Environmental effects on dynamic stem circumference variation in mangrove trees

Tree stems swell and shrink daily, which is thought to reflect mainly dynamic changes in water volume. Daily patterns in stem circumference variation were measured with automatic dendrometer bands in diverse mangrove species in five mangrove forests across Australia and New Caledonia. The stems swelled during the day and shrank at night. Maximum swelling was highly correlated with daily maxima in air temperature, while the timing of stem swelling was not affected by either variation in soil salinity or levels of tidal inundation. Medium-term increases in stem circumference were highly sensitive to rainfall. Trees were defoliated to assess the role of foliar transpiration in stem swelling and shrinking. The pattern of daytime swelling was maintained in defoliated trees, indicating that processes other than canopy transpiration influence temporary stem diameter increments. These processes could include thermal expansion of stems, and more research is required to understand the processes contributing to stem shrinking and swelling.