Evapotranspiration of a declining Quercus robur (L.) stand from 1999 to 2001. II. Daily actual evapotranspiration and soil water reserve

Abstract

-The components of actual evapotranspiration (ET) -interception (In%), tree transpiration (T) and forest floor ET -were measured from 1999 to 2001 in a mixed stand dominated by declining pedunculate oaks. Sap flux density measurements (oaks and maple) and forest floor ET [38] were extrapolated to season and stand scales by regressions with potential evapotranspiration (PET) and leaf area index (LAI). Stand ET varies between 383 and 594 mm (ET/PET: 0.75-1.23). Oak transpiration (21-38% of stand transpiration) is lower than forest floor ET: forest floor can therefore not be neglected in this stand water balance. The soil water reserve dynamics deduced from those measurements reflects the inter-annual changes of water use. No water stress have been calculated on the 1999-2001 period, but it is suspected to have occurred previously; together with soil constraints and caterpillar defoliation, it could in part explain the severe oak decline symptoms. . La transpiration du chêne (21-38% de la transpiration du peuplement) est beaucoup plus faible que celle de la strate herbacée: cette strate ne peut dès lors pas être négligée dans le calcul du bilan hydrique de ce peuplement à plusieurs strates. La dynamique de la réserve en eau du sol, déduite de ces mesures, reflète les changements inter-annuels d'utilisation de l'eau par le peuplement. Aucun stress hydrique n'a été calculé sur la période 1999-2001, mais ce facteur est suspecté d'avoir joué un rôle dans les années antérieures; avec les contraintes édaphiques et les défoliations de chenilles, ce facteur pourrait en partie expliquer le dépérissement observé.transpiration / évapotranspiration / Quercus robur (L.) / dépérissement forestier / réserve en eau du sol

The functional role of temperate forest understorey vegetation in a changing world

“…In that sense, forest ET can be considered to be a conservative process with a shifting role of the overstorey versus understorey contribution. The thinned versus control stands of Vincke et al (2005) indeed show a similar total ET, but a variable contribution of the understorey (Table S4). Black and Kelliher (1989) and Wilson et al (2000) provide insightful reviews on the factors controlling understorey ET.…”

“…Although our data do not allow testing directions of effects, we assume that the negative correlations between overstorey and understorey functioning, as revealed by several of the reviewed studies (e.g. Jarosz et al, 2008;Vincke et al, 2005), are mainly a result of the mechanisms visualized in Figures 2 and 3 and not attributable to a feedback effect. However, our data do suggest that the effect of the understorey on tree regeneration cannot be neglected (Section 3.4), but whether these effects will alter overstorey functioning in the long term remains understudied (but see Thrippleton, Bugmann, & Snell, 2017).…”

Leaf area index development in temperate oak and beech forests is driven by stand characteristics and weather conditions

“…Previous studies reported similar LAI values for Belgium. Maximum LAI reached 2.5 m 2 m -2 in a 70 year old pedunculate oak stand (Gond et al 1999), 1.9-2.8 m 2 m -2 in a (declining) oak forest (Vincke et al 2005), 4-5.5 m 2 m -2 in a 90 year old beech stand (Aubinet et al 2002) and 3.5 m 2 m -2 in a mature mixed oak-beech stand (Mussche et al 2001). …”

Effets de chênes verts isolés sur les variations spatiales et temporelles de l’humidité du sol dans les dehesas du centre-ouest de l’Espagne

“…Thinning usually implies a higher water availability for remnant trees because a lower water interception and transpiration, resulting in a diminution of length and intensity of water stress [46]. This is especially relevant in dehesas, where the survival of trees facing severe drought conditions is only possible if the tree root system extends beyond the influence of the tree canopy [20].…”