Radial growing, cambial activity, and phenology of tree species in a subtropical forest in Southern Brazil

Understanding the factors that affect cambial activity can provide historical documentation of events influencing plant growth and development. This study aimed to link cambial activity and diameter increment of native and exotic species in a floodplain forest in SE Brazil with phenological and meteorological data to answer the following questions: Is species diameter growth influenced by meteorological variables and phenological behavior? Is cambial activity seasonal, with active and inactive periods? Is cell differentiation for initial wood formation triggered by any phenological phase? Diameter increment was measured with dendrometer tapes, cambial activity through vascular cambium samples collection, and phenological behavior through the intensity index. Vegetative structures (mature leaves, senescent leaves, and buds) and reproductive structures (anthesis, immature fruit, and mature fruit) were monitored on a monthly basis. The relationship between meteorological variables and phenophases that lead ro diameter increment was analyzed using multiple linear regression. Additionally, logistic regressions was employed to examine the connection between phenophase variables and cambial activity. The results indicate that the duration of the growing season differs among species, ranging from seven to nine months. Gymnanthes klotzschiana and Blepharocalyx salicifolius showed their highest rates of radial increment from November to March, while Hovenia dulcis and Ligustrum lucidum, from August to April. The increase in diameter for these species is positively influenced by specific phenophases. For G. klotzschiana, these include the presence of mature leaves, senescent leaves, and immature fruits, while for H. dulcis, the presence of mature leaves, senescent leaves, and mature fruits. Moreover, cambial activity is seasonal, with both active and inactive periods occurring mainly in the spring and summer in the four species studied. Different phenological signals were identified as triggers for the initial wood formation, namely, the presence of senescent leaves in G. klotzschiana, budding in H. dulcis, and mature fruits and senescent leaves in L. lucidum. No relationship was found between phenophases and cambial activity or inactivity periods in B. salicifolius.