Chickens and desertification

So I have around 25 chickens running around under pinyon/junipers. I have another 30 behind electronet fencing and they are rotated around the property. My wife's original plan was to keep the 25 chickens locked up in a small run. However, she lets them out every day so they free range over a 2 acre area. Sooo my question is, will these 25 chickens kill off my grass and desertify the area? Has anyone observed anything like that occuring? And, should we be locking up the chickens who are not being rotated around the property? What about seasons - can they free range in winter/summer and then be confined in spring?

Now for the stats on my land. The rainfall is 16 inches a year mostly arriving in July and August. The biome is pinyon/juniper/sagebrush and the major grass species is western grama.

Hi Skyler,
I suspect you will not have too much problem with 25 chickens on 2 acres as far as the ground cover is concerned. However, by allowing them free range, you will not be able to control this. If they have a favorite spot... they could easily turn it into dirt. 2 acres is plenty if they use all of it, but I imagine they will have their favorite spots which could be overgrazed. I personally think moving them around purposefully is the best balance of good living, protection for the chickens, and protection for the ground.

My first thought is to try it out, and if its a problem, then pen them up... but with chickens who have been raised to be in a pen, they seem to handle it ok, but chickens who have been free range, and then put in a pen, don't seem to handle it well.

Also, a warning that having chickens free range is a BIG calling card to all the chicken eating animals in the area.