Sylvan Stand Structure Models


The Sylvan Stand Structure Model is designed to apply stand dynamics principles to trees of any species in any mix anywhere in the world. To achieve this flexibility it requires more from the user than the typical forest growth model. The design concept in this model is that user should choose the data to be included the in parameter set so that it represents the forests that will be projected.

The Sylvan Stand Structure Model is being develop using software that allow for cross platform development. This approach allows people to use a computer environement they prefer, not one that we mandate.

Model Components


The model is designed to be able to use available data but this requires a high degree of flexibility and and some creativity in how to store and use functions with diverse models forms in a single model interface. To deal with this array of function types, we decided to use a old programming device, a function lookup table.

A lookup table is a sorted list of points along a function line, this is the data needed to plot the function in a graph. Intermediate points along the line are assumed to be linear interpolations of the points on either side of the desired point. This allows us to store any function as a sequence on points. You the user can determine the number of points used to represent the line. The beauty of this approach is that we can faithfully represent any functional equation form in a consistent standardized form. This also allows those with data and no function to reproduce a representations of the data and if no data is available the user can easily draw a line and it can be stored in this form of data structure.

Spatially explicit

Sylvan stand structure model uses spatially explicit information, from trees in a plot, to predict the likely change in the dimensions of each tree in the plot. Tree size change is predicted from crown size. Crown size is a function of species, site productivity and available space. Additionally, with way the data are stored allow the tracking of asymmetries necessary to address wood quality.

The Sylvan stand structure model uses Area Potentially Available (APA) (Brown 1965, and Nance 1987) to determine the chang in tree size and shape. This idea can be described as a set of circles or various sizes interacting dividing the space based on their relative size. The size of the circle is based on the maximum crown radius for a tree of that size. The formal description of this is a weighted and constrained Voronoi polygon.

The model is designed so that a user can collect all necessary data to parameterize the model from the plot they wish to grow or neighboring stands. Data collection is designed to take from one day to several days depending on the complexity of the stand structure.

Stand and tree history

One the very important component of this model is the stand and tree history. To be able to describe the relationships that Sylvan describes the model needs to know the size, shape and change in the tree dimensions of the the time since stand establishment or in the case of multi-cohort stands since tree establishment. Usually forester do not have this information. If available we can use the stand dynamics principles to predict the tree characteristics. The growth model predicts all these characteristics so our normal operating procedure is to create a stand similar your stand at a young age and then grow it forward in time.

Tree stem internal structure

Based on the information on crown size of ber time we can use that to infer tree taper, internal wood characteristics, wood characteristics, and asymetryies of the stem.

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Author: Dr. David R. Larsen
Created: March 21, 2007
Last Updated: January 16, 2013