Long-term control of the invasive tree Ailanthus altissima: Insights from Mediterranean protected forests

Ailanthus altissima is an invasive tree species which has colonized numerous ecosystems and affected ecosystem processes worldwide. Despite its importance as an invasive species and the high economic costs incurred from its spread, there is a lack of long-term management planning for its control. Although mechanical disturbance is commonly applied, the effect that this treatment may have exhausting its resprouting ability and also its joint effect with phytochemical treatments are poorly understood, especially in Mediterranean environments. We tested three treatments (plus a control) aimed to reduce A. altissima growth in Mediterranean forests throughout 5 years of study. The treatments (one cut stump, double cut stump and cut stump with glyphosate application) were repeated annually. General plant performance (biomass, height and resprout-type density) was measured yearly during the study. Water potential and stomatal conductance were also measured at the end of the study to evaluate particular ecophysiological factors which might affect the response of A. altissima to assayed treatments, together with leaf area index. Our results show that only the cut stump with glyphosate application treatment was able to reduce the long-term growth and spread of A. altissima. The treatments applied favoured collar sprout growth in response to disturbance events (treatments) opposite to the control, where new sprouts grew mainly from the root. Treated resprouts displayed ecophysiological changes depending on the assayed treatment. To our knowledge, this is the only study testing the long-term effect of both physical disturbance and phytochemical application on A. altissima growth. Our study further refines our knowledge on the effects of repeating both commonly and newly used treatments, improving our management techniques to reduce the presence and growth of this invasive tree.