bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling forest‐growth response to increasing CO2 concentration in relation to various factors affecting nutrient supply
Authors: Kirschbaum M. U. F. , Medlyn B. E. , King D. A. , Pongracic S. , Murty D. , Keith H. , Khanna P. K. , Snowdon P. , Raison R. J. 
Published: March 2003

AbstractIt is well recognized that photosynthesis of C3 plants is highly responsive to CO2 concentration. However, in natural ecosystems, plants are subject to a range of feed‐back effects that can interact with increased photosynthetic carbon gain in different ways so that it is not clear to what extent increased photosynthesis will translate into increased growth. To assess the probable growth response of nutrient‐limited forests to increasing CO2 concentration, we use a previously developed modelling framework and apply it under conditions where the supply of nutrients is affected by a range of different factors.Our analysis indicates that forest growth is likely to be highly stimulated by increasing CO2 concentration in forests with high fertility, in forests with nitrogen fixing plants, in those subject to fire or where nitrogen in wood is effectively removed from the biologically active cycle either through physical removal of stems in harvesting or through continued stem growth over long time periods. Forest growth is likely to be stimulated by CO2 concentration in both phosphorus‐ and sulphur‐limited forests provided nutrients in heartwood of trees are removed from the active nutrient cycle. Without this removal from the cycling system, however, sulphur‐limited forests should show little response to increasing CO2. In phosphorus‐limited forests without phosphorus removal, the response to increasing CO2 depends further on the equilibration state of the large pool of unavailable secondary phosphorus. Considered over periods of centuries during which the secondary pool has equilibrated, growth of phosphorus‐limited forests is likely to be only weakly stimulated by increasing CO2 concentration. However, over shorter periods, increasing CO2 concentration should lead to a substantial increase in productivity.In general, it can be concluded that systems that are more open with respect to nutrient gains and losses are likely to be more responsive to increasing CO2 concentration than systems where the amount of available nutrients is less variable. In more open systems, operation at a lower internal nutrient concentration as a result of increasing atmospheric CO2 concentration can lead to reduced nutrient losses per unit carbon gain. Our analysis shows that the effect of increasing CO2 on forest growth can differ substantially between forests due to interactions with a range of factors that affect nutrient supply. The response of a particular forest to increasing CO2 concentration can only be predicted if the main factors controlling nutrient supply and growth in that forest are understood and incorporated into an assessment.
The effects of water table manipulation and elevated temperature on the net CO2 flux of wet sedge tundra ecosystems
Authors: Oechel Walter C. , Vourlitis George L. , Hastings Steven J. , Ault Richard P. , Bryant Pablo 
Published: March 2003

Abstract
In situ manipulations were conducted in a naturally drained lake on the arctic coastal plain near Prudhoe Bay, Alaska (70 °21.98′ N, 148 °33.72′ W) to assess the potential short‐term effects of decreased water table and elevated temperature on net ecosystem CO2 flux. The experiments were conducted over a 2‐year period, and during that time, water table depth of drained plots was maintained on average 7 cm lower than the ambient water table, and surface temperatures of plots exposed to elevated temperature were increased on average 0.5 °C. Water table drainage, and to a lesser extent elevated temperature, resulted in significant increases in ecosystem respiration (ER) rates, and only small and variable changes in gross ecosystem productivity (GEP). As a result, drained plots were net sources of ≈ 40 gC m–2 season–1 over both years of manipulation, while control plots were net sinks of atmospheric CO2 of about 10 gC m–2 season–1 (growing season length was an estimated 125 days). Control plots exposed to elevated temperatures accumulated slightly more carbon than control plots exposed to ambient temperatures. The direct effects of elevated temperature on net CO2 flux, ER, and GEP were small, however, elevated temperature appeared to interact with drainage to exacerbate the amount of net carbon loss. These data suggest that many currently saturated or nearly saturated wet sedge ecosystems of the north slope of Alaska may become significant sources of CO2 to the atmosphere if climate change predictions of increased evapotranspiration and reduced soil water status are realized. There is ample evidence that this may be already occurring in arctic Alaska, as a change in net carbon balance has been observed for both tussock and wet‐sedge tundra ecosystems over the last 2–3 decades, which coincides with a recent increase in surface temperature and an associated decrease in soil water content. In contrast, if precipitation increases relatively more than evapotranspiration, then increases in soil moisture content will likely result in greater carbon accumulation.
Preliminary estimates of the potential for carbon mitigation in European soils through no‐till farming
Authors: SMITH PETE. , POWLSON DAVID S. , GLENDINING MARGARET J. , SMITH JO. U. 
Published: March 2003

