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Aeration is a common range management technique used in southern Texas and northern Mexico to reduce shrub cover and increase biomass of more palatable forages. Guajillo (Acacia berlandieri Benth.) is an important forage plant for deer and domestic livestock throughout its range in northeastern Mexico and southern Texas. It responds to top removal, such as by aeration, by producing large numbers of juvenile sprouts which can have higher total leaf nitrogen content up to 6 months after treatment. However, the concentration of phenolic amines, potentially toxic secondary plant chemicals, may also increase. We compared concentrations of tyramine and N-methyl-phenethylamine (NMP), 2 prominent phenolic amines that can negatively affect reproduction in herbivores, between juvenile (regrowth) and mature stems of guajillo in areas that had been aerated and also between mature stems in aerated and control sites. Aeration increased NMP but not tyramine concentrations in mature stems. Juvenile stems had higher total nitrogen concentration than mature stems but also had higher amine concentrations until about 1 year after aeration. A greater percent of total nitrogen was incorporated into amines in juvenile stems (2.5-6.0%) than mature stems (1.8-4.2%). Amine concentrations peaked in summer and early autumn, a period when herbivores may rely heavily on browse because forbs are scarce. Our results suggest that while aeration may result in higher nitrogen concentrations in guajillo, increases in amines may limit benefits to herbivores. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020