ABSTRACT Unter ungünstigen Umweltbedingungen können benachbarte Pflanzen das Überleben, Wachstum ... more ABSTRACT Unter ungünstigen Umweltbedingungen können benachbarte Pflanzen das Überleben, Wachstum und die Fitness positiv beeinflussen. Die vorliegende Studie untersucht den seltener bekannten Fall der intraspezifischen Facilitation. Dabei beeinflussen bereits etablierte Gehölzpflanzen die Etablierung von gleichartigen Sämlingen positiv. In Erweiterung der üblichen Betrachtungsweise wird dabei das Zusammenspiel von positiven und negativen Interaktionen während der Keim- und Anwuchsphase betrachtet. Felduntersuchungen wurden auf einer hypersalinen Fläche auf der Halbinsel Bragança (Nordbrasilien) durchgeführt, die durch ein gestörtes hydrologisches Regime gekennzeichnet ist. Nach mehreren Dekaden, siedelten sich Büsche der Mangrovenart Avicennia germinans in einigen Teilen der Fläche an. Während der hier vorgestellten Studie wurden drei verschiedene Entwicklungsstadien der Wiederbesiedlung (geringe, mittlere und hohe Vegetationsbedeckung) auf Grundlage von Satellitenbildern bestimmt. Verschiedene Pflanzenparameter(Pflanzenhöhe und Kronenradius), wurden von jedem Busch gemessen. Die Pflanzen wurden in Sämlinge und größere Pflanzen unterteilt und die Stammposition jeder Pflanze aufgenommen. Für die Messung der lokalen Interaktionsintensität wurde der Hegyi-Index benutzt. Dieser ermöglicht die gleichzeitige Betrachtung von positiven (facilitation) und negativen (Konkurrenz) Interaktionen zwischen Nachbarpflanzen. Räumliche Punktmusteranalysen wurden mit dem Interaktionsindex kombiniert, um die Bedeutung und die Stärke der Interaktionstypen für verschiedene Wiederbesiedlungsphasen zu untersuchen. Das räumliche Muster der Pflanzen ist in allen Entwicklungsstadien aggregiert, was sich auch im Interaktionsindex für Sämlinge widerspiegelte. Darüber hinaus zeigte der Index ein frühes Umschalten von Facilitation zu Konkurrenz mit zunehmendem Entwicklungsstadium. Dieses Ergebnis spiegelt sich nicht im räumlichen Muster wider, was auf Selbstausdünnungsprozesse zurückzuführen ist. Diese sind mit den individuellen Wachstumsprozessen gekoppelt und benötigen mehr Zeit für messbare Veränderungen. Die aktuelle Studie erweitert das ökologische Konzept sowohl von intraspezifischen als auch interspezifischen positiven Pflanzeninteraktionen, da die Bedeutung und Stärke im Vergleich zu simultan vorhandenen Konkurrenzprozessen betrachtet werden. Darüber hinaus liefern die Ergebnisse Empfehlungen für die Planung von Renaturierungsprojekten degradierter Flächen, da diese bisher keine positiven Interaktionen berücksichtigen: bei ungünstigen Umweltbedingungen sollte das Pflanzmuster von regelmäßigen Abständen hin zu mehr aggregierten Anpflanzungen umgestellt werden, um die Erfolgschancen der Etablierung zu vergrößern.
This study presents mesoFON, an individual-based mangrove forest dynamics model that advances bey... more This study presents mesoFON, an individual-based mangrove forest dynamics model that advances beyond current models by describing crown plasticity of mangrove trees. The crown plasticity routines take advantage of the fields-of-neighborhood (FON) approach and account for the trunk bending and the differential side branch growth mechanism. Competition for above-/below-ground resources is dealt with separately in this model. Offspring production depends on tree growth and rises with tree ontogeny.
The main objective of the MADAM project (Mangrove Dynamics and Management) is to generate the sci... more The main objective of the MADAM project (Mangrove Dynamics and Management) is to generate the scientific basis enabling the sustainable stewardship of the resources of the Caeté mangrove estuary in Northeast Brazil in the sense of integrated coastal (zone) management. To achieve this, it is necessary to acquire in-depth knowledge of natural processes as well as of the relevant institutional, cultural, economic, social and political dynamics. Causal linkages within the ecosystem, as well as between ecosystem, economy and society, are analysed and explained via dynamic and trophic modelling. Scenario construction is intended to forecast the effects of acute or chronic interference on utilized resources, and to answer wider, management-related questions (e.g. restoration of destroyed areas, utilization potential for aquaculture). This paper describes the project strategy as developed and modified in the context of research results from the initial 2-yr project phase. It is argued that a continuous discussion process is essential to assess the validity of the strategies formulated at the beginning of a medium-time project, particularly if the project is of interdisciplinary nature.