AbstractIn this paper we estimate the European potential for carbon mitigation of no‐till farming using results from European tillage experiments. Our calculations suggest some potential in terms of (a) reduced agricultural fossil fuel emissions, and (b) increased soil carbon sequestration. We estimate that 100% conversion to no‐till farming would be likely to sequester about 23 Tg C y–1 in the European Union or about 43 Tg C y–1 in the wider Europe (excluding the former Soviet Union). In addition, up to 3.2 Tg C y–1 could be saved in agricultural fossil fuel emissions. Compared to estimates of the potential for carbon sequestration of other carbon mitigation options, no‐till agriculture shows nearly twice the potential of scenarios whereby soils are amended with organic materials. Our calculations suggest that 100% conversion to no‐till agriculture in Europe could mitigate all fossil fuel‐carbon emissions from agriculture in Europe. However, this is equivalent to only about 4.1% of total anthropogenic CO2‐carbon produced annually in Europe (excluding the former Soviet Union) which in turn is equivalent to about 0.8% of global annual anthropogenic CO2‐carbon emissions.
Assessment of annual carbon exchange in a water‐stressed Pinus radiata plantation: an analysis based on eddy covariance measurements and an integrated biophysical model
Authors: Arneth A. , Kelliher F. M. , Mcseveny T. M. , Byers J. N. 
Published: March 2003

AbstractWe used a combination of eddy flux, chamber and environmental measurements with an integrated suite of models to analyse the seasonality of net ecosystem carbon uptake (FCO2) in an 8‐year‐old, closed canopy Pinus radiata D.Don plantation in New Zealand (42°52′ S, 172°45′ E). The analyses utilized a biochemically based, big‐leaf model of tree canopy photosynthesis (Ac), coupled to multiplicative environmental‐constraint functions of canopy stomatal conductance (Gc) via environmental measurements, a temperature‐dependent model of ecosystem respiration (Reco), and a soil water balance model. Available root zone water storage capacity at the measurement site is limited to about 50 mm for the very stony soil, and annual precipitation is only 660 mm, distributed evenly throughout the year. Accordingly the site is prone to soil moisture deficit throughout the summer. G
c and Ac obtained maximum rates early in the growing season when plentiful soil water supply was associated with sufficient quantum irradiance (Qabs), and moderate air saturation deficit (D) and temperature (T). From late spring onwards, soil water deficit and D confined Gc and Ac congruously, which together with the solely temperature dependency of Reco resulted in the pronounced seasonality in FCO2. Reflecting a light‐limitation of Ac in the closed canopy, modelled annual carbon (C) uptake was most sensitive to changes in Qabs. However, Qabs did not vary significantly between years, and changes in annual FCO2 were mostly due to variability in summer rainfall and D. Annual C‐uptake of the forest was 717 g C m–2 in a near‐average rainfall year, exceeding by one third the net uptake in a year with 20% less than average rainfall (515 g C m–2).
Increased growth in elevated [CO2]: an early, short‐term response?
Authors: Centritto Mauro , Lee Helen S. J. , Jarvis PauL. G. 
Published: March 2003

