Alexander Komarov

A comparison of the performance of nine soil organic matter models using datasets from seven long-term experiments

Nine soil organic models were evaluated using twelve datasets from seven long-term experiments. Datasets represented three different land-uses (grassland, arable cropping and woodland) and a range of climatic conditions within the temperate region. Different treatments (inorganic fertilizer, organic manures and different rotations) at the same site allowed the effects of differing land management to be explored. Model simulations were evaluated against the measured data and the performance of the models was compared both qualitatively and quantitatively. Not all models were able to simulate all datasets; only four attempted all. No one model performed better than all others across all datasets. The performance of each model in simulating each dataset is discussed. A comparison of the overall performance of models across all datasets reveals that the model errors of one group of models (RothC, CANDY, DNDC, CENTURY, DAISY and NCSOIL) did not differ significantly from each other. Another group (SOMM, ITE and Verberne) did not differ significantly from each other but showed significantly larger model errors than did models in the first group. Possible reasons for differences in model performance are discussed in detail.

ROMUL — a model of forest soil organic matter dynamics as a substantial tool for forest ecosystem modeling

This paper discusses a model of forest soil organic matter based on the concept of succession stages of soil organic matter decomposition marked by different groups of soil fauna inherent to forest soils in contrast to well-mixed agricultural soils with microbiology kinetics. This model allows the calculation of the dynamics of soil organic matter and the corresponding dynamics of nitrogen, including the evaluation of the amount of mineral nitrogen which is available for plants. The input parameters are the amount and quality of litter input, climatic data and initial amounts of soil organic matter and corresponding nitrogen. The litter may be split into different cohorts which are characterised by different ash and nitrogen contents and location on/in a soil as above-ground and below-ground litter cohorts. A specially developed simulator of soil climate is also described. A comparison was made with a previous, more restricted version of this model. The origin of the differences is discussed in detail. Examples of simulation scenarios show a wide range of possible applications for the model as a separate unit of models for forest ecosystems dynamics.

EFIMOD 2: a model of growth and cycling of elements in boreal forest ecosystems

Abstract The model EFIMOD 2 was developed for the description of tree (stand) growth and biological turnover of elements in boreal and temperate forest ecosystems. The model has the following features. (i) It is a spatially explicit stand-level simulator for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. Karst) and Pendula birch (Betula pendula L.) on different forest soils growing under different climatic conditions in Europe; each stand consists of individual trees for which growth is modelled depending on the tree’s position within the stand and local light, water and available nutrient conditions. (ii) The model has a tree-based submodel for total biomass distributed between several biomass compartments. (iii) The calculations include natural regeneration as well as ground vegetation dynamics. (iv) The soil submodel (ROMUL) is used to assess organic matter dynamics and nitrogen availability for tree growth as a function of soil temperature, soil moisture content and litter quality. (v) EFIMOD 2 calculates nitrogen cycling and accounts for atmospheric nitrogen deposition, nitrogen fixation and leaching, vegetation uptake, litter fall and nitrogen redistribution within and between trees and soil horizons. (vi) Monte–Carlo simulations are done to simulate the extent of naturally oscillating variability. EFIMOD 2 allows for short-term and long-term simulations of natural and managed forest ecosystem dynamics over a wide range of forest sites, climatic conditions and silvicultural regimes. The model calculates dendrometric parameters for every tree, including undergrowth and seedlings, total growing stock, and pools of coarse woody debris and soil organic matter, with special reference to carbon and nitrogen dynamics. The model is effective for assessing wood productivity and evaluation of forest management regimes to meet criteria and indicators of Sustainable Forest Management. This includes a general evaluation of biodiversity and soil sustainability. The model system allows for the direct use of standard forest inventory data. Output variables include carbon and nitrogen pools in the stand and soil, CO2 emissions, and tree (stand) growth and yield.

A combined simulation model of Scots Pine, Norway spruce and Silver birch ecosystems in the European boreal zone

A combined (hybrid) spatially distributed individual-based model of a forest ecosystem (EFIMOD) has been elaborated for a Scots pine, Norway spruce and Silver birch stand of the European boreal zone. This model represents a realization of the concept of a ‘single plant ecosystem’ (Chertov, 1983a). EFIMOD simulates the biological cycle of every tree with an expedient soil pot in a stand. The tree models calculate the total leaf, fine root and litter mass using a set of the characteristic ecological tree parameters. The soil sub-model simultaneously allows for a calculation of the rate of tree litter and soil organic matter mineralization with the corresponding carbon dioxide and nitrogen release for plant growth. The validation of the model, with various initial stand densities on different soils, shows a relatively realistic picture of tree growth, stand selfthinning and soil changes. Convergence of leaf/needle mass has been observed at various initial stand densities. An application of EFIMOD for a qualitative evaluation of climate change effects shows fairly different reactions of the mentioned ecosystems in relation to productivity, leaf mass and soil organic matter pool. There is a shift in the timing of the first intensive selfthinning in young stands. A strong oscillation of leaf/needle mass has also been observed. # 1999 Elsevier Science B.V. All rights reserved.

