MATERIALS AND METHODS

Study area: The study was conducted in March 2007 at the Chenini community. The study area is located in the Governorate of Tataouine (Southern Tunisia) and is characterized by an arid Mediterranean bioclimate with a moderate winter. Rainfall is low and sporadic; the mean annual is estimated to be around 100 mm. Temperatures are generally cold in winter and hot in summer with a mean annual of about 20.1 °C. The water balance is greatly affected by the low dense soil cover and exposition to winds. Potential evapo-transpiration is estimated around 1699 mm year^-1 in average (Tataouine meteorological station, 1949-2000 period). Rangelands are dominant the land use and cover about 40,000 ha (53% of the Chenini community area). Most of them (24,000 ha) are communal and subjected to continuous heavy grazing.

As suggested by the community in the framework of the realisation of the CDP, the IFAD project (PRODESUD) put in rest the communal rangeland of Guelb El Fguira which covers 4000 ha for a period going from 2 to 3 years depending on the state of improvement of its productivity.

The experiment was conducted in spring (month of March) 2007, the second year protection, both inside the protected area (P) and in its surrounding area (G) which is subjected to continuous extensive grazing. Plant cover, annual and perennial species covers, species richness as well as rangeland production were the main assessed indicators. The rainfall quantity was very low during the first year (34 mm) and reached 68 mm in the second year.

Measurements and data analysis: The following observations and measures were carried out:

All data obtained were subjected to several statistical analyses (analysis of variance and Duncan test) by using the SPSS (11.5) software (SPSS, 2002). The management mode (P or G) was the independent variable while total plant cover, species cover, biomass production and range value were the dependent variables.

RESULTS

The analysis of variance (R² = 0.93) of total plant cover produced highly significant differences (p < 0.001) between the two applied management modes. Total plant cover was higher in P than in G (Table 1). The statistical analysis of the perennial species cover (Adjusted R² = 0.68) produced significant differences for management mode (p < 0.001) but the annual species cover seems to be independent on protection (p < 0.0722).

The results of the species richness of both studied sites show that P presented the highest values of total plant species, of perennials and of perennial grasses (Table 2). The application of the rest technique, coupled with a relatively favourable climatic conditions, has permitted a good regeneration and establishment of seedlings mainly of some perennial grasses such as Stipa lagascae, Penniseteum dichotomum and Stipagrostis plumosa, characterized by their high range value. These species can be considered as protection increasers and heavy grazing decreasers. The number of annual species is comparable for both sites. It seems that these species are more dependent on rainfall availability than on the management mode.

The analysis of variance (R² = 0.96) of means of biomass production and range value produced highly significant differences (p < 0.0003) between the two applied management modes. This emphasizes the beneficial effect

Table 1:	Variation of Total Plant (TPC), Annual (AC) and Perennial (PC) Covers (%) in relation to management mode of the communal rangeland of Chenini, Southern Tunisia

Table 2:	Variation of species richness in relation to management mode of the communal rangeland of Chenini, Southern Tunisia

Table 3:	Impact of two years rangeland rest (P) on biomass and range value as compared to those of the grazed site (G) of the Chenini communal rangeland

of the application of the rangeland rest technique on these pastoral indicators. Table 3 shows that the rest technique induced an increase of about 8 times the aerial biomass production and about 3 times the range value and the forage availability.

DISCUSSION

The impact of the rest technique on the total plant cover was highly significant. These results corroborate those achieved in other ecologically comparable zones (Gallacher and Hill, 2006; Ouled Belgacem et al., 2006b) which indicate progressive increase of the Total Plant Cover (TPC) in the protected area as compared to the overgrazed one, characterized by the bare soil extension. In fact, protection permits soil fixation and the improvement of its structure as due to the abundance of litter resulting from trapping plant dead parts (Ould Sidi Mohamed et al., 2002). The significant increase of Perennial Cover (PC) in the protected rangeland may be attributed to the development of the vigour of the adult individuals as well as by the good establishment of new seedlings (Ouled Belgacem et al., 2006b; Tarhouni et al., 2007b). The effect of protection on Annual Cover (AC) is not significant since the abundance of annuals is more dependent on rainfall availability (Westbrooke et al., 2005).

The species richness, which simultaneously affects the structure and the functioning of plant communities, is influenced by the rainfall regime and varies from season to other. It is applied as a measurement of biodiversity for the qualitative characterization of the ecosystem since any increase of the species richness may induce the restoration process of the degraded ecosystem (Bonet, 2004; Zhang et al., 2005). In arid area, rainfall the main factor affecting the temporal plant distribution. Grazing pressure does not affect the annual species richness variability (Sheuyange et al., 2005).

During humid years, a high germination of annuals is observed in all arid areas of North Africa and West Asia however perennial ligneous species seem to have high adaptation towards aridity but to be more affected by disturbances. The richness of therophytes and their abundance often qualified therophytisation indicate their good adaptation to climatic stress. The important and chronic disturbance leads to the decrease of the flora richness and the replacement of perennials by annuals.

Results show that perennial grasses are protection increasers and grazing decreasers (Noy-Meir et al., 1989; De-Val and Crawley, 2005) since they are largely more abundant in the protected area. These results are therefore consistent with the results of Floret (1981) who found that restoration was achieved by a constant increase in the density and cover of existing species. Chamaephytes, the most abundant perennial species, can resist intense or frequent disturbances by growing less tall and resprouting and tend to be less palatable than most grasses (Jauffret and Lavorel, 2003). This response is negative because it reflects the concurrent degradation of vegetation cover and soil. The rarity of grasses in the grazed area confirms their weak resistance to continuous grazing. The rarefaction of grasses constitutes, according to several researchers Van de Koppel and Rietkerk (2000), Hendrickson and Berdahl (2002) and Ouled Belgacem et al. (2006b), a good indicator of the state of deterioration of the plant cover.

Results show also a significant increase of the biomass production as well as the range value due to the application of 2 year rest technique. The vigorous growth of existing species and the regeneration of degraded or even disappeared very palatable species are the main reason of the increase of these indicators and the improvement of the productivity.

According to Table 3, the short term protection permitted an increase of about 88 Forge Units (FU) per hectare, which means that this technique induces an added production of about 352000 in the whole protected rangeland (4000 ha). This value is equivalent to a production of about 352 tones of barley. Consequently, with the increase of the prices of feeding resources, mainly barley (which is more preferred by local population as supplementary food for their animals), it seems that communal rangeland rest is an important technical option for the improvement of the productivity. Moreover, such technique may be suggested as a tool for drought mitigation and animal feeding resources cost alleviation in addition to its role in the conservation of biodiversity and natural resources.

ACKNOWLEDGMENTS

The study was conducted in the framework of the Mashreq-Maghreb project, authors are grateful to ICARDA, IFAD and AFSED for technical and financial support.