Comparative Analysis of Invasion Intensity of Box Elder (Acer negundo l.) and Sosnowskyi Hogweed (Heracleum sosnowskyi Manden).

Acer negundo is most invasive woody tree, while Heracleum sosnowskyi is most invasive herbal plant species in Lithuania. The purpose of this study is to determine these two species invasion intensity levels. The research of the spread of Heracleum sosnowskyi and Acer negundo was carried out in the regions of Pasvalys and Kaunas. The research focuses on the spread features of these plants, most effective control measures and the level of invasion. The results showed that water had larger influence on the spread of Acer negundo rather than wind as some spontaneous trees were found in all 10 kilometres of onshore area. The longest distance from the parent tree in urban territory revealed to be approximately 100 meters. These plants fruit abundantly; one mature tree of Acer negundo produces approximately 70 thousands of seeds. Heracleum sosnowskyi matures about 7.5 thousands of seeds/1 m². The most effective control measure for Acer negundo is destroying spontaneous seedlings since cutting of the grown trees isn’t effective, they re-grow from the stumps. Digging is more effective than spraying with herbicides for the control of Heracleum sosnowskyi, because only 45 % of the spontaneous seedlings re-grow after digging while even 85 % of them re-grow after spraying. Calculated level of invasion shows that Heracleum sosnowskyi has higher pest plant score than Acer negundo. [ABSTRACT FROM AUTHOR]