Salim Belyazid

Global topics and novel approaches in the study of air pollution, climate change and forest ecosystems

Research directions from the 27th conference for Specialists in Air Pollution and Climate Change Effects on Forest Ecosystems (2015) reflect knowledge advancements about (i) Mechanistic bases of tree responses to multiple climate and pollution stressors, in particular the interaction of ozone (O3) with nitrogen (N) deposition and drought; (ii) Linking genetic control with physiological whole-tree activity; (iii) Epigenetic responses to climate change and air pollution; (iv) Embedding individual tree performance into the multi-factorial stand-level interaction network; (v) Interactions of biogenic and anthropogenic volatile compounds (molecular, functional and ecological bases); (vi) Estimating the potential for carbon/pollution mitigation and cost effectiveness of urban and peri-urban forests; (vii) Selection of trees adapted to the urban environment; (viii) Trophic, competitive and host/parasite relationships under changing pollution and climate; (ix) Atmosphere-biosphere-pedosphere interactions as affected by anthropospheric changes; (x) Statistical analyses for epidemiological investigations; (xi) Use of monitoring for the validation of models; (xii) Holistic view for linking the climate, carbon, N and O3 modelling; (xiii) Inclusion of multiple environmental stresses (biotic and abiotic) in critical load determinations; (xiv) Ecological impacts of N deposition in the under-investigated areas; (xv) Empirical models for mechanistic effects at the local scale; (xvi) Broad-scale N and sulphur deposition input and their effects on forest ecosystem services; (xvii) Measurements of dry deposition of N; (xviii) Assessment of evapotranspiration; (xix) Remote sensing assessment of hydrological parameters; and (xx) Forest management for maximizing water provision and overall forest ecosystem services. Ground-level O3 is still the phytotoxic air pollutant of major concern to forest health. Specific issues about O3 are: (xxi) Developing dose-response relationships and stomatal O3 flux parameterizations for risk assessment, especially, in under-investigated regions; (xxii) Defining biologically based O3 standards for protection thresholds and critical levels; (xxiii) Use of free-air exposure facilities; (xxiv) Assessing O3 impacts on forest ecosystem services.

Assessing the risk of N leaching from forest soils across a steep N deposition gradient in Sweden.

Nitrogen leaching from boreal and temporal forests, where normally most of the nitrogen is retained, has the potential to increase acidification of soil and water and eutrophication of the Baltic Sea. In parts of Sweden, where the nitrogen deposition has been intermediate to high during recent decades, there are indications that the soils are close to nitrogen saturation. In this study, four different approaches were used to assess the risk of nitrogen leaching from forest soils in different parts of Sweden. Nitrate concentrations in soil water and C:N ratios in the humus layer where interpreted, together with model results from mass balance calculations and detailed dynamic modelling. All four approaches pointed at a risk of nitrogen leaching from forest soils in southern Sweden. However, there was a substantial variation on a local scale. Basing the assessment on four different approaches makes the assessment robust.

A dynamic modelling approach for estimating critical loads of nitrogen based on plant community changes under a changing climate

A dynamic model of forest ecosystems was used to investigate the effects of climate change, atmospheric deposition and harvest intensity on 48 forest sites in Sweden (n = 16) and Switzerland (n = 32). The model was used to investigate the feasibility of deriving critical loads for nitrogen (N) deposition based on changes in plant community composition. The simulations show that climate and atmospheric deposition have comparably important effects on N mobilization in the soil, as climate triggers the release of organically bound nitrogen stored in the soil during the elevated deposition period. Climate has the most important effect on plant community composition, underlining the fact that this cannot be ignored in future simulations of vegetation dynamics. Harvest intensity has comparatively little effect on the plant community in the long term, while it may be detrimental in the short term following cutting. This study shows: that critical loads of N deposition can be estimated using the plant community as an indicator; that future climatic changes must be taken into account; and that the definition of the reference deposition is critical for the outcome of this estimate.

DECOMP - a semi-mechanistic model of litter decomposition

The decomposition of organic matter in a forest ecosystem is simulated by DECOMP, a process-based, semi-mechanistic model built on system dynamic principles. The model divides a litter into four different substrate quality classes with different decomposition rates which are differently influenced by temperature, soil moisture content, pH and aluminum concentration in the soil solution. The model is presented with its core equations and parameter values, but also presented from a system dynamics perspective in its context as a cornerstone in a forest-soil-atmosphere model. DECOMP is aimed at simulating long-term dynamics of decomposition over several forest management rotations, and to function in concert with other model components used in forest modeling. The model is evaluated against empirical data and shows good resemblance when simulating decomposition of Scots pine needle litter with data from a four-year litter bag field experiment.

Modelling the impact of climate change and atmospheric N deposition on French forests biodiversity.

