Ecological modelling

Canopy Photosynthesis models Spatially explicit models

Canopy Photosynthesis models

Measuring the primary production of whole canopies has become an increasingly important aspect of ecological research. Questions pertaining to plant competition for light at the community level, to concern over changes in canopy flux rates resulting from global warming or increasing atmospheric CO2 can in part be addressed with data on whole canopy photosynthesis. Since photosynthesis measurements of individual foliage elements will generally not represent the behaviour of the whole plant (due to differences in age, physiology and exposure to microclimatic conditions), an important method for estimating these fluxes has involved the use of whole-canopy photosynthesis models. Together with Prof. Dr. R.J. Ryel (Dept. of Forest, Range, and Wildlife Science, Utah State University, Logan, UT, USA) we developed a class of these models that scale up from single leaf estimates to the whole canopy.

 Canopy photosynthesis models generally consist of two interconnected components. (1) a single-leaf photosynthesis submodel, and (2) a microclimatic submodel that incorporates the interactions of structure with the physical environment. The structure of the canopy is typically divided into subregions of similar foliage characteristics, and the microclimatic conditions at defined time-steps are determined with the microclimatic submodel. Rates of photosynthesis are then calculated for representative foliage elements within each subregion, weighted appropriately for foliage density and summed to generate whole plant or canopy rates. Our models range from relatively simple for homogeneous single-species canopies, to complex for diverse multispecies canopies, and are frequently used formulations suitable for addressing a range of ecological questions. Recently a new subroutine was developed, which allows to quantitatively assess the effect of photoinhibition on the short term and long-term carbon gain of plant species.

 Layer Model

Figure: A mixed herbaceous canopy subdivided into layers according to our multispecies model for homogeneously structured canopies. Structural parameters (Leaf area index, stem area index, leaf angles, stem angles) of each species are assumed to be homogeneous within each layer. The canopy is assumed to have infinite extension into all directions (no sidelighting)

Figure: Representation of individual plants as a series of concentric cylinders subdivided into layers. Foliage density and orientation is assumed similar within each subunit. Individual plants can be grouped to form a multi-individual canopy with calculations conducted for each member or representative members. Light attenuation for an individual plant would be affected by neighbouring plants when such a canopy is defined. The matrix of points indicates locations where light interception and photosynthesis are calculated (from Beyschlag and Ryel 1999)

Figure: Application of our cylinder model for calculation of whole tree photosynthesis (see Beyschlag et al. 1994


Analyzing vegetation pattern dynamics with spatially explicit models

Spatially explicit models (cellular automata) are increasingly being employed for analysis and visualization of vegetation dynamics. Presently we are developing such models for the analysis of vegetation pattern formation during successional processes. The results of our various competition and disturbance experiments will be used for creating the rules for these models. According to our experimental setup  we work with grids of hexagons. Plant individuals can either be modeled as single hexagons (e.g. for the simulation of disturbance events), or as a group of hexagons where lateral growth and competitive interactions can be expressed as changes in the number of hexagons per plant individual. Preliminary versions of these models are already running.

Figure: Hexagonal grid for simulation of disturbance effects in open acidic grasslands. Red cells: Corynephorus canescens, orange cells: Hieracium pilosella, green cells: Polytrichum piliferum, white cells: disturbed areas (without vegetation)




RYEL, R., BARNES, P.W., BEYSCHLAG, W., CALDWELL, M.M., FLINT, S.D. (1990): Plant competition for light analyzed with a multi­species canopy model. I. Model development and in­fluence of enhanced UV-B condi­tions on photosynthesis in mixed wheat and wild oat canopies. Oecologia 82: 304-310

BEYSCHLAG, W., BARNES, P.W., RYEL, R., CALDWELL, M.M., FLINT, S.D. (1990): Plant competition for light analyzed with a multi­species canopy model. II. Influence of photosynthetic charac­teristics on mixtures of wheat and wild oat. Oeco­logia 82: 374-380

