The endemic Moroccan species Argania spinosa is considered the most grazed tree species in its distribution area. Since grazing exerts an important effect on plant performances, we attempted to explore the impact of grazing on A. spinosa. Thus, we performed a comparative field experiment where seasonal variations of gas exchange, photochemical efficiency, relative water content, photosynthetic pigment content, and stomatal features were assessed in grazed and ungrazed trees. The net photosynthetic rate was increased in grazed trees in spring and autumn, the favorable seasons. Enhancement of photosynthetic performance may be due to the high stomatal conductance registered in grazed trees. This mechanism may compensate for the lost leaf area, in order to recover from grazing stress. In addition, grazed trees exhibit a better photochemical efficiency, use water more economically and show lower oxidative stress. However, results obtained in summer show that the compensation mechanism could be limited by summer drought. Since the key to preserving the future of forests is sustainable forest management, our results suggest that proper grazing management can be a control tool to increase plant performance and improve species resilience.

Lianas are woody climbing plants and are thought to impact the hosting trees negatively. Ephedra altissima is a liana rising on the Moroccan endemic tree Argania spinosa (L.) Skeels. In this study, our objective was to investigate the impact of the liana on the Argan tree’s physiology and leaf morphology. For that purpose, we compared gas exchange, relative water content, photosynthetic pigment content, and leaf dry mass per unit area of Argan trees associated and not associated with the liana. Our study on individual leaves does not give evidence of the existence or absence of aboveground competition between the liana and the hosting tree. Indeed, photosynthetic rates may suggest that no aboveground competition is occurring. In contrast, pigment content suggests a shading effect of the liana on the hosting tree during the winter season. Otherwise, Argan associated with the liana exhibited a high Chl a/b ratio at the beginning of the dry season, suggesting a belowground competition for nutrient resources. On the other hand, WUEi results indicate that the impact of the liana on the Argan tree may go through seasons with belowground competition for water during spring. The increased LMA values registered in trees associated with the lianasuggest the existence of belowground competition for nutrient resources that persist throughout the year.