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Since the late 1980's the productivity of monocultures vs. mixed-species forests has been the subject of studies by forest managers and ecologists. Mixed plantations have been established in different proportions to determine if mixtures could provide greater yields and more benefits than monocultures of the component species, as well as to understand if they could be an interesting economic option. An experimental design trial was set up in the north of Portugal in a replacement series with pure and mixed Castanea sativa Mill. and Pseudotsuga menziesii (Mirb.) Franco. The objective of this study was to assess growth dynamics and compare the aboveground biomass and net primary production of the two species in pure and mixed treatments in proportions 1:1 and 1:3. The growth was measured at 7, 11, 15, 17, 19, 27 and 28 years after planting and aboveground net primary production was estimated at age 28. As a component of the mixed treatments, P. menziesii exhibited greater height, diameter and aboveground biomass than C. sativa. Relative yield total indicated a higher productivity in the mixtures compared with the pure treatments. Early in the development, pure treatments and mixtures had similar aboveground biomass per hectare, but later the mixtures showed higher yield than pure treatments. The mixture productivity increase through time appears to be the result of both canopy stratification and better use of site resources. The aboveground net primary production was also higher in mixed than in the pure treatments. We are most grateful to Carlos Fernandes and Carlos Brito for their help with the field data collection, to Armindo Teixeira and Helena Ferreira for their help in the laboratory. This study was funded by FCT research in project PTDC/AGR-CF/68186/2006 and FCT Program SFRH/PROTEC/50127/2009 info:eu-repo/semantics/publishedVersion

The effects of forest management on soil carbon (C) and nitrogen (N) dynamics vary by harvest type and species. We simulated long-term effects of bole-only harvesting of aspen (Populus tremuloides) on stand productivity and interaction of CN cycles with a multiple model approach. Five models, Biome-BGC, CENTURY, FORECAST, LANDIS-II with Century-based soil dynamics, and PnET-CN, were run for 350 yr with seven harvesting events on nutrient-poor, sandy soils representing northwestern Wisconsin, United States. Twenty CN state and flux variables were summarized from the models' outputs and statistically analyzed using ordination and variance analysis methods. The multiple models' averages suggest that bole-only harvest would not significantly affect long-term site productivity of aspen, though declines in soil organic matter and soil N were significant. Along with direct N removal by harvesting, extensive leaching after harvesting before canopy closure was another major cause of N depletion. These five models were notably different in output values of the 20 variables examined, although there were some similarities for certain variables. PnET-CN produced unique results for every variable, and CENTURY showed fewer outliers and similar temporal patterns to the mean of all models. In general, we demonstrated that when there are no site-specific data for fine-scale calibration and evaluation of a single model, the multiple model approach may be a more robust approach for long-term simulations. In addition, multimodeling may also improve the calibration and evaluation of an individual model.

Studies about the productivity of forest ecosystems help to quantify sequestered carbon and provide data that are used in forest management. Forests in northern Portugal are an important economic resource, but their productivity in scenarios of future climate change is not yetwell understood. The objectives of this study were to evaluate and compare simulated net primary production (NPP) andNPPbased onmeasured data of twotree species located in the Vila Real district forests, pine (Pinus pinaster Aiton) and oak (Quercus pyrenaica Willd.) and assess their simulatedNPPin diverse climate conditions, including future climate scenariosandincreasing atmospheric CO2 concentrations. An ecosystem process model, Biome-BGC, which simulates carbon, nitrogen and water cycles of forest ecosystems close to equilibrium conditions, was used to examine the importance of site and ecophysiological factors on the productivity of these forests. Climate change scenarios and increased CO2 concentrations were tested to explore potential responses of the studied species. The model provided good estimates of NPP. There was a strong correlation between the simulated and measured NPP values in the pine (15) and oak (15) stands. The NPP of these forests are predicted to increase in the future with a CO2 increase whereas in a climate with higher temperature and lower soil moisture, the NPP will decrease. These results confirm that precipitation is a very important climate variable to growth and productivity in the Mediterranean forest ecosystems. This study also demonstrated the ability of Biome-BGC to accurately simulate forest ecosystems behaviour and encourages the application of model simulations in Portugal info:eu-repo/semantics/publishedVersion