BARNES, P.W., BEYSCHLAG, W., RYEL, R., FLINT, S.D., CALDWELL, M.M. (1990): Plant competition for light analyzed with a multi­species canopy model. III. Influence of canopy struc­ture in mixtures and monocultures of wheat and wild oat. Oecologia 82: 560-566

BEYSCHLAG, W., RYEL, R.J., ULLMANN, I. (1992) Experimental and modelling studies of competition for light in roadside grasses.  Botanica Acta 105: 285-291

RYEL, R.J., BEYSCHLAG, W., CALDWELL, M.M. (1993) Foliage orienta­tion and carbon gain in two tussock grasses as asssessed with a new canopy gas exchange model. Functional Ecology 7: 115-124

BEYSCHLAG, W., RYEL, R.J., CALDWELL, M.M. (1994) Photosynthesis of vascular plants. Assessing canopy photosynthesis by means of simulation models. In: Schulze E.D., Caldwell M.M. (eds.) Ecophy­siology of Photosynthesis; Ecological Studies Vol. 100, pp. 409-430. Berlin Heidelberg New York (Springer)

BEYSCHLAG, W., RYEL, R.J., DIETSCH, C. (1994) Shedding of older needle age classes does not necessarily reduce photosynthetic primary production of Norway spruce. Analysis with a three-dimensional canopy photosynthesis model. Trees, Struct. Funct. 9: 51-59

RYEL, R.J., BEYSCHLAG, W., CALDWELL, M.M. (1994) Light field heterogeneity among tussock grasses: Theoretical considerations of light harvesting and seedling establishment in tussocks and uniform tiller distributions. Oecologia 98: 241-246

RYEL, R.J., BEYSCHLAG, W. (1995) Benefits associated with steep foliage orientation in two tussock grasses of the American Intermountain West. A look at water-use-efficiency and photoinhibition. Flora 190: 1-10 

RYEL, R.J., BEYSCHLAG, W., HEINDL, B., ULLMANN, I. (1996) Experimental studies on the competitive balance between two central European roadside grasses with different growth forms. 1 Field experiments on the effects of mowing and maximum leaf temperatures on competitive ability. Botanica Acta 109: 441-448

BEYSCHLAG, W., RYEL, R.J., ULLMANN, I., ECKSTEIN, J. (1996) Experimental studies on the competitive balance between two central European roadside grasses with different growth forms. 2. Controlled experiments on the influence of soil depth, salinity and allelopathy. Botanica Acta 109: 449-455 

BEYSCHLAG, W. RYEL, R.J. (1997) Modelling leaf/canopy photosynthesis. In: Raghavendra A. S. (ed.) Photosynthesis a Comprehensive Treatise; pp. 305-319; Cambridge, Cambridge University Press 

BEYSCHLAG, W. (1997) Canopy photosynthesis models - a valuable tool for ecological research. EcoSys (Suppl.) 20: 81-87

WERNER C., CORREIA O., RYEL, .R.J , BEYSCHLAG, W. (1998) Modelling whole- plant primary production of macchia species: assessing the effects of photoinhibition and foliage orientation. Revista de Biologia (Lisboa) 16: 247-257

BEYSCHLAG, W., RYEL, R.J. (1999)  Canopy Modelling. In: Pugnaire, F, Valladares F. (eds.). Handbook of Plant Functional Ecology. New York, Marcel Dekker pp. 771-800

Sickendiek, F., Ryel, R.J.,  Beyschlag, W. (1999) Parametrisierung und Validation eines Lichtinterzeptionsmodells für Strauchflechten. in: Beyschlag, W., Steinlein, T. (eds) Ökophysiologie pflanzlicher Interaktionen; Bielefelder Ökologische Beiträge 14: 302-306

WERNER, C., RYEL, R.J., CORREIA, O., BEYSCHLAG, W. (2001) Structural and functional variability within the canopy and its relevance for carbon gain and stress avoidance. Acta Oecologica 22: 129-138 

Werner, C., Correia, O., Ryel, R.J., Beyschlag, W. (2001) Effects of photoinhibition on whole plant carbon gain assessed with a photosynthesis model. Plant, Cell and Environment 24: 27-40