Livestock excreta facilitate invasive weed establishment and dominance in pastures through physical niche creation and nutrient pulses

Abstract

Globally, invasive weeds jeopardize pasture productivity and biodiversity, prompting extensive control efforts which are often hampered by an incomplete understanding of how livestock activities, particularly excreta deposition, facilitate weed invasion. Focusing on southwest Chinese pastures, we combined field surveys and controlled experiments to investigate how livestock excreta facilitate the establishment and dominance of the global invasive weed Rumex obtusifolius L. through physical and nutrient-mediated pathways. Field surveys confirmed a strong positive association between excreta deposition and the distribution of R. obtusifolius across diverse pasture landscapes. Experimental manipulations revealed a two-stage facilitation mechanism: (1) Initial physical suppression by dung patches (via light exclusion and anaerobic soil) eliminated intolerant species, substantially reducing local richness (61.6 % after 30 days) and creating establishment opportunities; and (2) Subsequent multi-nutrient enrichment from overlapping dung and urine deposition promoted R. obtusifolius dominance, with dung addition increasing R. obtusifolius height ∼10-fold and ramet number ∼11-fold compared to controls (p < 0.001). Combined dung-urine treatments amplified growth by 32.4 % (p = 0.002) through stoichiometric complementarity, where nitrogen emerged as the primary growth driver (91.3 % biomass increase; p < 0.001). Crucially, clonal reproduction required concurrent multi-nutrient availability, averaging nearly 4 ramets/plant, compared to less than 1 in nitrogen treatments. These findings directly inform pasture management, highlighting that effective invasive weed control and productivity maintenance in pastoral systems require integrating livestock excretion management. Practical strategies, such as adjusting grazing patterns and targeted excreta removal, limit localized nutrient over-enrichment and help conserve pasture ecosystems in an ecologically sound manner.