I would like to create a buffer around point. This is simple with ArcMap using the buffer tool. But is it possible to create the buffer considering also the true surface area of the landscape (consider also the slope distance using digital terrain model). In this case the buffer on slope will not be the circle but irregular ellipse. Are there any solution in ESRI or any packages in R?
Check out the Path Distance tool in Spatial Analyst. If I understand you correctly, you are essentially wanting a 3d-distance surface for which you can create a distance buffer. Using the Path Distance tool, use points as source locations, do not input a cost raster, and only input your DEM as the surface raster. The values in the surface raster are used to calculate the actual surface distance that will be covered when passing between cells. Extract values below a threshold that represents your 3d-distance buffer and create a polygon from this. I don't believe all situations will give you an ellipse unless your DEM slopes in a single direction within you buffer.