A dynamic coupled biogeochemical-ecological model was used to simulate the effects of nitrogen deposition and climate change on plant communities at three forest sites in France. The three sites had different forest covers (sessile oak, Norway spruce and silver fir), three nitrogen loads ranging from relatively low to high, different climatic regions and different soil types. Both the availability of vegetation time series and the environmental niches of the understory species allowed to evaluate the model for predicting the composition of the three plant communities. The calibration of the environmental niches was successful, with a model performance consistently reasonably high throughout the three sites. The model simulations of two climatic and two deposition scenarios showed that climate change may entirely compromise the eventual recovery from eutrophication of the simulated plant communities in response to the reductions in nitrogen deposition. The interplay between climate and deposition was strongly governed by site characteristics and histories in the long term, while forest management remained the main driver of change in the short term.

NutsFor a process-oriented model to simulate nutrient and isotope tracer cycling in forest ecosystems

Abstract We developed a process-oriented model called NutsFor that simulates nutrient cycling of major cations (Ca, Mg, K, Al, NH 4 , Na) and anions (NO 3 , SO 4 , Cl) and the stable isotope tracers for each of the respective elements at the scale of an ecosystem (isotopic fractionation are not simulated). We tested the ability of NutsFor to reproduce major element and stable isotope tracer ( 26 Mg and 44 Ca) cycling with the data from 35-yr old beech stand in France. NutsFor correctly reproduced the measured trends in soil solution chemistry for most major elements. The high similarity between modeled and measured distribution of 26 Mg and 44 Ca tracers in the ecosystem provided a unique and robust way to evaluate the hypotheses grounding the model and study the efficiency of Mg and Ca cycling at this very nutrient-poor site.

Proposing a Strict Epidemiological Methodology for Setting Empirical Critical Loads for Nitrogen Deposition

Currently empirical critical loads are derived from manipulation experiments and field survey data and more recently these data have come under scrutiny as our understanding of how ecosystems respond to reactive nitrogen (Nr) deposition evolves. The importance of background nitrogen (N) deposition and the significance of the starting N capital, cumulative N, are now recognized. This has led to a credibility rating against which experimental data can be evaluated. However, there is still no robust and transparent system in place for setting empirical critical loads for nitrogen deposition. This chapter discusses some of the issues involved in the evaluation of the available data and proposes a testable approach to carry the system forward.

Mapping critical loads for nitrogen based on biodiversity using ForSAFE-VEG: introducing the basic principles

This chapter describes the basic principles inside the VEG extension to the ForSAFE model system. It allows changes in ground vegetation to be calculated, an important part of biodiversity. In the VEG model, the basis for modelling ground vegetation dynamics is a competition strength model based on soil chemistry promoting and retarding factors, nutrients, water and light. The strength is used in a competition model to assign ground area to each plant type considered. The ForSAFE-VEG is freely available from the authors and is used for assessing critical loads for acidity and nitrogen in Europe and United Sates, based on biodiversity criteria.

Evaluation of Plant Responses to Atmospheric Nitrogen Deposition in France Using Integrated Soil-Vegetation Models

The aim of this chapter is to give an overview of plant responses to nitrogen (N) deposition by using two dynamic biogeochemical models coupled with a vegetation module: VSD+-VEG and ForSAFE-VEG. The biogeochemical models were first validated on some French forest sites from the ICP-Forests network. A French vegetation table (which is now part of a European database) containing 230 species with their appropriate ecological environmental parameters, was set up. The outputs of each model in terms of plant response to atmospheric nitrogen deposition were compared to measured values for one forest stand. The two models underestimated the occurrence of certain herbs and grasses and overestimated (ForSAFE-VEG) or underestimated (VSD+-VEG) the presence of certain mosses. This allowed us to improve the validation and thus the calibration of some parameters. For the simulated period ForSAFE-VEG indicated some variations in the occurrence of the plant groups, the mosses group showing the highest increase and indicating a high sensitivity to atmospheric N deposition. No significant changes in the occurrence percentage of plant groups were observed by running the VSD+-VEG model, this model being less sensitive than ForSAFE-VEG to simulate tenuous vegetation changes. The observed changes over time in the dominant ground plant groups using ForSAFE-VEG could be related to changes in site environmental conditions, but only the influence of the maximum N deposition was obvious. Further investigations are needed to compare the performance of the two models on other sites, but these tests of the ForSAFE-VEG and VSD+-VEG models showed promise for simulating the link between N deposition and vegetation diversity.

Use of an Integrated Soil-Vegetation Model to Assess Impacts of Atmospheric Deposition and Climate Change on Plant Species Diversity

To realistically simulate possible future changes in plant species diversity, it is imperative to include the effects of both climate change and atmospheric deposition. Both factors have direct effects on the vegetation, such as the favouring of nitrophilous plants under elevated nitrogen (N) deposition or the elimination of drought-sensitive plant species under dry climatic conditions. To account for these confounding or reinforcing effects, integrated models are needed. ForSAFE-Veg is a dynamic model integrating the different forest ecosystem processes and feedbacks that make up the web of interactions and responses to climatic conditions and atmospheric deposition. The model was used to simulate forest ecosystems at 48 sites in Sweden and Switzerland. The evaluation of the model performance was satisfactory in regard to soil chemistry and plant community composition. The model was then used to simulate the separate and combined effects of the foreseen climate change and scenarios of N and sulphur (S) deposition levels. According to the simulations, the future change in plant community composition due to climate change alone will be bigger than the change avoided by the current decrease in atmospheric depositions.