Spatial and temporal patterns of throughfall volume in a deciduous mixed-species stand

SummaryThe effects of canopy structure on the spatial and temporal patterns of throughfall (TF) in deciduous mixed-species stands remains poorly documented. TF was collected on a rain event basis in an oak–beech stand, within 12 structural units of contrasting densities (low, LD; high, HD) and species composition (beech, oak, mixture) delimited by three neighbouring trees. A roof was installed at the centre of each unit, and gutters were placed at the periphery of the LD units. Based on selected rain events, a simplified mass balance approach was used to describe water fluxes reaching and leaving the canopy. During the leafed season, the proportions of incident rainfall (RF) collected as TF on the roofs steadily increased with increasing RF up to a RF volume of about 5 mm; for larger RF volumes, TF proportions stabilised around 55% under pure (LD, HD) beech and HD mixture, and around 65% under pure (LD, HD) oak and LD mixture. During the leafless period, TF proportions (on average 60%) were independent of RF but were still affected by local stand characteristics (HD mixture < HD beech < HD oak < LD beech and mixture < LD oak). At canopy saturation, lateral transfers as branch flow (BF) were substantial (35 ⩽ (BF/RF)% ⩽ 46) in all plots, and were significantly higher in the HD units compared to the LD plots in the leafless period; part of BF falled down as indirect TF before reaching the trunks, except in the HD units during the leafless season where stemflow and BF were similar. A mechanistic numerical model using rainfall partitioning parameters determined in this study allowed to successfully describe real-time throughfall measurements.

Research highlights
► We measured throughfall volume (TF) on a rainfall basis in a mixed oak-beech stand.
► TF was collected in zones of contrasted canopy type between three adjacent trees.
► Zone ranking according to TF was: beech, dense mixture < oak, low density mixture.
► TF at crown edge > TF near the stems before saturation, and inversely at saturation.
► At saturation, branch flow/rainfall > 30% and depended on canopy type and season.