SummarySaplings of four clones of Sitka spruce and cherry were grown for three and two growing seasons, respectively, in open top chambers at two CO2 concentrations (≈ 350 and ≈ 700 μmol mol–1) to determine whether the increase in total biomass brought about by enhanced [CO2] is a result of a transient or persistent effect in nonlimiting conditions. Classical growth analysis was applied to both species and mean current relative growth rate of total dry mass (RT) and leaf dry mass (RL), and period relative growth rate of total dry mass (

) and leaf dry mass (

) were calculated. Sitka spruce saplings and cherry seedlings showed a positive growth response to elevated [CO2], and at the end of the experiments both species were ≈ 40% larger in elevated [CO2] than in ambient [CO2]. As a result, the period mean

and

were significantly higher in elevated [CO2]. The differences in plant dry mass at the end of the experiments were a consequence of the more rapid growth in the early phase of exposure to elevated [CO2]. After this initial phase mean RT and RL were similar or even lower in elevated [CO2] than in ambient [CO2]. NAR of both species was much higher in elevated [CO2], whereas both LAR, SLA, and LMR showed the opposite trend. The higher LAR and SLA of plants in ambient [CO2] contributed to a compensation by which they maintained RT similar to that of elevated [CO2] saplings despite lower NAR and photosynthetic rate. However, when the same size the trees were similar amongst the [CO2] treatments, indicating that one of the main effect of elevated [CO2] on tree growth is to speed‐up early development in all aspects.
Seasonal patterns and environmental control of carbon dioxide and water vapour exchange in an ecotonal boreal forest
Authors: Hollinger D. Y. , Goltz S. M. , Davidson E. A. , Lee J. T. , Tu K. , Valentine H. T. 
Published: March 2003

SummaryCarbon dioxide, water vapour, and sensible heat fluxes were measured above and within a spruce dominated forest near the southern ecotone of the boreal forest in Maine, USA. Summer, mid‐day carbon dioxide uptake was higher than at other boreal coniferous forests, averaging about – 13 μmol CO2 m–2 s–1. Nocturnal summer ecosystem respiration averaged ≈ 6 μmol CO2 m–2 s–1 at a mean temperature of ≈ 15 °C. Significant ecosystem C uptake began with the thawing of the soil in early April and was abruptly reduced by the first autumn frost in early October. Half‐hourly forest CO2 exchange was regulated mostly by the incident photosynthetically active photon flux density (PPFD). In addition to the threshold effects of freezing temperatures, there were seasonal effects on the inferred photosynthetic parameters of the forest canopy. The functional response of this forest to environmental variation was similar to that of other spruce forests. In contrast to reports of carbon loss from northerly boreal forest sites, in 1996 the Howland forest was a strong carbon sink, storing about 2.1 t C ha–1.
Tree seedling responses to in situ CO2‐enrichment differ among species and depend on understorey light availability
Authors: Hättenschwiler S.T.ephan , Körner C.H.ristian 
Published: March 2003

SummarySeedlings of six major European temperate forest tree species (Fagus sylvatica, Acer pseudoplatanus, Quercus robur, Taxus baccata, Abies alba, Pinus sylvestris) were exposed to 360, 500, and 660 μL CO2 L−1 in the understorey of a 120‐y‐old forest over two growing seasons. Seedlings rooted in the natural forest soil within 36 open‐top chambers (12 OTCs per CO2 treatment), each with a different known quantum flux density (QFD) ranging from 0.36 to 2.16 mol m−2 d−1 (= 0.8% to 4.8% of full sun). In contrast to a frequent assumption the natural CO2 concentration in the understorey is close to the ambient concentration in the free atmosphere during daytime. The CO2‐effect on seedling growth differed greatly among species and was strongly codetermined by microsite‐specific QFD. Biomass production in the deep‐shade tolerant species Fagus and Taxus increased by 73% and 37% under elevated CO2 in low QFD microsites but was not significantly different among CO2‐treatments in high QFD microsites. The less shade‐tolerant species Acer, Quercus, and Abies showed no significant response to elevated CO2 in low QFD microsites, but increased their biomass by 39%, 25%, and 55% in high QFD microsites. In the shade‐intolerant Pinus, seedling survival was too low for a safe conclusion. Our data showed that the largest relative responses to increasing CO2 occurred at a comparatively small increase from 360 to 500 μL L−1 with only small and non‐significant changes with a further increase to 660 μL L−1. Subtle shifts in the availability of light can totally reverse interspecific differences in the CO2 response. Given these different responses, we conclude that increasing atmospheric CO2 is likely to induce changes in species composition of temperate forests due to altered chances of recruitment. However, these shifts will depend on light patterns in the understorey, and thus on canopy structure, disturbance patterns and forest management.
The uncertainty in simulations by a Global Biome Model (BIOME3) to alternative parameter values
Authors: Hallgren W. S. , Pitman A. J 
Published: March 2003

