions of the British Left in its proclaimed attempts to connect with anti-colonial forces around the Empire. To put it in a nutshell, the essays we have gathered here seek neither to celebrate nor to deplore but to understand.

To take steps towards a more balanced and more complex understanding of the question, we were also driven by a number of common assumptions, which were probably implicit at the start but which are worth summing up in a more explicit way in this concluding essay. For those pre-conceptions, seen from another angle, were also hypotheses that needed to be tested. One of those assumptions was that the building of bridges between anticolonialists in the metropole and around the Empire, between left-wing opponents of imperialism in Britain and working-class rebels in the colonies, was not doomed from the 7

In the case of the British Labour Party, trade unions and cooperatives, many studies have shown that they were too integrated in the domestic institutions, too afraid of rocking the boat, to behave as consistent internationalists. In the case of the much smaller communist movement, especially once it was Stalinised, its policy seems to have been determined more by the interests of the Kremlin bureaucracy than by those of colonial peoples and workers.

start. Obstacles on that road were numerous, as our chapters confirm in many different and complementary ways. Labour movement leaders were in general more loyal to the Empire than to their class sisters and brothers in the colonies. Workers in Britain and their cousins in the white dominions were often imbued with the dominant ideology, and not immune to the official and media discourses on the Britons' superiority and civilising mission. Under particular circumstances, those vague and mostly dormant conceptions were actually formulated in the clear-cut, unashamed language of white labourism and racial socialism. 8 But the picture was always more mixed. Even in Australia and South Africa there were militants attached to the values of internationalism and antiracism, minorities who preserved at least in principle the possibility of a connection with the non-white oppressed and exploited. 9 The range of possible positions on the racial question inside the labour movement is well illustrated by Neville Kirk's study of the life-long relationship between Britain's Tom Mann and Australia's Bob Ross, two socialist labour leaders and friends who adopted contrasting, indeed contradictory stances on the matter. While Mann was a consistent anti-racist, Ross was a staunch defender of the White Australia policy. 10 As for the sentiments of the rank-and-file, they were not homogenous either, combining prejudice or even rejection with sympathy for the poor, and at times, though more rarely, the sense of a common destiny. Most of our chapters testify therefore both to the existence of a solid colour bar, and to the possibility that some activists on the left tried to cross it, and not always in vain. 11 8 Jonathan Hyslop, 'The Imperial working class makes itself "white": White Labourism in Britain, Australia and South Africa before the First World War ', Journal of Historical Sociology, 12.4 (1999), 398-421. Another one of those assumptions was the idea that labour mobilisations in the colonies could not be reduced to a subset of nationalist and anti-colonial resistance, that they deserved to be studied in their own right, that the working-class rebellions that accompanied the fights for national liberation had a logic and potentialities of their own, even though most of them ended up being subsumed within a nationalist framework. This is the fruitful option embraced by Sumithra Janaka Biyanwila in his recent history of trade unions in Sri Lanka: to consider trade unions not as 'accessories of political parties' or 'small footnotes in larger political tapestries', not just as supporting actors but main players. 12 Biyanwila observes that the passage from colonial rule to independence saw not only the emergence of combative trade unions on the tea plantations and in the garment industry, but also their incorporation into the Sinhala Buddhist state, reproducing in another setting the model of integration into the state apparatus as theorised by Sidney Webb. This explains why the unions are so often seen as playing second fiddles. Comparable evolutions took place during the decolonisation process in the West Indies and Africa too, where trade-union struggles became subordinated to 'national liberation' and, in exchange for their association with the new dominant parties and the co-optation of their leaders, lost much of their subversive and oppositional power. In spite of that, and because writing history is precisely about not taking the end of the story for granted, the chapters gathered here, in particular in Part Two, make a point of not assuming that this subordination was a foregone conclusion.

What emerges here is a common determination to recapture the sense of uncertainty that accompanied the final decades of the British Empire. With hindsight, it is easy to forget the array of possible futures that emerged from anti-colonial resistance, in particular when it took the shape of massive working-class movements, before such initiatives from below were constrained by the framework of the new nation-states. 13 It is easy to forget the dreams and practical attempts of the radical minorities who believed that coordinated efforts across borders might lead not only to the destruction of the British Empire but to that of capitalism and imperialism in general, and to its replacement by some form of universal socialism. So, while our edited volume helps understand why the 1945-1965 anti-colonial revolts were eventually not led under the flag of socialist internationalism but under that of national liberation, it also emphasises the roads not taken, to retrieve, in a gesture inspired by E.P.

Thompson's philosophy, the sheer sense of openness and opportunity so prevalent in the phase when the foundations of the British Empire started to shake. 14

Where do we go from here?

The list of the themes and locations that we have left untouched or have only been able to tackle superficially is too long to be presented here. But, developing some of Neville Kirk's concluding remarks, I wish to outline in this final part several dimensions that may deserve more attention in future research.15

Organisations. Some branches of the British labour movement which do not appear in the following pages should undoubtedly be rescued from oblivion. This is particularly necessary because, in spite of the remarkable expansion of the social and cultural history of the British Empire since the 1980s (which came as a very useful corrective to narrow, top-down traditionalism), it has for the most part concerned itself with the attitudes of sections of the wider 'people' rather than specifically with the labouring classes and their labour movements. 16 The cooperative movement's investment in the imperial field and the way the promoters of cooperation navigated the decolonisation process are areas where more inquiries are surely needed, if only to test how the intentions of the MacDonald and Attlee governments to use cooperation as a vehicle for enlightened imperialism translated on the ground. Beyond co-operators, none of the social, cultural and educational networks through which workers tried to organise voluntary individual and collective self-help should be neglected by historians of decolonisation. If we turn to political groups, the Trotskyists' approach to anticolonialism would also be worthy of further inquiry, in the wake of important publications on their general history. 17 Here the focus would once again be on minute groupings with limited impact on the bulk of the working class. But as a tendency whose opposition to British imperialism rarely wavered, Trotskyism deserves more than a footnote.

International relations. On a different level, future historians might also be tempted to relate labour and decolonisation issues more firmly to the context of Cold War tensions, as illustrated by Sibley's chapter in this volume. The rivalry between the World Federation of Trade Unions (WFTU) and the International Confederation of Free Trade Unions (ICFTU) from the moment of the split in 1949 was played out on a global scale that included British territories, and many aspects of that competition for influence affected colonial workers in their relation to their employers as well as in their political engagements. From the sending of African American activists as emissaries to West Africa to the fomenting of strikes so as to upset anti-imperialist regimes, the American Federation of Labor (AFL)'s manoeuvres merit closer examination, as does the relationship between Soviet foreign policy and the trade unions attracted to the WFTU.

Rank-and-file workers in the metropole. Looking beyond the workers who at one point or another in their life were members of national and international organisations, it is the workers that did not belong to trade unions or political parties who in many ways remain a terra incognita for the labour historian. Though the contributors to this volume share a common determination not to write a history of 'big men', or 'big women', and a common desire to shed light on the material conditions and mental preoccupations of the labouring majority, the reconstruction of rank-and-file attitudes towards imperialism and decolonisation is not so easy -certainly more complex than the study of the positions of activists for whom political expression was as essential as breathing. Common people do not leave as many written traces behind as the 'uncommon' militant, hence our difficulties in imagining their mentalities. One of the rare blind spots in Stephen Howe's study of anti-colonialism was precisely that: a focus on the politics of organised Labour that left the social question of working-class attitudes somehow in the background. The dominant attitude in high places -in ministries, in TUC and Labour Party headquarters, on Fleet Street -was to discard the demands of colonial workers as immature, or as the work of agitators. But to what extent did British workers adhere to such visions? Our collection revisits -without providing any definite or unilateral answer -the usual paradox: being subordinate, the British worker could feel solidarity with other subordinates around the world; but belonging to the richest nation in the world, he or she could share the paternalistic ideology of the ruling class. 18 Further 18 On metropolitan attitudes towards colonial workers, Laura Tabili's work is essential reading. See: "We Ask for British Justice." Workers and Racial Difference in Late Imperial Britain (London, 1994); Global Migrants, Local Culture. Native and Newcomers in Provincial England, 1841-1939 (Basingstoke, 2011).

attention should be given to the variety of labour responses to the imperial system, especially as individuals and groups could and did change their attitudes to empire and colony over time.

Besides, working-class attitudes in the metropole should not be artificially homogenised. If decolonisation and the break-up of the United Kingdom can be seen as interrelated processes, maybe there is reason to wonder whether labour perceptions of decolonisation differed significantly in England, Wales, Scotland and Northern Ireland.

