Our Forestry Officers and GIS officer recently tested a high quality GPS for this purpose. However although claiming sub-metre accuracy, the results were not very good, with the same trees being shown in more than one position after several readings. That test was also in an open area. Within a woodland there might be even more difficulty. If you do test a system, make sure you can download results to GIS so you can check accuracy. We have decided not to pursue this for the time being and are now thinking of looking at laser range finders to help with traditional surveying.
