Hartmut Bossel

treedyn3 forest simulation model

Abstract The treedyn 3 forest simulation model is a process model of tree growth, carbon and nitrogen dynamics in a single-species, even-aged forest stand. It is based on the treedyn model. Major changes include the computation of sun angle and radiation as a function of latitude and day of the year, the closed-form integration of canopy production as a function of day and hour, the introduction of tree number, height, and diameter as separate state variables, and different growth strategies, mortalities, and resulting self-thinning as function of crowding competition. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: tree number, base diameter, tree height, wood biomass, nitrogen in wood, leaf mass, fine root mass, fruit biomass, assimilate, carbon and nitrogen in litter, carbon and nitrogen in soil organic matter, and plant-available nitrogen. The model includes explicit formulations of all relevant ecophysiological processes such as: computation of radiation as a function of seasonal time, daytime and cloudiness, light attenuation in the canopy, and canopy photosynthesis as function of latitude, seasonal time, and daytime, respiration of all parts, assimilate allocation, increment formation, nitrogen fixation, mineralization, humification and leaching, forest management (thinning, felling, litter removal, fertilization etc.), temperature effects on respiration and decomposition, and environmental effects (pollution damage to photosynthesis, leaves, and fine roots). Only ecophysiological parameters which can be either directly measured or estimated with reasonable certainty are used. treedyn 3 is a generic process model which requires species- and site-specific parametrization. It can be applied to deciduous and coniferous forests under tropical, as well as temperate or boreal conditions. The paper presents a full documentation of the mathematical model as well as representative simulation results for spruce and acacia.

Simulation model of natural tropical forest dynamics

Abstract Assessments of the long-term natural regeneration of tropical forests following selective logging are today mostly based on extrapolation of limited empirical observations. Mounting evidence suggests that current logging policies overestimate forest regrowth by a wide margin, and are therefore not sustainable. The need for more reliable assessment of natural forest growth dynamics has led to the development of a vertically and spatially structured dynamic simulation model of natural forest development. The model accounts explicitly for biomass and tree numbers in five distinct canopy layers (seedlings, saplings, poles, main canopy, emergents). Energy accounting of assimilation and dissimilation rates leads to biomass, diameter, and height growth in each layer. Leaf mass in each layer determines photoproduction, and light and photosynthesis conditions in lower layers. Transitions to higher layers, mortalities in each layer, and seed events are accounted for. The basic model simulates the development dynamics of a forest gap. Parallel computation of spatially distributed single gap models with stochastic mortalities and seed dispersal provides a simulation of the spatial dynamics of the tropical forest mosaic. Simulation results are provided with parameters corresponding to unlogged and logged Malaysian lowland dipterocarp forest.

Simulation of multi-species tropical forest dynamics using a vertically and horizontally structured model

Abstract The mutual interaction of forest growth and light conditions causes vertical and horizontal differentiation in the natural forest mosaic. The associated physical processes should be represented in simulation models describing long-term forest dynamics. The FORMIX2 (tropical) forest simulator incorporates the multi-storey canopy layer structure of the natural tropical forest, the basic processes of gap succession dynamics and gap interaction by tree fall and seed dispersal, several functionally different species groups (emergents, main canopy trees, pioneers, woody treelets and forest-floor herbs) and the energy (carbon) balance of assimilation, dissimilation, and increment resulting from the differing light conditions for the various canopy layers in the gap-size areas of a forest mosaic. The vertically and horizontally structured FORMIX2 model produces time-dependent results (average per hectare data) for stem numbers, diameter distributions, basal areas, standing crop and yield, as well as dynamic views of the forest profile and of spatial forest development, as a function of logging method and intensity and silvicultural treatment. The model has been applied in an exploratory investigation to compute the long-term development of (a) virgin forest and (b) logged-over forest in Sabah, using prototypical data. The results obtained agree with empirical data.

Modelling forest dynamics: Moving from description to explanation

Abstract Descriptive (statistical) models of forest growth cannot cope with changing environmental and management conditions. Since explanatory models attempt to capture the essential eco-physiological processes of forest growth, they are better-suited for the computation of forest dynamics under changing conditions, even when long-term empirical observations are not possible or feasible. Requirements of forest simulation models are analyzed, and essential processes of forest growth which must be represented in structurally valid models are discussed. Steps in obtaining valid but compact tree models for complex forest simulations are outlined, and recent software developments (object-oriented programming) are assessed with respect to their potential for forest simulation models.

Policy assessment and simulation of actor orientation for sustainable development

Abstract Understanding, assessing, and simulating behavior requires knowledge of the precepts that are explicitly or implicitly orienting behavior. Human actors can be viewed as (conscious) self-organizing systems attempting to remain viable in a diverse environment containing other self-organizing systems (other human actors, organisms, ecosystems, etc.), all driven by their own viability (sustainability) interests. These fundamental system interests, or basic orientors, have emerged in response to general environmental properties and are therefore identical across self-organizing systems: existence, effectiveness, freedom of action, security, adaptability, coexistence. Even in simulated actors learning to ‘survive’ in a difficult environment, the basic orientors emerge in the (simulated) evolutionary process — but different actors may evolve into different ‘cultural types’ with different orientor emphasis. Since balanced attention to all basic orientors is crucial for viability, the set of orientors can be used to derive indicators that facilitate comprehensive viability and sustainability assessments. The paper outlines the theoretical approach of ‘orientation theory’ and its application to the assessment and simulation of sustainable development issues. The formal approach of mapping indicators on basic orientors and assessing sustainability dynamics is illustrated using Worldwatch indicator time series. In an actor simulation this approach is used to successfully guide a small global model onto a sustainable path with high ‘quality of life’.