Rank-and-file workers in the colonies. Another question worth examining more profoundly than our collection does is the relation of white workers in the Dominions to the decolonisation process. Above all, it seems that the area where the greatest strides forward should be taken concern the colonial labourers themselves. Both Curless's work on the Sudan and Hyde's work on Kenya have allowed our knowledge of that proletarian experience to expand, but every territory that was ever coloured in red on the world map would deserve such scrutiny. We need to know much more about the unpaid women and children employed in the imperial economy, even when the International Labour Organisation (ILO) started to elaborate international norms against coerced labour and British governments pretended to combat unfree labour. 19 As for the distinction between purely industrial and purely political strikes in the colonies, it should be teased out in every context, as one can well imagine that economic and anti-colonial considerations were not confined to separate areas in the striking workers' brains. In this respect the exploration of a 'new' source may prove fruitful: since the revelation in 2011 that the Foreign Office had hidden more than one million papers that should have been declassified, those documents have slowly been made accessible to researchers. However, major obstacles remain: one is the fact that British authorities destroyed a significant proportion of their archives while retreating from the colonies; another is that the archives that were saved reveal the contours of the 'official mind' more directly than those of the masses' psychology.

Varieties of anticolonialism.

In terms of its spatial scope, this collection could not, given its limited size, cover the British Empire as a whole. Appropriately contextualised continuities and changes in the nature and meanings of imperialism and colonialism, but also of anticolonial nationalism, thus merit further investigation. Some omissions the editors regret more than others. One of course is that of Arab and Jewish workers and activists, especially at a moment when the labour movement in Britain stands accused of antisemitism. Studying how anti-colonialists of the socialist kind, whatever their ethnic origin and whether living in the metropole or in the Mediterranean world, discussed the future of Palestine after the departure of the British or imagined a solution to the persecution of the Jews would have been immensely rewarding. Just as frustrating is the absence of a chapter on anti-colonialism and decolonisation in the West Indies. That absence is maybe even more regrettable when we recall that the role of working-class rebellions in the anti-colonial process was probably more visible and essential than in any of Britain's colonies. Whether in Guiana, Tobago or Trinidad, it was the wave of labour unrest of the 1930s that opened the way to the fight for independence. Many of the men who came to power in the 1950s and 1960s -from Grantley Adams and Clement Payne in Barbados to Alexander Bustamante and Norman Manley in Jamaica -were popular leaders, though not always trade unionists, who had shaped and been shaped by those fiery years. 20 Analysing the link between industrial disputes and anti-colonial nationalism in the West Indies would have been relevant to our collection, especially as those disputes were never just Caribbean affairs: a significant amount of the strikes leaders had lived in the British Isles and could rely both on a rich metropolitan experience and on their transnational connections. 21 Those men had their foibles and shortcomings, and as the leaders of newly emancipated countries they did not succeed any more than their African counterparts in putting an end to worker exploitation or to the domination of Anglo-American capital. But should this volume on labour and decolonisation have a sequel, it should pay due attention to their story, and to that of the labouring women and men who mobilised with them. This would shed light more generally on the important and much neglected area of relations between, on the one hand, elite nationalist movements and, on the other hand, the mobilisation of labour and other popular movements -an area which requires much wider and deeper examination and explication.

Race and gender. Individuals and groups could hold complex and contradictory attitudes, including slave and free women. 22 Future studies should address, where appropriate, both issues and relations of gender and race more extensively and intensively than has often been the case in the past and contribute to new and exciting developments in the intersection of political economy, environmental and labour history as applied to empire and imperialism. 23

Comparative perspectives. Finally, an approach that our chapters do not adopt systematically but which is promising indeed, is the method which compares the British imperial experience with other imperial experiences, and also considers our historical objects from a trans-imperial perspective. The interest in the comparative angle is evident when one thinks about labour and British decolonisation in comparison with the French case, especially at a moment when French historians embracing transnational and 'from below' perspectives seem to be reaching a wider readership. 24 The balance of forces inside the Left in the post-war years was completely different in Britain and in France, with an overwhelming Labour Party facing a smallish CPGB on the one hand and a massive PCF (Parti communiste français) facing a declining SFIO (Section française de l'Internationale ouvrière) on the other. Yet that discrepancy did not significantly affect the attitude of the Left towards anti-imperial revolts in the colonies. In May 1945, the bloody repression of the nationalist troubles in Algeria took place under the auspices of a coalition government comprising both SFIO and PCF ministers.

As for the war against Algerian independence, it was launched by Guy Mollet, an SFIO prime 22 Diana Paton, No Bond but the Law. Punishment, Race and Gender in Jamaican State Formation,1780-1870 (Durham, 2004); Philippa Levine, Gender and Empire (Oxford, 2017).

23

Mike Davis, Late Victorian Holocausts. El Nino Famines and the Making of the Third World (London, 2000).

24

Patrick Boucheron (ed.), Histoire mondiale de la France (Paris, 2017). Gérard Noiriel, Une histoire populaire de la France, de la guerre de Cent Ans à nos jours (Marseilles, 2018). Michelle Zancarini-Fournel, Les luttes et les rêves : une histoire populaire de la France de 1685 à nos jours (Paris, 2016). minister who was given full powers in 1954 by a majority in the National Assembly that included PCF representatives, representatives who during most of the war called for 'peace in Algeria', not independence. 25 As in the British case, colonial workers fought for the independence of their countries with little support from metropolitan French socialists. This does not mean that the French proletariat was as supportive of the state's military intervention as the parties speaking in its name, as testified by the numerous spontaneous protests against conscription, and the often humane behaviour of working men wearing the uniform. 26 In contrast to SFIO and PCF positions, the political and material support brought by anarchist and Trotskyists to the Algerian independence fighters has recently been studied more closely.

But it was not without its paradoxes, one of them being that the two biggest Trotskyist groups in France, the PCI and the OCI, disagreed as to which tendency of the nationalist movement should be helped, with the former siding with the FLN (Front de libération nationale) and the latter with the MNA (Mouvement national algérien). Such dilemmas were certainly not a French preserve and historians would benefit immensely from comparing the choices made by the radical Left across imperial metropoles.

Trans-imperial perspectives. This would naturally lead, beyond comparisons, to a study of the circulation of ideas and activists across imperial borders. That trans-imperial angle has already helped enhance our understanding of decolonisation, in particular in the works which 25 Alain Ruscio, Les communistes et l'Algérie. Des origines à la guerre d 'indépendance, 1920-1962 (Paris, 2019). Jacques Le Gall, La question coloniale dans le mouvement ouvrier en France, 1830-1962 (Pantin, 2013).

26

Many of those initiatives were taken by PCF sympathisers who at that moment did not follow the party line or were not aware that their actions contradicted it. Comparable individual trajectories were observed during the war in Indochina, where dozens of French soldiers with communist sympathies deserted to join the ranks of Ho Chi Minh's army and became his 'white soldiers'. See Jacques Doyon, Les soldats blancs de Ho Chi Minh (Paris, 1973). consider the military support that Britain brought to the French Empire in Indochina, to the Dutch one in Indonesia, or to the 'American Empire' during the Korean War. The study of anti-colonialism and of labour responses to imperialism would also gain from such an approach, as shown by Gasteuil's chapter and its emphasis on cross-imperial networks. 27 Mélanie Torrent, for example, has highlighted the contrast between the Labour Party's moderation in dealing with British imperial interests and its whole-hearted support, at the very same moment and mostly via MCF initiatives, to the FLN in its war against France. There is certainly much to learn from case studies that, likewise, include several imperial zones in their scope and explore the crossing of imperial borders, allowing intriguing parallels to be made. 28 *** Since our 2013 conference in Paris, news from around the world has confirmed how timely the gathering was. In recent years, the deaths of important nationalist figures who, in their youth, had been fellow travellers of the British Left, have reminded us of the long-neglected connection between Empire and Labour. Michael 'King Cobra' Sata, who died on 28 October 2014, had been a platform sweeper, a baggage porter and a trade unionist at Victoria Station long before joining the fight for independence and becoming Zambia's fifth president in 2011.

Calling himself a social-democrat until the very end, he was known to use fiery language to denounce the foreign capitalists' hold over the country's copper mines. Lee Kuan Yew, the founding father of independent Singapore, who died on 23 March 2015, had campaigned for 27 Michael Goebel explores similar networks in his Paris, capitale du tiers monde. Comment est née la révolution anticoloniale, 1919-1939 (Paris, 2017).

28

On the need for historians of the British Empire to become less strictly British and more global in their outlook, see Simon J. Potter and Jonathan Saha, 'Global History, Imperial History and Connected Histories of Empire', Journal of Colonialism and Colonial History, 16.1 (2015). Whatever the point of focus, there is ample scope to widen and deepen our knowledge and understanding of labour, imperialism, colonialism and decolonisation. It will be a demanding but rewarding task successfully to meet this wide-ranging research agenda. 30 29 Jacqueline Jenkinson, Black 1919. Riots, Racism and Resistance in Imperial Britain (Liverpool, 2009).

