Drivers of the circumferential variation of stemflow inputs on the boles of Pinus sylvestris L. (Scots pine)

The spatial variability of stemflow on the bole of trees has rarely been the focal point of stemflow studies, despite its potential importance for stemflow-induced changes to soils. This study helps close this data gap by supplying quantitative data on possible drivers of circumferential variation of stemflow on the boles of two Pinus sylvestris L. (Scots pine). Hence, the objectives of the present study were to quantify the circumferential spatial variability of stemflow on tree stems and to assess how some biotic and abiotic factors affect this variability. Continuous stemflow data observed for two trees within a mature stand of Scots pine during a 20-month period (May 2018 to December 2019) showed the existence of preferential flowpaths around the stem, with patterns of stemflow distribution differing between the two trees. Data suggest that biotic factors (trunk lean, bark morphology and tree neighbourhood) have a greater influence on stemflow distribution on tree stems than abiotic factors (rainfall intensity peaks). Our comprehensive spatio-temporal fine-scale measurements strongly support prior observations of non-uniform stemflow. Further studies of stemflow distribution across tree species and aboveground vegetative surfaces are needed to improve our mechanistic understanding of stemflow dynamics vis-à-vis rainfall interception processes and to gain further insight as to how the circumferential variation of stemflow on tree boles alters stemflow–soil interactions.