It would seem like the air layer process would put a strain on the mother but the opposite occurred here.   This was my first air layer and I changed my mind and removed the cup a few days ago to let the roots dry up.  The mother plant is positively become my healthiest potted sapling.  It became robust soon after the air-layer rooted.  I cant figure out why, because the rooting cup contained only sphagnum moss and a little of the same potting mix the mother is in.   I used no fertilizer.    Has anyone else noticed this vigor with air layers?   

Wounding can appear to invigorate plants since we only see what happens above the ground, but from the mother plant's perspective it is still an overall energy loss.  When they are mending/rooting wounds they have much less activity in the calvin cycle which is where most of the internal maintenance and root hardening happens.

My personal experience has been the same as what you're experiencing, that there's more growth going on post wound, and that is probably even fine in a relatively safe controlled environment.  But really we're just seeing that more energy is being put into new development than overall organism development.  In an environment where survival is marginal, that is to say there's a bunch of similar organisms undergoing x, y, and z conditions and only so many will survive, then fewer would probably survive with that additional stress and overall inefficiency.

But human intervention through gardening is like cheating.  

I hope that all made sense, it's been a little bit of a festive night.  ;-)  

Thanks Greg,   a little deep but I think I get the drift of it.   I'd heard about old timers would hit the trunk of a non bearing fruit tree with a baton and it would shock it into fruiting.  I didnt actually wound it but by attaching the rooting medium , did it wound itself by making roots?  .......  festive night, you say?    party on!