30

Since the 2013 conference at the Sorbonne Nouvelle, Gareth Curless and I have set up a "Labour and Empire" working group that meets every two years at the European Labour History Network (ELHN) conferences, and occasionally in between. For making those events possible, for constant financial and technical support, I wish to thank my research team, CREW (Centre for Research on the English-speaking World), and everyone at the Maison de la Recherche de la Sorbonne Nouvelle, especially Patrick Belmonte. For inspiring many of the reflections summed in these final pages, I am grateful to all the colleagues and friends who, over the years, have taken part in the adventure, and to those who, in the future, will make sure it goes on.

9Kirk,

  Comrades and Cousins. 10 Kirk, Transnational Radicalism. 11 See Kirk's conclusion in this volume and his reflections on the "global colour line" explored by Lake and Reynolds.

13

  On counter-factual history, see Quentin Deluermoz and Pierre Singaravélou's stimulating Pour une histoire des possibles : analyses contrefactuelles et futurs non advenus(Paris, 2016).14 On crossroads and paths not taken, see also Michael Collins, 'Decolonisation and the "Federal Moment"', Diplomacy and Statecraft, 24.1 (2013), 21-40.

16Kirk,

  Labour and Politics of Empire, 7 (footnotes 8, 9, 11); 25 and 26 for references to the work of Porter, MacKenzie and related scholars.

  17

  EvanSmith and Matthew Worley (eds), Against the Grain. The British FarLeft from 1956 (Manchester, 2014). JohnKelly, Contemporary Trotskyism. Parties, Sects and Social Movements in Britain (London, 2018).

20

  See Colin A. Palmer's trilogy: Eric Williams and the Making of the Modern Caribbean (Chapel Hill, NC, 2006); The Politics of Power. Cheddi Jagan and the Struggle for British Guiana's Independence (Chapel Hill, NC, 2010); The 1938 Labor Rebellion and the Birth of Modern Jamaica (Chapel Hill, NC, 2014).

  combining, for example, commitments, on the one hand, to national liberation and social transformation with, on the other hand, racialised and gendered boundaries and exclusions. Some, such as Wilkinson and Pankhurst, made genuine 'universalising' attempts to overcome differences between the West and the East. Their attempts embraced anti-racism, support for women and feminism and class-based solidarity and internationalism. As such, as highlighted by Perry in relation to Wilkinson, these attempts constitute an important challenge to the key tenet of post-colonial and Subaltern Studies that cultural difference and the assumptions, values and practices of Orientalism formed an insuperable barrier to the development of genuinely equal bonds of solidarity between radicals in the West and the East. There is nonetheless room for further studies of how principled anticolonialism or internationalism did not necessarily exclude racist or sexist prejudice. Labour historians of imperialism and colonialism would be well advised to follow the example of feminist historians in more thoroughly examining the issue of women, agency and conditioning in metropole and colony, 21 Hogsbjerg, Braithwaite.

the

  Labour Party in the late 1930s and his People's Action Party (PAP), founded in 1954, gave allegiance to the Socialist International for about two decades. His proclaimed progressivism did not stop him from accepting honours such as the Knight Grand Cross of the Order of St Michael and St George in 1972, the Freedom of the City of London ten years later, and a place at the top of Rockefeller's International Council and of the Forbes' Brain Trust -an indication that a socialist past did not necessarily exclude access to the upper echelons of the global capitalist class. With the passing of Tony Benn on 14 March 2014, one of the pioneers of the MCF disappeared, granting historians one more motive to start looking back more seriously at the part played by the labour movement in the British experiences of decolonisation. Over the past decade, labour issues from Britain's ex-colonies have been unusually prominent in the headlines, from the Marikana massacre in South Africa (16 August 2012) to the Rana Plaza collapse in Bangladesh (24 April 2013), raising questions about the reality of emancipation for the labouring masses in the post-colonial world, and revealing to large audiences the perpetuation of a form of neo-imperial world order. The workers exploited at the Rana Plaza produced clothes to be sold on Britain's high streets by household brands such as Primark and Store 21. As for the Lonmin company who refused to pay the platinum miners in Marikana a living wage and asked for police and army intervention to put an end to the strike, it is listed on the London Stock Exchange and belongs to the FTSE 250. The way the capitalist market connects workers with each other across borders and oceans, within a structure that is fundamentally unequal, is still striking -another reason why the timing for this collection seems appropriate. Many centenary 2019 commemorations also resonate with the questions raised at our 2013 conference. 1919 was indeed a year of global unrest in which issues of class, empire and race were addressed in violent and often contradictory ways. 1919 was the year when British ports saw white sailors physically attack colonial sailors in most British ports. 29 But 1919 was also the year of the foundation of the Communist International, an International whose anticolonial and antiracist positions were much sharper than its predecessors. Contemporary reasons to think of labour and empire in connected ways are therefore plentiful, as two major conferences convened in 2019 have confirmed: the first -'Imperial Legacies of 1919' -at the University of North Texas on 18-20 April; the second -'The Global Challenge of Peace: 1919 as a Contested Threshold to a New World Order' -at Newcastle University, on 17-18 May 18. Hopefully the coming months and years will see the present momentum confirmed and stimulating new studies flourish and circulate, as ideas should, across frontiers and continents.

Sumithra Janaka Biyanwila, The Labour Movement in the Global South. Trade Unions in Sri Lanka(London, 2010).

See Kirk's concluding chapter in this volume.

See Beverly Grier, Invisible Hands. Child Labor and the State in Colonial Zimbabwe (Portsmouth, New Hampshire,

2006).

Home Rule for India League (HRIL), British Auxiliary, The Waste of Loyalty (London: HRIL, 1916).

Home Rule for India League (HRIL), British Auxiliary, What India Wants (London: HRIL, 1916). Labour Party, Advisory Committee on Imperial Questions, The Colonies. The Labour Party's Post-War Policy for the African and Pacific Colonies' (London: Labour Party, 1943). Movement for Colonial Freedom (MCF), Objects and Constitution (London: MCF, 1961). Socialist Labor Party (SLP), Workers of the World Unite. Declaration on the Dissolution of the Communist International (New York: New York Labor News Company, 1943). World Federation of Trade Unions (WFTU), Shafie Ahmed El Sheikh. Son of the Sudanese People and International Trade Union Leader (Prague: WFTU, 1972). Conference and congress reports Comintern, Workers of the World and Oppressed Peoples, Unite!: Proceedings and Documents of the Second Congress, 1920 (edited by Riddell, John -London: Pathfinder, 1991). Communist Party of Great Britain (CPGB), 27 th Congress Report (London: CPGB, 1961). Communist Party of Great Britain (CPGB), We Speak for Freedom. Proceedings of the Conference of Communist Parties of the British Empire, Beaver Hall, London, February 26-March 2, 1947 (London: CPGB, 1947). Conference of the Peoples of Europe-Asia-Africa Against Imperialism (CPEAA) (Report of the first international) (London: CPEAA, 1948). Saklatvala Papers, British Library -Oriental and India Office Collections (BL-O&IOC), London. Security Service Records (KV), The National Archives, Kew. Trades Union Congress (TUC) Archive, Modern Records Centre (MRC), University of Warwick.

Dailies and periodicals (a selection)

The place of publication is specified only when situated outside of the British Isles.

Bulletin d'information du

Congrès des peuples contre l'impérialisme [Paris] Bulletin d'informations du Comité d'initiative pour un Mouvement pour la Justice et la Liberté Outre-Mer [Paris] Bulletin du Mouvement pour les Etats-Unis socialistes d'Europe [Paris] Call (The) Clarion (The) Comment Commonweal Communist (The) Communist Review Daily Herald Daily Mail Daily Worker East African Standard [Nairobi] Englishman (The) [Calcutta] For A Lasting Peace, For A People's Democracy! [Belgrade] 25 Gibraltar Chronicle [Gibraltar] Hindustan Times [New Delhi] India Bulletin Indus. The Journal of the Indian Students' Union Informations internationales [Paris] Inkululeko Juin 36 [Paris] La Gauche révolutionnaire [Paris] La Révolution prolétarienne [Paris] Labour Leader Liberation [Johannesburg] Madras Weekly Mail [Madras] Manchester Guardian Marxism Today Masses New Age [Cape Town] New Clarion New Dawn New Leader (The) New Statesman (The) Plebs Socialisme et Liberté [Paris] Socialist (The) [Melbourne] Socialist Leader (The) Statesman (The)

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Olivier Duchene
email: olduchene@isara.fr

Camille Bathellier

Benjamin Dumont

Christophe David

Florian Celette

Weed community shifts during the aging of perennial intermediate wheatgrass crops harvested for grain in arable fields

Keywords: Perennial grain, intermediate wheatgrass, weed traits, weed communities, on-farm trials

