Wrapping up 2012

Nearing the end of 2012 and the total number of posts on this blog has been even fewer this year than in 2011. At least I have been tweeting a bit more of late. Here’s a quick round-up of activities and publications since my last post with a look at some of what’s going on in 2013.

The Geoforum paper on narrative explanation of simulation modelling is now officially published, as is the first of two Ecological Modelling papers on the Michigan forest modelling work. Citations and abstract for both are below, and are included on my updated publications list. I’ll post more details and info on each in the New Year (promise!). I’ll likely wait to summarise the Michigan paper until the second paper of that couplet is published – hopefully that won’t be too long as it’s now going through the proofs stage.

The proceedings for the iEMSs conference I attended in Leipzig, Germany, this summer are now online. That means that the two papers I presented there are also available. One paper was on the use of social psychology theory for modelling farmer decision-making, and the model I discuss in that paper is available for you to examine. The other paper was a standpoint contribution to a workshop on the place of narrative for explaning decision-making in agent-based models. From that workshop we’re working on a paper to be published in Environmental Modelling and Software about model description methods for agent-based models. More on that next year too hopefully.

In one of my earlier posts this year I talked about agent-based modelling spatial patterns of school choice (I’ll get the images for that post online again soon… maybe). I’ve managed to write up the early stages of that work and have submitted it to JASSS. We’ll see how that goes down. I hope to continue on that work in the new year also, possibly while in New Zealand at the University of Auckland. I’ll be in Auckland visiting and working with George Perry and David O’Sullivan, with whom I published the recent Geoforum paper (highlighted above). On the way to New Zealand I’ll be stopping off in Los Angeles for the Association of American Geographers conference which I haven’t been to previously and which should be interesting.

So that’s it for 2012. A New Year’s resolution for 2013 – post at least once every month on this blog! Especially from Down Under.

Happy Holidays!

Millington, J.D.A., O’Sullivan, D., Perry, G.L.W. (2012) Model histories: Narrative explanation in generative simulation modelling Geoforum 43 1025–1034
The increasing use of computer simulation modelling brings with it epistemological questions about the possibilities and limits of its use for understanding spatio-temporal dynamics of social and environmental systems. These questions include how we learn from simulation models and how we most appropriately explain what we have learnt. Generative simulation modelling provides a framework to investigate how the interactions of individual heterogeneous entities across space and through time produce system-level patterns. This modelling approach includes individual- and agent-based models and is increasingly being applied to study environmental and social systems, and their interactions with one another. Much of the formally presented analysis and interpretation of this type of simulation resorts to statistical summaries of aggregated, system-level patterns. Here, we argue that generative simulation modelling can be recognised as being ‘event-driven’, retaining a history in the patterns produced via simulated events and interactions. Consequently, we explore how a narrative approach might use this simulated history to better explain how patterns are produced as a result of model structure, and we provide an example of this approach using variations of a simulation model of breeding synchrony in bird colonies. This example illustrates not only why observed patterns are produced in this particular case, but also how generative simulation models function more generally. Aggregated summaries of emergent system-level patterns will remain an important component of modellers’ toolkits, but narratives can act as an intermediary between formal descriptions of model structure and these summaries. Using a narrative approach should help generative simulation modellers to better communicate the process by which they learn so that their activities and results can be more widely interpreted. In turn, this will allow non-modellers to foster a fuller appreciation of the function and benefits of generative simulation modelling.

Millington, J.D.A., Walters, M.B., Matonis, M.S. and Liu, J. (2013) Modelling for forest management synergies and trade-offs: Northern hardwood tree regeneration, timber and deer Ecological Modelling 248 103–112
In many managed forests, tree regeneration density and composition following timber harvest are highly variable. This variability is due to multiple environmental drivers – including browsing by herbivores such as deer, seed availability and physical characteristics of forest gaps and stands – many of which can be influenced by forest management. Identifying management actions that produce regeneration abundance and composition appropriate for the long-term sustainability of multiple forest values (e.g., timber, wildlife) is a difficult task. However, this task can be aided by simulation tools that improve understanding and enable evaluation of synergies and trade-offs between management actions for different resources. We present a forest tree regeneration, growth, and harvest simulation model developed with the express purpose of assisting managers to evaluate the impacts of timber and deer management on tree regeneration and forest dynamics in northern hardwood forests over long time periods under different scenarios. The model couples regeneration and deer density sub-models developed from empirical data with the Ontario variant of the US Forest Service individual-based forest growth model, Forest Vegetation Simulator. Our error analyses show that model output is robust given uncertainty in the sub-models. We investigate scenarios for timber and deer management actions in northern hardwood stands for 200 years. Results indicate that higher levels of mature ironwood (Ostrya virginiana) removal and lower deer densities significantly increase sugar maple (Acer saccharum) regeneration success rates. Furthermore, our results show that although deer densities have an immediate and consistent negative impact on forest regeneration and timber through time, the non-removal of mature ironwood trees has cumulative negative impacts due to feedbacks on competition between ironwood and sugar maple. These results demonstrate the utility of the simulation model to managers for examining long-term impacts, synergies and trade-offs of multiple forest management actions.

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