ABSTRACT In classical theoretical ecology there are numerous standard models which are simple, ge... more ABSTRACT In classical theoretical ecology there are numerous standard models which are simple, generally applicable, and have well-known properties. These standard models are widely used as building blocks for all kinds of theoretical and applied models. In contrast, there is a total lack of standard individual-based models (IBM's), even though they are badly needed if the advantages of the individual-based approach are to be exploited more efficiently. We discuss the recently developed ‘field-of-neighborhood’ approach as a possible standard for modeling plant populations. In this approach, a plant is characterized by a circular zone of influence that grows with the plant, and a field of neighborhood that for each point within the zone of influence describes the strength of competition, i.e., growth reduction, on neighboring plants. Local competition is thus described phenomenologically. We show that a model of mangrove forest dynamics, KiWi, which is based on the FON approach, is capable of reproducing self-thinning trajectories in an almost textbook-like manner. In addition, we show that the entire biomass-density trajectory (bdt) can be divided into four sections which are related to the skewness of the stem diameter distributions of the cohort. The skewness shows two zero crossings during the complete development of the population. These zero crossings indicate the beginning and the end of the self-thinning process. A characteristic decay of the positive skewness accompanies the occurrence of a linear bdt section, the well-known self-thinning line. Although the slope of this line is not fixed, it is confined in two directions, with morphological constraints determining the lower limit and the strength of neighborhood competition exerted by the individuals marking the upper limit.
ABSTRACT Disturbances play a crucial role in various forest ecosystems and represent major shapin... more ABSTRACT Disturbances play a crucial role in various forest ecosystems and represent major shaping forces in forest succession and spatio-temporal processes. In this study, we simulated different disturbance regimes using the individual-based mangrove forest model KiWi. Frequent small-scaled gaps caused by lightning strikes and rare medium-sized patches caused by hurricanes were produced with varying size, severity and frequency. Additionally, a mixed regime including both lightning strikes and hurricanes was simulated. All three scenarios produced the same tree mortality rate over the simulation periods. We analyzed the temporal and spatial variations in these disturbances, taking into account their homogenizing or heterogenizing effects on the forest structure of a simulated area of 25 ha. All disturbance regimes produced significantly more homogenizing effects on the spatial forest structure than an undisturbed scenario. The hurricane regime produced a temporal heterogenization of the forest structure, while the small-scaled frequent lightning strike gaps were not able to contribute to additional heterogeneity. This shows that the explicit implementation of the disturbances generates different forest structures. The simulation results were integrated into an existing conceptual model for mangrove forest dynamics.
... Muhammad Ali Imron 1 , Uta Berger 2 , Sven Herzog 2. ... Contact Address: Muhammad Ali Imron,... more ... Muhammad Ali Imron 1 , Uta Berger 2 , Sven Herzog 2. ... Contact Address: Muhammad Ali Imron, Gadjah Mada University, Faculty of Forestry, Wildlife Ecology and Management, Bulaksumur, 55281 Yogyakarta, Indonesia, e-mail: muhammadali.imron gmail.com. Valid HTML 3.2!
The sensitivity of outputs and structures of different individual-based models were compared acro... more The sensitivity of outputs and structures of different individual-based models were compared across two different predator-prey systems; Panthera Population Persistence (PPP) and Backswimmer-Daphnia (Notonecta IBM) . The PPP model is spatially explicit, whereas in the fooduptake-submodel of the Notonecta IBM, distances are empirically included in differential equations. Both models differ significantly in their complexity and detailedness of process description. The PPP considers 29 parameters, whereas the backswimmer submodel (in its curent state) includes 8 parameters and is less complex. Extensive sensitivity analyses using improved Morris methods (PPP model) and/or the One Factor At A Time (OAT) screening technique (backswimmers) reveal that, in both models, the foragung radius is the most important factor beside all other factors and processes considered. A review of publications presenting various prey-predator models confirms this as a general pattern. The results suggest to carefully consider spaces within foraging models, independent of predator-prey-system and model type.
