Article

Effect Of Protection On Plant Community Dynamics In The Mediterranean Arid Zone Of Southern Tunisia: A Case Study From Bou Hedma National Park

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Abstract

Ecosystems protected from heavy grazing impacts, such as national parks and refuges, are generally considered to sustain higher plant species diversity and better ecosystem composition and structure compared to heavily grazed areas. To evaluate the impact of livestock grazing, we sampled vegetation characteristics from two areas having different grazing intensity levels. The first site has high protection from grazing and is located inside the Bou Hedma National Park in Southern Tunisia. The second site has a low protection from grazing and is situated within an open area located immediately outside the park boundary where human populations and their livestock have unrestricted access to ecosystem resources. Total plant cover, density, perennial species cover and their contribution were compared between the two grazing level sites. Results show that considerable positive effects occur in the areas protected from grazing. As compared to the overgrazed (open) sites. Several species known for their high palatability, such as Cenchrus ciliaris L., Salvia aegyptiaca L., Echiochilon fruticosum Desf. and Helianthemum sessiliflorum Desf., are more abundant inside the park than outside. These results are very important for managers to apply this technique as a tool for increasing the resilience of arid ecosystems, qualified very vulnerable to climate change. Copyright © 2011 John Wiley & Sons, Ltd.

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... This unprecedented work stands out with a concise ecological understanding, driving to a better land resources management. Ecological attributes related to the vegetation cover structure, such as perennial species density, annual species density, species diversity and vegetation cover are important indicators to footprint environmental disturbances specifically industrial pollution (Belgacem et al., 2011). These attributes may describe the vegetation state and allow a better understanding of floristic composition, evidencing the emergence of both sensitive and tolerant species under pollutant impact and responding to various environmental factors (Fakhry and Migahid, 2011;Jauffret and Lavorel, 2003). ...
... where n is the number of hits in all plant species and N is the total number of hits multiplied by 100 (Belgacem et al., 2011). The relative abundance (RA) was assessed. ...
... ( 2) where ni is the number of hits of species i (Belgacem et al., 2011). It should be noted that the linear analysis allowed the identification of key species and their respective frequencies. ...
Article
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Industrial pollution remains a driving force to ecosystem alteration. Pollutants are released in the atmosphere interacting in turn with other components of earth system such as plant species. Despite the long-term exposition of vegetation cover to pollution is drastically devastating, less is known about the contribution of ecological indicators for its monitoring. The aims of this study are (i) to introduce the ecological indicators in assessing the cement dust impact on plant species and its biomonitoring and (ii) to screen new indicator species for phytoremediation studies. Floristic surveys were conducted in the cement plant closeness following quadrat method. Vegetation indicators such as total plant cover, perennial and annual species densities and diversity were assessed. Bioindicator species were identified using the bioaccumulation factor (BF) and translocation factor (TF). A decrease of perennial species richness and a decline of total vegetation cover by 7 times as well as a diversity decrease ranging from 2.99 to 2.31 were found pertinent indicators of land degradation in the industrial area. Annual species densities were significantly affected by cement pollution. Species like Lygeum spartum, Atractylis serratuloides and Gymnocarpos decander arise as indicators of heavy metals pollution. Pollution in the cement plant vicinity excluded sensitive species like Helianthemum kahiricum, Stipa tenassissima, Plantago coronopus. This study allowed the identification of indicator species of potential use in phytoremediation applications and emphasized the possibility of relaying on the vegetation indicators to assess the impact of cement pollution.
... 1 Under such scenarios, and especially so in resource challenged ecosystems, much of the biodiversity and production levels are unlikely to be utilized sustainably without effective management. 2 Because biomass production is usually low in resource-challenged ecosystems, the rate of degradation, and eventual desertification, is accelerating because of overutilization. 1 In such ecosystems, effective management is needed for sustainable plant growth and survival, as rainfall availability is unreliable, uncontrolled grazing is high, and soil nutrient status is poor. 2,3 Therefore, strategies that promote sustainable management of biodiversity are needed, for instance, by establishing and maintaining protected areas. 2 In arid and semiarid areas, animal production is influenced by the quality and quantity of available feed resources. ...
... 1 Under such scenarios, and especially so in resource challenged ecosystems, much of the biodiversity and production levels are unlikely to be utilized sustainably without effective management. 2 Because biomass production is usually low in resource-challenged ecosystems, the rate of degradation, and eventual desertification, is accelerating because of overutilization. 1 In such ecosystems, effective management is needed for sustainable plant growth and survival, as rainfall availability is unreliable, uncontrolled grazing is high, and soil nutrient status is poor. 2,3 Therefore, strategies that promote sustainable management of biodiversity are needed, for instance, by establishing and maintaining protected areas. 2 In arid and semiarid areas, animal production is influenced by the quality and quantity of available feed resources. 4 In these areas, overgrazing has reduced the nutritional and productivity levels of many rangelands by up to 25%. 3 Plants grazed by animals, or used for supplementary forage in rangelands, are often generally low in nitrogen, digestible energy, and mineral content. ...
... 2,3 Therefore, strategies that promote sustainable management of biodiversity are needed, for instance, by establishing and maintaining protected areas. 2 In arid and semiarid areas, animal production is influenced by the quality and quantity of available feed resources. 4 In these areas, overgrazing has reduced the nutritional and productivity levels of many rangelands by up to 25%. 3 Plants grazed by animals, or used for supplementary forage in rangelands, are often generally low in nitrogen, digestible energy, and mineral content. ...
Article
• The information from this study is important for helping promote a more sustainable use of resources, such as grasses and shrubs, and in increasing an understanding of the utilization dynamics and their impact on potential recovery in the study area and beyond.• This study contributes insight toward ensuring the achievement of conservation measures outside protected areas to restore biodiversity in degraded habitats, through comparing the plant characteristics between a protected and unprotected site.• This study substantiates other findings, which suggest that using protected areas is one of several strategies that need to be adopted for recovering lost biodiversity and ensure their effective management.• This study improves our understanding of how shifts in vegetation characteristics resulting from land use change and management can modify the recovery of, in the case of Cholistan, previously grazed vegetation.
... 1 Under such scenarios, and especially so in resource challenged ecosystems, much of the biodiversity and production levels are unlikely to be utilized sustainably without effective management. 2 Because biomass production is usually low in resource-challenged ecosystems, the rate of degradation, and eventual desertification, is accelerating because of overutilization. 1 In such ecosystems, effective management is needed for sustainable plant growth and survival, as rainfall availability is unreliable, uncontrolled grazing is high, and soil nutrient status is poor. 2,3 Therefore, strategies that promote sustainable management of biodiversity are needed, for instance, by establishing and maintaining protected areas. 2 In arid and semiarid areas, animal production is influenced by the quality and quantity of available feed resources. ...
... 1 Under such scenarios, and especially so in resource challenged ecosystems, much of the biodiversity and production levels are unlikely to be utilized sustainably without effective management. 2 Because biomass production is usually low in resource-challenged ecosystems, the rate of degradation, and eventual desertification, is accelerating because of overutilization. 1 In such ecosystems, effective management is needed for sustainable plant growth and survival, as rainfall availability is unreliable, uncontrolled grazing is high, and soil nutrient status is poor. 2,3 Therefore, strategies that promote sustainable management of biodiversity are needed, for instance, by establishing and maintaining protected areas. 2 In arid and semiarid areas, animal production is influenced by the quality and quantity of available feed resources. 4 In these areas, overgrazing has reduced the nutritional and productivity levels of many rangelands by up to 25%. 3 Plants grazed by animals, or used for supplementary forage in rangelands, are often generally low in nitrogen, digestible energy, and mineral content. ...
... 2,3 Therefore, strategies that promote sustainable management of biodiversity are needed, for instance, by establishing and maintaining protected areas. 2 In arid and semiarid areas, animal production is influenced by the quality and quantity of available feed resources. 4 In these areas, overgrazing has reduced the nutritional and productivity levels of many rangelands by up to 25%. 3 Plants grazed by animals, or used for supplementary forage in rangelands, are often generally low in nitrogen, digestible energy, and mineral content. ...
Article
On the Ground • The information from this study is important for helping promote a more sustainable use of resources , such as grasses and shrubs, and in increasing an understanding of the utilization dynamics and their impact on potential recovery in the study area and beyond. • This study contributes insight toward ensuring the achievement of conservation measures outside protected areas to restore biodiversity in degraded habitats, through comparing the plant characteristics between a protected and unprotected site. • This study substantiates other findings, which suggest that using protected areas is one of several strategies that need to be adopted for recovering lost biodiversity and ensure their effective management. • This study improves our understanding of how shifts in vegetation characteristics resulting from land use change and management can modify the recovery of, in the case of Cholistan, previously grazed vegetation.
... good climate and deep, permeable soil). This process is rarely encountered in dry areas, however, and usually requires human intervention either by reducing disturbances (e.g. by fencing or prohibiting ploughing in vulnerable areas), or accelerating regeneration (e.g. by re-seeding some plant species) (Attia et al., 2013;Ouled Belgacem, Tarhouni & Louhaichi, 2013). The effects of fencing, however, seem to be temporary in arid ecosystems when compared to other ecosystem protection actions. ...
... The effects of fencing, however, seem to be temporary in arid ecosystems when compared to other ecosystem protection actions. Being fenced off for a long period can be more harmful for the diversity of the natural vegetation cover than regular grazing on arid areas (Le Floc'h, 2001;Slimani, Aidoud & Roz e, 2010;Ouled Belgacem, Tarhouni & Louhaichi, 2013). The objective of this study was to determine the effects of long-term fencing and overgrazing on the floral diversity and vegetation cover inside (fenced) and outside (disturbed) Sidi Toui National Park for the period 1990-2011. ...
... Likely, the long period of fencing resulted in the extinction of plant species that required moderate grazing for their renewal (the plant tufts becoming too large and old, the soil surface was crusted and prevents new seedlings establishment and so the floristic diversity decreased [authors' observation]). The increase in perennial species can be attributed to the fencing effects that allowed PC regeneration when the irreversibility threshold has not been crossed (Ouled Belgacem, Tarhouni & Louhaichi, 2013). After twenty years of fencing , the plants had become more vigorous and older (authors' observations). ...
