Bernard Saugier - Academia.edu (original) (raw)

Papers by Bernard Saugier

Annales des Sciences Forestières, 1989

Annales des Sciences Forestières, 1994

— The stem volume and biomass (stem + branches) production, net photosynthesis of mature le... more — The stem volume and biomass (stem + branches) production, net photosynthesis of mature leaves and leaf area production of 5 poplar (Populus) clones, Populus trichocarpa x deltoides (Raspalje and Beaupré), Populus x euramericana (Robusta) and P trichocarpa (Columbia River and Fritzi Pauley), were studied during the first year of growth in an experimental high density plantation (15 600 plants ha-1). Significant differences were found in volume production, woody biomass production, total leaf area and net photosynthesis. Above-ground biomass production was 3.5 times higher in Raspalje than in Robusta. The best performing clones (Raspalje, Beaupré) were those with large leaves, high leaf area index and high photosynthetic rates. A positive relationship between leaf photosynthetic capacity and above-ground biomass production was also noted for 4 of the 5 clones. The euramerican clone Robusta was an exception, showing high photosynthetic rates, but low biomass production. This discrepancy was mainly due to the lower leaf area of this clone, and possibly also due to a larger carbon allocation to below-ground biomass (Barigah, 1991). The root/shoot ratios at the end of the first season in the clones Raspalje and Robusta were 1.23 and 1.79, respectively. net photosynthesis / leaf area / biomass production / Populus Résumé — Photosynthèse, surface foliaire et productivité de 5 clones de peuplier dans leur première année. Des plants issus de boutures de 5 clones de peuplier (Populus trichocarpa x deltoides (Raspalje et Beaupré), P x euramericana (Robusta) et P trichocarpa (Columbia River et Fritzi Pauley) ont été cultivés en peuplement dense (15 600 tiges ha-1). Des mesures d'assimilation de CO 2 et de croissance (surface foliaire, volume de tiges, biomasse aérienne) ont été réalisées sur les jeunes plants. L'accumulation de biomasse du clone le plus performant (Raspalje) représentait 3,5 fois celle observée dans le clone le moins performant (Robusta). Les clones les plus performants (Raspalje, Beaupré) étaient également caractérisés par une surface foliaire importante et une assimilation nette foliaire élevée. Les différences de surface foliaire entre clones étaient liées à des différences de surface individuelle des feuilles et non au nombre de feuilles par arbre, qui était quasi constant. La biomasse aérienne était posi-tivement corrélée à la capacité photosynthétique foliaire pour 4 clones. Cependant le clone Robusta, de capacité de production faible, présentait une photosynthèse foliaire élevée. Cette faible production de biomasse aérienne chez Robusta était due à un faible développement foliaire et probablement aussi à un investissement en biomasse racinaire important (Barigah, 1991) ; le rapport de la biomasse racinaire à la biomasse aérienne était respectivement de 1,23 et de 1,79 pour les clones Raspalje et Robusta.

Journal of Geophysical Research, 1994

Kumar and Monteith' s (1981) model for the remote sensing of crop growth has been used to estimat... more Kumar and Monteith' s (1981) model for the remote sensing of crop growth has been used to estimate continental net primary productivity (NPP) as well as its seasonal and spatial variations. The model assumes a decomposition of NPP into independent parameters such as incident solar radiation (So), radiation absorption efficiency by canopies (J), and conversion efficiency of absorbed radiation into organic dry matter (e). The precision on some of the input parameters has been improved, compared to previous uses of this model at a global scale: remote sensing data used to derivef have been calibrated, corrected of some atmospheric effects, and filtered; e has been considered as biome-dependent and derived from literature data. The resulting global NPP (approximatively 60 Gt c per year) is within the range of values given in the literature. However, mean NPP estimates per biome do not agree with the literature (in particular, the estimation for tropical rain forests NPP is much lower and for cultivations much higher than field estimates), which results in zonal and seasonal variations of continental NPP giving more weight to the temperate northern hemisphere than to the equatorial zone. 53 Gt c, while the Ajtay et al. [1979],Fung et al. [1987] and Box [1988] estimates are 58 Gt c, 48 Gt c and 68 Gt c, respectively. Estimating NPP more precisely is important to understand the global carbon cycle: it is the greatest annual carbon flux from the atmosphere to the biosphere, and it is considered to be the main cause of the seasonal fluctuations in atmospheric CO 2 concentration [Fung, 1986]. The balance between NPP and respiration rate by nonphotosynthetic organisms (net ecosystem productivity (NEP)) determines whether there is accumulation of some of the excess atmospheric carbon by the biosphere, as assumed with indirect proofs: Tans et al. [1990] deduced from scenarios on CO 2 absorption by the oceans that to fit the observed atmospheric variations of CO 2 concentration, the land biosphere should also be a sink for CO 2, this sink being located in the northern hemisphere. To estimate terrestrial NPP, two methods are available: (1) extrapolating field measurements for local NPP to the biosphere, using a vegetation map and (2) modelling plant productivity at the biosphere level. There are three main types of productivity models: (1) statistical models; Lieth [1975] presents various models correlating NPP to mean annual temperature,

