Floristic study of weed communities associated to argan cultivation

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Abstract In contrast to the homogenized biodiversity of intensive agriculture, the argan forest is shaped by low-intensity, traditional silvo-pastoral practices that foster a highly heterogeneous landscape. This study addresses a critical research gap by examining how indigenous systems, such as the Agdal, and argan canopy microclimates support endemic and stress-tolerant species. Consequently, these traditional management regimes preserve unique weed assemblages that would otherwise be lost in high-input agroecosystems. While weeds cause significant economic losses in agroecosystems, their communities within Morocco’s argan biosphere remain poorly characterized. This study aimed to identify weeds in argan cultivation and analyze their distribution, diversity, and impact in relation to area, location, and year. Across all study sites, we recorded 147 weed species from 34 families, with Asteraceae (17.7%), Poaceae (14.4%), and Fabaceae (11.1%) being the most dominant. The community was characterized by a predominance of therophytic (63%), dicotyledonous (84%), and annual (73%) species. All monitored parameters such as Shannon Index and species richness were significantly influenced by the three studied factors: sampling area, location, and year. Species diversity (H’) was highest in Ezzaouite and Tamajloujt, while species richness was greatest across four sites. Notably, 28 species were common to all three sampling areas, whereas 30 were unique to watering basins. Annual rainfall emerged as the strongest predictor of weed diversity and abundance. The Partial Harmfulness Index (PHI) identified 25 potentially harmful species, 20 of which had a PHI > 1000. Among the identified taxa, Emex spinosa (PHI = 3230) and Chenopodiastrum murale (PHI = 3057) emerged as the most problematic species, exhibiting high infestation potential across the study sites. Furthermore, several high-impact species like Mesembryanthemum nodiflorum and Zygophyllum creticum showed near-ubiquitous distribution, with relative frequencies reaching 99% and 91%, respectively. The study advocates for a targeted integrated weed management strategy that prioritizes the selective suppression of 25 high-impact species, specifically within watering basins and following rainfall pulses, to maximize agricultural productivity while preserving the unique ecological equilibrium and floral diversity of the Argan Biosphere Reserve.

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