Article
In dry areas, natural plant communities are mainly affected by climatic stress and human disturbances – overgrazing, plowing, and biomass harvesting – that accelerate their degradation. Management techniques, including creation of national parks (fencing), are needed to conserve natural resources/biodiversity. The long-term effects of protection on the plant communities should be monitored. This study assessed the results of long-term protection on the composition and diversity of the natural plant communities of Sidi Toui National Park (southern Tunisia) using the point-quadrat method and ecological indicators of the ecosystem structure. Comparison of these indicators for the period 1990-2011 inside (fenced) and outside (disturbed) the Park showed that regeneration of natural vegetation increased during the first decade of the fencing period (1990-2001), but declined during the period (2008-2011). After a long period of fencing, plant tufts were bigger and aged, and the ecosystem dynamics decreased. In the absence of animal activities, the hardpan at the soil surface impedes seedling emergence. This suggests that long-term fencing is not recommended for conserving floral diversity in dryland ecosystems. To ensure and maintain the regeneration of these ecosystems, fencing periods alternating with controlled grazing (by introducing wild herbivores) are recommended.
... The Biosphere Reserve of BouHedma constitutes a transition environment between semi-arid and desert vegetation in Tunisia (Schlesinger et al. 1990). It is a genetic and biological resource threatened by anthropogenic activities, mainly grazing and climatic pressure (drought), to which are added recent global changes (Floret and Pontanier 1982;Ouled Belgacem et al. 2013). The protection and conservation of natural habitats is becoming a global concern (Dupuy et al. 1999;Noumi 2010). ...
... In North Africa, defenses and grazing have been shown to cause degradation of steppe vegetation and hinder the reconstitution of major characteristics (cover, composition, and production) of pre-existing vegetation from three to six years of defense (Bourbouze 1997). Studies of Abdallah et al. (2008); Ouled Belgacem et al. (2013) reported that heavy grazing make palatable species replaced by less desirable ones. Nevertheless, defending can turn out to be harmful, and can lead to a drop in productivity, the recovery and externalization of interspecific competition and a blockage of the biological recovery after more than ten years (Noumi 2010). ...
Article
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Anthropic effects and global change threaten biodiversity and genetic resources. Thus, their conservation becomes a primary necessity. This work aims to assess the conservation conditions for vegetation and causes that limit the progressive dynamics of the vegetation cover after a long period of defense. Using the quadrat point method, his work was conducted in two fenced zones and an unfenced zone of the Biosphere Reserve of BouHedma in a Tunisian arid climate. A total of 66 transects were investigated. In each transect species richness and, α and β indices were determined. The α and β diversity showed a low similarity in family and species composition in the studied zones. The Poaceae and Asteraceae families were the most representative in the studied zones and the most used for grazing. These results highlight that long-term conservation contributes to minimizing the reduction of biodiversity in the reserve. It is necessary to minimize razing and deforestation, especially in the unfenced zone. Thus, the setup of barriers and fences is highly recommended to retain the soil. In addition, finding an effective communication plan with the local population and visitors seems to be crucial.
... G means graze, E6 means exclosure for six years, E16 means exclosure for sixteen years. & Louhaichi, 2013;Dorrough, Ash, & Mcintyre, 2004). The results from this study showed that grazing exclusion increased the density of perennials, which are generally palatable (Table 1). ...
... In contrast, the density of annuals significantly decreased (Table 1). The increased vegetation levels in the long-term exclosures could be due to the improvement in soil conditions, which is similar to the studies conducted in other deserts (Belgacem et al., 2013;Pei et al., 2008). ...
Article
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Exclosure is a simple and effective rangeland restoration approach, which is widely used in China, and is conducive to the recovery of degraded vegetation and soil. Plant and soil properties in a desert steppe on the southeastern edge of the Junggar basin after 6 and 16 years of grazing exclusion were measured and compared with open grazing lands. The results showed that vegetation cover increased with exclosure time, while the abundance decreased over time; the species richness, diversity, and evenness indexes of the annual plants decreased after 6 years of grazing exclusion and recovered after 16 years of grazing exclusion. The soil was significantly restored during the 16‐year exclosure period because soil fertility increased and soil pH decreased; however, the soil was not effectively restored after 6 years of exclosure because the soil pH had increased and soil organic matter and total nitrogen had decreased, even though available nutrients and total phosphorus had significantly increased. Therefore, these results were contrary to previous studies, which reported that rangeland can be restored by a short‐term exclusion system in this region, and that grazing exclosures should be established and widely used in degraded rangelands to restore the vegetation and soil. Long‐term exclosure to improve soil and vegetation conditions is crucial if the restoration and sustainable use of the rangeland in the Junggar desert are to be promoted.
... grazing pressure, conversion of rangelands to farmlands, fuelwood removal, and construction) lead to rangeland degradation, habitat change, desertification, and biodiversity loss (Al-Rowaily et al., 2015;Yirdaw et al., 2017). Humans' ecosystem management strategies affect structure and function of brittle ecosystems at local and regional scales (Enright and Miller, 2007;Belgacem et al., 2013;Jafari et al., 2017). In the long-term periods (e.g. ...
... National parks and other protected areas are established to protect biodiversity and maintain ecological stability via restriction in livestock grazing and other human interventions. Although the effects of national parks on wildlife population, plant species diversity, and ecosystem composition and structure have been studied (Belgacem et al., 2013;Tarhouni et al., 2017), studies on ecological stability and ecosystem functionality are rather rare. ...
Article
This study aimed to evaluate the application of landscape function analysis (LFA) and some soil quality indicators for the assessment of the structure and function of Steppe rangelands in arid regions of Ghamishloo National Park, Isfahan, central Iran. Three zones with different protection levels/grazing intensities, including a national park with wild herbivores, a peripheral protected area where both livestock and wild herbivores were present, and an adjacent grazing-free area where wild herbivores were absent, were selected. Eleven soil surface indicators were assessed to measure soil stability, infiltration, and nutrient cycling indices in various zones. Eighty-seven soil samples were collected in the study area and their characteristics, including pH, electrical conductivity (EC), total nitrogen, phosphate, soil organic carbon (SOC), particulate organic matter (POM), microbial respiration, and mean weight diameter (MWD), were measured. The results showed that although structural attributes (patch area index and landscape organization index) and LFA functional attributes varied significantly between the sites with various management histories (P < 0.05), these attributes along with total patch area and number of patches per 10 m did not have significant differences between the protected and grazing-free area. Most soil quality indicators were also significantly different between the national park and grazing-free area, but MWD, SOC, and POM were not significantly different between the protected and grazing-free areas (P < 0.05). High protection level (i.e. lower grazing impact) led to more soil stability and higher proportion of macro-aggregates in the national park area compared to other areas. The methods used in this study are applicable for exploring the role of national parks in maintaining the structure and function of ecosystems in similar ecoregions.
... grazing pressure, conversion of rangelands to farmlands, fuelwood removal, and construction) lead to rangeland degradation, habitat change, desertification, and biodiversity loss (Al-Rowaily et al., 2015;Yirdaw et al., 2017). Humans' ecosystem management strategies affect structure and function of brittle ecosystems at local and regional scales (Enright and Miller, 2007;Belgacem et al., 2013;Jafari et al., 2017). In the long-term periods (e.g. ...
... National parks and other protected areas are established to protect biodiversity and maintain ecological stability via restriction in livestock grazing and other human interventions. Although the effects of national parks on wildlife population, plant species diversity, and ecosystem composition and structure have been studied (Belgacem et al., 2013;Tarhouni et al., 2017), studies on ecological stability and ecosystem functionality are rather rare. ...
... National parks and protected areas in general play an important role in maintaining biodiversity, preserving endangered species and providing ecosystem services, such as water filtration or air cleaning (Gaston et al., 2008;Belgacem et al., 2013). Today, protected areas cover over 15% of the 5 global terrestrial and inland water areas and the goal for 2020 is to increase them to 17% (Juffe-Bignoli et al., 2014). ...
... On the one hand, one can compare areas with similar environmental conditions but with different states of protection. In 35 most cases, this approach is based on a comparison of the protected area with its surroundings (Wasiolka and Blaum, 2011;Belgacem et al., 2013). ...
Article
National parks are established to reduce human influence on nature and contribute to species conservation, biodiversity and ecological services. Other states of protection like the UNESCO world heritage sites, for example, are created for maintaining culturally important places or lifestyles. In the Matobo Hills (Zimbabwe) both states of protection are present, a national park and a world heritage site. In addition, the land outside the National Park belongs to two different systems of ownership, namely "common" (i.e. community-owned) and "not-common" (privately or governmentally owned) land. In this paper, we investigated how the state of protection and the ownership affected the land use and land cover. We derived maps using Landsat images from 1989, 1998 and 2014 by supervised classification with Random Forests. To compensate for the lack of ground data we inferred past land use and land cover from recent observations combining photographs, Google Earth images and change detection. We could identify four classes, namely shrub land, forest, patchy vegetation and agricultural area. The Matobo National Park showed a stable composition of land cover during the study period and the main changes were observable in the surroundings. Outside the national park, forest increased by about 7%. The common lands have changed substantially and their agricultural area decreased. We attribute this development to the Fast Track Land Reform, which took place in the early 2000s. Our approach shows that combining information on recent land cover with change detection allows to study the temporal development of protected areas.
... These require scientific follow up of the plantations, including their ecological and socio-economical values (CDM-Home, 2010). Reforestation of A. tortilis is hypothesised to induce local climatic change in the Biosphere Reserve with consequences as 1) change of soil temperature, 2) improvement of soil fertility and nutrient status (Abdallah et al., 2008;Noumi et al., 2010aNoumi et al., , 2010b, 3) improvement of the soil water availability (Noumi and Chaieb, 2012), 4) biodiversity increase (Abdallah et al., 2008), 5) influence on the cloud formation process inducing precipitation, and 6) interception of water by tree leaves and trunks mitigating erosion processes (Belgacem et al., 2013). The impact of this local climate change is already felt outside the Biosphere Reserve, where the local rural population depends on rain fed agriculture and water resources originating from water infiltrated on the mountains of the Bou-Hedma (Ouessar, 2011). ...
