My Dear Mounir Louhaichi; Here are few links attached please go through them. They may help you. regards and Thanks

http://www.sciencedirect.com/science/article/pii/S0140196305003198

http://link.springer.com/article/10.1007/s00267-003-9110-9

http://www.sciencedirect.com/science/article/pii/S0269749101002159

Dear Mounir,

I have been researching on this topic. Here I have little space to give you details and references. I will be happy to provide you with information and discuss with you about this topic.

Regards, 

Dr. Alfredo J. Escribano.

Carbon sequestration by Coastal flora....book by TERI press...Mitra and Zaman 2014

Carbone sequestration and production are part of a dynamic system. Above and below ground net primary production (NPP) is a good indicator for C production potential. However, to estimate this for rangelands over large areas, generally a modelling/extrapolation approach is necessary. In Australia with its approx. 70% rangelands, extrapolation relies on few sampling location and limited time frames. There are models estimating NPP for the whole continent and yes the results have a high range of uncertainty. See for example the review from Roxburgh SH, Barrett JD, Berry SL, Carter JO, Davies ID, Gifford RM et al., A critical review of model estimates of net primary productivity for the Australian continent. Funct Plant Biol 31:1043–1059 (2004).

One if the research issues in Australia for modelling soil C more accurately is the amount of litter that is incorporated into the soil. If you want broad regional numbers, modelling can help, but beware of the differences in model assumptions, structure and associated uncertainties. The message is that if you want detailed estimates, you first need to do field research at location because regional variation will swart extrapolation to the broad scale.

Dear Mounir,

Can you read a text written in Spanish? If so, I can send you an extract of my doctoral thesis, where I carried out an in-depth review in this topic. I researched just that: rangelands and/or agroforestry systems in semi-arid areas. My case was the 'dehesa', the oldest and most used agroforestry systems and rangeland of Europe. It is located in SW Spain.

Regards,

Dr. Alfredo J. Escribano.

You may want to make your question more precise.  Are you interested in the instantaneous or average rate of carbon removal from the atmosphere ?  In that case you want to consult the atmospheric flux literature and look at the supporting data that have been collected in a number of flux measurement field experiments around the globe.  The biogeochemical dynamics data center at Oak Ridge is a good starting point (http://daac.ornl.gov/).  On the other hand, if you are interested in the long term storage of carbon, which only occurs in soils in these systems, you need to consult the literature and experimental data on soil composition and processes in (semi-)arid rangelands.  Those aspects are very dependent on local conditions and climate, as well as grazing use patterns, and so are not easily generalized.  Long-term studies of specific locations in your region of interest with active grazing would be your best source.

Thanks Donald for bringing this clarification. In fact I am more interested in the long term storage of carbon in the soil which as you rightly said variable from site to site.

Mounir - try to find the work from 

Emilio Laca, Doug Johnson, Tagir Gilmanov,  Nicanor Saliendra etc ....Research on CO2 Flux in the steppe of Karnap - Tym - Uzbekistan and in Kazk + 12 sites in USA 

Doug Johnson USDA-ARS, Logan UT  -may be retired 

Gus