Soil temperature and weather factors as key drivers of flowering phenology and nectar production in black locust (Robinia pseudoacacia L.) in Hungary

<br>The black locust (<i>Robinia pseudoacacia </i>L.) isthe second most planted tree species worldwide, and the most common inHungary. Phenotypic traits, particularly flowering patterns, are well-established indicators ofthe species' response toclimate change. This study examined four forest subcompartments across three Hungarian regions: Northern-Central, Eastern and Southern-Central. The aim was toidentify climatic factors correlating with the onset and duration ofthe flowering period. Additionally, the relationships between these factors and nectar weight and sugar concentration were defined. Results indicate astrong negative correlation between precipitation levels and flowering time: lower accumulated and average precipitation during the spring months ofthe preceding year was associated with adelayed flowering period inthe following year (<i>r</i><i></i>=<i></i>–0.922, <i>r</i><i></i>=<i></i>–0.918, <i>P</i>=<i></i>0.05). However, when examining the 14-day period (<i>r</i><i></i>=<i></i>0.829) before blooming orexamining from 1 January (<i>r</i><i></i>=<i></i>0.929, <i>r</i><i></i>=<i></i>0.890), the results indicate that other environmental factors may play amore dominant role. Furthermore, the number ofchill and heat days was found toaffect the starting date (<i>R</i>²<i></i>=<i></i>0.819, <i>R</i>²<i></i>=<i></i>0.765).