The AGU Bookshelf which appears on EOS is an excellent source of perspective on climate and other geophysical issues. In the December 21 2010 issue there is an interview of Peter S. Eagleston By C. Schultz titlled
Schultz, C. (2010), Range and Richness of Vascular Land Plants: The Role of Variable Light, Eos Trans. AGU, 91(51), doi:10.1029/2010EO510015.
The abstract summary of the interview
“The observation that the number of species decreases—while at the same time the average range of local species increases—with increasing latitude is known within ecological circles as Rapoport’s rule. In the AGU monograph Range and Richness of Vascular Land Plants: The Role of Variable Light, former AGU president Peter S. Eagleson seeks a cause for Rapoport’s rule. Using a tightly focused analysis, Eagleson delves into the complex interactions that govern ecosystems to propose the primary importance to range and richness of one key variable, the locally incident shortwave radiation. In this interview, Eos talks with Eagleson.”
The key finding of the importance of short wave radiation with respect to the range, richness and latitude of vascular land plants (which make up about 98% of all land plants) is summarized in this interview. Excerpts include the answers from Eagleston
“One of the troubles that I have with more complicated models is the extent to which they are made to fit the data. In hydrology, for example, there is a need to go from point behavior to that of the full-scale watershed. With the computer, there is the possibility of aggregating millions and millions of little pieces into a whole. But with those millions and millions of little pieces go many more millions of parameters, and to me it seems like it becomes an exercise simply to find the best fit, where you’re not sure if you’ve really represented the physics in a meaningful way. At least for the data set that you have you can show that the model represents what happened, but I’m not sure you can prove that it’s going to do what happens tomorrow in many cases.”
“…..each species has its own maximally productive shortwave flux,[thus] selection of local species should be, approximately, a function solely of the shortwave flux. Because there are good statistics for the shortwave flux, I can say I have good statistics for the species. I don’t know what the species are, and I can’t name them. I can’t tell you whether that’s a maple or a bush of some kind, but I can tell you the average and the variance of the local species distribution. So that allows me to make the transfer from what I have, the local shortwave flux statistics, to what I need, the statistics of local species. With this, I can get an idea of the range.”
“I remember reading that the variance in shortwave flux will likely be the first thing to change as our atmosphere warms. We won’t see that much of a change in the average value of the shortwave flux, but we will see more of a change in frequencies of cloudiness and precipitation. These changes will have some effect on species range and richness, but all I can really say is that according to my model the local range of species will increase and local richness of species will decrease if the variance of the shortwave flux
increases. That’s assuming that the average shortwave flux stays roughly the same at a given latitude.”
This interview indicates that skillful prediction of local short wave fluxes is a necessary requirement to accurately predict how the distribution of plants could change in the future (it is not a sufficient condition since we also need to predict changes in landscape by human activities, nitrogen deposition, and increased biogeochemical effects from added CO2, as well as alteration as exotic plant species, insect infestations, etc alter the natural biodiversity. Surface air temperature, apparently, is not a good indicator, except to the extent it is correlated with the short wave radiation.