ABSTRACT Unter ungünstigen Umweltbedingungen können benachbarte Pflanzen das Überleben, Wachstum ... more ABSTRACT Unter ungünstigen Umweltbedingungen können benachbarte Pflanzen das Überleben, Wachstum und die Fitness positiv beeinflussen. Die vorliegende Studie untersucht den seltener bekannten Fall der intraspezifischen Facilitation. Dabei beeinflussen bereits etablierte Gehölzpflanzen die Etablierung von gleichartigen Sämlingen positiv. In Erweiterung der üblichen Betrachtungsweise wird dabei das Zusammenspiel von positiven und negativen Interaktionen während der Keim- und Anwuchsphase betrachtet. Felduntersuchungen wurden auf einer hypersalinen Fläche auf der Halbinsel Bragança (Nordbrasilien) durchgeführt, die durch ein gestörtes hydrologisches Regime gekennzeichnet ist. Nach mehreren Dekaden, siedelten sich Büsche der Mangrovenart Avicennia germinans in einigen Teilen der Fläche an. Während der hier vorgestellten Studie wurden drei verschiedene Entwicklungsstadien der Wiederbesiedlung (geringe, mittlere und hohe Vegetationsbedeckung) auf Grundlage von Satellitenbildern bestimmt. Verschiedene Pflanzenparameter(Pflanzenhöhe und Kronenradius), wurden von jedem Busch gemessen. Die Pflanzen wurden in Sämlinge und größere Pflanzen unterteilt und die Stammposition jeder Pflanze aufgenommen. Für die Messung der lokalen Interaktionsintensität wurde der Hegyi-Index benutzt. Dieser ermöglicht die gleichzeitige Betrachtung von positiven (facilitation) und negativen (Konkurrenz) Interaktionen zwischen Nachbarpflanzen. Räumliche Punktmusteranalysen wurden mit dem Interaktionsindex kombiniert, um die Bedeutung und die Stärke der Interaktionstypen für verschiedene Wiederbesiedlungsphasen zu untersuchen. Das räumliche Muster der Pflanzen ist in allen Entwicklungsstadien aggregiert, was sich auch im Interaktionsindex für Sämlinge widerspiegelte. Darüber hinaus zeigte der Index ein frühes Umschalten von Facilitation zu Konkurrenz mit zunehmendem Entwicklungsstadium. Dieses Ergebnis spiegelt sich nicht im räumlichen Muster wider, was auf Selbstausdünnungsprozesse zurückzuführen ist. Diese sind mit den individuellen Wachstumsprozessen gekoppelt und benötigen mehr Zeit für messbare Veränderungen. Die aktuelle Studie erweitert das ökologische Konzept sowohl von intraspezifischen als auch interspezifischen positiven Pflanzeninteraktionen, da die Bedeutung und Stärke im Vergleich zu simultan vorhandenen Konkurrenzprozessen betrachtet werden. Darüber hinaus liefern die Ergebnisse Empfehlungen für die Planung von Renaturierungsprojekten degradierter Flächen, da diese bisher keine positiven Interaktionen berücksichtigen: bei ungünstigen Umweltbedingungen sollte das Pflanzmuster von regelmäßigen Abständen hin zu mehr aggregierten Anpflanzungen umgestellt werden, um die Erfolgschancen der Etablierung zu vergrößern.
This study presents mesoFON, an individual-based mangrove forest dynamics model that advances bey... more This study presents mesoFON, an individual-based mangrove forest dynamics model that advances beyond current models by describing crown plasticity of mangrove trees. The crown plasticity routines take advantage of the fields-of-neighborhood (FON) approach and account for the trunk bending and the differential side branch growth mechanism. Competition for above-/below-ground resources is dealt with separately in this model. Offspring production depends on tree growth and rises with tree ontogeny.
The main objective of the MADAM project (Mangrove Dynamics and Management) is to generate the sci... more The main objective of the MADAM project (Mangrove Dynamics and Management) is to generate the scientific basis enabling the sustainable stewardship of the resources of the Caeté mangrove estuary in Northeast Brazil in the sense of integrated coastal (zone) management. To achieve this, it is necessary to acquire in-depth knowledge of natural processes as well as of the relevant institutional, cultural, economic, social and political dynamics. Causal linkages within the ecosystem, as well as between ecosystem, economy and society, are analysed and explained via dynamic and trophic modelling. Scenario construction is intended to forecast the effects of acute or chronic interference on utilized resources, and to answer wider, management-related questions (e.g. restoration of destroyed areas, utilization potential for aquaculture). This paper describes the project strategy as developed and modified in the context of research results from the initial 2-yr project phase. It is argued that a continuous discussion process is essential to assess the validity of the strategies formulated at the beginning of a medium-time project, particularly if the project is of interdisciplinary nature.
