Critical climate periods in ecosystems

Maps of Konza showing the slopes of the relationships between NDVI and precipitation from DOY 105–214, Also shown are the univariate distributions of these slopes. Colors of slopes on maps correspond to colors in histograms.

Last July, I added an entry on the role of the timing of heat waves and drought for ANPP at Konza. This was recently published in PNAS. In review, the work takes a look at how the timing of interannual variation in temperature and precipitation affect grass production.

As much as the specific results and the proviso that the timing of climate variability can matter as much its magnitude, the technique should become important in examining other long-term records. Any long-term record that is repeated at roughly the same time every year can be used. We've applied it to ANPP, streamflow, bison weight gain, carbon flux, and flowering so far.

I think another area where the technique has potential is with remote sensing data. In the paper, Andrew Elmore applied the technique to NDVI data from MODIS and Adam Skibbe overlaid data on elevation and woody cover. The unique results is we could now look at the spatial pattern of sensitivity to the climate variability. We saw that pixels with woody species and low-elevation sites showed low sensitivity to variation in mid-season precipitation. Essentially vegetation and sites that could tap into deep water had lower sensitivity to precipitation variability.

In this particular case we didn't test whether different areas showed different timings of sensitivity, but with longer remote sensing records spread over a larger spatial area, it certainly could be tried. We could ask how climate sensitivity varies with latitude or aspect or between major vegetation types.

I think the critical climate period approach has its limitations, but will generate a number of insights in the near future. As we apply the technique to different aspects of ecosystem functioning we'll get a better understanding of the multiple connections between climate and organisms.

www.pnas.org/cgi/doi/10.1073/pnas.1118438109
http://www.nsf.gov/news/news_summ.jsp?cntn_id=123134&org=NSF&from=news