Journal of Experimental Botany, 1992

... a decrease in dark respiration (Chmora, Slobodskaya, and Nichiporovich, 1976; Du Cloux 1984; ... more ... a decrease in dark respiration (Chmora, Slobodskaya, and Nichiporovich, 1976; Du Cloux 1984; Gifford, Lambers, and Morison, 1985; Reuveni and Gale ... assumed a direct inhibition of some enzymes of the respiratory chain by CO, (Shaish, Roth-Bejerano, and Itai, 1989; Palet ...

Terre de refuge pour certains, jungle glacee depourvue de reperes pour d'autres, la taiga est... more Terre de refuge pour certains, jungle glacee depourvue de reperes pour d'autres, la taiga est foret entre toutes les forets. Tour a tour dense et clairseme, peuple de trembles, de bouleaux, d'epiceas, de pins et de melezes, cet ermitage ou coulent fleuves et rivieres abrite de nombreuses communautes boreales. Lorsqu'on chemine vers le nord, aux confins de cette gigantesque mosaique chromatique, le regard porte au loin sur des steppes denudees, des collines recouvertes d'une vegetation rase, d'immenses prairies marecageuses parsemees de lacs. La toundra, porte ouverte sur le monde arctique, revele toute sa demesure.

that establishes if groundwater recharge can be determined by optimising vegetation parameters ag... more that establishes if groundwater recharge can be determined by optimising vegetation parameters against soil moisture*

Tree Physiology, 1997

Three independent methods were used to evaluate transpiration of a boreal forest: the branch bag,... more Three independent methods were used to evaluate transpiration of a boreal forest: the branch bag, sap flow and eddy covariance methods. The branch bag method encloses several thousand needles and gives a continuous record of branch transpiration. The sap flow method provides a continuous record of sap velocity and an estimate of tree transpiration. The eddy covariance method typically measures evaporation rates between a forest and the atmosphere. We deployed an extra eddy covariance system below the forest to estimate canopy transpiration by difference. The three systems detected small water vapor fluxes despite a plentiful supply of energy to drive evaporation. We also observed that transpiration rates were low even when the soil was well supplied with water. Low rates of transpiration were attributed to the canopy's low leaf area index and the marked reduction in stomatal conductance as vapor pressure deficits increased. Water vapor fluxes, derived from the sap flow method, lagged behind those derived by the branch bag method by 1 to 2 h. The sap flow method also suffered from sampling errors caused by the non-uniformity of flow across the sapwood and the spatial variability of sapwood cross section throughout the forest. Despite technical difficulties associated with hourly measurements, daily totals of transpiration agreed well with values derived from micrometeorological systems.

Journal of Hydrology, 1984

Prediction of forest water balance for estimation of, e.g. stress periods, is always subjected to... more Prediction of forest water balance for estimation of, e.g. stress periods, is always subjected to the conflict between data availability and the desire to approach physical reality. The model described in this paper was conceived to work with routine meteorological data while still retaining the basic physics. Values of all its nine parameters were estimated independently for a 120 yr.-old oak stand in Fontainebleau forest near Paris, France. Weekly measurements of soil-water content and throughfall served as validation for the wet 1981 and the dry 1982. Model sensitivity w~ assessed to changes in the values of the surface and aerodynamic resistances, the interception capacity, the field capacity and the soil-water content at onset of soil-water stress. A comparison of different formulae to predict potential transpiration/evaporation clearly demonstrated the necessity to include a surface resistance term in a forest transpiration formula. The aerodynamic resistance was less important and the simple threshold formulation for interception did not always work well. The overall behaviour of the model was primarily limited by the availability of precipitation data very near the study site.

Global Change Biology, 1996

We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (... more We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement. Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985). Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10-15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35-50%) in a tropical rain forest. It also increases after thinning or during a dry spell. A set of 5-10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend. For modelling purposes, tree canopy conductance (gc) was calculated from Penman-Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of g^ for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.

