HYDROLOGICAL PROCESSES Hydrol. Process. 22, 4130–4141 (2008) Published online 2 April 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.7013 Precipitation water storage capacity in a temperate mixed oak–beech canopy Fr´ ed´ eric Andr´ e,* Mathieu Jonard and Quentin Ponette Universit´ e catholique de Louvain, Facult´ e d’Ing´ enierie Biologique, Agronomique et Environnementale, Unit´ e des Eaux et Forˆ ets, Croix du Sud 2/009, 1348 Louvain-la-Neuve, Belgium Abstract: The storage capacity of a temperate mixed oak–beech stand was investigated as a function of stand density and species composition. Measurements were performed in selected zones delimited by three neighbouring trees. Three independent approaches were compared: (i) a spraying laboratory experiment to estimate the water storage on foliage before and after dripping; (ii) a mechanistic model describing rainfall partitioning within the forest canopy and providing estimates of foliage storage capacities; and (iii) linear regression analyses to evaluate the canopy (foliage C branches) storage capacity using the relationship between throughfall and rainfall. Good agreement was generally observed between the laboratory experiment and the mechanistic model estimates, while estimations from the regression method tended to exceed those from the other approaches. Storage capacity estimates ranged from 0Ð22 mm to 0Ð80 mm for pure oak zones, from 0Ð24 mm to 1Ð12 mm for mixed zones and from 0Ð53 mm to 1Ð17 mm for pure beech zones. The increase of storage capacity with increasing proportion of beech in the canopy resulted from higher beech LAI compared with oak. Similarly, for mixed and pure beech canopies, storage capacity was higher for high density zones than for low density zones as a result of the increase in LAI with increasing local basal area; in contrast, for pure oak, the storage capacity was not related to basal area because of the lower shade-tolerance of this species compared with beech. Copyright  2008 John Wiley & Sons, Ltd. KEY WORDS throughfall; storage capacity; Quercus petraea; Fagus sylvatica; mixed-species stand Received 2 August 2007; Accepted 22 January 2008 INTRODUCTION Interception is that part of rain falling on tree organs that subsequently evaporates without reaching the ground. It may represent an important component of the hydro- logical cycle, particularly in forest ecosystems (Calder, 1990). Two components can be distinguished based on temporal dynamics: evaporation during rain, and water evaporated once rain has ceased. Evaporation during rain depends, on one hand, on meteorological factors regulating evaporation rate and, on the other hand, on vegetation type whose roughness affects the aerody- namic conductance (Monteith, 1965). The meteorologi- cal conditions after rainfall affect the rate of evapora- tion while the volume evaporated is essentially deter- mined by the amount of water stored on vegetation at rainfall end; the latter depends both on the volume of the rain event and on vegetation characteristics. A rele- vant concept in characterising vegetation from a hydro- logical point of view is ‘storage capacity’, generally defined as the amount of water stored on vegetation once dripping stops at the end of a rainfall event suf- ficient to exceed the capacity of the vegetation to retain water on its surface (Leyton et al., 1967; Rutter et al., 1972). * Correspondence to: Fr´ ed´ eric Andr´ e, Universit´ e catholique de Louvain, Facult´ e d’Ing´ enierie Biologique, Agronomique et Environnementale, Unit´ e des Eaux et Forˆ ets, Croix du Sud 2/009, 1348 Louvain-la-Neuve, Belgium. E-mail: frederic.andre@uclouvain.be Several methods, either direct or indirect, have been used to determine storage capacity. Direct methods are the cantilever deflection method (Hancock and Crowther, 1979), the ray-attenuation methods (Calder and Wright, 1986; Bouten et al., 1991) and artificial wetting of veg- etative surfaces (Aston, 1979; Herwitz, 1985; Hutch- ings et al., 1988; Liu, 1998). The two former methods need specific and sophisticated instrumentation while the latter method is inexpensive, but difficulties may arise in scaling canopy storage capacity from specific storage capacities determined for the different plant parts. Indirect methods correspond to graphical estima- tion of canopy storage capacity (Leyton et al., 1967) and model optimisation (Rutter et al., 1972, 1975; Rut- ter and Morton, 1977; Gash, 1979; Gash et al., 1995, Whelan and Anderson, 1996). Indirect methods are rather inexpensive but need a rather long period of measure- ments. This study aimed at comparing estimates of storage capacity for canopy zones of contrasted densities and species composition, using different low-cost methods: a spraying laboratory experiment, a regression method based on Leyton’s approach and a mechanistic modelling exercise; for this latter method, two cases were consid- ered, accounting for or neglecting storage of water on branches during the foliage saturation phase. In addi- tion, storage capacities (foliage, woody organs, total) of beech and oak trees were assessed as a function of tree size. Copyright  2008 John Wiley & Sons, Ltd.