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

The perennial grain Kernza™ is the result of ongoing efforts by The Land Institute (Kansas, USA) to domesticate intermediate wheatgrass (IWG, Thinopyrum intermedium, (Host) Barkworth & D.R. Dewey). This grain became a figurehead of new perennial grain crops that could revolutionize cropping systems [START_REF] Crews | Going where no grains have gone before: From early to mid-succession[END_REF][START_REF] Dehaan | Roadmap for Accelerated Domestication of an Emerging Perennial Grain Crop[END_REF][START_REF] Duchene | Integrating multipurpose perennial grains crops in Western European farming systems[END_REF][START_REF] Ryan | Managing for Multifunctionality in Perennial Grain Crops[END_REF]. Besides provisioning farmers with food and feed biomass in the form of grain and forage over several years, the deep root system and year round soil cover of this perennial crop [START_REF] Sainju | Root biomass, root/shoot ratio, and soil water content under perennial grasses with different nitrogen rates[END_REF][START_REF] Sakiroglu | How does nitrogen and forage harvest affect belowground biomass and nonstructural carbohydrates in dual-use Kernza intermediate wheatgrass?[END_REF] could provide important additional benefits, including nutrients leaching mitigation [START_REF] Culman | Soil and Water Quality Rapidly Responds to the Perennial Grain Kernza Wheatgrass[END_REF][START_REF] Jungers | Reduced nitrate leaching in a perennial grain crop compared to maize in the Upper Midwest[END_REF], soil erosion control, and carbon storage, [START_REF] Audu | Perennial cereal grain cultivation: Implication on soil organic matter and related soil microbial parameters[END_REF][START_REF] Kim | Carbon and water dynamics of a perennial versus an annual grain crop in temperate agroecosystems[END_REF][START_REF] Sprunger | Perennial grain crop roots and nitrogen management shape soil food webs and soil carbon dynamics[END_REF].

IWG could also potentially outcompete weeds by increasing the timespan of light and soil resource capture in each year [START_REF] Lanker | Farmer perspectives and experiences introducing the novel perennial grain Kernza intermediate wheatgrass in the US Midwest[END_REF][START_REF] Ryan | Managing for Multifunctionality in Perennial Grain Crops[END_REF]. This expectation is supported by published studies, in which grasslands were identified as better competitors of weeds compared to annual crops [START_REF] Dominschek | Crop rotations with temporary grassland shifts weed patterns and allows herbicide-free management without crop yield loss[END_REF][START_REF] Schuster | Weed regulation by crop and grassland competition: critical biomass level and persistence rate[END_REF]. The weed suppression effect from integrating perennial forage and temporary grasslands in cropping systems often corresponds to a shift in weed communities, driven by changes in the disturbance regime and resource gradients [START_REF] Fried | Consistent response of weeds according to Grime's CSR strategies along disturbance and resource gradients in Bordeaux vineyards[END_REF][START_REF] Gaba | Agroecological weed control using a functional approach: a review of cropping systems diversity[END_REF]. Community ecology and trait-based approaches can be used to describe the general patterns of these changes on a functional basis [START_REF] Fried | Trajectories of weed communities explained by traits associated with species' response to management practices[END_REF][START_REF] Fried | Environmental and management factors determining weed species composition and diversity in France[END_REF][START_REF] Grime | Trait convergence and trait divergence in herbaceous plant communities: Mechanisms and consequences[END_REF]. For instance, tillage increases the development of 'ruderal' species (i.e., annuals with fast growing strategies, early flowering, and higher Specific Leaf Area (SLA; [START_REF] Dominschek | Crop rotations with temporary grassland shifts weed patterns and allows herbicide-free management without crop yield loss[END_REF][START_REF] Fried | Consistent response of weeds according to Grime's CSR strategies along disturbance and resource gradients in Bordeaux vineyards[END_REF]. In comparison, systems with reduced or no tillage (e.g., grasslands) tend to favor grass and perennial weed species [START_REF] Adeux | Cropping system diversification does not always beget weed diversity[END_REF]Meiss et al., 2010a,b). Other contributing factors include the intensity of grazing and cutting events, which affect how much light penetrates the canopy, filtering weed species depending on their morphology and ability to regrow (Meiss et al., 2010a;[START_REF] Meiss | Effects of biomass, age and functional traits on regrowth of arable weeds after cutting[END_REF][START_REF] Renne | Disturbance persistence in managed grasslands: shifts in aboveground community structure and the weed seed bank[END_REF][START_REF] Schuster | Grazing intensities affect weed seedling emergence and the seed bank in an integrated crop-livestock system[END_REF][START_REF] Smith | Annual mowing maintains plant diversity in threatened temperate grasslands[END_REF]. Trophic soil conditions represent an orthogonal driver of the structure of weed communities with, for example, species with greater seed mass and plant height favored in richer soils compared to poor soils [START_REF] Fried | Consistent response of weeds according to Grime's CSR strategies along disturbance and resource gradients in Bordeaux vineyards[END_REF].

Cropping systems that have minimal yield losses due to weed competition tend to correspond to systems with diversified weed communities, with higher weed evenness and lower weed biomass, compared to more problematic situations with dominant and competitive weed species [START_REF] Adeux | Mitigating crop yield losses through weed diversity[END_REF]. Thus, a shift in the structure of weed communities following changes to cropping systems could generate problems, depending on the dominance and fitness of species under novel growing conditions.

Due to the novelty of IWG crops, associated field data about weed development remain scarce, and sometimes contradictory; yet, weed management has been identified by farmers as one of the main challenges in Kernza field trials [START_REF] Duchene | Caractérisation fonctionnelle et performances d'une céréale vivace (Thinopyrum intermedium) : une alternative agroécologique pour les systèmes de grandes cultures d'Europe occidentale[END_REF][START_REF] Lanker | Farmer perspectives and experiences introducing the novel perennial grain Kernza intermediate wheatgrass in the US Midwest[END_REF]Law et al., 2021a). [START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF] and [START_REF] Dick | Kernza Intermediate wheatgrass (Thinopyrum intermedium) grain production as influenced by legume intercropping and residue management[END_REF] reported that weed biomass in summer declined during IWG regrowth (second and third year of growth). In contrast, Law et al. (2021a) recorded consistent weed biomass in the summers of successive years, with the development of perennial grass communities (Poa trivialis, Phleum pratense). During IWG establishment, following sowing in fall, conditions for weed growth are analogous to annual grain stands. Land preparation steps, that vary depending on farming systems, are designed to favor the seed germination and seedling emergence of crops. During the subsequent weeks and months, crop seedlings establish their first roots, leaves, and tillers; consequently, their ability to compete with weeds is initially limited, depending on the rate at which it can occupy space and use resources (i.e., regulated by relative growth rate and sowing density). However, after the first year, the growth and management of IWG widely differs to that of annual grain systems, because regrowth in fall is enabled by perennating organs, such as the root and plant crown; consequently, yearly tillage and soil preparation operation are obsolete. This regrowth ability enhances the efficiency of resource capture and use over time [START_REF] Culman | Soil and Water Quality Rapidly Responds to the Perennial Grain Kernza Wheatgrass[END_REF][START_REF] De Oliveira | Energy, water and carbon exchange over a perennial Kernza wheatgrass crop[END_REF][START_REF] Vico | Tradeoffs between water requirements and yield stability in annual vs. perennial crops[END_REF]. However, when IWG is harvested for grain, it cannot be cut at regular intervals during the cropping season, as implemented when harvesting grassland as forage. Only fall or early spring harvest operations are possible, before stem elongation. Thus, a noticeable change in land use is required when cultivating IWG as a perennial grain crop, particularly regarding the disturbance regime (no annual tillage and no regular cutting events in spring) and resource availability over multiple years (because resource capture and use efficiency change over time). Such changes drive shits in the structure of the weed community [START_REF] Dominschek | Crop rotations with temporary grassland shifts weed patterns and allows herbicide-free management without crop yield loss[END_REF][START_REF] Fried | Consistent response of weeds according to Grime's CSR strategies along disturbance and resource gradients in Bordeaux vineyards[END_REF], as demonstrated by Law et al. (2021a) in fields containing IWG grain crops. Therefore, it is important to assess the structure of weed communities over successive growing seasons to determine the importance of IWG cultivation in filtering weed species initially present through habitat change under field conditions. This study explored how weed communities change under IWG cultivation in the temperate arable fields of western Europe (France), from crop establishment to 4-years of growth.

Biomass, composition, and traits were analyzed. We hypothesized that both weed biomass and community composition in fields would alter in response to changes in the disturbance regime and resource gradients following IWG establishment. Potentially problematic weed species were also identified that might require specific attention and management practices in future research or production fields.

MATERIALS & METHODS

Experimental sites description

This study was conducted using three on-farm trial sites (1, 2, and 3) of 0.3-0.4 ha each in the south-east of France. IWG was established in the fall of 2017 (site 1 and 3) and fall of 2018 (site 2), and was grown until the summer of 2021. Data on IWG yields and weed development were collected in each successive year to analyze the nature and intensity in the shifts of the weed community. Table 1 provides information on field locations, management operations, and main soil and climate characteristics. At each site, samples were taken from four subplots (10*20 m) to account for any effect of field heterogeneity. The three sites were cropped for at least the last 10 years with a three-year rotation of annual crops, which are common in the region (rapeseed or maize -winter wheat -winter barley or winter rye). Winter wheat preceded the sowing of IWG at all sites, and maize was grown before wheat. Site 3 was managed with direct sowing practices, whereas sites 1 and 2 were managed with standard tillage operations, including mold-board ploughing and harrowing. All sites were managed with herbicides to control weeds in annual crops and before IWG planting; however, weeds were not treated in any form (mechanical or chemical) during IWG growth. Each year at grain maturity (after the last sampling event in summer), direct combine harvesting was used to harvest both grain and straw.