... Atriplex halimus L.) (Ouarda et al., 2009). Belgacem et al. (2013) describe the vegetation of Bou-Hedma linked to the local morphology: the mountain massif is dominated by Juniperus phoenacea L., Periploca angustifolia Labill., Rhus tripartitum (Ucria) Grande, Olea europea L., Rosmarinus officinalis L. and Stipa tenacissima L. The piedmont is covered by Artemisia herba-alba Asso, Anarrhinum brevifolium Coss. & Kralik, Gymnocarpos decander Forssk. ...
... For instance, the Tunisian vegetation has undergone a severe decline over the course of the last century under the long-term impact of livestock and human exploitation (Le Houerou 2000;Tarhouni, Ben Hmida, and Neffati 2014). Particularly, the plant species, diversity, abundance, composition, and life forms have also been altered (Ouled Belgacem, Tarhouni, and Louhaichi 2011). Heavy grazing has left Tunisian ecosystems with a homogenized flora consisting only of annual grasses highly tolerant to herbivory and other forms of anthropic and climatic disturbance (Gondard et al. 2003;Jauffret and Lavorel 2003). ...
Article
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The effect of water stress, salinity and temperature on the germination of Stipa capensis seeds were estimated herein. Seed germination was determined over different temperatures (10 °C, 15 °C, 20 °C, 25 °C and 30 °C), across a range of osmotic potentials of the polyethylene glycol solutions (0.0; −0.2; −0.5; −0.8; −1.6 MPa) and four salinity levels (0, 50; 100; 150 mmol/l −1) in four replicates of 50 caryopses for a period of 20 d. Results showed that temperature significantly affected the germinative percentage of Stipa capensis seeds (p < .001). The optimum temperature was 20 °C. The final germination percentage increased at the sub-optimal temperature range (10 °C-20 °C). However, from 20 to 30 °C, the final germination percentage decreased. The base temperature (Tb) was thus determined at 11.36 °C and the ceiling temperature (Tc) at 31.55 °C. Moreover, the highest germination percentage was found in osmotic potential 0 MPa (81 ± 2.4%). The increase in PEG 6000 concentration resulted in an important decrease of germination percentage, with only 40% of seeds germinating at 0.8 MPa. Stipa capensis was also sensitive to high salinity (150 mmol/ l −1) with a 29 ± 1.5 germination percentage. Overall, the study has shown the ability of Stipa capensis seed to germinate under low temperatures , water and salt stress that characterize most arid and semi-arid regions.
... In the case of the Middle East, the data is notably biased towards Israel, where high mountains are only present in the northeast. Nevertheless, in these two zones, the importance of mountains sometimes emerges, as highlighted by Glasser et al. (2012) in Israel, El Aich (2018 in Morocco, and Belgacem et al. (2013) in Tunisia. ...
Article
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Mediterranean pastoral systems are providers of a wide array of Nature’s Contribution to People (NCP). They are ‘complex systems’ characterized by limited resources and socio-economic dynamics currently threatened by climate and social changes. Despite a growing number of scientific articles dealing with NCP, there is a high risk that the existing literature has left out the complexity of such systems. In the light of ongoing social, economic, and climatic changes in the Mediterranean basin, neglecting the complexity of pastoral systems can lead to significant research biases, missing the priorities affecting the stability and continuity of such systems. A combination of frameworks of analysis provided by the Millennium Ecosystem Assessment and by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services was applied to understand if and to what extent the complexity of Mediterranean pastoral systems has been considered in the available literature. Most of the 126 papers report studies conducted in the European Union zone (102 papers), with the majority in Spain (50). Fewer studies have been conducted in the Middle East (15 papers) and Africa zones (9 papers). Despite results confirming the importance of pastoral systems as providers of NCP, most of the eligible papers focused on regulating NCP. A lack of a multisectoral approach and integration of knowledge suggests that the complexity of Mediterranean pastoral systems has been overlooked by researchers. The creation of ‘hybrid knowledge’ bridging the expertise of different stakeholders could be the key ingredient to properly address the complexity of Mediterranean pastoral systems.
... The results demonstrated that protection significantly increased the total plant cover. Similar results were reported in similar agroecological zones [96,47,97,98,99,100,101,102,12,13,103,67,104,79], indicating progressive increase of total vegetation cover in protected areas as compared to grazed areas which are often characterized by the expansion of bare soil. ...
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The purpose of this study is to evaluate the impact of enclosure as a technique for the restoration of degraded rangelands on plant community structure in El-Bayadh (North West Algerian steppe). Protection of degraded rangelands is widely considered to be the most effective and practical way to conserve plant diversity and maintain ecosystem composition and structure. The ecology of restoration and rehabilitation is part of the possible actions more to limit the extansion of the degradation of this ecosystem and erase or mitigate the consequences but, it is necessary to know the performance of the steppe ecosystem. The quadrat point method was used. A total of 10 surveys were carried out in each stations, several indicators of ecosystem attributes such as diversity, richness, total plant cover, perennial plant cover, annual plant cover, soil surface elements cover and pastoral value were compared between enclosure and grazed areas. The findings revealed considerable positive effects of protection on the scored parameters (Increase in floristic richness and diversity, increased in plant cover and litter, decrease in stones elements and wind veil, increase in pastoral value). However, the result semphasized a negative effect of enclosure on vegetation dynamics. For the soil surface elements, the enclosure (protection) decreases the cover stones and wind veil due to the cessation of the degradation of the bedrock by wind erosion and a good fixation of the sand by the vegetation, also the fencing has allowed the increase of the litter cover which is vital for the environment, because when it is not consumed, litter favors infiltration and germination of seeds and its presence can provide "islands" of fertility where sediment and nutrients are trapped contributing to increased floristic richness and diversity in these environments. This was observed by the occurrence of the bare silty crust on the soil surface which may constitute an obstacle to water infiltration and seeds germination, for this we suggest that this parameter be retained for the opening of these aminaged rangelands (enclosure) for grazing.
... Pour sauver les rares formations pré-forestières, il ne suffit pas seulement d'interdire le pâturage ou de règlementer l'accès du bétail, mais il faudrait sauvegarder les fragments de prairie pour remettre en place les procès dynamiques naturels et faciliter l'émergence de nouveaux fragments de végétation ligneuse grâce à des mises en défens. En effet, une autre possibilité serait soit (i) la création de surfaces d'enclos à déplacer après une dizaine d'années (Jeddi & Chaïeb, 2010 ;Abdallah et al., 2011 ;Belgacem et al., 2013), c'est-à-dire une fois que les plantes ligneuses protégées ont atteint une hauteur qui les met à l'abri des herbivores (Fazan et al., 2021), soit (ii) l'adoption d'une stratégie de rotation du pâturage pour donner à la végétation la possibilité de repousser et aux ligneux de produire fleurs et graines (Gamoun & Hanchi, 2014). ...
Article
The two field missions carried out in March 2014 and April 2015 as part of the PIM Initiative have enabled to draw up the first list of the vascular flora of the two Kuriat islands (eastern Tunisia), which until now were very poorly known from a botanical point of view. A total amount of 168 species or subspecies of vascular plants belonging to 42 different families have been recorded on the archipelago, including some that are very rare in Tunisia, as well as twelve terrestrial habitats of heritage interest and more than twenty different vegetation units. The main disturbance factors threatening the quality and integrity of the local plant landscape are the gull colony on Petite Kuriat and goat overgrazing on Grande Kuriat.
... Polygonum equisetiforme is a perennial herb belongs to the Polygonaceae family (Asensi and Díez-Garretas, 2011). P. equisetiform grows in large area in Tunisia, platicity of plants help to adapt dryland to moist soils (Belgacem et al., 2013). The resistance to such extreme climatic events was strongly related to many compounds that were used for adaptive functions. ...
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Purpose: The Polygonum equisetifome is a prospective plant source of high protein, unsaturated fatty acids, and useful safe bioactive molecules. Therefore, the aim of this study was to optimize the ultrasonic aqueous extraction of phenols from P. equisetifome roots using Box-Behnken design based statistical modeling, and to evaluate the antioxidant and antibacterial efficiencies of P. equisetifome root extracts against pathogenic bacteria. Methods: In this study, the box-behnken design was used to optimize the extraction of phenols. The extraction temperature (30–70◦C), ultrasound assisted extraction (UAE) time (1–9 min), and liquid-solid ratio (35–45 mL/g) were investigated as the factors that influence the phenolic yield (Y1) and their DPPH (1,1-diphenyl-2-picrylhydrazyl) scavenging activity (Y2). Results: The optimal conditions for both responses were 50◦C, 5 min, and 40 mL/g. At these conditions, Y1 reached its maximum to be 45.321 mg GAE/g dry weight and Y2 to be 120.354 µmol Trolox/g dry weight. The P. equisetifome roots contained water soluble phenol, high anthocyanin, and condensed tannins. Interestingly, the P. equisetifome extracts showed a relation to its antioxidant and antibacterial activities, FRAP (Ferric-reducing/antioxidant power), and ABTS scavenging activity were determined. The morphological and physico-chemical features of the extract were analyzed using SEM-EDX, FT-IR, and minimum inhibitory concentration (MIC) was analyzed against several pathogenic bacteria. The antibacterial activity of the extract showed that the extract is more efficient against Staphylococcus aureus, while the P. equisetifome extracts showed efficient MIC against S. aureus, followed by Bacillus cereus.
... The productivity of ecosystems is decreased, along with the diversity and relative abundance of species, by factors such as soil degradation, drought, global warming, extinction of perennially palatable species, overgrazing, and humancaused activities [1,2]. Numerous researchers have noted seasonal variations in the chemical or biological components of a variety of plant species, for example Peters et al. [3], Ramírez-Briones et al. [4], Huang et al. [5], El-Absy [6]. ...
