Daniel Auclair

Analytical study of a stochastic plant growth model: Application to the GreenLab model

A stochastic functional-structural model simulating plant development and growth is presented. The number of organs (internodes, leaves and fruits) produced by the model is not only a key intermediate variable for biomass production computation, but also an indicator of model complexity. To obtain their mean and variance through simulation is time-consuming and the results are approximate. In this paper, based on the idea of substructure decomposition, the theoretical mean and variance of the number of organs in a plant structure from the model are computed recurrently by applying a compound law of generating functions. This analytical method provides fast and precise results, which facilitates model analysis as well as model calibration and validation with real plants. Furthermore, the mean and variance of the biomass production from the stochastic plant model are of special interest linked to the prediction of yield. In this paper, through differential statistics, their approximate results are computed in an analytical way for any plant age. A case study on sample trees from this functional-structural model shows the theoretical moments of the number of organs and the biomass production, as well as the computation efficiency of the analytical method compared to a Monte-Carlo simulation method. The advantages and the drawbacks of this stochastic model for agricultural applications are discussed.

Diameter and height growth curves for widely-spaced trees in European agroforestry

Predicting timber volume can be important for decision- making. Conventional forest growth models are generally based on mensuration data acquired in fully stocked homogeneous tree stands, and do not consider the wide spacings often adopted in European agroforestry. In order to test the possibility of adapting conventional forestry growth models, diameter and height growth were measured on widely spaced trees. Parameters of a Gompertz double exponential function were adjusted for several tree species planted at wide spacings. Spacing, vegetation control, and individual tree shelters affected the parameters. At wide spacings, the asymptote for diameter growth was larger, and the asymptote for height growth smaller, compared to conventional forestry.

Virtual reality for cultural landscape visualization

Although land managers and policy-makers generally have a good experience of what result can be expected from their decisions, they are often faced with difficulty when trying to communicate the visual impact of a management option to stakeholders, particularly when the landscape exhibits a high cultural value. Three-dimensional visualization of the landscape is often used for communicating with the stakeholders. A challenge in participatory methods for integrated assessment and policy planning is to view future changes in land use, according to scenarios. A 3-D landscape visualization component, SLE (“Seamless Landscape Explorer”), has been developed, which is launched after a scenario simulation to allow for exploration of landscape changes. Pressures causing such changes are translated into changes in the spatial configuration of the landscape. The different types of land-use are visualized thanks to a library of detailed textures, and vegetation can be added. This has been applied to a study of four scenarios in the French Mediterranean region, which were set up as part of a participatory process for discussing the planning of the regional peri-urban and agricultural policy, in an area dominated by the typical culturally sensitive Mediterranean matorral, (“garrigue” shrubland) surrounding the Pic Saint-Loup mountain. Examples of visualization are shown and discussed here.

Practical methods for non-destructive measurement of tree leaf area

In an agroforestry context, the knowledge of leaf area is an important parameter to take into consideration because tree foliage shades the intercrop. Single leaf measurement (for example leaf length and width) is a widely used method to estimate leaf area in a rapid non-destructive way. In this study, the objectives were to estimate the leaf area of different leaf sizes and shapes for Acacia mangium Willd. (Mimosaceae), Tectona grandis L. (Verbenaceae), Hevea brasiliensis Muell.-Arg. (Euphorbiaceae), and Swietenia macrophylla King. (Meliaceae) Indonesian agroforestry trees. In order to characterise leaf area in field conditions a digital photograph method was used. Leaf length was measured in order to build relationships between leaf length versus actual leaf area. Additional measurements obtained from the digital pictures such as lamina width, number of leaflets, leaflet length and width were recorded in order to test the benefit regarding leaf area estimation based only on the leaf length model. The combination of these different linear leaf measurements led to various degrees of precision of leaf area estimation. The different models can then be chosen according to a compromise between the accuracy of leaf area estimation and the time allocated to field measurements.

Intensive or extensive cultivation of short rotation hybrid poplar coppice on forest land

Abstract An intensive short rotation treatment was compared with a low input extensive treatment on Populus trichocarpa × deltoides (Beaupre) coppiced at two- or three-year intervals on a previously wooded land in central France. Each individual plot contained 400 stools, in order to allow a reasonable extension to large-scale plantations. The extensive treatment generally led to high mortality, poor height and diameter growth, and a small number of sprouts per stool. Total mean annual biomass production amounted to 3·5 t in the intensive treatment and 0·6 t in the extensive treatment. These relatively low figures represent ‘field yields’ which may be obtained in average conditions, compared with ‘record yields’ obtained in very controlled conditions. Short rotation coppice culture should include a good soil preparation in order to ensure a favourable establishment of the stumps.