ABSTRACT In classical theoretical ecology there are numerous standard models which are simple, ge... more ABSTRACT In classical theoretical ecology there are numerous standard models which are simple, generally applicable, and have well-known properties. These standard models are widely used as building blocks for all kinds of theoretical and applied models. In contrast, there is a total lack of standard individual-based models (IBM's), even though they are badly needed if the advantages of the individual-based approach are to be exploited more efficiently. We discuss the recently developed ‘field-of-neighborhood’ approach as a possible standard for modeling plant populations. In this approach, a plant is characterized by a circular zone of influence that grows with the plant, and a field of neighborhood that for each point within the zone of influence describes the strength of competition, i.e., growth reduction, on neighboring plants. Local competition is thus described phenomenologically. We show that a model of mangrove forest dynamics, KiWi, which is based on the FON approach, is capable of reproducing self-thinning trajectories in an almost textbook-like manner. In addition, we show that the entire biomass-density trajectory (bdt) can be divided into four sections which are related to the skewness of the stem diameter distributions of the cohort. The skewness shows two zero crossings during the complete development of the population. These zero crossings indicate the beginning and the end of the self-thinning process. A characteristic decay of the positive skewness accompanies the occurrence of a linear bdt section, the well-known self-thinning line. Although the slope of this line is not fixed, it is confined in two directions, with morphological constraints determining the lower limit and the strength of neighborhood competition exerted by the individuals marking the upper limit.
ABSTRACT Disturbances play a crucial role in various forest ecosystems and represent major shapin... more ABSTRACT Disturbances play a crucial role in various forest ecosystems and represent major shaping forces in forest succession and spatio-temporal processes. In this study, we simulated different disturbance regimes using the individual-based mangrove forest model KiWi. Frequent small-scaled gaps caused by lightning strikes and rare medium-sized patches caused by hurricanes were produced with varying size, severity and frequency. Additionally, a mixed regime including both lightning strikes and hurricanes was simulated. All three scenarios produced the same tree mortality rate over the simulation periods. We analyzed the temporal and spatial variations in these disturbances, taking into account their homogenizing or heterogenizing effects on the forest structure of a simulated area of 25 ha. All disturbance regimes produced significantly more homogenizing effects on the spatial forest structure than an undisturbed scenario. The hurricane regime produced a temporal heterogenization of the forest structure, while the small-scaled frequent lightning strike gaps were not able to contribute to additional heterogeneity. This shows that the explicit implementation of the disturbances generates different forest structures. The simulation results were integrated into an existing conceptual model for mangrove forest dynamics.
... Muhammad Ali Imron 1 , Uta Berger 2 , Sven Herzog 2. ... Contact Address: Muhammad Ali Imron,... more ... Muhammad Ali Imron 1 , Uta Berger 2 , Sven Herzog 2. ... Contact Address: Muhammad Ali Imron, Gadjah Mada University, Faculty of Forestry, Wildlife Ecology and Management, Bulaksumur, 55281 Yogyakarta, Indonesia, e-mail: muhammadali.imron gmail.com. Valid HTML 3.2!
The sensitivity of outputs and structures of different individual-based models were compared acro... more The sensitivity of outputs and structures of different individual-based models were compared across two different predator-prey systems; Panthera Population Persistence (PPP) and Backswimmer-Daphnia (Notonecta IBM) . The PPP model is spatially explicit, whereas in the fooduptake-submodel of the Notonecta IBM, distances are empirically included in differential equations. Both models differ significantly in their complexity and detailedness of process description. The PPP considers 29 parameters, whereas the backswimmer submodel (in its curent state) includes 8 parameters and is less complex. Extensive sensitivity analyses using improved Morris methods (PPP model) and/or the One Factor At A Time (OAT) screening technique (backswimmers) reveal that, in both models, the foragung radius is the most important factor beside all other factors and processes considered. A review of publications presenting various prey-predator models confirms this as a general pattern. The results suggest to carefully consider spaces within foraging models, independent of predator-prey-system and model type.
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Papers by Uta Berger