Trees were cut down for fuel, to make things (bridges or bunkers) and to provide a clear field of fire for guns. The resulting stumps would make life difficult for tanks.
You can make them easily from cut down twigs or short lengths of pipe cleaner twisted together and soaked in dark brown paint before gluing to a small card base. The problem is that the wire inside the pipe cleaner makes it very stiff once painted and if trodden on it would likely puncture the skin.
I wanted quite a few stumps, and I wanted them to be safe to stand on as they were for a child playing toy soldiers, so I did not want to use cut down twigs or pipe cleaner.
The core of the tree is string, a length of which was looped over a door handle and twisted by passing left over right repeatedly (so it doesn't unravel). When twisted give it a coating of cheap paper gum - this contracts as it dries and the result is less obviously twisted. Hang the resulting 'stick' up to dry.
Once dry take the 'stick' and wrap it with a strip of a single ply of kitchen roll, use a strip wide enough to go round the string a couple of times, about an inch wide worked for me. Apply a little PVA glue and rub this over the paper with wet fingers, pressing it into the string. Hang this up to dry.
Once it has dries mix up some 'bark brown' paint (I used some domestic red emulsion mixed with acrylic black, yellow and green as that is what was in front of me). Coat the stick with this and again hang it up to dry.
When thoroughly dry cut the stick with scissors into lengths between 6 and 10mm long. The paint will not have affected the string because of the Gum, so you get a brown 'bark' with a yellowish white core of the 'tree'.
Cut a length of card, I used cornflake packet card, and glue the lengths onto this with a blob of Uhu (this dries a bit faster than PVA and doesn't shrink). Set aside to dry.
When dry cut the strip up and roughly trim each base to a more circular shape. Paint the bases with a dark green paint, wiping this along the edges so they will not show up as light when finished. Set aside to dry.
For thicker stumps use more string, had I thought about it I would have done one set with two lengths, one with three and one with four to introduce more variation. The two-string size is just thick enough to worry a tank driver I think.
When dry you can add some scenic dressing, Dill weed (from the kitchen) added round the stump looks good as chipping's, teased out pan scourer washed with light green paint (after teasing) can be added for 'rough grass' and small clumps of cheap paint brush bristles can be placed into blobs of PVA to make long grasses.
I made him about twenty stumps, enough to suggest some serious logging, the actual time spent was probably no more than fifteen minutes but spread over a couple of days as I waited for things to dry.