There is an assumption in the question, that there is still viable seeds of the local native plants in the soil, from which this restoration will take place? In California 99.99% of our native grassland wildflowers and grasses were spatially extinct about 150 years ago from exotic animal grazing.

Unless those original native seeds have a century-long longevity in the soil, we are going to have to spend a ton of money to reseed the place, to get it to recover like what I am doing at http://www.ecoseeds.com/arastradero.html

We have data on low-productivity grassland in Eastern Austria from several exclusion experiments, suggesting that it takes about 20-30 yrs till grazing-sensitive plant species (eg Phragmites australis) are dominating.

It depends on a myriad of factors: size of excluded area, degree of disturbance caused by grazers, tenacity of invasive species, regional climate change, etc. In the southwestern US there are a number of areas where grazers have been removed or excluded for many decades (some up to 100 yrs) and there is virtually no return to the pre-domestic livestock grazing conditions.

There are quite some studies down on the impacts of elephants (CERU at the University of Pretoria) but also on smaller herbivores at the University of KwaZulu Natal - might be worth to have a look into these studies

A lot of state and transition models will help you figure this out. They can often tell you how long and to what affect grazing will have on the vegetation. Australia has been using them for a while now, and the United States USGS is now actively creating them based on their soil maps. You might want to see if anyone has developed one for the area you are interested in. If you cant find one in your area like Jeffrey Kopateck said there are a myriad of factors. I think the most important factors are:

Figure out what type of grazers

The animals per unit area

How often they have been grazed there

The vegetation, how well it bounces back after being grazed.

It may never recover. Depends on the level of disturbance, what kind of grazers are they? native or introduced?, how long have they impacted on the system. Has the system crossed a threshold of disturbance to which there are barriers to returning to the pre disturbance states? State and transition models can be useful but need to accurately describe states and the triggers for transition. Need to realy understand your system See Richard Hobbs re novel ecosystems - may have some useful concepts.

There are so many variables but Prach and Hobbs highlight productivity and stress (disturbance level) as key factors in determining if spontaneous succession will be successful - this is a general paper but it is relevant to grazing disturbance. Maybe this will help guide you to further work...

Prach, K. and R. J. Hobbs (2008). "Spontaneous succession versus technical reclamation in the restoration of disturbed sites." Restoration Ecology 16: 363-366

It will also depend on if the rangeland is a grassland, a seeding woodland or a suckering woodland because recovery of physical structure in woodlands is very important and can take longer than recovery of plant diversity, especially in seeding woodlands.

Also check out this paper about reaching recovery targets:

Rey-Benayas, J. M., A. C. Newton, et al. (2009). "Enhancement of biodiversity and ecosystem services by ecological restoration: a meta-analysis." Science 325: 1121-1124.

This is a complex topic with recovery potential and time being specific to each vegetation type/biome/disturbance history scenario.

I agree with must of the answers here, but I think most of the systems won't recover unless exclusion is follow with restoration measures. As Garry Rogers said, the conditions may have changed over time (even climatic), so sometimes it might be imposible to return to a pre-grazed state.

Missing is fire. Grasses will survive - more than - burning, woody plants will not.

It will be recover if you calculate the allowable grazing yield specially in case of fodder shrubs. While in case of annual native vegetation It will be recover if it grazed after seed maturity and fall.

Also, our results in Jordan showed that range protection from 3 - 5 years will recover deteriorated rangeland but it is dependent in soil characters and rainfall amount and distribution.

Ecosystems are resilient and a plant community can rebound; it does it all the time and it is adapted to an area for a reason. But evolution and adaptation are unidirectional. It would never be the same. If change is of large magnitude, some community components might be favored that hinder the recovery of the "original" community. If grazers are removed, assuming that grazers caused unacceptable change, the ecosystem would tend to recover. But, the recovery would be affected by the many other factors that influence a community: rainfall, temperature, presence of invasive species, among others.

This year I was estimated productivity and stocking rate for new site located within the mounted range had been protected for 2 years only. Results showed that the % of native vegetation cover was increased from 2.6 % in the open access range to 14.7 % in the protected site. Also, stocking rate was 0.03 and 0.6 head / ha / 90 day for the open access and protected site respectively. Thus, protection is recommended for natural range restoration. But how long it will be? It is dependent in many factors as I mention before and as Ricardo Mata-Gonzales said.

How long the protection period should be really depends on your objectives. You have been observing a positive response to protection, the next decision is where do you want to get? I would set a level of recovery that is acceptable for your operation and that, given adequate levels of use, provides self recovery as much as possible. This is really a question that should be locally answered.

I would like to share my experience. My colleagues and I once worked with smallholder farmers in semi-arid areas of my country (Zimbabwe) where there had been serious degradation of the range land. The season was a good one. The affected areas were restored; biomass production rose, species composition and cover also improved. We did this after having made a survey to find out what vegetation species were suitable for the affected areas. We then went ahead and broadcast mixed seed of the same species towards the onset of the first rains. This worked successfully and our farmers were very impressed.

I think a lot depends on where you are in the world - as the role of other factors varies hugely between temperate and tropical areas. Issues such as the nutrient levels and soil structure will have been influenced by long term grazing such that it is unclear if ranges will automatically revert to their before grazing state - and a lot will depend on seed banks and distance to sources for seeds.

