Exotic avenue plantations turning foe: Invasive potential, distribution and impact of Broussonetia papyrifera in Chandigarh, India

Abstract

Broussonetia papyrifera (L.) L'Hér. ex Vent. (common name: paper mulberry; family: Moraceae) is an invasive exotic tree from eastern Asia, which has been introduced to different parts of the world, including India, for both commercial and non-commercial purposes. It has been intentionally planted as an avenue tree in tropical and subtropical urban landscapes. Recently, it has spread beyond original plantings to become invasive in urban areas. The present study was conducted to determine the invasive potential, distribution, and impact of B. papyrifera on understorey vegetation and soil characteristics in a subtropical urban ecosystem in Chandigarh, India. It was observed that both sexual and vegetative reproduction contribute to the invasion success of B. papyrifera. The distribution of B. papyrifera in Chandigarh, India, was estimated according to the Importance Value Index, and the 14 study sites were classified into four invasion categories, i.e., uninvaded, sparsely invaded, moderately invaded, and highly invaded. The results revealed that B. papyrifera is rapidly invading the city, particularly at urban-forest interfaces. The impact of B. papyrifera on the alpha diversity of invaded areas was assessed by quantifying the diversity, richness, and evenness of the understorey species. The soil in highly invaded areas was more acidic with greater conductivity, phenolic content, and organic carbon content, implying that either B. papyrifera alters soil physico-chemical properties or prefers to inhabit soil with such characteristics. Invasion of B. papyrifera results in displacement of vegetation either via competitive exclusion or allelopathy. Thus, we advise that conservation managers and government bodies discourage its further cultivation and take necessary actions to control its spread.