Article
The present study was undertaken to understand adaptive behavior and the possibility of osmotic adjustment adopted by three plant species to tolerate harsh environmental conditions during the winter and summer seasons based on some soil and plant variables as well as the relationships among them. The plant species studied are Hyoscyamus muticus L. (H. muticus), Anabasis setifera Moq. (A. setifera) and Teucrium polium L. (T. polium) and were collected from Tayma Governorate, Tabuk region, Saudi Arabia. ANOVA results showed that the plant species, depths, and their interaction significantly affected most physicochemical properties of the soil supporting three plant species. Also, the plant species, seasons, and their interaction highly significantly affected photosynthetic pigments and proline contents. The highest values for pH and Ec in A. setifera soil, for Na+, Mg++ and Cl- in H. muticus soil, and for other studied chemical properties in T. polium soil were recorded. Significantly increased water content % was observed in A. setifera soil at 20-40 depth across the winter season. Chlorophyll a (Chl.a), chlorophyll b (Chl.b) and Chl.a+b contents in H. muticus plants and Chl.a/b, total carotenoids, total pigment and proline contents in T. polium plants were significantly increased in comparison to the other plant species. Compared to the winter season, the amount of proline and photosynthetic pigments increased significantly in the summer season. The principal component and biplot analysis displayed that the three plant species were quite separated based on the variables studied, and showed positive correlations among most soil and plant variables, but these associations varied in their degree and consistency. The positive correlations were observed for PC1 with K+, Ca++, HCO3- and SO4-- in soil as well as Chl.a/b, total carotenoids, total pigment and proline in T. polium plants. While PC2 showed highly positively correlated to Na and Mg in soil as well as Chl.a, Chl.b and Chl.a+b in H. muticus plants. As a result, the above soil chemical properties are associated closely with the above plant variables in the two previous plant species. The statistical study shows that due to its adaptive behavior and potential for osmotic adjustment, T. polium type generally adapts better to the dry desert environment and seasonal changes.
... Along the same line, ecological attributes related to the vegetation cover structure, such as species density and phytovolume are important indicators of footprint environmental disturbances, specifically industrial pollution (Belgacem et al., 2011). To explore the pollution impact at the ecological scale, spatial dissimilarities may serve to assess the pollution impact on plant species (Bayouli et al., 2021). ...
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Exploring fluoride impacts on species' survival strategies and predicting later pollution effects on community structure is a key question in ecological studies. To address this issue, a field study was conducted during two seasons on fluoride-contaminated soil in southern Tunisia. Gabes was the most polluted site, with almost 1600 ppm. Smara was the reference site, with almost 56 ppm. F accumulations were above the usual background concentrations. Fluorine (F) concentrations in the plant aerial part of Atractilys serratuloides, an arid gypsum-tolerant plant species that is abundant in the surroundings of superphosphate factories in Tunisia, reached around 300 ppm in Gabes. Simultaneously, plant seasonal development (life cycle) monitoring was also carried out to assess the shoot vegetative growth and phenological stages of Atractilys serratuloides under fluoride pollution. Earlier reproduction events (flowering and fructification) were detected at the expense of reduced shoot vegetative growth of this species in both polluted sites, especially in the summer season. This strategy may enhance A. serratuloides' earlier achievement of its reproduction stage and thus fosters its chance of colonizing the F-enriched soils in the factories' surroundings.
... Soil pollution drivers (factors) can have a large impact on individual species, plant groupings, and ecosystems [4]. Previously, it was documented that environmental disturbances can be identified by looking at species diversity, annual species density, perennial species density, and vegetation cover. ...
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Because sewage sludge is contaminated with heavy metals, its disposal in the soil may pose risks to the ecosystem. Thus, heavy metal remediation is necessary to reduce the associated risks. The goal of this research is to introduce a heavy metal resistant species and to assess its phytoremediation, oxidative damage markers and stress tolerance mechanisms. To this end, field research was done to compare the vegetation of polluted sites to that of a healthy site. We found 42 plant species identified in the study, Sesuvium portulacastrum L. was chosen because of its high relative density (10.3) and maximum frequency (100 percent) in the most contaminated areas. In particular, S. portulacastrum plants were characterized by strong Cu, Ni, and As uptake. At the organ level, to control growth reduction and oxidase damage, particularly in roots, increased detoxification (e.g., metallothionein, phytochelatins) and antioxidants mechanisms (e.g., tocopherols, glutathione, peroxidases). On the other hand, flavonoids content and the activity of glutathione-S transferase, glutathione reductase and dehydroascorbate reductase were increased manly in the shoots. These biochemical markers can be applied to select tolerance plant species grown under complex heavy metal contamination. Our findings also introduced S. portulacastrum to reduce soil contamination0associated risks, making the land resource available for agricultural production.
... Plants 2021,10, 2031 ...
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Rangelands of Tunisia show a great indigenous species diversity with considerable potential as forage for livestock. However, information on their fodder yield and quality is scanty and restricted to few species. The objective of the study was to evaluate the nutritive values of selected key perennial species based on their biomass yield, chemical composition, in vitro organic matter digestibility (IVOMD), and mineral composition. The species evaluated included four grass species (Stipa lagascae Roem. and Schult., Stipa tenacissima L., Stipagrostis plumosa (L.) Munro ex T. Anderson, and Stipagrostis pungens (Desf.) de Winter.) and eight shrub species (Anthyllis henoniana Coss. ex Batt., Argyrolobium uniflorum (Deene.) Jaub. and Spach., Echiochilon fruticosum Desf., Gymnocarpos decander Forssk., Helianthemum kahiricum Delile., Helianthemum lippii (L.) Dum. Cours., Plantago albicans L. and Rhanterium suaveolens Desf.). Results showed that shrub species contained higher concentrations of the crude protein (CP), acid detergent lignin (ADL), but lower neutral detergent fiber (aNDFom) and acid detergent fiber (ADFom) concentrations than grasses. The greatest concentration of CP was 135 g/kg DM for R. suaveolens. The greatest aNDFom concentration was found within the grasses with maximum of 744.5 g/kg DM in S. plumosa. The shrub species E. fruticosum, A. uniflorum, P. albicans, G. decander, R. suaveolens, and A. henoniana had the highest IVOMD with over 500 g/kg DM and have the potential to supply energy to livestock. Overall, the moderate to high protein, low fiber, and high in vitro digestibility measured for shrubs, suggest they have high nutritional values and can be used to enhance local livestock production.
... Bisigato et al. (2008) reported that several factors, such as climate variations, species composition, degradation threshold, and physical and biological soil conditions, could also lead to the absence of significant changes in carbon levels between grazed and protected sites in some studies. On the other hand, our results corroborate those of Ouled Belgacem et al. (2013b) that palatable species cannot tolerate long-term protection and require moderate grazing to reactivate their growth. ...
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Long-term protection of arid ecosystems changes the vegetation and soil structures. The quantification of aboveground biomass and carbon content are among the principal indicators to evaluate these changes. Most methods used to quantify these parameters are costly, time consuming and destructive. In this paper, two non-destructive methods were compared: digital image processing and biometric measurements. Aboveground biomass and carbon content of five perennial shrubs were studied inside and outside Sidi Toui National Park, southern Tunisia. The effect of long-term protection on aboveground biomass and carbon content was assessed. The main results indicated that both methods provided similar aboveground biomass and carbon values. Aboveground biomass and carbon content were strongly correlated with canopy cover and biovolume (R² ˃ 0.7). Positive linear relationships were found for all the studied species. Apart from the large canopy cover of Haloxylon schmittianum and Haloxylon scoparium, the obtained results showed that long-term protection had no significant effect on aboveground biomass and carbon content for the other species. These results suggest that digital charting technique is an accurate method for assessing rangeland productivity in a timely and cost-efficient manner and that long-term protection is not always suitable for enhancing carbon content and therefore ecosystem resilience under climate change conditions.
... lanatus in the fall. These perennial species are known for their palatability with high nutritive value for both domestic and wild herbivores, and for their seasonal variability of tissue water and nutrient contents (Abdel-Razik et al., 1988;Saltz and Ward, 1994;Sharaf El-Din and El-Kady, 2001;Cunningham, 2009;Belgacem et al., 2013). For example, Salz and Ward (1994) reported seasonal preferences of P. sickerbergeii by Dorcas gazelles in the Negev Desert and Egyptian tortoises (Attum et al., 2007a). ...
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We studied the diet and vegetation composition of Egyptian tortoise, Testudo kleinmanni , habitat in North Sinai, Egypt. Dietary data was recorded through direct observations and the vegetation composition was recorded through the use of quadrats and line transects in 66 sampling points (33 in tortoise areas and 33 in non-tortoise areas). Our results showed that vegetation of Egyptian tortoise habitat had high species richness, Simpson’s diversity index, and vegetation cover in contrast to areas without Egyptian tortoises. These tortoises ate thirty four species of plants, a majority of these being perennials, with most feeding observations occurring in spring and winter. The consumption of perennials may enable Egyptian tortoises to find and consume food in an arid environment with low, variable and unpredictable rainfall. The plants most consumed were rare in our vegetation survey, suggesting food preferences. Our study suggests that Egyptian tortoises, which rely on vegetation for food and refugia, may suffer if vegetation cover and richness decrease.
... Grazing exclusion could improve vegetation composition and soil quality parameters due to the absence of grazing in degraded rangelands of Iran (Mofidi et al., 2013). Also, grazing exclusion enhances the abundance, species diversity, and production of palatable species, and declines the development of unpalatable species (Baghestani Maybodi et al., 2006;Belgacem et al., 2013;Kairis et al., 2015). On the other hand, Sigcha et al. (2018) reported a clear influence of grazing exclusion on soil properties and plant community composition and structure; however, no influence was found on species diversity. ...
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The effects of grazing rest on rangelands are different in different climates and knowledge of these effects is necessary to apply a correct management. For this purpose, this study was carried out on the Vegetation Cover (VC) and Forage Production (FP) of range species as a model of steppe rangelands of Iran at the Nir Range Research Station in Yazd province, Iran. In the study area, different grazing intensities were applied until the end of the grazing season of 2006 and thereafter, the whole area was under exclusion. VC and FP were measured in each of the experimental plots once in May 2007 and again seven years later in May 2014. The results of vegetation data analysis in 2007 showed that the heavy grazing intensity applied in the past caused the reduced vegetation cover and forage production of two desirable species i.e. Salsola rigida and Stipa barbata as well as increased vegetation cover and forage production of Launaea acanthodes and increased forage production of Scariola orientalis as undesirable species. The results of vegetation data analysis in 2014 showed that the lowest VC and FP of S. rigida were recorded in the experimental plots under heavy grazing intensity. In other experimental plots, there was no significant difference in VC and FP of this species (p>0.05). There was no significant difference of VC and FP in other species and total species in different experimental plots (p>0.05). Thus, during the 7-year rest period, although the negative effect of grazing on S. barbata is resolved, it remains on S. rigida and the resulting degradation is not completely compensated during this period and needs more time. Therefore, S. barbata showed a better resistance to grazing as compared with S. rigida. According to the results, if steppe rangelands are grazed heavily in the short-term, an intermediated-term grazing rest could improve the vegetation to the previous state.