Application of the forest ecosystem model EFIMOD 2 to jack pine along the Boreal Forest Transect Case Study

Sustainability of forest ecosystems and climate change are two critical issues for boreal forest ecosystems in Canada that require an understanding of the links and balance between productivity, soil processes and their interaction with natural and anth ropogenic disturbances. Forest ecosystem models can be used to understand and predict boreal forest ecosystem dynamics. EFIMOD 2 is an individual tree model of the forest-soil ecosystem capable of modelling nitrogen feedback to productivity in response to changes in soil moisture and temperature. It has been successfully applied in Europe, but has not been calibrated for any forest ecosystem in Canada. The objective of this study was to parameterize and validate EFIMOD 2 for jack pine in Canada. Simulated and measured results agreed for changes in tree biomass carbon and soil carbon and nitrogen with increasing stand age and across a climatic gradient from the southern to northern limits of the boreal forest. Preliminary results from scenario testing indic...

Modelling the long-term dynamics of populations and communities of trees in boreal forests based on competition for light and nitrogen

Abstract This paper describes an individual-based and spatially explicit model for computing the long-term succession of a population or community of trees and the turnover of carbon and nitrogen in a forested ecosystem. In the model ecosystem trees are located within a simulated plot in a grid of cells that are sufficiently small to contain not more than one tree. Each tree consists of five mass compartments (stem, branches, leaves/needles, coarse roots and fine roots) and has its own area, varying in time, for the acquisition of nitrogen. Each tree competes with its nearest neighbours for light and nitrogen; i.e. growth depends on the limitations on light or nitrogen. The calculation of biomass production is based on the potential biomass increment, obtained by means of an integrating parameter for tree net primary production (NPP) in the form of the maximum possible biological productivity of the leaves/needles. Growth under the limited light and soil nitrogen are calculated, and the smaller of the two is used as the realised growth. The total growth of each tree is allocated to different mass compartments using species-specific proportions related to the age of the tree. The litter cohorts are assumed to decompose to form a pool of soil organic matter (SOM) in a manner that is dependent on climatic conditions and the quality of the litter. The simulated plot has an explicit nitrogen–carbon balance based on the turnover of these in the ecosystem linked to the dynamics of organic matter in the soil. The model, which allows standard forest inventory data to be used as input, has been constructed using an object-oriented approach. Comparison of the output of the model with growth and yield tables shows that the current model provides quite similar time courses for the main tree parameters (height, diameter, basal area, etc.) in the case of Scots pine ( Pinus sylvestris ), Norway spruce ( Picea abies ) and birch ( Betula pendula ) throughout Finland (60–70°N).

Integrating forest simulation models and spatial-temporal interactive visualisation for decision making at landscape level

Abstract The article represents an attempt to integrate long-term forest ecosystem modelling with modern techniques of exploratory data analysis. The idea of the integration was to build up a prototype system for forestry decision-making at landscape (forest enterprise) level to support the spatially oriented tasks arising from Criteria & Indicators (C&I) of Sustainable Forest Management (SFM). A model test was performed on a small forest plot consisting of various stands (forest inventory compartments) with two scenarios of silvicultural regimes. A combined spatially explicit forest simulation model efimod 2 and the descartes software system designed to support visual exploration of spatially referenced data were used in the experiment. The visualisation of simulation results on a sequence of interactive maps. It also allows direct representation of time series and spatial patterns of forest dynamics in a graphical form, and analysis of the dynamical trends under various silvicultural regimes. The diversity of ecosystem reactions in various stands was explored, and the possibilities for spatial combination of various strategies and zoning of the forest area were tested. We are sure there is a need to create a new, user-friendly modelling system integrating forest ecosystem models with exploratory data visualisation for methodologically easy and expressive decision-making based on expert evaluation and a long-term simulation at the forest enterprise or landscape level.

