Gender structure of Tree-of-Heaven (Ailanthus altissima (Mill.) Swingle) in the protected natural area 'Bajfordova šuma' on the territory of Belgrade: The basis for biological control of its expansion and planned reduction

Abstract

Tree-of-Heaven (Ailanthus altissima (Mill.) Swingle) is an invasive tree species in Serbia that threatens the floristic biodiversity in natural stands and urban areas. It is a heliophyte with rapid growth in the initial phase of development and a well-expressed adaptability to different environmental conditions in open habitats. With early maturity and abundant fruiting almost every year, and the ability of seeds to be transported far from the maternal tree, the tree-of-heaven can rapidly colonize the stands (with disturbed stand structure) of other tree species. It is also a dioecious woody plant. If gender dimorphism of tree-of-heaven is used as a criterion for tree selection in thinning, it can be applied to affect the generative expansion of the species. Within the stand canopy closure, it can be used to influence the growth and survival of generative and vegetative offspring. Differentiation of fruit bearing-female and non-fruit-bearing-male trees is carried out during the flowering phase on the basis of its inflorescences. Selection of fruitbearing-female flowers is carried out during the whole year by checking for the presence of fruit and inflorescence petioles that are retained in the crown after the fruit shedding. Gender dimorphism of the species served as the basis for the gender structure determination in the protected natural area ,,Bajfordova šuma" in Belgrade. Out of 40.08 ha of the protected natural area, tree-of-heaven was recorded individually or in groups, in an area of 27.09 ha, with 131 sexually differentiated trees with diameters within the range of 5-74 cm and heights within the range of 5-21 m. Within the aforementioned number of trees, the share of female and male trees is almost equal, but varies spatially. The recorded female and male trees are the basis for monitoring, planned reduction and tree-of-heaven growing in a non-invasive form in the protected natural area ,,Bajfordova šuma"