I have been told that topping or heavily pruning Staghorn Sumac will cause the plants to suffer sever reduction in their root mass. Does anyone know if this is a fact or just a supposition?
These usually grow in clumps via suckering. Do you have only one individual? Usually, you get continuously emerging new stems and they grow more new individuals than those that die. They are ~short lived~ individuals, but the clump carries on forever. Not only won't heavy pruning of an individual kill the roots, but they will respond with, "I'll call your bet and raise you the pot limit..." There is a rule of thumb: to affect the growth of a woody plant the least, prune in autumn or winter. To reduce the size/growth the most, wait until the new growth is complete, and then prune. There is some amount of energy stored in the roots that will support some size of top growth. Heavy pruning will be responded to by extra growth, like waterspouts in some kinds of trees, suckering in others. Pruning in autumn doesn't affect the amount of growth energy stored in the roots for next season and that growth will just be distributed to whatever wood you leave. If you let the roots grow a whole new spring canopy and then cut lots of that, you can steal that energy and limit how much new growth will be available to replace what you stole. It will respond. You may get suckers coming up all over the place: lawn, driveway cracks, 5 feet away, 10 feet away, more... The most efficient way to steal energy without waking the dragon is to defoliate the whole tree after the foliage is mature, ~June something. Cut the leaves off ~1" or so away from the trunk. Not flush with the trunk. Your neighbors will think you're crazy, --or stupid. It can respond by re-growing a new top on that existing architecture from secondary buds normally dormant, but it won't be able to store as much growth for next year as normal. The following spring let it completely fill out the canopy and trim ~1/3 of your goal. Do the next 2/3 in the next two years and bingo, you will have a smaller tree. You'll have to deal with some suckers, the exact number is only guessable. Remember to deal with suckers and growth by letting them leaf-out and then chop them off below the surface. Don't let them live long enough to feed the roots. This advice comes with an Oklahoma Guarantee: 10 minutes or 10 miles, whichever occurs first.