... These areas were thus characterised by higher erosion, and lower top hamper and basal cover than BK areas. Such disturbance leads to a reduction in biodiversity survivability, decline of vegetation cover, reduced species diversity, a decrease in herbaceous biomass production and introduction of invasive species (Kairis, Karavitis, Salvati, Kounalaki, & Kosmas, 2015;Belgacem, Tarhouni, & Louhaichi, 2013). In the NBK areas, high proliferation of unpalatable grass species such as Sporobolus pyramidalis and Heteropogon contortus that are not ideal bee forages is a peculiar phenomenon ascribed to augmented browsing and grazing open spaces, thereby creating niches for weeds (Kaufmann & Krueger, 1984;Hiernaux, 1998;Loucourgarg et al., 2004). ...
... Camel (Camelus dromedarius Linnaeus, 1758) herbivory is frequently cited as the main cause of rangeland decline on the Arabian Peninsula (Batanouny 1990;Assaeed 1997;Ferguson, McCann, and Manners 1998;Abed and Hellyer 2001). Several fenceline studies comparing camel presence to absence have demonstrated increased plant biomass and biodiversity on the excluded side, particularly for herbaceous and smaller woody shrubs (Shaltout, El-Halawany, and El-Kady 1996;Gallacher andHill 2006a, 2006b;Ouled Belgacem, Tarhouni, and Louhaichi 2013;Al-Rowaily et al. 2015), but complete exclusion from herbivory is a socio-politically unsustainable management option for most rangelands. A dramatic increase of domesticated camel populations over the last few decades has displaced smaller wild ungulates in Dubai (Gallacher and Hill 2006b), and although the establishment of the Al Marmoum conservation reserve (Khafaga, Simkins, and Gallacher 2018) has reversed this trend, camels still far exceed sustainable levels across the Arabian Peninsula. ...
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Hyper-arid rangeland vegetation is typically dominated by large woody species which are often overlooked in herbivory studies. Long-term responses of tall shrub populations to herbivory change are poorly understood in the Arabian Peninsula. Population and size of 1559 individuals from four shrub species were assessed over an 11-year period under two herbivory regimes, one in which domestic livestock (camels) were replaced by semi-wild ungulates (oryx and gazelles) before, and the other during, the study period. Each shrub species exhibited a different response to the change in herbivory. Populations of Calotropis procera decreased dramatically. Populations of both Calligonum polygonoides and Lycium shawii increased through sexual reproduction, but the spatial distribution of recruits indicated different modes of seed dispersal. Average lifespans were estimated at 22 and 20 years respectively. The persistence strategy of Leptadenia pyrotechnica was similar to tree species of this habitat in that vegetative regrowth was prioritized over recruitment, and average lifespan was estimated at 95 years. Shrub responses to changes in ungulate management are therefore species-specific. Response of individual plant size was faster than response of population size, which was limited by slow sexual recruitment (L. pyrotechnica) or localized seed dispersal (C. polygonoides).
... The alteration in species composition affects soil fertility due to changes in belowground biomass and organic matter content, thus reducing soil carbon sequestration (Scholes 1990; Klumpp et al. 2009). Further, land degradation leads to a reduction in resilience of host species, reduction of vegetation cover, decreased species diversity, and reduced herbaceous biomass production (Kairis et al. 2015;Belgacem et al. 2013). Nonetheless, disturbances such as overgrazing favors establishment of invader species, survival, and dominance of short-lived, unpreferred annual plant species rather than the palatable perennial species (Byers 2002). ...
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Introduction: Land degradation is a serious environmental problem of our time. In Kenya, it is estimated that 30% of the total land mass is severely degraded. Suswa catchment within Narok County is a good example with gullies of over 25 m deep and 30 m wide. In response to the increasing land degradation in the area, the Sustainable Land Management (SLM) project rehabilitated the catchment through establishment of soil and water conservation structures such as cutoff drains, semicircular bunds, and water retention ditches. Despite the various rehabilitation approaches carried out, little research has been done to ascertain their effect on successful vegetation recovery. This coupled with the fact that many restoration approaches have failed in East Africa and Kenya in particular gave drive to the study. The objective of this study was to determine the effects of rangeland rehabilitation on herbaceous species composition and diversity in a severely degraded rangeland. Methods: To assess the diversity of aboveground herbaceous layer in the rehabilitated and degraded areas along a slope (upper, middle, and lower), line transect and quadrat count methods were used. Within each slope position, three 100-m-long transects were placed across the hill parallel to one another 30 m apart using a tape. The species hit, the closest species to the hit, and hits on bare ground were recorded. Along the same transects, 1-m² quadrats were placed 25 m apart and aboveground biomass determined by the use of the destructive method. In the determination of species richness, diversity, relative abundance, percentage cover, and species composition, the Shannon-Wiener diversity index was used. Data collected on vegetation attributes was subjected to analysis of variance (ANOVA) using Genstat and Tukey’s HSD post hoc used in means separation where F values were significant. Results: The results showed that percent cover (74.67%), aboveground biomass (1459 kg/ha), relative abundance, richness, composition, and diversity of perennial grasses significantly (P ≤ 0.05) increased downslope and were higher in the rehabilitated area than in the degraded area. On the contrary, forbs and annual grasses were significantly (P ≤ 0.05) higher within the degraded area compared to the rehabilitated area and increased upslope. Conclusions: In general, herbaceous species diversity, species richness, relative abundance, percent composition, biomass production, and percent cover of perennial grasses significantly increased downslope and were higher in the rehabilitated area compared to the degraded area. On the contrary, the same attributes for forbs and annual grasses were higher in the degraded area and increased upslope. The study concluded that effective rangeland rehabilitation has the potential to enhance vegetation regeneration and hence forage productivity.
... However, fodder species vary greatly in proportion of intake by livestock. Preferred species tend to be grazed heavily, especially when animals are allowed to graze yearlong (Tastad et al., 2010;Ouled et al., 2011). Selective grazing can change the composition of the plant community and reduce productivity of primary forage species, thus affecting rangeland productivity (Louhaichi et al., 2009). ...
... Artemisia herba-alba, Anarrhinum brevifolium, Gymnocarpos decander and Helianthimum kahiricum colonize the piedmont. The flat area is dominated by pseudo-savannah vegetation with Acacia tortilisraddiana as the only tree species, and understorey stratum is dominated by species, like, Rhanterium suaveolens, Cenchrus ciliaris, Haloxylon schmittianum, H. scoparium and Salvia aegyptiaca(OuledBelgacem et al., 2013). ...
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The present study aims to analyze the habitat selection of the Scimitar horned oryx, reintroduced in Bouhedma National Park (south Tunisia) and to identify the phytoecological factors affecting their occurrence during winter 2011 and spring 2012. Multivariate analyses of variance (MANOVA) performed by SAS package revealed that the vegetation is not the main factor in the selection of habitat by oryx in the park. It avoids glaze and mountain areas despite the presence of palatable species.
... Some scholars have reported that there are very few terrestrial ecosystems that are have not changed around the Mediterranean region (Aronson et al 1993a(Aronson et al , 1993bBelgacem et al 2013). Floret and Pontanier (1982) reported that one-third of Tunisia territory is in danger of desertification. ...
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The Republic of Tunisia, located in northern Africa, has various environmental challenges caused by anthropogenic practices such as over grazing, deforestation and desertification. The conversion of natural ecosystems is the major cause of plant biodiversity loss. Tunisia can be divided into three main climatic zones including a northern Mediterranean climate zone, a central steppe climate zone, and a southern desert climate zone. Because of this great environmental diversity, there are distinctive vegetation and various genetic resources in Tunisia. This research was conducted to investigate plant biodiversity within the various bioclimatic zones and to characterize useful plant resources in Tunisia. We investigated endemic, medicinal and aromatic, desert, and soil erosion control plant species.
... Previous studies reported positive results of site protection and passive management as a restoration strategy in Mediterranean areas (Le Houréou, 2000;Mekuria & Aynekulu, 2013; Ouled Belgacem et al., 2013), as well as its cost-effectiveness (Birch et al., 2010). However, the success of this strategy depends on several factors related to site biotic and abiotic conditions as well as structural and functional ecosystem damage and resilience (Vallejo et al., 2012). ...
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The limited amount of studies addressing the long-term effectiveness of restoration actions to combat land degradation is a constraint for current landscape restoration planning and implementation. Remote sensing data provide a unique opportunity for gathering information on the spatial and temporal variability of restoration processes, and may contribute to fill this knowledge gap. The aim of this study is to compare different management actions undertaken in Mediterranean degraded rangelands (i.e. dense pine plantations, thinned pine plantations, protection and passive management) by analyzing landscape composition and pattern change assessed from object-based classification of aerial photograph of 1954, 1977, and 2006. Results show a clear link between landscape composition and structure and the different restoration actions, allowing comparison between their spatial and temporal dynamics. All restoration actions promoted an increase in woody vegetation cover compared to non-restored areas. However, only protection and passive management favoured the restoration of dense, complex and well-connected patches of native Mediterranean maquis. The proposed methodology is discussed with respect to its applicability for future Mediterranean landscape restoration planning in a wider geographic and ecological perspective.
... The reappropriation of such ancient techniques, such as protection, has been successful in combating erosion and land degradation. The nature of the vegetation also changed under protection (Ouled Belgacem et al., 2011). In addition to this, some species can be used for combating land degradation , restoring and rehabilitating degraded land (Gui et al., 2011; Li et al., 2011; Wu et al., 2012; Chigani et al., 2012; Zucca et al., 2014). ...