SummaryThe sensitivity of a global biome model (BIOME3) to uncertainty in parameter values was investigated by testing the model's sensitivity to minimum and maximum parameter values obtained from an extensive literature search. Simulations were conducted replacing the default parameter value by each of the maximum and minimum values determined from the literature. In doing so, the aim was to identify those parameters where the use of an alternate (observed) value leads to a significant change in the simulation of plant functional types at a global scale, in order to identify those which are functionally important to the model. BIOME3 was found to be insensitive to changes in the majority of its parameters, providing a generally sound foundation for confidence in model simulations. However, there was considerable sensitivity shown to over a quarter of the parameters. Three main types of parameters led to a change in plant functional types distribution relative to the control simulation: (i) parameters affecting the photosynthesis parameterization; (ii) parameters affecting the evapotranspiration parameterization; and (iii) root distribution which affected both parts of the model. The main causes of sensitivity were changes in the photosynthesis parameters leading to differential changes in plant functional type's net primary productivity. This caused a shift in the competitive balance between specific plant functional types or between C3 and C4 plant types, and a consequent change in their global distribution. Changes to the evapotranspiration parameters and root distribution similarly affected net primary productivity and soil moisture, and often led to shifts in the competitive balance between grass and trees. Changes in the value for several poorly known parameters produced substantial changes in the distribution of plant functional types, and reduced the κ‐statistic to a large degree, indicating areas of potential uncertainty in the model. This suggests that great care must be taken in prescribing values to these parameters and provides guidance on which parameters need further attention in observational work.
Regional analysis of soil–atmosphere nitrous oxide emissions in the Northern Atlantic Zone of Costa Rica
Authors: Plant Roel A. J. 
Published: March 2003

SummaryRegional analysis of greenhouse gas emissions is becoming increasingly important in answering questions related to environmental change, and typically employs a Geographic Information System (GIS) linked with a process‐based simulation model. For the Northern Atlantic Zone (NAZ) in Costa Rica (281 649 ha), a regional analysis of soil–atmosphere nitrous oxide fluxes from the dominant land‐use types forest, cattle pastures, and banana plantations was performed with both deterministic and stochastic variable representations. The stochastic representation accounted for soil and land management variability across nongeoreferenced fields within 1572 georeferenced land units in 13 relevant classes. Per class, frequency distributions of field‐scale fluxes were simulated with a process‐based model and Monte Carlo methods. Stochastic incorporation of both soil and land use variability resulted in areal (i.e. land unit‐scale) fluxes that were 14–22% lower than estimates based on averaged inputs. Soil heterogeneity was dominant.In addition, spatial flux patterns for current (1992) land use and two alternative land‐use scenarios were evaluated using stochastic inputs. With current management, the regional nitrous oxide‐N flux (standard deviation in parentheses) from agricultural land was 0.43 (0.13) Gg y−1. Replacing natural grasses with mixtures of grasses and N‐fixing species on relevant soil types and introducing different forms of banana plantation management (alternative I) increased the regional flux by 51% to 0.65 (0.22) Gg y−1. When all natural grasses were replaced by fertilized improved species and allowing different forms of banana plantation management (alternative II), the regional flux increased by 126% to 0.97 (0.68) Gg y−1.Using the revised IPCC methodology, the 1992 nitrous oxide emission from agriculture in the NAZ was estimated to be 0.32 Gg y−1. Due to formidable data requirements, regional analysis may not easily be used to produce country‐level estimates. However, regional analysis does provide a valuable benchmark against which the more straightforward IPCC methodology can be evaluated.
Soil CO2 efflux measurements in a mixed forest: impact of chamber disturbances, spatial variability and seasonal evolution
Authors: Longdoz B. , Yernaux M. , Aubinet M. 
Published: March 2003

