Intra- and interannual variations of transpiration, leaf area index and radial growth of a sessile oak stand (Quercus petraea)

Abstract

— Bud-burst, leaf area index (LAI), transpiration, soil water content and radial growth of a 35-year-old Quercus petraea stand were measured during 5 successive years (1989)(1990)(1991)(1992)(1993). At the beginning of 1992, half of the stand was thinned. The increase of stand transpiration during spring was linearly correlated to the development of LAI. During the second part of the season, although LAI continued to increase because of rhythmic shoot development, transpiration was strongly reduced as soil water content decreased. The transpiration/potential evapotranspiration (T/PET) ratio decreased sharply as soon as relative extractable water (REW) dropped below 0.4. Likewise, cumulated stand transpiration varied among years because of variability in soil water availability, LAI and canopy structure. A linear relationship, similar to the one observed for weekly variations, was noted between T/PET and LAI; maximum LAI ranged from 3.3 to 6 in this ring-porous species. Seasonal circumference measurements showed that 43% of the annual increment was achieved before leaf development, hence before canopy transpiration and CO 2 assimilation were started. Tree ring area was significantly correlated to the cumulated transpiration; a water-use efficiency variable was defined at both tree and stand level. transpiration / leaf area index / drought / circumference increment / Quercus petraea Résumé — Variations intraet interannuelles de transpiration, d'indice foliaire et de croissance radiale d'un peuplement de chêne sessile (Quercus petraea). Le débourrement, l'indice foliaire (LAI), la transpiration, la teneur en eau du sol et la croissance en circonférence d'un peuplement de Quercus petraea âgé de 35 ans ont été mesurés pendant 5 années successives (1989 à 1993, fig 6). Au début de l'année 1992, la moitié du peuplement a été éclaircie. L'augmentation de la transpiration du peuplement au printemps était linéairement corrélée à LAI (fig 2). Au cours de la seconde partie de la saison, même si LAI continuait à augmenter en raison de la croissance rythmique des pousses, la transpiration était fortement réduite par la sécheresse édaphique. Le rapport transpiration/ETP diminuait rapidement dès que la fraction disponible de l'eau du sol chutait en dessous de 0,4 (fig 3). De même, la transpiration cumulée du peuplement variait entre les années avec la disponibilité en eau du sol, le LAI et la structure du couvert. Une relation linéaire similaire à celle observée à l'échelle hebdomadaire a été mise en évidence entre T/ETP et LAI pour une gamme de LAI s'étendant de 3,3 à 6,0, selon les années et la densité des traitements (fig 8). Les mesures d'accroissement en circonférence au cours de la saison ont montré que 43 % de l'accroissement annuel était réalisé avant le développement des feuilles (fig 4), donc avant la reprise de transpiration et d'assimilation du carbone. La surface de chaque cerne était significativement corrélée à la transpiration cumulée au cours de la saison de végétation (fig 10). Une variable d'effi...

Exploring Growth Variability and Crown Vitality of Sessile Oak (Quercus Petraea) in the Czech Republic

“…Earlywood begins forming approximately three weeks before bud break (Bergès et al, 2008). In the period before bud break, a significant part of the stem increment has already been formed: Barbaroux and Bréda (2002) estimate 30%, while Bréda and Granier (1996) estimate 43%, but the latter study included not only earlywood, but also part of latewood. The spring mobilization of carbohydrates is likely to also be related to the conducting elements of oak as large tracheids are very sensitive to winter embolism.…”

Leaf Size and Leaf Area Index in Fagus sylvatica Forests: Competing Effects of Precipitation, Temperature, and Nitrogen Availability

“…Tree leaf area and stand leaf area index (LAI, the one-sided cumulative surface area of all leaves per unit ground area) are of paramount importance for forest biogeochemical fluxes because radiation interception, productivity, canopy conductance, and stand transpiration are all closely linked to LAI (Gholz and others 1990;Bré da and Granier 1996;Kozlowski and Pallardy 1997;Welander and Ottoson 1997).…”

Daily and seasonal variation of stem radius in oak

“…Diurnal and seasonal variation in stem radii in trees in connection with other processes, environmental conditions and tree parameters represents an important characteristic of tree physiology and was studied by different authors ( [1,15,17,25,30,35,38] [9,12].…”