The concept of discrete description of plant ontogenesis and cellular automata models of plant populations

The article represents a link between the concept of discrete description of the ontogenesis of plants and the cellular automata approach for the spatial-temporal modelling of plant population dynamics. The continuous process of individual plant development may be subdivided into several stages on the basis of morphological indicators reflecting functional importance of plants at different stages. The number and duration of age stages may vary from species to species, among life-forms within species, and under different environment conditions. The duration of age stages and the probability of transition from one stage to another for a given plant depend on the plant’s neighbourhood pattern, the type of ontogenesis and the site conditions. Such data are available from numerous field studies. The presented approach allows simulation of a plant population as a set of cellular automata located on a plane. The age stages of these automata can be changed according to simple rules, which reflect the types of plant ontogenesis, different life spans of age states, and different sizes of plants in the neighbourhood. This approach is different from matrix models, which are usually used for this purpose, in that here we can directly simulate the role of space interactions in the population dynamics. We constructed some cellular automata models based on experimental data, which reflect the ontogenesis types and life-forms of plants. The models demonstrate that simple rules of plant development with simply defined local interactions lead to complicated dynamics. The results show new possibilities of applications of discrete simulation modelling for analysis of plant populations and community dynamics.

Chapter Eighteen Uncertainty and Sensitivity Issues in Process-based Models of Carbon and Nitrogen Cycles in Terrestrial Ecosystems

Many process-based models of carbon (C) and nitrogen (N) cycles have been developed for northern forest ecosystems. These models are widely used to evaluate the long-term decisions in forest management dealing with effects like particulate pollution, productivity and climate change. Regarding climate change, one of the key questions that have sensitive political implications is whether northern forests will sequester atmospheric C or not. Whilst many process-based models have been tested for accuracy by evaluating or validating against observed data, few have dealt with the complexity of the incorporated procedures to estimate uncertainties associated with model predictions or the sensitivity of these predictions to input factors in a systematic, inter-model comparison fashion. In general, models differ in their underlying attempts to match natural complexities with assumed or imposed model structure and process formulations to estimate model parameters, to gather data and to address issues on scope, scale and natural variations. Uncertainties may originate from model structure, estimation of model parameters, data input, representation of natural variation and scaling exercises. Model structure relates to the mathematical representation of the processes modelled and the type of state variables that a model contains. The modelling of partitioning among above- and below-ground C and N pools and the interdependence among these pools remain a major source of uncertainty in model structure and error propagation. For example, most soil C models use at least three state variables to represent the different types of soil organic matter (SOM). This approach results in creating three artificial SOM pools, assuming that each one contains C compounds with the same turnover rate. In reality, SOM consists of many different types of C compounds with widely different turnover rates. Uncertainty in data and parameter estimates are closely linked. Data uncertainties are associated with high variations in estimating forest biomass, productivity and soil organic matter and their estimates may be incomplete for model initialisation, calibration, validation and sensitivity analysis of generalised predictor models. The scale at which a model is being used also affects the level of uncertainty, as the errors in the prediction of the C and N dynamics differ from site to landscape levels and across climatic regions. If the spatial or temporal scale of a model application is changed, additional uncertainty arises from neglecting natural variability in system variables in time and space. Uncertainty issues are also intimately related to model validation and sensitivity analysis. The estimation of uncertainties is needed to inform decision processes in order to detect the possible corridor of development. Uncertainty in this context is an essential measure of quality for stakeholder and decision makers.

Tree species composition affects productivity and carbon dynamics of different site types in boreal forests

The objective was to analyse how differences in the initial proportions of tree species and site fertility affect carbon sequestration in living biomass and soil. We used the individual-based simulation model EFIMOD, which is able to simulate spatially explicit competition between trees for light and nutrients. Simulations were carried out for three site types with distinct initial stocks of soil nutrients. For each site, the 100-years undisturbed dynamics of monocultures and mixtures of three tree species (Betula pendula Roth, Pinus sylvestris L. and Picea abies (L.) H. Karst.) was predicted. Changes in the proportions of competing tree species were dependent on the fertility of the site: on poor sites, pine was the most competent species, while on rich sites, spruce increased its proportion during stand succession. Net primary production (NPP) and soil respiration were the highest in stands of two coniferous species and in stands with a high initial proportion of pine. Mixed stands were more productive than monocultures; the highest overyielding was observed with mixtures of two coniferous species. Simulated NPP and carbon stocks in all pools increased from poor to rich sites. The highest carbon stocks in standing biomass were observed for mixtures of conifer species and three-species mixtures; the greatest accumulation of forest floor occurred in stands with high proportions of pine.