I am using LAI values to assess vegetation growth over large areas. I want to be able to identify areas that are doing well and areas that are decreasing based on the changes in pixel values. Ideally I would like to generate another raster file that shows a standard deviation value over the 50 different raster layers I have, or something along those lines.
You should be looking at the GRASS module r.series
Let's say you have LAI rasters in GRASS named lai_201501, lai_201412, lai_201411, etc... then at the GRASS command prompt you can run:
lai_list = `g.list type=rast pat="lai_*"` r.series input=$lai_list output=lai_stddev method=stddev