Disturbance Interaction model pt 2

posted Mar 13, 2012, 12:53 PM by Brian Buma   [ updated Mar 13, 2012, 1:03 PM ]
I've been working on this spatially explict resistance/resilience spatial model for a bit now, and it's going well.  At this point you specify how ecosystem resistance and resilience (currently there are two cover types to work with) develop over time, so each cover type can develop differently (think how grass is pretty flamable after only a couple years, compared to a regenerating forest with spare understory, for example).  Resistance and resilience are goverened by their own development functions, obviously.  This seems simple, but for two cover types, two disturbances, and both a resistance and a resilience function for each disturbance AND each cover type, it gets complex fast.  BUT, with some iterations and the wonder of leaving-a-computer-running-for-many-days, it works pretty well.  I've attached a pdf poster-style of the results for some "neutral" runs.  By "neutral," I mean there was no bias in the functions, they were either identical for the cover types or mirrored (e.g. disturbance 1 favored cover 1, disturbance 2 favored cover 2).  Some of the runs included a climate change component.
I removed the interaction component for some of the runs to compare the influence of resistance or resilience indepenetly.  Results were pretty interesting.  I was expecting resilience-based interactions to be important for cover-type switching, for obvious reasons- loss of resilience basically ensures changes in cover type.  But it was resistance interactions that ruled the day.  In retrospect, it makes sense- if a disturbance makes you more vulnerable to another disturbance (say a pathogen) than they will likely compound, and if one disturbance rate is rising due to climate change (e.g. fires), it may increase landscape susceptibility to other disturbances where we wouldn't necessarily expect climate change to have any effect. 
Of course, this is just the first few official runs, and the parameters chosen have an influence that will be further investigated.  For instance, the rate of increase/decrease in resilience was higher than that for resistance, as that seemed to be more reflective of the reality of N American forests, which were in my mind while setting up the runs (although it is supposed to be generic, you have to start somewhere).  Further work to come... 
 Pdf at end of post, download it using arrow on the right for higher resolution.
Brian Buma,
Mar 13, 2012, 1:00 PM