Data collection 2.2.1. Canopy biomass, composition, and grain yields

Data collection started in the fall of 2017 (sites 1 and 3) and 2018 (site 2) following crop establishment, and ended in the summer of 2021, corresponding to the fourth (sites 1 and 3) or third (site 2) year of IWG growth. During this period, canopy (IWG and weed) biomass and composition were measured: i) each fall (at the end of November), corresponding to the end of vegetative growth before winter; ii) each spring at the crop heading period (mid-May) and flowering stage (mid-June); and iii) in summer at grain maturity (late-July to mid-August). The two spring sampling periods were chosen to obtain a comprehensive overview of weed biomass development, because the peak growth period significantly differs among species, depending on their respective growth dynamics and phenology. In summer, IWG spikes were collected separately from straw. The spikes were then threshed with a manual thresher (NEWEEK), and weighed to estimate grain yields.

For all sampling events at the 3 sites, canopy biomass was sampled after weed species had been identified in two 0.5 m² quadrats on each of the four subplots (1 m² sample per subplot), by cutting the aboveground biomass 5 cm above the soil surface. The entire set of weed species identified at each site is provided in Table 1 and2. The soil cover of weed species was estimated by visual observation, and was rated on a 10% grade scale. For each sampled quadrat, IWG biomass was separated from weeds, and weed species were separated from each other. IWG and weed biomass were oven-dried at 65 °C for 48 h before weighing. The relative biomass of each weed species was presented as the proportion of total weed biomass per quadrat. This approach allowed us to construct a relative abundance table based on biomass units instead of individual plants [START_REF] Wilhm | Use of Biomass Units in Shannon's Formula[END_REF]. This table was used for the statistical analyses (diversity indexes, RLQ analysis). Biomass is thereafter expressed in tons of dry matter per hectare (t DM.ha -1 ). In summer, grain yields were obtained by oven-drying and weighing threshed grains in a similar way to the rest of IWG biomass. Yields were calculated and expressed on a 15% humidity basis. The harvest index were calculated as the ratio between grain yields and total aboveground biomass.

Traits of weed species

Eight functional traits of weeds were selected as potentially responding to IWG growth under field conditions (Table 2). These traits corresponded to the main ecological features related to resource use. These traits were life history (annual, perennial), phenology, plant division (monocotyledons, broadleaves), plant earliness (month corresponding to the start of the flowering period), average height, specific leaf area (SLA, as a proxy of photosynthetic capacity and growth rate), nitrogen, moisture and light requirements. The last three were described using Ellenberg's indicator values [START_REF] Julve | Baseflor. Index botanique, écologique et chorologique de la flore de France[END_REF]; namely, L -light (from 1-deep shade to 9-full light), F -moisture (from 1-extreme dryness to 12-submerged plant), and N -nitrogen (from 1extremely infertile to 9-extremely rich). Values for all weed species identified in this study were collected from online databases and the published literature (Table 2). and intercepts were checked. The correlations between the random intercept and slope were low (< 0.25). IWG grain yields and harvest index were analyzed using similar models (without sampling period effect). Variables were log-transformed as necessary to improve normality.

Least-squares means were computed and used for pairwise comparisons (post hoc analysis, α = 0.05, lsmeans and cld functions) (Piepho, 2004) to determine the significance among mean values following significant (p-value < 0.05) factor effects and interactions. When identified as relevant by the model, correlations between crop and weed biomass were tested with Pearson coefficients, and their associated significance (t test).

Structure, diversity, and traits of the weed community

Analysis of weed communities during spring was performed using both spring sampling events (heading and flowering time). Weed diversity was calculated using Shannon's diversity index, based on biomass units (rather than individuals), according to the following equation:

𝐻 ′ = -∑ 𝑝𝑖ln𝑝𝑖 𝑠 𝑖=1
where p is the proportion of total weed biomass of a given weed species, and s is the number of species present. Mean values were calculated for each site for each growing season, and the species evenness index was obtained by dividing 𝐻 ′ by ln(𝑆), which corresponds to 𝐻 𝑚𝑎𝑥 .

Multivariate analyses were used to examine differences in the structure of the weed community. Nonmetric multidimensional scaling (NMDS) ordination [START_REF] Oksanen | Multivariate Analysis of Ecological Communities in R 35[END_REF] was used to visualize differences in community structure. For NMDS, Bray-Curtis dissimilarity coefficients were calculated using transformed (Wisconsin double standardization) species relative abundance values. A minimum stress to halt iterations was set at 0.01 with 100 restarts. The relationship between weed community structure and IWG stand age (duration of crop presence) was tested through permutational multivariate analysis of variance using distance matrices (Adonis function; [START_REF] Oksanen | Community Ecology Package[END_REF]. Considering that the null hypothesis (random dispersion of weed species) was unlikely due to the effect of repeated measures within sites and subplots over the four years, blocking (sites) and nesting (subplots in sites)

arguments were added to produce a permutational test to compare the effect of stand age within different groups (here the subplots nested in sites). Then, a three-table ordination method (RLQ analysis) [START_REF] Dray | Combining the fourth-corner and the RLQ methods for assessing trait responses to environmental variation[END_REF][START_REF] Dray | Testing the Species Traits-Environment Relationships: The Fourth-Corner Problem Revisited[END_REF] was used to investigate the relationship between weed community traits and IWG growth using the library ade4 [START_REF] Chessel | The ade4 package -I : One-table methods[END_REF]. RLQ analysis enabled the joint structure of three matrices to be assessed; namely, R (environmental characteristics of samples), L (species distribution across samples) and Q (species traits) [START_REF] Dolédec | Matching species traits to environmental variables: a new three-table ordination method[END_REF][START_REF] Dray | Combining the fourth-corner and the RLQ methods for assessing trait responses to environmental variation[END_REF]. The matrix R contained three environmental variables: site code (1, 2, 3), age of IWG stands, and sampling year for each sample. The matrix L contained the standardized relative abundances of weeds.

The matrix Q contained the eight trait values for each of the 26 weed species (Table 2).

Correspondence analysis was carried out on the L-matrix. For the R and Q tables, mixed principal component analysis were performed [START_REF] Hill | Principal Component Analysis of Taxonomic Data with Multi-State Discrete Characters[END_REF], conserving row weight of the correspondence analysis of the L table. Finally, a fourth-corner statistic was computed [START_REF] Dray | Testing the Species Traits-Environment Relationships: The Fourth-Corner Problem Revisited[END_REF], in which the link between traits and environment variables were measured by Pearson correlation, Chi2, or Pseudo-F index (ratio of between-cluster variance), depending on the type of variable (i.e., quantitative or qualitative). Significance was tested by a permutation procedure, resulting in 5,000 Monte Carlo permutations of the rows of matrices R and Q [START_REF] Dolédec | Matching species traits to environmental variables: a new three-table ordination method[END_REF].

RESULTS

Biomass of IWG and weeds

Biomass and yields of IWG

The mixed model showed that sampling period, stand age, and their interaction had highly significant effects on IWG biomass (p-value < 0.001). Weed biomass had no significant effect (p-value = 0.15). During the first year of growth (establishment year), IWG biomass was consistently lower compared to the subsequent years, in both fall and spring (Figure 1, Table S1). IWG biomass was very low (0.087 t DM.ha -1 on average) during the first fall (Figure 1a). This low biomass corresponded to small seedlings with four to five leaves maximum. During the first spring biomass was 2.53 and 6.10 t DM.ha -1 (heading and flowering stages respectively), and rose to and 6.09 t DM.ha -1 in summer (harvest) (Figure 1).

On average, IWG biomass during fall increased across the four years (Figure 1). At flowering and harvest, biomass was highest during the second year of growth (12 and 13 t DM.ha -1 , respectively). Biomass was similar in the third and fourth growing seasons (9.36 and 8.76 t DM.ha -1 at flowering, respectively). The highest IWG grain yield was obtained during the first and second years of growth, and then dropped in the third and fourth years (Figure 2a). Summer and spring weed biomass did not significantly affect grain yield. Grain yield was associated with mean harvest indices of 0.05 to 0.16 (Figure 2b). The harvest index was highest in the first year of growth, and then decreased in the second year, due to higher IWG biomass not leading to higher grain yields.

