Heiner Schäfer

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).

Simulation of forest stand dynamics, using real-structure process models

Abstract The dynamic richness of forest ecosystem response to climate, management and pollution stress cannot be adequately described by traditional descriptive growth-and-yield simulators, but requires sufficiently detailed models of the underlying eco-physiological processes and their structural interactions (real-structure models). Two such models are described, and representative results presented. The generic real-structure model TREEDYN describes stand growth, and its carbon and nitrogen dynamics in interaction with corresponding soil processes, using ten nonlinear differential equations. The state variables are: leaf, fine-root, wood, fruit, and assimilate biomass; carbon and nitrogen in litter and soil organic matter; and plant-available nitrogen. The model has been applied to both a broadleaf tree ( Acacia auriculiformis ) under tropical conditions, and to a coniferous tree ( Picea abies ) under European conditions. The real-structure model SPRUCOM simulates Norway-spruce stand growth, including the light-competition-induced self-thinning process, using 30 non-linear differential equations for each of four tree competition classes. The state variables in this case are: needles (7 classes); corewood; sapwood (18 rings); branches; coarse roots; fine roots; and assimilate. The model has been used, in particular, for the study of stand production as a function of air pollution affecting leaf efficiency and/or fine-root turnover. Both models employ a full description of light attenuation and photosynthetic production in the canopy. The models are parameterized by species-and region-specific real-system parameters; no time-series data are required for this purpose. For more efficient computation in management tools, a condensation of complex models to simpler models may be required, while maintaining structural, behavioral, empirical, and application validity. Work on this aspect is briefly reported.

Process-Oriented Models for Simulation of Growth Dynamics of Tropical Natural and Plantation Forests

A systems analysis of tree growth in a tropical rain forest was carried out to develop the simulation model FORMIX for representing inherent growth dynamics of tropical forests and assessing the consequences of logging strategies currently applied. Emphasis was put on a correct representation of the physiological processes mainly involved in the temporal development of biomass growth within a forest gap of a typical size of 100 – 400 m2. On the gap level the model distinguishes between five canopy layers containing seedlings, saplings, poles, main canopy trees, and emergents. It comprises submodels for the light attenuation within the crowns, photoproduction, respiration, biomass turnover, deadwood losses, tree mortality, growth, and fructification. An imaginary forest was constructed connecting several of such gap models and including interrelations between them caused by fallen dead trees and seed dispersal. For simulation, the model was preliminarily parametrized using data for lowland dipterocarp forests in West Malaysia. Simulation runs showed that there is an internal regeneration cycle determining growth of tropical forests. Logging operations — especially their frequency and intensity — were judged in the light of this ‘eigendynamics’. In addition to this first application, the model can be used to determine gaps in empirical data, to integrate empirical results of different disciplines, and to check the consistency of given data sets.

Modelling stocks and flows of carbon and nitrogen in a planted eucalypt stand

Abstract In order to provide accurate assessments of the development of monoculture tree plantations, the generic process model TREEGROW has been developed (on the basis of the model TREEDYN). This dynamic simulation model represents tree growth, and carbon and nitrogen dynamics in single species, even-aged forest stands. It contains detailed descriptions of tree-physiological (photosynthesis, respiration, growth and renewal of biomass, etc.) as well as soil-biological (decomposition, N-mineralisation, humification, etc.) processes. Several computer runs demonstrate the temporal development of a eucalypt stand (in South China), from planting to maturity as a function of various environmental and harvesting conditions. Simulations particularly show the negative consequences of litter removal on soil fertility and hence on stand productivity. If applied to different climatic scenarios, the model shows that potential benefits to tree growth arising from anthropogenic elevated concentrations of CO 2 and other trace compounds in the atmosphere can be negated in the case of insufficient nutrient supply. In addition to these first applications, the model can be used to determine deficits in empirical data, to integrate empirical results of different disciplines, and to check the consistency of given data sets.

Modell zur Entwicklung eines Fichtenbestandes bei lichtkonkurrenzbedingter Stammzahlreduktion

Das Wachstum von Pflanzen wird u.a. masgeblich durch das absorbierbare Licht und die Verfugbarkeit von Wasser und Nahrstoffen bestimmt. Ubersteigt auf einer Flache die Summe der Anforderungen aller Einzelpflanzen an diese Umweltfaktoren die gegebenen Ressourcen am Standort, so mussen die einzelnen Pflanzen um jene zwangslaufig in Wettbewerb treten, um ihr Uberleben sicher zu stellen. Die Produktivitat der Einzelpflanzen und — in geringerem Mase — der (nutzbare) Ertrag des Kollektivs ist dann abhangig von der Dichte des Bestandes und dem „Durchsetzungsvermogen“ der Individuen bzw. der „Konkurrenzkraft“ der jeweiligen Spezies. Mit fortschreitender Bestandesentwicklung bzw. zunehmender Grose der Einzelpflanzen steigt deren individueller Bedarf an Licht, Wasser und Nahrstoffen, so das pro Flache (selbst bei nicht nachlassenden Ressourcen) eine immer geringere Anzahl von Pflanzen ausreichend versorgt werden kann. Die unterversorgten geraten gegenuber den aufgrund gewisser Umweltkonstellationen und genetischer Dominanzen bevorzugten Pflanzen zunehmend ins Hintertreffen; nach Unterschreitung des Existenzminimums sterben sie ab. Dieser in Waldbestanden als „Selbstlauterung“ bezeichnete Prozes ist wegen seiner Konsequenzen — grosere Dimensionen der Einzelbaume — von der Forstwirtschaft erwunscht, sie bedient sich sogar seit jeher zusatzlich mehr oder minder gezielter Pflanzungs-, Lauterungs- und Durchforstungsstrategien, um die Wertleistung der Einzelstamme sowie die Stabilitat gegenuber Windwurf und Schneebruch zu steuern und weiter zu steigern [1],

Computersimulation des Baumsterbens

‘Neuartige’ Waldschaden fuhren in Mitteleuropa zu einem Waldsterben bisher unbekannten Ausmases. Als primare Ursache mussen Schadstoffe in der Luft gelten, wobei es bisher nicht gelungen ist, einen bestimmten Schadstoff als Verursacher zu isolieren. Weiter ist bisher umstritten, ob die Schadigung primar uber die Wurzeln oder uber die Blattorgane erfolgt (s. z. B. HATZFELDT 1983, RAT/UMWELTFRAGEN 1983, KATALYSE 1983). Die Ahnlichkeit der auf sehr unterschiedlichen Standorten beobachteten Symptome deutet jedoch auf eine fortschreitende, und schlieslich todliche Beeintrachtigung der Funktionsfahigkeit des dynamischen Systems Baum. Sie ausert sich in langjahrigen Zuwachsverlusten, vorzeitigem Laubabwurf, hohen Feinwurzelverlusten und schlieslich raschem Zusammenbruch.

Systemanalyse und Simulation der Wachstums- und Entwicklungsdynamik von Waldbäumen unter dem Einfluß von Luftschadstoffen

Die bundesweite Waldschadenserhebung 1986 [1] ergab, das an 53.7 % aller Baume Schaden auftreten, die sich vorwiegend auf Immissionseinwirkungen zuruckfuhren lassen. Zur Entwicklung von Strategien, die zur Verhinderung weiterer Schaden fuhren konnen, ist es nicht nur wichtig, die direkten Schadensmechanismen als solche, sondern auch die Dynamik der Schadigung zu verstehen.