###### Abstract  
_Ailanthus altissima_ (\(AA\)) is an invasive tree species rapidly spreading worldwide, colonizing both urban and agricultural or forestry environments. This three-year study aimed to assess its effects on the growth and yield traits of the Koroneiki olive cultivar under co-cultivation in pots, combined with two irrigation regimes, full and deficit irrigation (60% of full). Within each irrigation regime, olive trees were grown either in the presence or absence (control) of \(AA\). The trial evaluated several parameters, including vegetative growth, yield traits, and oil quality characteristics. Co-cultivation with \(AA\) had no significant impact on tree growth after three years, though it significantly reduced oil content per fruit. Antioxidant capacity of the oil improved under deficit irrigation, while \(AA\) presence did not significantly affect it, except for an increase in o-diphenyl concentration. Neither the fatty acid profile nor squalene levels were significantly influenced by either treatment. Fruit weight and color were primarily affected by deficit irrigation. During storage, olive oil quality declined significantly, with pre-harvest treatments (presence or absence of \(AA\) and full or deficit irrigation regime) playing a critical role in modulating several quality parameters. In conclusion, the presence of \(AA\) near olive trees did not substantially affect the key quality indices of the olive oil, which remained within the criteria for classification as extra virgin. _Ailanthus altissima_ (Tree of Heaven) on Yield Performance and Olive Oil Quality Parameters of Young Olive Trees cv. Koroneiki Under Two Distinct Irrigation Regimes. _Appl. Sci._**2025**, 15, 7678. [[https://doi.org/10.3390/app1514768](https://doi.org/10.3390/app1514768)]([https://doi.org/10.3390/app1514768](https://doi.org/10.3390/app1514768))  
1  
_Ailanthus altissima_ (Mill.) Swingle, commonly known as the tree of heaven, is a fast-growing, deciduous, invasive tree species belonging to the Simaroubaceae family [1, 2, 3]. It exhibits remarkable adaptability to diverse soil types and climatic conditions [3]. The rapid spread of _Ailanthus_ is facilitated by its vigorous vegetative propagation, prolific seed production, and tolerance to various abiotic stresses [2, 4, 5]. Its seeds are dispersed over long distances by wind, and the tree readily regenerates from root suckers and cut stumps [4, 5]. A key mechanism contributing to _Ailanthus_ expansion is its allebotathic capacity, which is the release of phytotoxic compounds that suppress the growth of nearby plant species [2; 5; 6]. These compounds are mostly concentrated in the roots and bark [1; 3; 6], although they are also present, to a lesser extent, in the shoots, seeds, and wood [6]. The presence of _Ailanthus_ has been shown to negatively affect neighboring vegetation through reduced photosynthetic activity, altered soil pH, and depleted soil fertility [3; 4]. Controlling _Ailanthus_ is particularly challenging, as both mechanical and chemical control measures often prove ineffective [7; 8; 9]. In recent decades, its spread has intensified across urban, forest, and agricultural landscapes, where it displaces native and economically important plant species [7]. The olive tree (_Olea europaea_ L.) is considered one of the earliest domesticated tree crops [10; 11]. Approximately 85% of global olive groves are concentrated in the Mediterranean basin, with Spain, Greece, and Italy leading in the production of both olive oil and table olives [12]. Extra virgin olive oil (EVOO) is widely recognized for its high nutritional value and exceptional oxidative stability, making it a premium vegetable oil. This stability is attributed to its fatty acid composition [13; 14; 15] and to a variety of secondary natural antioxidants, including squalene, carotenoids, tocopherols, and phenolic compounds [14; 15; 16].