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Desert rangelands are characterized by low and highly variable rainfall regime, low forage production and high heterogeneity in the distribution of natural resources. This study was carried out in the desert rangelands of Tunisia to evaluate the response of different rangelands to annual rainfall in terms of aboveground net primary production (ANPP) and rain use efficiency over a 10-year period (2003–2012). In general, ANPP values were relatively low (123 kg DM.ha−1.yr−1) but would tend to increased with increasing annual rainfall for all rangeland types. The highest value of ANPP was observed from Stipagrostis pungens and Hammada shmittiana communities (sandy soil) during the wet year 2011. In contrast, rain use efficiency (RUE) tends to decline with the highest annual rainfall and varied among rangeland types and with an average of 1.9 kg DM.ha−1.mm−1.yr−1. RUE tended to be higher during dry years and lower during wet years and tended to be higher on S. pungens and H. shmittiana (sandy soils) and lower on Helianthemum kahiricum (loamy soils). Therefore, understanding how rainfall affects productivity in rangelands is critical for predicting the impact of land degradation on the functioning of these ecosystems. It can be used to explain production decline associated with desertification as well as to assessing rangeland conditions. This article is protected by copyright. All rights reserved.
... Livestock overgrazing is considered as the main causes of rangeland degradation through lowering both the productivity and resilience of host species, reduction of vegetation cover, increase of unpalatable species, decrease of species diversity, and alteration of soil structure and compactness (Kairis et al., 2015;Belgacem et al., 2013;Zhou et al., 2011;El-Keblawy et al., 2009;Keya,1998;and Mainguet, 1994). Effects of grazing on the plant community and soils are viewed as destructive agents because of the reduction of ground cover, productivity and soil erosion (Al-Rowaily, 1999;Manzano and Návar, 2000;Firincio lu et al., 2007;Al-Rowaily et al., 2012). ...
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Livestock grazing is one of the main causes of rangeland degradation in Saudi Arabia. Fencing to exclude grazers is one of the main management practices used to restore vegetation and conserve biodiversity. The main objectives of this study were to investigate the changes in plant diversity and abundance, floristic composition and plant groups of the major life forms in response to thirty five years of grazing exclosure in western Saudi Arabia. These vegetation attributes and palatability were compared in 30 sampling stands located in the excluded and grazed sites. Our results showed that livestock exclusion significantly increased covers, density and species richness of annuals, grasses, perennial forbs, shrubs and trees. Exclosure enhanced the abundance and richness of palatable species and depressed the development of weedy species. About 66.7% of the recorded species at the excluded site were highly palatable compared to 34.5% at the grazed site. In contrary, about 55.2% unpalatable species were found in the grazed site compared to 25.8% in the protected site. Jaccard’s similarity index between the excluded and grazed sites showed lower values of 0.39%, 0.40% and 0.31% at levels of families, genus and species, respectively. The results suggest that establishing livestock exclusion may be a useful sustainable management tool for vegetation restoration and conservation of plant diversity in degraded rangelands of arid regions.
... Several works showed the beneficial effect of fencing on plant communities in highly disturbed zones, such as sandy steppes in southern Tunisia (Floret & Pontanier, 1982;Waechter, 1982;Le Houerou, 1995;Ouled Belgacem & Neffati, 1996). Short grazing periods alternated with periods of fencing are more favourable than strict long-term protection (Floret, 1981;Ouled Belgacem, Tarhouni & Louhaichi, 2013). Controlled grazing reduces aerial parts of some plant species and allows the root system to support their water needs in arid areas where the evaporative demand is high (Le Floc'h, 2001). ...
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During last decades, the natural vegetation cover in southern Tunisia, mainly dominated by dwarf and sparse shrub, was continuously disturbed under various human activities especially on sandy soil (easily eroded). The ecological characteristics (soil structure and texture, vegetation, topography...) of sandy steppes, with Rhanterium suaveolens Desf., enhanced their sharp decline. This study aims to investigate the vegetation status of two R.suaveolens steppes (R: protected; r: degraded) under different conditions in five sites belonging to southern Tunisia using the quadrat point method and some ecological indicators. Main results show that vegetation cover is related to climatic conditions. Plant density is mainly affected by rainfall and human activities. The annual and perennial density and cover are high during the rainy season (spring) compared with the dry one (fall). The degraded steppes (r) are mainly dominated by annual plants but the protected steppes (R) contain more perennials. This work can be very useful for the sustainable sandy steppes management under different stress and human disturbances in dry area. It presents a great national and international importance (economic, social, nature conservation...) such as job creation and limiting rural exodus.
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Stress in plants refers to environmental circumstances that have a negative impact on plant growth, development, or production. Stress causes changes in gene expression, cellular metabolism, growth rates, crop yields, and other plant responses. Many elements are absorbed by plants from the soil. Some of the elements that are absorbed are known as essentials since they are necessary for plants to complete their life cycle. Heavy metals such as cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) may have varying effects on plant health. Heavy metal concentrations have an influence on plant metabolite activity.Increased levels of lead (Pb) in the soil generate a number of metabolites and oxidative stress symptoms in plants, including reduced growth, shoot development, root growth, and fresh weight in eggplant (Solanum melongena L.) seed treated with 50 ppm and 500 ppm concentrations of Pb together with control. At 500 ppm concentration, the most significant decrease in seed germination % was noted. While it was discovered to be 100% under control, it drops by up to 45% in Pb. In contrast, high amounts of lead (500 ppm) lowered the fresh weight of seedlings of the Solanum melongena L. plant while showing increases in germination %, root length, and shoot length. As the concentration of lead increases it becomes more toxic so that plant growth is reduced.
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Plants are a vital part of the world’s biological diversity and have great economic and cultural importance. Plant biodiversity balances ecosystems, protects watersheds, mitigates erosion, affects climate, and provides shelter for many animal species. This study aimed to determine plant diversity in relation to the soil properties of semi-arid rangelands along a gradient at the watershed scale in the Oued Chabro, Algeria. Plants and soil were sampled at 27 points distributed in three sampling sites (upstream, midstream, and downstream). The floristic data was analyzed using species richness estimators, life forms, spatial occurrence, and multiple factor analysis. Moreover, the effects of soil properties on the taxonomic structure of plant communities in the sampling sites were analyzed using Pearson correlations. The characterized flora included 42 plant species classified into 18 families, and Asteraceae (38.1%), Poaceae (14.3%), Brassicaceae (7.1%), Amaranthaceae (4.8%), and Chenopodiaceae (4.8%) were the most representative in terms of species. The species Atractylis delicatula was dominant (relative abundance = 81.5%). The upstream site was characterized by a high vegetation cover, high species abundances, and richness in plant families and genera. Significant correlations were observed in this area between the number of genera, number of families, number of species, family richness, Pielou evenness index, and Simpson’s concentration index. The upstream site was characterized by chamaephytes and phanerophytes; 16 species were exclusively present in this section. Two species were found in the midstream site and one (Scolymus hispanicus) was found in downstream site. The upstream site was positively correlated with plant litter, the midstream with barren soil, and the downstream study area was negatively correlated with coarse-grained materials and vegetation cover. This study demonstrated that differences in life forms, richness, and diversity exist among the three sampling sites due to the soil differences and the positions along the watershed.
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The Indian Himalayan belt is renowned for its diverse topographic and climatic conditions, acts as home to many rare, endemic, and endangered ethnomedicinal plants. The present study aimed to document the medicinal plants and their indigenous uses in the Buakhal area of Pauri Garhwal (Uttarakhand, India) through personal interactions with local villagers. This study resulted in the documentation of 100 plant species of medicinal importance belonging to 87 genera and 45 families. Among these, seven species were trees, 17 shrubs, 71 herbs, and five climbers. Using the whole plant body (30% spp.) for the herbal preparations in the studied area, followed by the use of the leaves (28% spp.) and roots (21% spp.). Among the recorded plant species, Begonia picta, Berberis aristata, Bergenia ciliata, Centella asiatica, Dicliptera bupleuroides, and Malaxis acuminata were the medicinal plant species frequently extracted (from wild) by the villagers. The local floral diversity is used to treat gastrointestinal disorders, skin diseases, respiratory disorders, liver disorders, etc. However, important traditional knowledge and cultural practices are decreasing in the younger generation across the ethnic groups of the country due to modernization. The traditional knowledge and wisdom must be maintained and passed on to future generations.
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The short-term fencing effects on vegetation in dryland landscape depressions are analyzed and the economic performance of grazing-only and integrated grazing with cropping in regard to land capital are compared. The goal is to suggest efficient strategic choices and more profitable land allocation of lowlands in dry areas. To analyze the vegetation, 12 cages each 2 m² were installed at three sides of a depression (4 east, 4 middle and 4 west side). Natural vegetation was recorded in the inside and outside cages during the spring of 2015, 2016 and 2018. Pastoral productivity was also calculated. To study the economic performance of cropping systems, local owner-farmers representing three cropped areas (1, 3 and 9 ha) were interviewed using socioeconomic surveys. The main results showed that short-term fencing increased diversity (24% to 61% in the middle cages). This improvement is due to annuals and the recruitment of palatable perennials. Economic evaluation showed that grazing is more profitable than integrated management, except for diversified and large cropped areas. The strategic recommendations for efficient, profitable and sustainable lowland allocation are short-term fencing with grazing-only in small depressions, and diversified crops mixed with grazing in larger depressions.
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Climate change and degradation of natural resources pose daunting challenges in arid and semi-arid rangelands of southern Mediterranean region. Overcoming these challenges requires considerable management actions efforts. In this context, the current two-year (2017/2018 and 2018/2019) study investigated the effects of soil surface scarification and reseeding of rangelands with sulla (Hedysarum coronarium L.) on botanical composition, biomass production, water productivity and pastoral value in the Sbaihia community, Tunisia. The experimental design consisted of a randomised complete block design with six replications. The treatments were: (i) soil surface superficial scarification; (ii) reseeding sulla following soil scarification; and, (iii) control. Despite the relatively important interannual variation, the highest aboveground net primary production (2 307 and 5 330 kg dry matter ha⁻¹), water productivity (9.5 and 11.8 kg DM mm⁻¹), and pastoral value (2 099 and 4 853 forage units ha⁻¹) values were recorded in the rangelands reseeded with sulla in both growing seasons. Sulla contribution in the species composition of reseeded rangelands increased from 1.7% in 2018 to 2% in 2019. Although soil surface scarification increased the vegetation cover, its effect on biomass production was not significant. Therefore, combined soil scarification and reseeding well-adapted native forage species has a great potential to improve productivity of semi-arid rangelands.
