Thinning Can Reduce Losses in Carbon Use Efficiency and Carbon Stocks in Managed Forests Under Warmer Climate

Forest carbon use efficiency (CUE, the ratio of net to gross primary productivity) represents the fraction of photosynthesis that is not used for plant respiration. Although important, it is often neglected in climate change impact analyses. Here we assess the potential impact of thinning on projected carbon cycle dynamics and implications for forest CUE and its components (i.e., gross and net primary productivity and plant respiration), as well as on forest biomass production. Using a detailed process-based forest ecosystem model forced by climate outputs of five Earth System Models under four representative climate scenarios, we investigate the sensitivity of the projected future changes in the autotrophic carbon budget of three representative European forests. We focus on changes in CUE and carbon stocks as a result of warming, rising atmospheric CO2 concentration, and forest thinning. Results show that autotrophic carbon sequestration decreases with forest development, and the decrease is faster with warming and in unthinned forests. This suggests that the combined impacts of climate change and changing CO2 concentrations lead the forests to grow faster, mature earlier, and also die younger. In addition, we show that under future climate conditions, forest thinning could mitigate the decrease in CUE, increase carbon allocation into more recalcitrant woody pools, and reduce physiological-climate-induced mortality risks. Altogether, our results show that thinning can improve the efficacy of forest-based mitigation strategies and should be carefully considered within a portfolio of mitigation options

Satellite-based terrestrial production efficiency modeling

Production efficiency models (PEMs) are based on the theory of light use efficiency (LUE) which states that a relatively constant relationship exists between photosynthetic carbon uptake and radiation receipt at the canopy level. Challenges remain however in the application of the PEM methodology to global net primary productivity (NPP) monitoring. The objectives of this review are as follows: 1) to describe the general functioning of six PEMs (CASA; GLO-PEM; TURC; C-Fix; MOD17; and BEAMS) identified in the literature; 2) to review each model to determine potential improvements to the general PEM methodology; 3) to review the related literature on satellite-based gross primary productivity (GPP) and NPP modeling for additional possibilities for improvement; and 4) based on this review, propose items for coordinated research

Extending the SPOT-VEGETATION NDVI time series (1998-2006) back in time with NOAA-AVHRR data (1985-1998) for southern Africa

A new consistent long-term normalized difference vegetation index (NDVI) time series at a 1-km2 resolution for Southern Africa that is based on the data from Satellite Pour l'Observation de la Terre VEGETATION (VGT) (1998-2006) and the National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (AVHRR) (1985-1998) has been produced for vegetation-dynamics monitoring purposes. This paper presents the evaluation of the newly processed AVHRR data set, as well as the integration of this data set with the VGT archive. First, the AVHRR processing chain and the resulting AVHRR data set have been investigated with respect to calibration accuracy, cloud masking, and atmospheric and geometric correction. Second, different calibration approaches, spectral response (SR) functions, spatial resolutions, overpass times, and geometries of observation for the VGT and AVHRR data sets have been compared for a common observation period. The application of published correction functions accounting for the SIR differences for both sensors considerably improved the consistency between both data sets. An r2 of 0.85 is obtained between paired samples of the NDVI from the VGT and the newly processed AVHRR archive. After the application of the correction functions, the slope of the regression line between the two NDVI data sets was much closer to the 1: 1 line. The performance of the correction functions differed among vegetation types. The largest reduction in the root-mean-square error between the NDVI of both sensors is obtained from areas with higher biomass. Large parts of the remaining variability are suggested to be attributed to the bidirectional reflectance distribution function effects, as demonstrated by the intersensor NDVI time-series variability versus the intrasensor NDVI time-series variability

Does energy dissipation increase with ecosystem succession? Testing the ecosystem exergy theory combining theoretical simulations and thermal remote sensing observations

The ecosystem exergy theory is an ecosystem succession theory based on thermodynamics and hypothesizes that energydissipationincreases with ecosystem maturity. It was developed along with a number of specially designed dissipation indicators, derived from thermal remote sensing. The theory provides an interesting method for the rapid evaluation of the degree of naturalness and/or the maturity of an ecosystem, e.g. in land use impact assessment studies. However, lack of proof of the validity of the ecosystem exergy theory has limited its application. In addition, it remains unsolved whether the dissipation indicators are influenced by meteorological conditions, how they are related with each other and which dissipation indicator has the largest discriminative power. In this study, the ecosystem exergy theory and the dissipation indicators have been evaluated using theoretical simulations and observational data. A theoretical model was applied to assess the influence of ecosystem properties and of meteorological conditions on the dissipation indicators. With respect to the observations, the dissipation indicators were calculated with two series of DAIS-imagery, obtained during the summers of 1998 and 2001 in the sandy and sandy loam regions of Flanders (Belgium), respectively. For all dissipation indicators, differences between major land use types, between different forest tree species and age classes and between agricultural crop types were analysed. Simulations and observations showed that the dissipation indicators are highly correlated with each other. Solar exergy dissipation (SED) had the highest discriminative power and can be recommended when all land uses or ecosystems are measured simultaneously, possibly complemented with the standard deviation of surface temperature within the considered land unit. If data are not measured simultaneously, the Evaporative fraction (EF), which we suggest as a new dissipation indicator in this study, can be recommended because of its robustness to meteorological conditions and its high discriminative power. The simulations and observations elicited that dissipation indicators are very suitable for the detection of differences in energydissipation between agricultural crops, less so for the detection of differences in forest management. The simulations supported to a large extent the main hypothesis of the ecosystem exergy theory. Higher energydissipation is obtained through increased evapotranspiration or increased surface roughness, two aspects generally related with succession in terrestrial ecosystems from non-vegetated land to forest. This was confirmed by the observations. The energydissipation increased with an increasing degree of naturalness of the major land use and with increasing forest stand age. However, the ecosystem exergy theory was not confirmed for forest succession from the pioneer to the climax phase. Poplar plantations, which are equivalent to the early successional aggradation phase, showed higher energydissipation than forests equivalent to late successional stages, in contrast with the ecosystem exergy theory.status: publishe