Visualising Changes in Agricultural Landscapes

Although land managers and policy-makers generally have a good experience of what result can be expected from their decisions, they are often faced with difficulty when trying to communicate the visual impact of a future management option to all stakeholders (local and regional decision-makers, land managers, landscape planners, and various communities involved in outdoor activities). Three-dimensional visualisation of the landscape is often used for communicating with the stakeholders. Static, web-based landscape visualisation tools have made considerable progress in recent years, such as for example Google Earth, covering the entire planet in 3D. Such visualisations are based on aerial (satellite) imagery, at a specific date, but are not dynamic. The challenge in methods for integrated assessment of agricultural systems (such as developed in SEAMLESS) is to view future changes in land use, according to scenarios.

Stochastic modelling of tree annual shoot dynamics

Abstract• ContextModelling annual shoot development processes is a key step towards functional–structural modelling of trees. Various patterns of meristem activity can be distinguished in tree shoots, with active periods of phytomer production followed by rest periods. This approach has seldom been integrated in functional–structural tree models.• AimsThis paper presents theoretical research work on modelling and computation of the dynamics of tree annual shoots using stochastic processes with various development patterns: continuous or rhythmic, monocyclic or polycyclic, “seasonal” or “a-seasonal”, with preformation or neoformation produced from meristem functioning.• MethodsThe renewal theory is used to compute stochastic aspects of phytomer production, resulting from meristem extension or rest periods and meristem mortality.• ResultsContinuous development can be modelled with a Bernoulli process, while rhythmic development is modelled by alternation between extension and rest periods, the duration of each period following specific distributions.• ConclusionThe application of such stochastic modelling is the estimation of organ production during tree development as a component of the demand in functional–architectural tree models, used for computing biomass production and partitioning.

Assessing the Visual Impact of Agroforestry Management with Landscape Design Software

In a case study in the Cévennes (France), various agroforestry management options have been simulated with the AMAP landscape design and visualization software. The terrain was described through a digital elevation model. Information concerning the farm structure was integrated in a geographic information system. The AMAP database provides accurate 3-dimensional plant architectural models, built according to the botanical concepts developed by the Montpellier Institute of Botany. Individual tree computer mock-ups were computed for each species present, at the desired ages, in order to simulate landscape evolution with time. Images of the scene were computed and observed on the screen from several virtual viewpoints. Several management options have been tested and visualized, providing a basis for discussion between partners concerning spatial organization, such as the layout of forest and agricultural plots.

Short rotation forestry : an agricultural case study of economic feasibility

Abstract The economic feasibility of short rotation forestry was studied assuming growth on agricultural land in central France. The annual discounted average gross margin was used as a criterion of comparison between short rotation forestry and traditional annual agricultural crops (wheat, maize, sunflower). Using average assumptions concerning cost, yield and selling price, short rotation forestry is not competitive with the other crops studied. In the present economic conditions, even if some of the inputs and initial assumptions (fertilization, selling price) are modified, the results remain unchanged. Some suggestions are made concerning agricultural policy at the state or community level.

Connecting an architectural plant model to a forest stand dynamics model—application to Austrian black pine stand visualization

Abstract• ContextForest stand dynamics models simulate the growth of trees in stands; based on field measurements and system knowledge, they provide a relatively precise representation of forest growth and are well adapted for forest management purposes. Architectural models describe the structure of plants according to ontogenetic development processes; as a support of biomass production and partitioning at organ scale, they simulate individual tree development.• AimsThe aim of this study was to link a stand dynamics model and an architectural model to simulate stand dynamics, in which the ecological or silvicultural modelling from the stand model and the architecture representation could be integrated, to provide individual tree details at the stand level.• MethodsStand-level simulations of Austrian black pine dynamics provided global results on tree growth from the empirical forest growth model PNN, and branching details for individual trees were provided by the functional–structural plant model (FSPM) GreenLab.• ResultsIndividual tree dynamics were computed, and the simulated trees were integrated at the stand level for visualizing two different management scenarios.• ConclusionBy combining a stand dynamics model adapted to forest management with an FSPM with detailed tree architecture, it is possible to simulate individual tree structure with consistent dimensions, adapted to ecological and silvicultural modelling for decision support in forest management.