Spatial variability of throughfall and stemflow in an exotic pine plantation of subtropical coastal Australia

Large-scale exotic pine plantations have been developed for timber production in subtropical Australia. Few studies investigate the spatial variability of both throughfall and stemflow in such managed pine plantations despite their acknowledged effects on the heterogeneity of hydrological and biochemical processes of forested ecosystems. To examine the spatial variability of rainfall under a 12-year-old pine plantation in a subtropical coastal area of Australia, we observed gross rainfall, throughfall and stemflow over a 1-year period. Our results show that the spatial variability of gross rainfall within a 50m×50m plot is minimal. Throughfall is significantly different among three tree zones (midway between rows, west and east side of trunks), particularly for rainfall <50mm, with the highest throughfall on the east side of the tree trunks (sum=85% of gross rainfall) and the lowest in the midway between tree rows (sum=68% of gross rainfall). These spatial patterns persist among 84% of recorded rainfall events. Spatial variability and time stability of throughfall are better explained by canopy interception of the inclined rainfall resulting from the prevailing easterly wind direction throughout the experiment. The annual stemflow is different among individual sample trees, which is mainly ascribed to the difference in tree size (e.g. projected canopy area and stem diameter). The outcomes of this study would help future investigators better design appropriate sampling strategies in these pine plantations under similar climate conditions.