Does energy dissipation increase with ecosystem succession? Testing the ecosystem exergy theory combining theoretical simulations and thermal remote sensing observations

The ecosystem exergy theory is an ecosystem succession theory based on thermodynamics and hypothesizes that energy dissipation increases with ecosystem maturity. It was developed along with a number of specially designed dissipation indicators, derived from thermal remote sensing. The theory provides an interesting method for the rapid evaluation of the degree of naturalness and/or the maturity of an ecosystem, e.g. in land use impact assessment studies. However, lack of proof of the validity of the ecosystem exergy theory has limited its application. In addition, it remains unsolved whether the dissipation indicators are influenced by meteorological conditions, how they are related with each other and which dissipation indicator has the largest discriminative power. In this study, the ecosystem exergy theory and the dissipation indicators have been evaluated using theoretical simulations and observational data. A theoretical model was applied to assess the influence of ecosystem properties and of meteorological conditions on the dissipation indicators. With respect to the observations, the dissipation indicators were calculated with two series of DAIS-imagery, obtained during the summers of 1998 and 2001 in the sandy and sandy loam regions of Flanders (Belgium), respectively. For all dissipation indicators, differences between major land use types, between different forest tree species and age classes and between agricultural crop types were analysed. Simulations and observations showed that the dissipation indicators are highly correlated with each other. Solar exergy dissipation (SED) had the highest discriminative power and can be recommended when all land uses or ecosystems are measured simultaneously, possibly complemented with the standard deviation of surface temperature within the considered land unit. If data are not measured simultaneously, the Evaporative fraction (EF), which we suggest as a new dissipation indicator in this study, can be recommended because of its robustness to meteorological conditions and its high discriminative power. The simulations and observations elicited that dissipation indicators are very suitable for the detection of differences in energy dissipation between agricultural crops, less so for the detection of differences in forest management. The simulations supported to a large extent the main hypothesis of the ecosystem exergy theory. Higher energy dissipation is obtained through increased evapotranspiration or increased surface roughness, two aspects generally related with succession in terrestrial ecosystems from non-vegetated land to forest. This was confirmed by the observations. The energy dissipation increased with an increasing degree of naturalness of the major land use and with increasing forest stand age. However, the ecosystem exergy theory was not confirmed for forest succession from the pioneer to the climax phase. Poplar plantations, which are equivalent to the early successional aggradation phase, showed higher energy dissipation than forests equivalent to late successional stages, in contrast with the ecosystem exergy theory. © 2011 Elsevier B.V

Comparative analysis of the actual evapotranspiration of Flemish forest and cropland, using the soil water balance model WAVE

International audienceThis paper focuses on the quantification of the green ? vegetation related ? water flux of a forest stand in the temperate lowland of Flanders. The underlying reason of the research was to develop a methodology for assessing the impact of forests on the hydrologic cycle in comparison to agriculture. The approach tested for calculating the water consumption by forests was based on the application of the soil water balance model WAVE. The study involved the collection of data from 14 forest stands, the calibration and validation of the WAVE model, and the comparison of the water use (WU) components - transpiration, soil and interception evaporation - between forest and cropland. For model calibration purposes simulated and measured time series of soil water content at different soil depths, period March 2000?August 2001, were compared. A multiple-site validation was conducted as well. Actual tree transpiration calculated with sap flow measurements in three forest stands gave similar results for two of the three stands of pine (Pinus sylvestris L.), but WAVE overestimated the actual measured transpiration for a stand of poplar (Populus sp.). A useful approach to compare the WU components of forest versus cropland is scenario analysis based on the validated WAVE model. The statistical Profile Analysis method was implemented to explore and analyse the simulated WU time-series. With an average annual rainfall of 819 mm, the results show that forests in Flanders consume more water than agricultural crops. A 30 years average of 491 mm for 10 forests stands versus 398 mm for 10 cropped agricultural fields was derived. The WU components, on yearly basis, also differ between the two land use types (transpiration: 315 mm for forest and 261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for forest and cropland, respectively). Forest canopy interception evaporation was estimated at 126 mm, while it was negligible for cropland