The drop in grain yield during the third growing season caused the harvest index to decline further. Biomass production at harvest was a good predictor of grain yield for the first growing season (R² = 0.74, p-value < 0.001); however, the correlation was not significant in the second year (R²= 0.06), and was much weaker in the third and fourth years (0.31 and 0.29, respectively; p-value<0.01).

Weed biomass

Sampling period and its interactions with IWG stand age and biomass significantly explained weed biomass (p-value < 0.01, < 0.05, < 0.01, respectively). In fall, weed biomass was 0.02 to 0.57 t DM.ha -1 . Biomass was significantly higher during the establishment year compared to the third and fourth year of growth, in which weed biomass was very low (Figure 1). A significant negative correlation was observed between the reduction in weed biomass and increase in IWG biomass during fall over the first three years of growth (Figures 1 and3), corresponding to a 92.3% reduction in mean weed biomass.

At crop heading and flowering, weed biomass reached a mean 1.29 and 1.72 t DM.ha -1 during the first year, and remained similar in the following three years (Figure 1). At site 3, where weed biomass was initially the lowest, a significant increase occurred the third year, reaching levels similar to sites 1 and 2 (Table S1). Overall, in spring, no significant relationship was found between IWG and weed biomass (Figure 3).

At harvest, weed biomass declined in all years (mean: 0 to 0.3 t DM.ha -1 , Figure 1), and was not influenced by the biomass or yield of IWG. This phenomenon reflected the delay between IWG and weed growth cycles, as almost all the weeds were senescent or had decayed when IWG was harvested.

Structure and traits of the weed community in spring

NMDS (stress = 0.163; Figure 4) showed that perennial IWG stands affected the structure of weed communities in the spring of all four cropping years. Spring sampling time had no effect (crop heading or flowering). The initial situation (first year) differed across the three sites.

However, these differences strongly declined over the study period, with year three and four largely overlapping, while being clearly distinct from the first year. The permutational test showed that IWG stand age significantly affected the structure of the weed community (p-value < 0.001). Weed species richness declined from the establishment year to the last growing season at all three sites (from 14 to 5, 12 to 4, and 18 to 6, respectively, for sites 1, 2, and 3).

For sites 1 and 2, Shannon diversity index declined (from 1.26 to 0.75, and 1.54 to 0.40, respectively); however, species evenness remained constant at site 1 (0.48 to 0.46) but dropped at site 2 (from 0.62 to 0.29). This trend at site 2 was attributed to the increasing dominance of Lolium perenne, followed by Poa trivialis, whereas the other species were highly variable. Site 3 had a stable species diversity index (from 0.96 to 0.90), due to a compensatory effect between lower species richness and higher evenness over the four years (0.33 to 0.50).

The initial dominance of Galium aparine and Veronica persica was progressively balanced by an increase in other species, such as Epilobium hirsutum, Bromus Sterilis, Arrhenatherum elatius, and Poa trivialis.

DISCUSSION

Biomass and grain yields of IWG

The biomass and yield of IWG in this study were consistent with those of previous studies [START_REF] Fernandez | Effects of nitrogen fertilization and planting density on intermediate wheatgrass yield[END_REF]Hunter et al., 2020a,b;Law et al., 2021a;[START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF].

Importantly, low grain yields, and variability in both grain and biomass production, likely represent a significant hurdle in adopting IWG as a novel perennial grain crop by farmers.

Low grain yields of IWG have been explored by many previous studies [START_REF] Altendorf | Floret site utilization and reproductive tiller number are primary components of grain yield in intermediate wheatgrass spaced plants[END_REF][START_REF] Cassman | Progress Towards Perennial Grains for Prairies and Plains[END_REF][START_REF] Cattani | Selection of a perennial grain for seed productivity across years: Intermediate wheatgrass as a test species[END_REF][START_REF] Tautges | Maintaining grain yields of the perennial cereal intermediate wheatgrass in monoculture v. bi-culture with alfalfa in the Upper Midwestern USA[END_REF], with dedicated breeding programs existing to improve them. Variability in yield might have been exacerbated in our study by the relatively low rate of nitrogen fertilization applied each year (50 kg N.ha -1 ) compared to the theoretical optimal range identified by previous studies on the role of nitrogen in building grain yields (61 to 96 kg N.ha -1 ; Fernandez et al., 2020; Jungers et al., 2017). As nitrogen content was not measured in our study, a definitive conclusion cannot be obtained about the balance between nitrogen input and nitrogen use by plants. Also, the plant allocation strategy in case of nitrogen deficiency is not known (translocation to roots, stems, leaves or grains). At 10 tons of aboveground biomass per hectare at flowering, nitrogen content in the aboveground tissue of IGW is about 1% (Fagnant et al., under revisions), representing 100 kg nitrogen in plant tissue per hectare. Between flowering and harvest, grain filling would likely cause overall nitrogen demand to slightly increase. Thus, more than 50 kg of the nitrogen required is not provided by fertilizers, and depends nitrogen availability in the soil pool, which tends to be underestimated because nitrogen in roots is not included in this calculation.

Besides, heterogeneity of plant emergence at establishment (not measured) and planting dates likely induced heterogeneous seedling vigor initially. However, all sites were planted early enough to allow sufficient GDD accumulation (~900 GDD) and tillering before winter and vernalization, based on [START_REF] Olugbenle | Optimal Planting Date of Kernza Intermediate Wheatgrass Intercropped with Red Clover[END_REF]. Variation in temperature and moisture conditions between growing seasons also caused heterogeneity in our study. For example, the 2019-2020 growing season was warmer, whereas the 2020-2021 growing season was wetter (Table 1).

Irrespective of site or climatic year, biomass production peaked during the second growing season, and likely corresponded to a peak in reproductive growth (i.e., many fertile tillers that induced stems elongation; [START_REF] Altendorf | Floret site utilization and reproductive tiller number are primary components of grain yield in intermediate wheatgrass spaced plants[END_REF][START_REF] Fernandez | Effects of nitrogen fertilization and planting density on intermediate wheatgrass yield[END_REF]Hunter et al., 2020a).

However, the harvest index dropped after the first year (Figure 2b), indicating a potential tradeoff between tiller density and tiller fertility. Previous studies also reported a decline in grain yield over time, driven by a decrease in the fertility of tillers and spikes [START_REF] Altendorf | Floret site utilization and reproductive tiller number are primary components of grain yield in intermediate wheatgrass spaced plants[END_REF][START_REF] Fernandez | Effects of nitrogen fertilization and planting density on intermediate wheatgrass yield[END_REF][START_REF] Hunter | Effects of defoliation and row spacing on intermediate wheatgrass i: Grain production[END_REF]. Regardless of the underlying yield components involved, this reduced fertility led to very low grain yields in the third and fourth years of growth (Figure 2a). Tillering is a complex process in grasses, as it is under multifactorial control (e.g., light quality, nutrient and water availability, defoliation regime, temperature; [START_REF] Assuero | Tillering Regulation by Endogenous and Environmental Factors and its Agricultural Management[END_REF]). This process is especially complex in perennial species, like IWG, for which the regulation of tiller emergence and differentiation in relation to environmental cues remain poorly understood [START_REF] Lafarge | Comment l'herbe pousse: développement végétatif, structures clonales et spatiales des graminées[END_REF][START_REF] Rouet | Interactions Between Environment and Genetic Diversity in Perennial Grass Phenology: A Review of Processes at Plant Scale and Modeling[END_REF]. Thus, more research is required to clarify tillering dynamics, which would allow appropriate management practices to be designed (e.g., planting design, mowing, grazing, fertilization, residue management) that maintain the production of fertile tillers over multiple growing seasons.

In our study, mixed models (section 3.1.1) and regression analysis (section 3.1.2, Figure 3) did not indicate that high or low weed biomass depressed IWG yields. This result supported that of [START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF], who showed that yield did not increase in plots where weeds were removed (starting from the second growing season) compared to unweeded plots. However, weeds are a major cause of yield loss in grain production [START_REF] Adeux | Mitigating crop yield losses through weed diversity[END_REF][START_REF] Barberi | Weed management in organic agriculture: are we addressing the right issues?[END_REF][START_REF] Oerke | Crop losses to pests[END_REF], largely due to competition for resources (light, nutrients, water;[START_REF] Zimdahl | Weed-Crop Competition: A Review[END_REF].

This competition is particularly deleterious for wheat yields during stem elongation and flowering (Fischer, 2020 and references therein). Yet in the current study, the highest weed biomass was recorded in late spring, during the elongation phase of IWG, up to anthesis (Figures 1 and3). Overall, our results (together with previous findings; [START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF] raise the question of why IWG biomass and grain production appear to be relatively insensitive to important spring weed biomass compared to annual grains. A recent study investigating how different weed communities impact winter cereals showed that weed biomass alone, especially when sampled late in the season, is a poor predictor of yield loss [START_REF] Adeux | Mitigating crop yield losses through weed diversity[END_REF]. The authors showed that weed-crop interference is better captured in terms of niche competition.