It depends on the intensity of grazing that the rangeland was subjected to. If the rangeland was subjected to heavy grazing, such that the plant reserves were depleted, it will not recover, even if thee e envoronmental conditions can be fine, invasion by secondary species will take place. If the grazing intensity is moderate or light, the rangeland will recover and be baxk to its previous state, that is subjective to the weather conditions though.

Yes that can happen. But...

This is entirely dependent on two things: site conditions and species reservoir. If the species that made up the pre-grazing state are still inside their propagation range. If the tree or bush species were removed from a large area, it might take a very long time. Secondly: Taking away the pre-grazing vegetation changed the environment the recent plants live in. It is not guaranteed, that this process is reversible.

How long this process takes depends on the availability of seeds of the original plants, their success in establishing species and the area they have got to cover. I don't know what the species composition of the pre-grazed state was, but species like the european common birch (betula pendula) disperse their seeds maybe a hundred meters. But only few of them will actually reach that outer perimeter. And even if they survive and thrive, it takes another 10-20 years before they are mature and produce seeds themselves. I hope that answers your question about the time that it takes.

You might get results faster and safer if you help the natural processes by introducing the required species, i.e. renaturation.

Under the impact of global (or local environmental) change and no human interference, you might see another ecosystem evolve. I am pretty sure, that you won't see the grazed areas stay grazed areas. Bushes and trees will take their place wherever this is possible, several species are specialized in repopulating disturbed areas.

There are several agroforestry systems that deal with degredation and try to avoid it. Mostly they involve rows of trees or bushes some 15-20m apart. That reduces the grazing area and productivity (because of light competition) but prevents extreme droughts and wind erosion to a certain degree.

There is an assumption in the question, that there is still viable seeds of the local native plants in the soil, from which this restoration will take place? In California 99.99% of our native grassland wildflowers and grasses were spatially extinct about 150 years ago from exotic animal grazing.

Unless those original native seeds have a century-long longevity in the soil, we are going to have to spend a ton of money to reseed the place, to get it to recover like what I am doing at http://www.ecoseeds.com/arastradero.html

I wanted to add a note about arid grasslands and soil nutrient thresholds for the survival of the native plant seedlings, which is a very often overlooked consequence of domesticated stock grazing.

In California we tried to replant local native grasses with close to zero success, until we discovered the problem that you can see at http://www.ecoseeds.com/good.example.html. The soil nutrients had been carried away in the grazing animal bodies, so after about 100 years, the soil nutrient levels dropped below the thresholds needed for native seedling survival.

Once we added the right amount of fertilizer, then everything sprouted and grew fine. But without that fertilizer, the land would probably take thousands to tens of thousands of years to rebuild the soil nutrients past the thresholds. And we also discovered with that project that each grassland species has its own seedling-survival nutrient threshold, which was very interesting.

Anyone working on restoring degraded grasslands worldwide, should check and see what the native seedling survival nutrient thresholds are for each species, and then check the degraded area and see if lack of fertility is a huge, massive, major problem that has to be corrected first.

A whole new branch of rangeland science should be established to study the removal of soil nutrient and soil organic matter by domesticated animals, and I believe future studies of arid grasslands of the world would produce a huge surprise to everyone, on how many areas will need fertilization to have adequate soil fertility for native seedling survival.

You can do some very simple ex-situ experiments like I did, by adding soil from the top 8 cm below the thatch layer, and put the soil in a box of the same depth, dimensions of the box do not need to be very big, 30 cm x 60 cm is what I use. Then sow locally collected native seeds and keep them constantly moist.

At the same time, you test those same native seeds on moist cotton, to check for percentage germination and days to germinate. If you do not get good results in your soil box like in the first box at http://www.ecoseeds.com/good.example.html then set up several boxes and add different fertilizers at different rates, until you get seedling percentage and survival close to what your cotton tests produced, and like what you see in the second box on the web page.

I have a simple protocol, if you can afford to send soil samples to a lab, to get the soil nutrient threshold numbers for each species in PPM of N-P-K and determine the thresholds for the pH and the threshold for the percentage of organic matter.

Anyone who would like to help get this new branch of rangeland science started, I would be interested in being involved in some studies to get some soil data into circulation at least through Researchgate and perhaps into some journal articles, so that the grassland managers around the world can add to their restoration and management plans, this aspect of minimal nutrient thresholds required by the native grassland seedlings in order to survive,

There should be a balance between grazers and the capacity of the land . This depends on many factors and differs from one situation to the other . In general controlling the number of grazers is better than removing them all together . Animals provide the fertilizer necessary for the land .

I'm in North Dakota, in the Great Plains of the USA. Here there is no pre-grazed state, the plant community evolved with grazing. We also have a population of cool season invasive grasses, primarily Poa pratensis. So if grazers are removed the site because dominated by Poa pratensis and production is reduced.

To reply to Saad Khorfan, there is a one-way soil-mineral mining process that goes on with domesticated grazing animals, that can be clearly seen in phosphorus, which gets carried away in the animal bones. Once the animals are taken off the land and consumed, unless their bones are dried and ground up and put back on the grazing land, your soil phosphorus gets mined, and you can cause the nutrients to drop below the native seedling survival thresholds.