The NIPHYS/CANIF project of the EEC has provided the unique opportunity to examine forest ecosystem processes and diversity along a transect through Europe ranging from north Sweden to central Italy. The main objectives of this study were (I) to identify and quantify effects of N deposition on ecosystem processes, particularly the C cycle, by extending the range of observations across a deposition maximum in central Europe, and (2) to study feedback effects between ecosystem processes and biodiversity. The study resulted in a very comprehensive and consistent set of data on ecosystem processes over a 5-year period. However, in contrast to earlier large-scale ecosystem studies (IBP: Reichle 1981; Acid Rain Programme: Last and Watling 1991), the samples were collected and data generated by the same scientists at all sites. This assured comparisons of results on a broad geographic scale. In addition, key parameters were assessed by different methods, and integrating parameters were collected for different processes, in order to test and verify predictions made at higher and lower scales, ranging from physiological responses to ecosystem level processes.In the following we attempt to reassess the data presented in detail in the preceding chapters and seek for an integrated analysis that addresses the following general questions:• What regulates the C and N fluxes in forest ecosystems? • Are there thresholds and non linear responses?• What are net ecosystem productivity (NEP) and net biome productivity (NBP) in managed systems and can they be inferred from process studies? • What role does biodiversity play in ecosystem functioning? Change of Ecosystem Processes Along the European TransectThe study of a transect through Europe was confronted with a range of intrinsic problems, one of which relates to the weather pattern. If a high-pressure cell resulted in dry and hot weather in Scandinavia, very wet conditions are found in southern Europe, and vice versa. Thus, it was difficult to collect data under conditions of comparable water status along such a transect in a single year. Even though the project lasted 5 years, we were not able to study the effects of the interannual variability of key parameters. The changing weather pattern, however, gave confidence that we are dealing with general (long-term) patterns in this analysis. Another problem arises

Summary: To assess the potential contribution of growing highly competitive crops to control Cyperus esculentus in the Netherlands, the influence of silage maize, hemp, winter barley and silage winter rye on emergence, growth and reproduction of this weed was studied in two field experiments. Growth and reproduction of C. esculentus (determined both as tuber production per plant and density of the weed in the subseuent crop maize) was reduced by each crop, compared to plots in which no crop was grown. In hemp, hardly any tuber production was observed. By growing a green manure crop after harvest of the winter barley the tuber production of the weed was reduced to about 40% of that in winter barley followed by fallow. Decreasing the light regime in a greenhouse experiment in the same order as was observed in the crops winter barley, maize and hemp, caused a similar reduction of tuber production to that found in the field. Therefore, it is suggested that competition for light is the main factor explaining the observed crop effects on the population dynamics of the weed. It is concluded that growing competitive crops as hemp in rotation may effectively complement chemical control of C. esculentus.

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Simulation models are useful to analyze and predict the effects of changes in atmospheric CO 2 concentration and N deposition on terrestrial ecosystems. The effects of such abiotic changes on ecosystem variables such as nitrogen mineralization and carbon accumulation can affect plant species composition, which in turn may affect various ecosystem processes. However, these interacting effects of plant species composition on ecosystem processes and vice versa are often not included in simulation models. In this paper, a model is developed that includes both plant competition and the flows of nutrients, carbon, and water through the ecosystem. Direct effects of changing atmospheric CO 2 on biomass, plant nitrogen concentrations, and litter quantity and quality are simulated together with indirect effects through changes in plant species composition. This model is validated against data from a primary succession chronosequence sere of Dutch inland dunes. For this validation, historical N deposition and atmospheric CO 2 concentration records are used. Simulated plant species biomass, organic matter C and N, and total C and N accumulation were found to correspond to measured data. The model simulated plant species replacement well at the different sites of the chronosequence even though the historic conditions differed much between the sites. Additional analyses of the effect of N deposition (preindustrial to present-day) and elevated CO 2 (preindustrial to present-day) in this ecosystem showed that N deposition had a strong effect both on vegetation development and on C and N accumulation. Compared to this, the stimulating effects of elevated CO 2 on vegetation development were relatively small. Elevated CO 2 affected early vegetation development, but the long-term response of vegetation development is dependent on N availability. In old mature forest, N deposition had only small effects while elevated CO 2 delayed forest aging. Indirect effects of CO 2 on C and N accumulation through changing plant competitive relations may ultimately be larger than direct CO 2 effects.

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