Functional Ecology, 2000

1. We present measurements of CO 2 fluxes over 2 years above and within a young Beech stand in th... more 1. We present measurements of CO 2 fluxes over 2 years above and within a young Beech stand in the east of France. This site is part of the Euroflux network set up to monitor fluxes over representative European forests. 2. The net ecosystem carbon (C) exchange was derived from continuous eddy flux measurements. Major components of the total flux (i.e. soil and above-ground biomass respiration and assimilation of leafy branches) were measured independently using chambers. The main C stocks (i.e. root, stem and branch biomass) were also quantified. 3. Daily minima of CO 2 flux were typically around-20 µ mol CO 2 m-2 s-1 during the period of full leaf expansion, while night-time ecosystem respiration varied between 5 and 15 µ mol CO 2 m-2 s-1. The seasonal pattern of net ecosystem assimilation was very close to that of net assimilation at the single branch scale. The seasonal variation of net ecosystem exchange was closely related to leaf expansion and soil water content during the dry year of 1996. 4. Measurements of ecosystem respiration (eddy flux) were corrected for CO 2 storage within the stand. This C flux showed a seasonal pattern, the maximum rates (4-7 g C m-2 day-1) occurring in spring and summer, and appeared to be correlated with soil temperature. Temporal variation of soil respiration showed the same pattern, and effects of both temperature and soil drying were found. Annual soil respiration was ≈ 70% of ecosystem respiration. Root respiration was 60% of the total below-ground respiration. 5. Annual net C exchange was-218 and-257 g C m-2 in 1996 and 1997, respectively, corresponding to net C uptake by the forest. These values are much lower than the annual biomass increment (stems and large roots) of the stand: 427 and 471 g C m-2 year-1 , respectively. The difference may be explained by a release of CO 2 from the decomposition of woody debris. 6. Ecosystem C loss by respiration was 800-1000 g C m-2 year-1. Gross C gain was 1000-1300 g C m-2 year-1. Ecosystem respiration therefore played a major role in the annual C balance of this forest.

Revue Forestière Française, 1999

La composition de l'atmosphère terrestreab eaucoup varié au cours des temps géologiques. Avant l'... more La composition de l'atmosphère terrestreab eaucoup varié au cours des temps géologiques. Avant l'apparition de la vie,l'atmosphèreé tait sans douted ominée par le gaz carbonique produit par les éruptions volcaniques,c omme c'est encorel ecas pour les planètes sans vie quin ous entourent,V énus et Mars.Au cours des temps géologiques,l'absorption du CO 2 par laphotosynthèse,et l'enfouissement de grandes quantités de carbone dans les roches sédimentaires ont progressivement réduit la teneur en CO 2 et élevél a teneur en oxygène de l'air. Àlafin du Secondaire,a u moment de l'extinction des dinosaures,il y avait encoree nviron deux fois plus de CO 2 qu'en 1800,a vant l'èrei ndustrielle (Berner,1994). La composition actuelle de l'atmosphère résulted 'uné quilibree ntred es processus biologiques comme la photosynthèsee t la respiration,et des processus physico-chimiques comme l'absorption du CO 2 par les eaux froides des océans, sous-saturées en CO 2 ,et son rejet par les eaux chaudes, sur-saturées en CO 2 .On sait,par l'analysed es bulles d'air piégées dans les glaces de l'Antarctiquee t du Groenland,quel a teneur en CO 2 de l'air a varié relativement récemment en fonction de la températured el aT erre,d'environ 200 ppmv (parties par million en volume) pendant les périodes glaciaires,àenviron 280ppmv pendant les périodes plus chaudes, comme celle quen ous connaissons depuis près de 100 00 ans (Barnola et al .,1991).

Modelisation parametrique et predictive de la biosphere terrestre par observations satellitaires ... more Modelisation parametrique et predictive de la biosphere terrestre par observations satellitaires ; Cet article presente un recapitulatif des divers modeles que nous avons developpes afin d'estimer les flux de carbone dans la biosphere terrestre, et des diverses utilisations d'observations satellitaires pour piloter, tester et ameliorer ces modeles. ; Le modele parametrique, dont le but est d'estimer la Productivite Primaire Nette a l'echelle globale, beneficie d'indices de vegetation satellitaires lui permettant de diagnostiquer a haute resolution spatiale et temporelle la fraction de rayonnement photosynthetiquement actif (f par ) absorbe par la vegetation. A l'echelle pluriannuelle, cette methode a demontre sa capacite a restituer la reponse du couvert vegetal aux perturbations climatiques telles que les evenements El Nino. Les estimations de f PAR satellitaire sont aussi utilisees pour evaluer les resultats d'un modele predictif de PPN base sur des pro...