I have obtained estimates of N based on a density surface model with percent forest as a covariate. Therefore, I used region.N to estimate N rather than multiply the density by the area. In fact, I had to estimate density by dividing N by the area because the estimate the model gave me was for the base value of the forest covariate. All that being said, the Expected N and realized N's were pretty close and I used the Realized N. However, I also wanted to estimate N within a small subset of the study area which had been previously estimated by another researcher. In that case, Expected and Realized N's were very different (Realized N much larger). When I incorporated the density surface into a GIS and summed the density values for each pixel within that small area, the total was very close to the Expected N. So why the difference? What estimate should I use? Thanks!
Joe