In other words, weed traits are critical for understanding their impact, with weeds that occupy the same niche as crops being the most deleterious. IWG likely displays high ecological complementarity with the weed flora encountered in typical annually disturbed agrosystems, such as those of this study, initially mitigating the impact of weeds on IWG yield. Further studies are required to test this hypothesis, and potentially identify the weed traits that are the most deleterious to IWG growth and grain yield in the field.

Does weed biomass change under IWG over time?

Our results showed that weed biomass declined during fall in all four years of IWG growth (Figure 1 and 3). This decline might have been due to increased competition with the crop in fall, as IWG biomass was significantly higher during regrowth periods compared to when it was establishment in the first fall (Figure 1). Alternatively, weed emergence might have declined because soil preparation and tillage operations were not implemented after sowing the crop.

Also, the composition of the weed community might have shifted towards grasses, which remain vegetative in fall. In any case, slow IWG growth during establishment in the first fall clearly made the crop prone to substantial weed development in the first months after sowing, with potentially enduring effects in terms of crop growth and weed management for farmers.

In spring, weed biomass was already high in the first year, and remained high throughout the experimental period, despite higher IWG biomass in spring during the regrowth years. These weed biomass levels tended to be higher than that recorded for grain crops, such as wheat and barley, under organic management, for which weed biomass rarely exceeds 0.5 t DM.ha - 1 [START_REF] Drews | Weed suppression ability of three winter wheat varieties at different row spacing under organic farming conditions[END_REF][START_REF] Lundkvist | Effects of organic farming on weed flora composition in a long term perspective[END_REF]. Such high weed abundance is not likely to be tolerated by farmers in strict grain cropping systems where weed biomass cannot be valorized as forage, and controlling weed seedlings is an important issue. Law et al. (2021a) reported stable weed biomass in spring over three years in IWG fields, whereas [START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF] reported a significant decline after the establishment year. Yet in the latter study, weed biomass was sampled at grain harvest in summer, when early weeds were likely to have already senesced. In fact, the significant decline in weed biomass recorded from the spring to harvest sampling periods in our study (Figure 1) shows that sampling weeds at IWG harvest might largely underestimate weed development, as most observed species grew in spring, and were already senesced at the IWG harvest stage. In addition, the initial mean weed biomass recorded in the current study was double that recorded by [START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF]; thus, weed pressure was less challenging in this previous study, and the diversity of weed species was lower (notably very few grass species).

The fact that weed biomass did not decline in spring over the four years contrasts with previous studies highlighting the value of temporary grasslands in promoting weed regulation for crop rotations [START_REF] Bretagnolle | The role of grassland areas within arable cropping systems for the conservation of biodiversity at the regional level[END_REF][START_REF] Dominschek | Crop rotations with temporary grassland shifts weed patterns and allows herbicide-free management without crop yield loss[END_REF][START_REF] Lemaire | Grassland-Cropping Rotations: An Avenue for Agricultural Diversification to Reconcile High Production with Environmental Quality[END_REF]Meiss et al., 2010a). However, data on temporary grasslands cannot be easily transposed to IWG fields because management practices notably differ. For instance, absence of mowing and grazing are absent in IWG fields, but are common practices during the entire spring period in grasslands [START_REF] Schuster | Effects of crop rotation and sheep grazing management on the seedbank and emerged weed flora under a no-tillage integrated crop-livestock system[END_REF][START_REF] Schuster | Grazing intensities affect weed seedling emergence and the seed bank in an integrated crop-livestock system[END_REF]. Since grain production is at stake, IWG tillers cannot be cut or grazed after the start of stem elongation until grain maturity in late July or early August. Consequently, many weed communities are able to complete their entire life cycle and produce new seeds for the following year before IWG is harvested. This phenomenon is particularly an issue with narrow-row planting (as is the case in this study), where mechanical weeding is technically challenging.

Unlike IWG grown in pure stands, grasslands generally harbor a mixture of different grass and/or legume species. Through complementarity and stabilizing niche differences [START_REF] Cardinale | Impacts of plant diversity on biomass production increase through time because of species complementarity[END_REF][START_REF] Duchene | Intercropping with legume for agroecological cropping systems: Complementarity and facilitation processes and the importance of soil microorganisms. A review[END_REF][START_REF] Hillerislambers | Rethinking Community Assembly through the Lens of Coexistence Theory[END_REF], functional diversity in mixtures generally allow a better use of resources, leaving less vacant space for weed species to develop. As such, previous studies highlighted the benefit of IWG intercropping with legumes to reduce weed biomass [START_REF] Law | Intercropping red clover with intermediate wheatgrass suppresses weeds without reducing grain yield[END_REF], but also to increase forage value [START_REF] Favre | Forage nutritive value and predicted fiber digestibility of Kernza intermediate wheatgrass in monoculture and in mixture with red clover during the first production year[END_REF] and stabilize grain yields over multiple years [START_REF] Dimitrova Mårtensson | Agronomic performance, nitrogen acquisition and water-use efficiency of the perennial grain crop Thinopyrum intermedium in a monoculture and intercropped with alfalfa in Scandinavia[END_REF][START_REF] Tautges | Maintaining grain yields of the perennial cereal intermediate wheatgrass in monoculture v. bi-culture with alfalfa in the Upper Midwestern USA[END_REF].

Do weed communities change with ageing IWG stands?

In our study, weed communities under ageing stands of IWG had lower diversity compared to those under young stands. Furthermore, as IWG stands aged, the composition of weed communities significantly shifted from primarily annual broadleaved weeds towards grass species and, to a lesser extent, perennial and earlier flowering species (Figure 5 and6). A larger number of sites is needed to confirm whether the life history and earliness of plants are robust drivers. Also, weed trait values could be improved by measuring the traits of studied samples rather than using trait values provided in databases at the species level. While this approach is sufficiently robust for some traits (e.g., plant division or life history), it does not account for the plasticity of other traits in a given environment (e.g., SLA, height). At our study sites, which had a history of annual rotation, a minimum of three years was required to observe shifts in the weed community under IWG. Similar changes were observed at other studies for both IWG (Law et al., 2021a;[START_REF] Zimbric | Effective weed suppression in dual-use intermediate wheatgrass systems[END_REF] and temporary grasslands [START_REF] Bretagnolle | The role of grassland areas within arable cropping systems for the conservation of biodiversity at the regional level[END_REF][START_REF] Hiltbrunner | Long-term weed community dynamics in Swiss organic and integrated farming systems[END_REF]Meiss et al., 2010a), with these studies reporting the selection of grass weed species in perennial stands over time (e.g., Poa trivialis, Phleum pratense).

At our study sites, the main grass species for which abundance increased included Poa trivialis, Lolium perenne, Agrostis capillaris, Arrhenatherum elatius, and Bromus sterilis. These species were mostly perennials that flowered earlier than IWG (Table 2; Figure 6). At one of the sites, the early annual Alopecurus myosuroides was also present; however, it was already relatively abundant in the first year, and no further increase was recorded. Among the few broadleaf species that were also able to grow under IWG aging stands, almost all were perennials (e.g., Taraxacum officinale, Epilobium hirsutum, and Potentilla reptans), except

Galium aparine.

The selection of species more adapted to co-existing with IWG reflected an interplay between differences in relative fitness and stabilizing niches [START_REF] Hillerislambers | Rethinking Community Assembly through the Lens of Coexistence Theory[END_REF]. The important changes that occurred when switching from an annually tilled system to a perennial system without tillage modify the fitness optimum for all species growing in a given agroecosystem, acting as a filter of weed species. In the current study, this phenomenon resulted in the clustering of weed species over time around two main functional traits: grass species and perennial habit, supporting previous studies [START_REF] Dominschek | Crop rotations with temporary grassland shifts weed patterns and allows herbicide-free management without crop yield loss[END_REF][START_REF] Fried | Consistent response of weeds according to Grime's CSR strategies along disturbance and resource gradients in Bordeaux vineyards[END_REF][START_REF] Mainardis | Comparison between flaming, mowing and tillage weed control in the vineyard: Effects on plant community, diversity and abundance[END_REF] minimally affected our trait-based analysis (Figure 6). Still, light demanding species (e.g., Viola arvensis, Cardamine hirsute, Achillea millefolium, Sonchus arvensis; Table 2) were systematically hindered, and there was a clear change in the light requirement of weed communities at site 3, likely due to species that were only found at this location (e.g.,

Cardamine hirsute, Sonchus arvensis, Galium aparine).

Among broadleaf species that continued to grow under IWG aging stands were Epilobium hirsutum and Galium aparine, which have a climbing morphology, contrasting to broadleaves with upright stature that are generally found in temporary grasslands (Meiss et al., 2010a). As mowing and grazing were not implemented at our three sites, the potential role of these two species in promoting or suppressing other weed species remains unexplored. However, as the value of IWG perennial grain is linked to its ability to produce both grain and forage [START_REF] Favre | Forage nutritive value and predicted fiber digestibility of Kernza intermediate wheatgrass in monoculture and in mixture with red clover during the first production year[END_REF][START_REF] Law | Multi-Criteria Assessment of the Economic and Environmental Sustainability Characteristics of Intermediate Wheatgrass Grown as a Dual-Purpose Grain and Forage Crop[END_REF][START_REF] Pugliese | Harvesting forage of the perennial grain crop kernza (Thinopyrum intermedium) increases root biomass and soil nitrogen cycling[END_REF], the interactions between different defoliation regimes and the assemblages of weed communities requires further research.

