Abstract
Alley cropping agroforestry is a land use practice in which arable crops are grown between tree rows. In such agroforestry systems, non-crop herbaceous vegetation develops on the tree rows, resulting in understory vegetation strips (UVS). UVS are perceived both as reservoirs for weeds and opportunities for biodiversity conservation. The purpose of this study was to assess the contribution of UVS to (i) plant spillover and (ii) plant diversity conservation, depending on their functional structure and the farming system. Vegetation surveys were carried out in May 2017 in South-Western France over 16 winter cereal fields (8 alley cropping agroforestry systems and 8 pure crop controls), half under conventional farming and half under organic farming. Using data on plant functional traits related to dispersal strategies and response to agricultural disturbances, we explained the mechanisms involved in plant spillover between habitats. The study revealed that very few species were able to disperse far into crop alleys, except perennial species producing rhizomes and stolons whose spread has been favored by tillage. The presence of UVS in agroforestry fields did not increase weed-crop ratio (i.e. weed coverage / weed and crop coverage) in adjacent crop alleys. On the other hand, UVS harbored richer and more abundant floras (with high proportions of species rarely found in arable habitats) compared to crop alleys and pure crop controls, especially under conventional farming. The functional approach provided insights for weed management in alley cropping agroforestry systems in order to optimize plant diversity conservation without increasing weed-crop ratio. This study showed the relevance of using the functional approach to understand the mechanisms behind plant spillover in cropping systems that integrate semi-natural habitats.
Highlights
The post-war agricultural intensification has led to worldwide losses of biodiversity due to the increase of both agrochemicals’ application and croplands, to the detriment of semi-natural habitats such as woodlots, grasslands, hedges and field boundaries (Stoate et al., 2001)
Pure crop controls 321 harbored 61 species whereas 70 species were found in crop alleys of agroforestry fields, over 322 108 m2 sampled per system
The second RLQ axis significantly separated quadrats according to the farming system but this variable had no significant effect on the functional structure of plant communities within UVS. 341 Figure 2. (a) Results of the fourth-corner analysis performed on dominant species of plant 342 communities located in the understory vegetation strips (UVS). (b) Results of the fourth343 corner analysis testing the link between RLQ axes and traits and environmental variables
Summary
The post-war agricultural intensification has led to worldwide losses of biodiversity due to the increase of both agrochemicals’ application and croplands, to the detriment of semi-natural habitats such as woodlots, grasslands, hedges and field boundaries (Stoate et al., 2001). Aavik and Liira (2010) showed that field boundaries are home to hemerophobic plant species, i.e. species sensitive to tillage and/or herbicides, as opposed to agrotolerant species. Such species have a high conservation value as they are declining in the context of intensive agriculture (Aavik et al, 2008). In the case of spontaneous plants, which are at the basis of agroecosystem food web, their spillover in arable fields could promote biodiversity conservation, and induce yield losses through competition with crops (Petit et al, 2011)
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