Regimes - Why Aren't People Using Them?

Introduction

If memory serves me correctly, Remsoft introduced the Regimes module back in 2009. At first, it did not generate a lot of interest, despite criticisms from some circles that Model I was better than Model II. It was an extra module to license, and frankly, it wasn't the easiest syntax to wrap your head around. But times have changed!

Regimes is now part of the base Woodstock license. And while the syntax isn't the easiest thing to master, I've come to appreciate how Ugo was able to incorporate Model I structure into Woodstock's inherent Model II framework. As a user of FORPLAN, I remember how meshing Model I and Model II in a single model resulted in a very clumsy interface. It was no surprise that few people used FORPLAN v.2. But it has been 15 years since Woodstock Regimes was released, and yet I still don't see a lot of clients using it. This poll I conducted confirms that:

Poll conducted week of April 22, 2024

Why Use Regimes?

In Woodstock, when you specify an action, you provide the operability criteria (development type + condition) that allows the interpreter to generate a decision variable for each DevType-condition combination. If there are 5 operable DevTypes and 5 conditions (e.g. age) when each DevType can be harvested, the interpreter will generate 25 decision variables. The beauty of Regimes is that it allows you to create decision variables for a sequence of events, rather just a single activity. 

So, for what kinds of forest management decisions are Regimes suited? I've seen many models in the US South where commercial thinning is always followed by a fertilization one year later. While the timing of the thinning is a decision, the fertilization is not. Before Regimes, modeling CT + fert required inventory outputs with somewhat unintuitive DevType masks to make it work and report the fertilization acres in the correct period:

*SOURCE .MASK(_THx(14)) @AGE(16) _INVENT _AREA
; add 1 to age because of age counter

Additionally, by relying on an inventory output, it makes your model run slower.

*REGIME rThin
*OPERABLE rThin

   .MASK(_THx(00)) _AGE >= 13 AND _AGE <= 18

 *PRESCRIPTION rxTF (thin and fert)

   _RXPERIOD _ACTION   _ENTRY 

       0       aTH    _INITIAL

       1       aFT     _FINAL

Using a regime and prescription, reporting acres treated relies only on action-based outputs and so your model runs faster.

What About Reforestation?

The poll numbers are interesting for a few reasons.

Two-thirds of the respondents have specific planting actions in their models. From a conceptual modeling perspective, this implies that there are alternatives for each harvested area (timing, species, planting density, etc.).

No one simply attributes reforestation acres and costs to harvest actions. I know there are many Woodstock users in Canada, and few of them use 1-year planning periods. Again, this implies reforestation alternatives for each harvested area.

Roughly one-third of the respondents are using regimes to model reforestation. (Disclosure: respondents work for client organizations for which I developed models recently).

Over the last 20 years, I've witnessed a shift from silvicultural evaluation models to highly prescriptive models. By this I mean that 20 years ago, a lot of the models I built evaluated multiple planting densities for each harvested area. As a result, there needed to be multiple planting actions to represent the alternatives. And because planting was a choice, there needed to be constraints to enforce reforestation policies.

These days, however, while there may be different reforestation prescriptions across the forest, there is generally only one prescription for each harvest area. And in that case, there really isn't a need to have separate decision variables for planting. Instead, one or prescriptions in a reforestation regime that begins with final harvest is all that is required. Fewer decision variables = faster matrix generation and solution. And an added bonus is that the reforestation constraints may not be required either.

So Why Haven't Things Changed?

While I was at Remsoft, we always taught reforestation as a distinct activity from harvesting in the Modeling Fundamentals course. I suspect that many of the analysts we taught just replicated that conceptual modeling framework in the models they developed. And my experience has been that organizations rarely revamp models once developed.

Because models are rarely scrapped and rebuilt, I suspect most analysts these days inherited models built by some predecessor (who probably has now left the organization). There is never time to redesign a model so the same structure persists, with annual updates to the AREAS file (to account for depletions) and yield tables.

Ready for a Change? Contact Me!

If your models haven't been updated in a while, maybe it is time to rethink things. Together, we can design a new conceptual framework that is efficient and easier to debug if problems arise. And if you'd like to apply some targeted training (for say, Regimes or conceptual modeling) we can do that too!