Yield stability under different management systems: water use efficiency and morphometric plasticity of poplar in agroforestry versus monoculture under Mediterranean conditions

In the face of escalating climate instability and water scarcity in the Mediterranean region, the transition from resource-intensive monocultures to resilient agroforestry systems is becoming imperative for sustainable biomass production. This study provides a comprehensive evaluation of the biometric performance, water use efficiency, growth performance and productivity indexes of Poplar (Populus spp.) cultivated in an agroforestry system versus a conventional high-density monoculture, under both irrigated and rainfed conditions. Field experiments conducted in Central Italy revealed a critical trade-off between absolute yield and biometric performance. While the irrigated monoculture system maximized total biomass production (16.83 t ha⁻1), it required substantial water inputs. Conversely, the rainfed agroforestry system, despite lower yields (11.59 t ha⁻1), demonstrated remarkable yield stability, achieving a Water Use Efficiency (5.32 kg mm⁻1 m⁻2) comparable to the high-input irrigated monoculture (5.21 kg mm⁻1). Furthermore, trees in agroforestry systems exhibited superior individual growth traits, with significantly greater stem diameters and heights compared to monoculture stands, indicating a shift from “quantity-driven” to “quality-driven” biomass production. These findings challenge the conventional paradigm of yield maximization, suggesting that agroforestry offers a superior strategy for sustainable intensification. By decoupling biomass production from heavy water dependence, agroforestry emerges as a key solution for maintaining bioeconomy supply chains in water-limited future scenarios.