SummaryA closed‐dynamic‐chamber system (CDCS) was used to measure the spatial and seasonal variability of the soil CO2 efflux (Fs) in beech and in Douglas fir patches of the Vielsalm forest (Belgium). First the difference between natural and measured soil CO2 efflux induced by the presence of the CDCS was studied. The impact on the measurements of the pressure difference between the outside (natural condition) and the inside of the chamber was found to be small (0.4%). The influence of wind disturbance in the closed chamber was tested by comparison with an open‐chamber system characterized by a different wind distribution. A very good correlation between the two systems was found (r2 = 0.99) but the open system yielded slightly lower fluxes than the closed one (slope = 0.88 ± 0.05). A measurement procedure has been developed to minimize the effect of the other sources of perturbation.The spatial and seasonal evolution of the soil CO2 efflux was obtained by performing regular measurements on 29 spots in the beech patch over a period of 12 months and on 24 spots in the Douglas fir patch over 8 months. For each spot, the experimental relationship between Fs and soil temperature was compared with the fitted line for an Arrhenius relationship with a soil temperature‐dependent activation energy.Soil temperature explains 73% of the seasonal variation for all the data. The spatial average of the soil CO2 efflux at 10 °C (Fs10) in the beech patch is 2.57 ± 0.41 μmol m−2 s−1, approximately twice the average in the Douglas fir patch recorded at 1.42 ± 0.22 μmol m−2 s−1.The litter fall analysis seems to indicate that soil organic matter quality and quantity may be one the reasons for this difference. Finally the annual soil CO2 efflux was calculated for the beech and Douglas fir patches (870 ± 140 and 438 ± 68 gC m−2 y−1, respectively). The beech value would represent 92 ± 15% of the annual ecosystem respiration estimated from the eddy covariance measurements.
Simulating the effects of climate change on the carbon balance of North American high‐latitude forests
Authors: Keyser A. R. , Kimball J. S. , Nemani R. R. , Running S. W. 
Published: March 2003

SummaryThe large magnitude of predicted warming at high latitudes and the potential feedback of ecosystems to atmospheric CO2 concentrations make it important to quantify both warming and its effects on high‐latitude carbon balance. We analysed long‐term, daily surface meteorological records for 13 sites in Alaska and north‐western Canada and an 82‐y record of river ice breakup date for the Tanana River in interior Alaska. We found increases in winter and spring temperature extrema for all sites, with the greatest increases in spring minimum temperature, average 0.47 °C per 10 y, and a 0.7‐day per 10 y advance in ice breakup on the Tanana River. We used the climate records to drive an ecosystem process model, BIOME_BGC, to simulate the effects of climate change on the carbon and water balances of boreal forest ecosystems. The growing season has lengthened by an average of 2.6 days per 10 y with an advance in average leaf onset date of 1.10 days per 10 y. This advance in the start of the active growing season correlates positively with progressively earlier ice breakup on the Tanana River in interior Alaska. The advance in the start of the growing season resulted in a 20% increase in net primary production for both aspen (Populus tremuloides) and white spruce (Picea glauca) stands. Aspen had a greater mean increase in maintenance respiration than spruce, whereas spruce had a greater mean increase in evapotranspiration. Average decomposition rates also increased for both species. Both net primary production and decomposition are enhanced in our simulations, suggesting that productive forest types may not experience a significant shift in net carbon flux as a result of climate warming.