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Purpose The purpose of this paper is to illustrate the benefits of reintroducing traditional grazing systems practices for improving arid rangelands. Grazing is the most extensive land use in southern Tunisia, but the rangelands have suffered many decades of severe degradation due to profound socioeconomic changes and the emergence of an agro-pastoral society in place of the former pastoral one. Traditional grazing systems ( gdel and herd mobility), which had historically allowed for grazing deferment and control of grazing livestock were abandoned. Yet grazing management strategies are important tools to sustain integrated livestock rangeland production systems in dry areas in the face of ongoing climate change and human pressure. Design/methodology/approach This study assesses the revival of traditional best practices of rangeland resting in a representative community. Total plant cover, species composition, flora richness and range production were determined in six rangeland sites subjected respectively to one, two and three years of rest; one and two years of light grazing after rest; and free grazing (control). Findings Results showed that dry rangelands keep their resilience to the negative effects of climate change once human pressure is controlled. A maximum of two years of rest is enough to sustainably manage the rangelands in southern Tunisia, as this protection showed considerable and positive effects on the parameters scored. Originality/value The revival of the traditional best practices under new arrangements adapted to current biophysical and socioeconomic conditions would be an excellent tool to mitigate the negative effects of frequent droughts and reduce the animal feed costs that poor farmers face.
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The scimitar-horned oryx is a large, arid-adapted and gregarious hippotraginae antelope named for its long, elegant backward-curving horns. Evidence of the presence and suggested abundance of scimitar-horned oryx includes realistic rock art dating back several thousand years, the frescoes and reliefs of ancient Egypt, and the depictions and writings of ancient Greek and Roman civilisations. Genetically, the North American, European, and Middle Eastern scimitar-horned oryx populations all have some unique lineages, although the majority of this diversity is represented in the EEP and SSP. In the four Tunisian protected areas subject to similar management regimes, initial post-release population growth phases displayed linear trends. The reintroduced scimitar-horned oryx populations are small and connected only through human-mediated translocation. Socio-economic justifications of current scimitar-horned oryx reintroductions have yet to be realised, while living close to these protected areas may also be seen as disadvantage if there are restrictions on access and land use.
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In Presa-harian Tunisia desertification has progressively become the major environmental problem during the last decades. Because of various human activities the natural vegetation is continuously degraded. These activities lead to overgrazing and decreasing plant cover, because of the regression of rangeland area (cropland extension) and the increase of the number of grazing animals. Such quantitative and/or qualitative degradation comes with irreversible changes of flora and, consequently, of the vegetation physiognomy marked by the dominance of unpalatable species. In order to study the interaction between seasonal drought and grazing on plant cover and diversity, many permanent transects were established at different distances around three watering points situated in the Tunisian arid zone. Plant cover and species richness dynamics were assessed and monitored during two seasons (fall and spring) using the quadrat - point method. The main results show that the impact of grazing in terms of reduction of the vegetation cover is more important during the fall. The vegetation cover can be considered to be a good structural indicator of the studied ecosystem. The alpha and beta diversities constitute good indictors for the ecosystem structure and are recommended to be estimated in future studies.
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A model of ecosystem degradation and three possible responses to it—restoration, rehabilitation, and real-location—is applied to ongoing projects in the arid mediterranean region of southern Tunisia, the subhumid mediterranean region of central Chile, and the semiarid tropical savannas of northern Cameroon. We compare both nonhuman and human determinants of ecosystem degradation processes in these contrasted regions, as well as interventions being tested in each. A number of quantifiable “vital ecosystem attributes” are used to evaluate the effects of ecosystem degradation and the experimental responses of rehabilitation on vegetation, soils and plant-soil-water relations. We argue that attempts to rehabilitate former ecosystem structure and functioning, both above- and below ground, are the best way to conserve biodiversity and insure sustainable long-term productivity in ecosystems subjected to continuous use by people in arid and semi-arid lands of “the South.” The success of such efforts, however, depends not only on elucidating the predisturbance (or slightly disturbed) structure and function of the consciously selected “ecosystem of reference,” but also on understanding and working with the socioeconomic, technical, cultural, and historical factors that caused the degradation in the first place.
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A general model is presented describing ecosystem degradation to help decide when restoration, rehabilitation, or reallocation should be the preferred response. The latter two pathways are suggested when one or more “thresholds of irreversibility” have been crossed in the course of ecosystem degradation, and when “passive” restoration to a presumed predisturbance condition is deemed impossible. The young but burgeoning field of ecological restoration, and the older field of rehabilitation and sustainable range management of arid and semiarid lands (ASAL), are found to have much in common, especially compared with the reallocation of lands, which is often carried out without reference to pre-existing ecosystems. After clarifying some basic terminology, we present 18 vital ecosystem attributes for evaluating stages of degradation and planning experiments in the restoration or rehabilitation of degraded ecosystems. Finally, we offer 10 hypotheses concerning ecological restoration and rehabilitation as they apply to ASAL and perhaps to all terrestrial ecosystems.
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Rangeland degradation has been widespread and severe throughout the Syrian steppe as a result of both unfavorable environmental conditions and human induced impacts. To explore the effectiveness of management-based strategies on establishing sustainable rangeland development, we compared the response of temporarily removing grazing from rangelands ecosystems to those under a continuous heavy grazing regime. Results indicated that ungrazed sites had both higher biomass production and plant species composition than grazed sites. Ungrazed plots produced more than fourfold herbaceous biomass production than continuously grazed plots (p < 0.001). Extent of plant cover was 20% greater in ungrazed plots than grazed plots (33.5 & 13.5%, respectively). Furthermore areas protected from heavy grazing had over 200% greater species composition. Thus, protection from grazing can increase forage production and species composition, but may not necessarily improve plant species available for livestock utilization. A more balanced grazing management approach is recommended to achieve an optimal condition of biomass production (quantity), vegetation cover, quality and available forage species that contribute to proving livestock grazing conditions.
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An initially uniform Holcus lanatus-dominated sward came partly under hay-making and partly under sheep-grazing. Preferential grazing by sheep resulted in grazing at different intensities giving rise to a macro-pattern of various plant communities. Besides this macro-pattern a micro-pattern developed in the grazed area, which was absent under hay-making. In the micro-pattern short, heavily grazed areas alternated with taller, lightly grazed patches, both having the same species composition. The heavily grazed area was characterized by equal amounts of monocots and dicots. The lightly grazed patches were dominated by Agrostis tenuis, and had a large amount of litter which probably causes the absence of mosses. The protein percentage of green material is higher in the heavily grazed areas than in the lightly grazed patches. Sequential charting indicated that the micro-pattern was more or less stable. An interaction between the vegetation micro-pattern and grazing patterns is suggested. Heavy grazing results in forage with a high protein content and hence attracts animals. Light grazing results in forage with a relatively low protein content, animals avoid the area and litter accumulates.
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This paper reviews the predictions and management implications of two current paradigms in the ecology and management of arid and semi-arid rangelands. The equilibrium model stresses the importance of biotic feedbacks such as density-dependent regulation of livestock populations and the feedback of livestock density on vegetation composition, cover and productivity. Range management under this model centres on carrying capacity, stocking rates and range condition assessment. In contrast, non-equilibrium rangeland systems are thought to be driven primarily by stochastic abiotic factors, notably variable rainfall, which result in highly variable and unpredictable primary production. Livestock populations are thought to have negligible feedback on the vegetation as their numbers rarely reach equilibrium with their fluctuating resource base. Recent studies suggest that most arid and semi-arid rangeland systems encompass elements of both equilibrium and non-equilibrium at different scales, and that management needs to take into account temporal variability and spatial heterogeneity.
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The role of herbivores in controlling plant species richness is a critical issue in the conservation and management of grassland biodiversity. Numerous field experiments in grassland plant communities show that herbivores often, but not always, increase plant diversity. Recent work suggests that the mechanisms of these effects involve alteration of local colonization of species from regional species pools or local extinction of species, and recent syntheses and models suggest that herbivore effects on plant diversity should vary across environmental gradients of soil fertility and precipitation.
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The study was carried out at the communal rangeland in the community of Chenini, Southern Tunisia aiming at assessing the effect of the rest technique on plant cover dynamics and productivity. In both protected and grazed (control) rangelands, total plant cover, species richness as well as biomass production and range value were determined. The results showed considerable and positive effects of protection on the parameters scored. The short term protection (2 years only) permitted an increase of the rangeland production of about about 352000 forage units, an equivalent of 352 tones barley. In addition to the conservation of biodiversity and natural resources, the communal rangeland rest may be considered as an interesting technical option and tool to face the increase of animal feeding resources costs and to mitigate drought in Southern Tunisia.
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Light gap disturbances have been postulated to play a major role in maintaining tree diversity in species-rich tropical forests. This hypothesis was tested in more than 1200 gaps in a tropical forest in Panama over a 13-year period. Gaps increased seedling establishment and sapling densities, but this effect was nonspecific and broad-spectrum, and species richness per stem was identical in gaps and in nongap control sites. Spatial and temporal variation in the gap disturbance regime did not explain variation in species richness. The species composition of gaps was unpredictable even for pioneer tree species. Strong recruitment limitation appears to decouple the gap disturbance regime from control of tree diversity in this tropical forest.
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Light gap disturbances have been postulated to play a major role in maintaining tree diversity in species-rich tropical forests. This hypothesis was tested in more than 1200 gaps in a tropical forest in Panama over a 13-year period. Gaps increased seedling establishment and sapling densities, but this effect was nonspecific and broad-spectrum, and species richness per stem was identical in gaps and in nongap control sites. Spatial and temporal variation in the gap disturbance regime did not explain variation in species richness. The species composition of gaps was unpredictable even for pioneer tree species. Strong recruitment limitation appears to decouple the gap disturbance regime from control of tree diversity in this tropical forest.