CONCLUSIONS

This study provided new evidence on the evolution of weed abundance and community composition under ageing IWG stands (establishment to four years). Biomass and yield performance of the perennial grain crop supported previous studies, with biomass production being lower during the first year, while grain yield substantially declined after the second harvest. While weed biomass tended to decrease in the fall of each year, it remained constant

Figure 1 :

 1 Figure 1: Total biomass of IWG and weeds (tons of dry matter per hectare) during fall (A),

Figure 2 :

 2 Figure 2: Grain yield (a) and harvest index (b) of IWG at harvest time during the first, second,

Figure 3 :

 3 Figure 3: Weed biomass as a function of intermediate wheatgrass (IWG) biomass in fall (a),

Figure 4 :

 4 Figure 4: Non-Metric Multidimensional Scaling (NMDS) analysis of the relative abundance of

Figure 5 :Figure 6 :

 56 Figure 5: RLQ analysis of the multiple relationships between species traits (life history,

Table 1 :

 1 Information about the on-farm trial sites, including location, main soil type, weather characteristics (OM = Organic Matter, GDD = Growing 166 Degree Day in base 0 °C), management timing and operations, and identified weed communities. 167

	Site		1	2	3
	Surface (ha)		0.31	0.38	0.33
	GPS coordinates (longitude; latitude)	5.1251; 45.4250	5.0920; 45.2746	5.1433; 45.3323
		Texture	Loam	Sandy-loam	Sandy loam
	Soil characteristics (0-30cm)	pH	7.6	6.7	6.8
		OM (%)	2.1	1.9	2.4
	IWG sowing date and rate (accumulated GDD until first frost)	20/09/2017, ~15kg/ha (882°C)	18/09/2018, ~15kg/ha (904°C)	05/09/2017, ~15kg/ha (1 112°C)
		2017-2018	12.2	-	10.9
	Mean temperature during the	2018-2019	12.3	11.1	11.3
	whole growing season (°C)	2019-2020	13.2	11.9	12.4
		2020-2021	12.6	11.5	11.6
		2017-2018	3775.4	-	3339.2
	Accumulated GDD during the	2018-2019	3808.5	3512.6	3509
	whole growing season	2019-2020	4080.4	3802.5	3841.5
		2020-2021	3854.1	3606.4	3743
		2017-2018	676.8	-	649.6
	Accumulated rainfall during the	2018-2019	535.3	667.2	630.2
	whole growing season (mm)	2019-2020	629.5	783.4	731.4
		2020-2021	651.2	832.6	801.4
	Tillage practices (CT = conventional tillage; NT = No tillage)	CT: plowing to a depth < 25cm (10/09/2017) + power harrow (20/09/2017) + tine seeder (20cm inter-row)	CT: plowing to a depth < 25cm (14/09/2018) + disc harrow (16/09/2018) + tine seeder (22cm inter-row)	NT: direct sowing with discer seeder (25cm inter-row)
	Nitrogen application date (ammonium-nitrate 50 kg N.ha -1 )	15/03/2018; 24/03/2019; 01/04/2020; 26/03/2021	02/04/2019; 05/04/2020; 27/03/2021	21/03/2018; 05/04/2019; 15/04/2020; 28/03/2021
	Harvest date		25/07/2018; 01/08/2019; 27/07/2020; 04/08/2021	11/08/2019; 07/08/2020; 16/08/2021	27/07/2018; 05/08/2019; 08/08/2020; 25/07/2021

Weed species identified on field (code in

Table 2) ACH. CHE. BRO. CAP. PAP. FUM. SON. LAM. POA. VIO. RUM. SEN. CER. STE. VER. ALO. ARR. TAR BRO. LAM. POA. VIO. SEN. CER. STE. VER. ARR. LOL. CAR. ANA. OXA. AGR BRO. CHE. PAP. SON. POA. CER. STE. VER. ARR. TAR. POT. LOL. CAR. EPI. GAL. GER. ANA. AGR

Table 2 :

 2 Traits selected to evaluate weeds with their descriptive values (symbol † provided with each trait indicates source reference and 168

	169	database).
					Ellenberg index ( †)			Earliness of	Average
							Life History		flowering (month	canopy	Average
		Species	Code	Light	Moisture	Nitrogen	( † †, † † †)	Division ( † †)	of the year)	height (m)	SLA ( † † †)
									( † †, † † †)	( † † †)
		Capsella bursa-pastoris	CAP	7	5	7	Annual	Broadleaves	3	0.22	30.02
		Papaver rhoeas	PAP	7	5	6	Annual	Broadleaves	4	0.40	33.07
		Fumaria officinalis	FUM	6	5	6	Annual	Broadleaves	4	0.20	28.54
		Lamium purpureum	LAM	6	5	7	Annual	Broadleaves	3	0.28	38.45
		Viola arvensis	VIO	8	4	6	Annual	Broadleaves	3	0.15	24.32
		Senecio vulgaris	SEN	7	5	7	Annual	Broadleaves	1	0.20	29.82
		Cerastium glomeratum	CER	7	5	5	Annual	Broadleaves	4	0.25	21.75
		Stellaria media	STE	7	5	7	Annual	Broadleaves	3	0.23	53.68
		Veronica persica	VER	6	5	7	Annual	Broadleaves	3	0.25	39.60
		Cardamine hirsuta	CAR	8	5	6	Annual	Broadleaves	3	0.19	27.78
		Galium aparine	GAL	6	6	8	Annual	Broadleaves	6	0.68	34.68
		Geranium dissectum	GER	5	6	6	Annual	Broadleaves	5	0.35	23.20
		Anagallis arvensis	ANA	7	4	5	Annual	Broadleaves	5	0.17	29.22
		Achillea millefolium	ACH	8	5	4	Perennial	Broadleaves	6	0.32	19.81
		Sonchus arvensis	SON	8	6	6	Perennial	Broadleaves	7	0.88	21.70
		Rumex obtusifolius	RUM	7	5	9	Perennial	Broadleaves	6	0.68	29.71

depending on which was analyzed as the response or explanatory variable). As our data collection included a repeated-measures structure (eight measurements taken per year in twelve subplots), the site effect and nested effect of each subplot per site were treated as random intercept effects, representing an uncontrolled (not chosen) effect from local conditions on IWG and weed growth (i.e., weed seed bank, soil, and climate conditions). The model also fits a random slope to account for the random interactions of sites with sampling period or stand age factors. Maximum likelihood of model and the covariance between random slopes

  . Furthermore, functional dissimilarity, such as different growing cycles, also facilitate coexistence by limiting competition between species. The later phenology of IWG (about 1630 average GDD accumulation from February 1 st to flowering;[START_REF] Duchene | Process-based analysis of Thinopyrum intermedium phenological development highlights the importance of dual induction for reproductive growth and agronomic performance[END_REF] compared to earlier temperate grass (<1300 GDD accumulation from February 1 st to flowering; e.g. Poa pratense, Arrhenantherum elatius, Lolium perenne, Dactylis glomerata, Festuca arundinacea, Alopecurus myosuroides;[START_REF] Cruz | Typologie fonctionnelle de graminées fourragères pérennes: une classification multitraits[END_REF] might explain why earlier grasses thrive in IWG fields. Changes to resource gradients(i.e., light, nitrogen, moisture)

†[START_REF] Hill | Technical annex-Ellenberg's indicator values for British plants[END_REF]

† †[START_REF] Julve | Baseflor. Index botanique, écologique et chorologique de la flore de France[END_REF]

† † †[START_REF] Kleyer | The LEDA Trait base: a database of life-history traits of Northwest European flora[END_REF]

FUNDING

This project was supported by a grant from the European Union through a Biodiversa funding for the project NAPERDIV. This work was also supported by a grant from the endowment fund TERRA ISARA. The authors have no conflict of interest to declare.

in each spring; however, the composition of the weed communities shifted. The species richness of weeds was also consistently lower under aging IWG stands, whereas evenness remained dependent on local site characteristics and initial weed communities. Grasses and perennials were largely favored over annual broadleaves; thus, strong fitness differences appear to drive community composition towards species with similar functional traits. In contrast, dissimilarity (e.g., phenological differences) might help to stabilize niche differences and favor particular species. The abundance of weed species co-existing with IWG demonstrates the need to assess the legacy effect of perennial grain in crop rotations. Such information could help optimize optimal management practices, including planting time and design, covered seeding, mechanical weeding, intercropping or mowing.

CONTRIBUTIONS