Generic simulation model of forest growth, carbon and nitrogen dynamics, and application to tropical acacia and european spruce

Abstract In order to provide accurate assessments of forest stand development even in the absence of long-term growth and yield observations (as may be the case in developing countries and for less well-known species), a generic dynamic (cybernetic) simulation model has been developed representing tree growth, and carbon and nitrogen dynamics in a single-species, even-aged forest stand. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: wood, leaf, fine root, fruit biomass; assimilate; carbon and nitrogen in litter; carbon and nitrogen in soil organic matter; and plant-available nitrogen. All parameters are measurable ecophysiological quantities (no statistical parameter estimation). The model includes explicit formulations of all relevant ecophysiological processes such as: temporal and spatial light distribution and photosynthesis in the canopy; respiration of all parts; assimilate allocation; increment formation; nitrogen fixation, mineralization, humification and leaching; forest management (thinning, felling, litter removal, fertilization, etc.); and environmental effects (air pollution and insect damage). Application of the model requires specification of 38 tree-specific and 15 region-specific parameters (obtainable - except for root data - from simple field estimates or laboratory measurements not requiring time-series studies), 10 initial conditions for the state variables and 13 scenario parameters (e.g. nitrogen input, maximum nitrogen-fixing rate, litter removal, thinning and cutting schedule, pollution damage to photosynthesis, leaves, or fine roots, time and severity of insect calamity). The simulation model has been applied successfully to study stand growth behavior under different conditions of soil quality, forest management, and pollution and insect damage for broadleaf trees in a tropical climate ( Acacia auriculaeformis ) Cunn. ex Benth. in South China) and coniferous trees in a temperate climate ( Picea abies (L.) Karst. in Central Europe). Despite the difference of species and climate, the model provides accurate representations of stand development under various conditions in both cases, yielding good agreement with standard yield tables (for spruce).

Dynamics of forest dieback: Systems analysis and simulation

Abstract The dynamics of tree growth under pollution damage affecting leaves and/or feeder roots have been studied using two dynamic models of basic tree processes. The first model (BAUMTOD) purposely uses relative quantities and a simple model, the second (SPRUCE) employs parameter data for spruce ( Picea abies ) and a more complex model formulation including e.g. seasonal effects. In the absence of pollution, this model reproduces normal growth data for spruce. As the impairment of leaves and/or feeder roots due to chronic pollution increases, growth at first slows down, and the tree enters a ‘stagnation mode’. If the chronic pollution remains ‘subcritical’, the tree may survive ‘indefinitely’ in the stagnation mode. However, if the chronic pollution becomes ‘supercritical’, the tree enters a ‘breakdown mode’ and will collapse suddenly. This collapse may take place even after many years of constant pollution stress and despite a ‘healthy’ appearance until about 2 years before the tree dies. Both models produce the three distinct behavioural modes: (1) growth, (2) stagnation, and (3) breakdown. The respective regions of dynamic behaviour are presented as a function of leaf and feeder root damage, and of tree age. The analysis suggests that the currently observed dieback of forests in many countries may be the ‘natural’ response to long-term (supercritical) chronic pollution stress. The simulations also suggest that only a rapid and drastic reduction of air pollution will be able to save the affected forests.

Real-structure process description as the basis of understanding ecosystems and their development

Abstract Behavior and structural dynamics of an ecological system are the product of the interaction of its specific structure with its specific environment. In contrast to descriptive (statistical, black ☐) models, which are designed to merely mimic behavior, real-structure models can contribute to the understandnig of ecosystems, of their emergent properties, of their self-organization and of their future development. A valid real-structure (explanatory, process) model in principle (1) not only allows analysis of the behavioral spectrum even for new environmental conditions, (2) but also permits analysis and prediction of system development and structural dynamics as a consequence of the interaction between system and environment. The key to this additional understanding is the realization that a ‘successful’ system incorporates processes for coping with the (six) fundamental properties of the environment (normal environmental state, sparse resources, variety, variability, change, partner systems) by (implicit) attention to six basic orientors (existence, effectiveness, freedom of action, security, adaptivity, consideration of other systems). Evaluation of the (relative) satisfaction of each of the basic orientors allows aggregated assessment of system performance and system limitations in a given environment, of coping deficiencies and resulting stress accumulation, of likely behavioral change and structural dynamics.

Viability and sustainability: Matching development goals to resource constraints

Abstract The consequences of our actions determine the horizon of our responsibility. ‘Responsible action’ requires taking into account the effects on the ‘viability’ of other systems in addition to our own. ‘Viability’ has several aspects which are ‘orthogonal’ and hence cannot be traded off against each other; a minimum of each ‘orientor’ aspect must be maintained. The various development paths open to a (social) system differ with respect to their short- and long-term effects on the viability of affected systems, hence a teleological approach is in order for setting, and constantly adjusting, goals and constraints of development to match available resources.

Experiments with an “intelligent” world model☆

Abstract This article deals with two of the major shortcomings of systems simulation studies for policy development : their failure to account for cognitive processes, and their usual neglect of normative criteria and the changes in these criteria. Within the framework of concept-processing and orientation theory, a formalised description of the process of state analysis by an “orientation module” is developed. In this process, current and likely future system states are projected (by a cognitive mapping process) on the systems orientors (in this case existence needs, security, freedom of action, adaptivity, and effectiveness). This assessment provides the inputs for policy development. The interactive approach uses Forresters World 2. The orientation module not only prevents the preprogrammed “pollution crisis” from occurring, but also leads to policies producing very satisfactory overall results, provided the planning horizon and the control sensitivity are sufficiently large. The results show that orientation modules can ensure “intelligent” behaviour of simulation models and can make computer-assisted policy development much more efficient.