Growth models are a central part of forest inventory and planning. Growth models are the systems of equations that estimate future forests. Even knowing what is on the land today often requires "growing" older forest measurements forward.
Where there is an opportunity for life, nature has seen fit to fill it. Forests are a great example. Trees are just one part of a forest but they have diversified into a variety of species, sizes and growth strategies that are highly specific to habitats and regions.
Modeling so much variety is a monumental task for sure, but forestry is primarily concerned with volume, value, carbon and habitat. It's a small lens through which to understand a forest for sure, but it's a lens nonetheless and that means forest growth models can focus on these views fairly well. At least well enough that forest planning and operations really should make use of them.
So how are growth models implemented in Assisi? What regions and species are available? How are they used? Can they be customized or can I add my own?
Here is an overview of how growth models are used in the Assisi Forest management software. Assisi's goal is to provide solutions for these needs while keeping the process and your data easily understandable. We've been successful for the most part do to the organized framework and database of Assisi Forest. A framework under development for over 25 years.
How are Models Implemented in Assisi?
Growth models are researched by many organizations such as universities, coops and private organizations. The models themselves can be available as published equations, source code or compiled components. Assisi implements all of these depending on the desires of the source organization.
When publications are available, Assisi's preferred choice is to implement them in its native C# language while making coefficients and options accessible through the interface. This provides the flexibly to set individual models by species, region or forest type but of course requires a decent understanding of the models themselves. Assisi has packaged most of its internally coded models into "Calibrations" that reflect the local regions.
When models are not yet published or not going to be, but a modeling group desires to make their models available in Assisi, Assisi has coded these models into external components whose source is owned and managed by the organization. This too allows Assisi to closely integrate model systems into its framework while giving the modeling organization ownership of the source code and a good framework for continued maintenance of their models. Assisi has done this in C++, FORTRAN and C# programming languages.
Some models are models are already available as compiled components. These have defined API's that Assisi wraps its framework around so that these component models are also accessible in the same ways as Assisi other models.
What Regions are Available in Assisi Forest?
Assisi works with growth models that cover most of North America. Because Assisi can translate units between imperial and metric, these models are not technically restricted to North America. Some of the model systems implemented are: ORGANON, Acadia, PMRC, CRYPTOS/CACTOS, NE TWIGS and FVS. Each of these systems have many individual equations, some have dozens. Most have been implemented directly in Assisi making them individually accessible. Others are implemented as a system of equations targeted at certain species and regions.
How are Models Used in Assisi Forest?
Assisi organizes models into a system called a "Calibration". A Calibration is collection of species, models, settings and coefficients organized together so that the Calibration can be assigned to specific stands or strata. A Calibration usually reflects a geographic region where species are expected to grow the same way, but can also be a strata where its coefficients and settings are forest type specific as well. A Calibration may also reflect what forest measurements are available and can be used on a data set.
All of these are done in Assisi Forest using models implemented in different ways and a database that makes it all accessible. The sample database included with an Assisi Forest license demonstrates many of these.
Can I Add my Own Models to Assisi?
Customizing models is a big part of setting up Assisi for your needs. All models in Assisi have settings and options for use. The options can be anything from growth factors to species to coefficients. It depends on the model chosen. Assisi can also regress height equations by species and forest type so that the models you choose are further calibrated to your lands.
But what if you want to use your own equations? In many cases, models of your own can be directly entered and parsed by Assisi. Taper, volume, growth, carbon and weight all have options for user defined equations. The sample database demonstrates many of these as well.
I hope this gives you a high level introduction to Assisi's approach to implementing growth models. Growth models are an active area of forest research and Assisi is honored to be able to work with so many luminaries over the years. We are also hopeful that after 25 years of development Assisi has become well organized and flexible enough to host models these models while making it all accessible to forest managers.
Whether your organization has its own internal development or has never used an inventory system, Assisi can likely fulfill a need!
Rich Howard
President Assisi Software