Evaluating the role of phenology in managing urban invasions: A case study of Broussonetia papyrifera

Multidisciplinary approaches are required for the management of invasive woody species in urban areas. In this context, phenological studies are a useful tool to understand tree development and devise suitable management strategies under urban forestry conditions. The significant role of phenology in attributing competitive advantages to invasive alien species has also been long recognized by community ecologists. Therefore, phenological calendars of invasive species may help in their detection, management and mitigation. In the present study, an attempt has been made to understand the invasive potential of an emerging invasive tree of urban landscapes, Broussonetia papyrifera (paper mulberry; Moraceae), through its phenological assessment by using a standardized numerical scale, BBCH (Biologische Bundesanstalt, Bundessortenamt, CHemische Industrie). The tree is native to southeastern and eastern Asia and the Pacific Islands, and is rapidly spreading across various tropical and subtropical regions. The phenology of B. papyrifera was described in eight principal growth stages (PGSs) with two developmental cycles in a year, presented as primary (January-June) and secondary (June-November) flushes. The observations were further supported by the corresponding dates, photographs, meteorological data (air temperature, precipitation, and photoperiod), and climatic water balance of the study area. Results suggest that the occurrence of two developmental cycles, a prolonged reproductive period, strategy to attract frugivores with brightly colored pulpy fruits, and ability to survive under a wide temperature range help in the spread of B. papyrifera. The phenological scale provided in this study describes accurate and precise developmental stages of the tree that can be used to devise efficient management strategies for its control in urban areas. The information can also be exploited for assessing the climatic conditions required for its prevalence, predicting its future geographic range, and further research.