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Recent attempts to streamline the identification of areas requiring immediate conservation attention have resulted in the development of prioritisation procedures that identify areas of biodiversity importance facing large threats in the near future. This study incorporated biodiversity data on bird and vegetation distribution with an assessment of land use suitability for cultivation and afforestation for the Limpopo Province of South Africa. The low altitude savanna regions in the northeast contain high species diversity, but are unsuitable to alternative forms of land use and are well conserved (by e.g., the Kruger National Park). The central and eastern mountain ranges, sites of high biodiversity, are suitable to dryland cultivation and afforestation and are thus potential conservation priorities. Areas with high biodiversity values, e.g., irreplaceable areas that contain biodiversity features essential for meeting conservation targets, were then investigated for their potential land-use threats in order to prioritise those needing immediate conservation actions. We suggest how losses of biodiversity could be minimised by reaching such decisions more quickly.
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In the Tunisian arid zone disturbances (e.g. overgrazing and agriculture) and stresses (e.g. aridity, low fertility) drive changes in the structure and functioning of rangelands, with a decrease in perennial plant cover, changes in floristic composition and erosion. Long-term monitoring requires (1) an understanding of the dynamics of vegetation change and associated ecological processes and (2) identification of relevant indicators. Using data from the arid zone of southern Tunisia we tested the hypothesis that plant functional response types could be used to address these two goals. We identified plant functional response types in response to a gradient of soil and vegetation types characterized by changes in perennial plant cover, dominant species and associated soil types. Vegetation samples were stratified by contrasted vegetation patch types with varying perennial plant cover (1.6 to 22%). We focused our analysis of trait responses within dwarf–shrubs, which are the dominants in typical steppe ecosystems of south Tunisia. Available trait data concerned morphology (plant height, leaf type), regeneration (dispersal mode, phenology and regeneration mode) and grazing value. Although we found it difficult to recognize ‘indicator response types’ that could be used directly to monitor changes in community composition, we were able to identify plant response syndromes that are relevant to long-term vegetation changes, and in particular degradation processes, in the region. Two main response types were identified: the decreaser type, made up of small or medium chamaephytes with high grazing palatability and the increaser type with medium to tall chamaephytes and low grazing palatability. These response types are proposed as key elements in a state-and-transition model of vegetation dynamics in the context of agropastoral disturbances and climatic and edaphic stresses.
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The present study provides preliminary assessments of the effect of protection and controlled grazing on the vegetation composition and phytomass in a Mediterranean desert ecosystem, 80 km W of Alexandria. Plots were fenced in 1974 and 1977, and different degrees of grazing pressure (no grazing, 25 and 50% of the grazing pressure freely practiced by the inhabitants) were applied. Changes in density, cover, frequency, phytomass and the phenological sequence of species were recorded and compared to those of the same species outside the fenced plots. Density and cover of perennials, frequency and presence of annuals, and total phytomass increased as a result of protection and controlled grazing. The arrangement of stands along ordination axes correlated with the degree of grazing pressure, which indicated that the distribution of species in the study area was more related to overgrazing than to the factors of the physical environment.
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The results of observations and measurements on five units of steppic vegetation in the mediterranean arid zone of S. Tunisia are presented in this paper. These units were totally protected against big herbivore grazing using barbed wire fencing during seven consecutive years.The steppes in question are composed of small shrublike chamaephytes. Annual plants appear when there is sufficient rainfall. This vegetation has been subjected to extensive overgrazing and is in general, degraded.Our objective was to study regeneration of the natural vegetation of five steppe types in order to recommend an optimum period for protection:1) a steppe on a gypseous crust resulting from overgrazing of the Zygophyllum album-Anarrhinum brevifolium association; 2) a steppe on a sandy, gypseous, rocky-surfaced colluvium resulting from overgrazing of the Rhantherium suaveolens-Artemisia campestris association, Atratylis serratuloides sub-association; 3) a very open steppe on a deep, gypseous, sandy colluvium-alluvium (sierozem) having the appearance of a post-cultivated grazed Plantago albicans facies of the Rhantherium suaveolens association; 4) a steppe in good condition on a deep, sandy-soiled plain representative of the Rhantherium suaveolens-Artemisia campestris association; 5) a post-cultivated facies of the Artemisia herba-alba-Arthrophytum scoparium association on a deep piedmont, loamy, and gypseous colluvium soil, traditionally cultivated with cereals. The effect of protecting these steppes was mainly the increase in cover of the perennial species. The cover of the steppe vegetation on sandy soils increased more than that of the steppes on loamy or gypseous crusts; this must be taken into consideration for pastoral management. The results also show that a protection period of 7 yr is not sufficient in an arid zone for new species to appear nor for succession to reach a next stage.
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The arid steppes north of the Sahara occupy an area of some 630,000 km², between the isohyets of 100 and 400 mm of mean annual rainfall (MAR), from the Red Sea to the Atlantic Ocean. Physiognomically they may be subdivided into perennial grass, dwarf shrub, tall shrub, crassulescent, succulent and pulvinate (or tragacanthic) steppes. Floristically they include some 2630 species of vascular plants, with a 26% rate of endemism; endemism is distributed into an eastern center (130 species), a western center (365 species) and an overall steppic nucleus (165 species). The limits between the east, central and west centers are approximately the 19°E and 0° of Longitude, respectively; while the regional limits are the Atlantic Ocean to the West and the Red Sea and Suez Canal to the east.
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We studied the influence of anthropogenic disturbance on forest structure and composition in the highly populated Montane Rain Forests of northern Chiapas, Mexico. We evaluated species richness, basal area and stem density on 81 circular plots (0.1 ha each) along a categorical disturbance gradient due to forest extraction, livestock grazing, and fires. A total of 116 tree species (>5 cm DBH) were recorded in three major forest types recognized by TWINSPAN. The three forest types were: Quercus–Podocarpus Forest (QPF), Pinus–Quercus–Liquidambar Forest (PQLF), and Pinus Forest (PF). The number of canopy and understory trees species, absolute density, and basal area decreased with disturbance intensity. Mean basal area of Pinus spp. was high at intermediate and severe disturbed sites (27 and 19 m2 ha−1, respectively), and low (0.2 m2 ha−1) in well preserved old-growth stands. Distribution of life forms was heterogeneous among forest types, with a high number of understory trees species in QPF, and an impoverished composition in PF. A first axis obtained by factor analysis, represented a combination of anthropogenic disturbance along with environmental and structural variables. Scores of the first factor explained almost 50% of variation, and was positively correlated with livestock grazing, firewood extraction, basal area of Pinus spp. and soil pH, and negatively associated with elevation, plant cover and basal area of Quercus spp. A second factor explained an additional 12% of variation and was associated with forest fires and timber extraction. Distribution of size classes in the QPF was significantly different (p<0.05) than in the other two forest types, including the largest individuals in all inventories. Our results suggest that small scale, but frequent anthropogenic disturbance, increases the dominance of Pinus and drastically decreases floristic richness, mostly understory trees. This points to the need of developing restoration practices aimed to attain highly diverse mixed forests from induced depauperate pinelands. On the other hand, the remnant MRF stands are currently under risk of deforestation in a highly populated Mayan territory, and their conservation under criteria of sustainable use may require finding alternative high value uses not included in conventional commercial forestry.
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Intro - The structure of rangeland plant communities is highly altered by competitive interactions among plants and the modification of competitive interactions by herbivory (Scholes & Archer 1997). However, by emphasising competititve interactions and herbivory, the positive effects that plants may have on each other have largely been overlooked until recently. Positive interactions, or facilitation, among plants have been shown to be important in many ecosystems around the world (Callaway 1995). Plants have been shown to directly enhance the fitness of other plants by protecting them from herbivores, via mycorrhizal connections, by attracting pollinators, or through interconnected webs of competitors. Neither direct or indirect facilitation occurs independently of competitive effects (Callaway 1995, 1997). Direct facilitation in savanna rangelands often occurs when overstory trees provide shade, nutrients, or water via hydraulic lift to herbaceous plants in their understorys (Parker & Muller 1982, Joffre & Rambal 1988, Callaway et.al. 1991, Vetaas 1992, Belsky 1994, Caldwell et.al. 1998). In oak-dominated savannas in California, the effects of Quercus douglasii H & A (Blue Oak) have been reported as both competitive (Murphy & Crampton 1964, Kay 1987) and facilitative (Holland 1980, Holland & Morton 1980). At the landscape level much of this variation appears to be correlated with climate (McClaran & Bartolome 1989), but individual 'facilitating and 'competing' blue oaks have been observed within metres of each other(Callaway 1991). In the first part of this paper I focus on a suite of positive and negative effects that may determine whether a blue oak facilitates or competes with understory plants.
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Thèse--Montpellier. At head of t.p. on v.2: Université d'Alger Institut de Recherches Sahariennes. Mémoire H.S. no. 6.
Article
grasslands typically assume that herbivore density is independent of the state of the vegetation, e.g., under the control of humans. We relax this assumption and investigate the mathematical implications of vegetation-regulated herbivore population dynamics. We show that irreversible vegetation change may also occur in systems where herbivore population dynamics are affected by changes in plant standing crop. Our analysis furthermore shows that irreversible vegetation change may occur for a larger set of soil and climatic conditions when herbivore numbers are independent of the vegetation, as compared to systems where vegetation density determines herbivore population size. Hence, our analysis suggests that irreversible vegetation change is less likely to occur in systems with natural herbivore population dynamics than in systems where humans control herbivore density.
Article
The study was carried out at two sites (Menzel Habib and national park of Sidi Toui) of southern Tunisia which provided an aridity gradient to evaluate the effect of long term protection on the regeneration of Stipa lagascae R. and Sch., a high range value bunchgrass. In both sites total plant cover as well as density of S. lagascae and Rhanterium suaveolens , the key species of the arid sandy steppe were determined inside and outside protected areas. Results showed considerable and positive effects of protection on the parameters scored. S. lagascae which was very rare in the freely grazed areas is more abundant in the protected areas than Rhanterium suaveolens , a chamephytic species. This is an indication that grasses such as Stipa are more competitive than chamaephytes for soil water and nutrients when not grazed. When degradation is still reversible, the application of restoration techniques may permit high regeneration of S. lagascae .
Article
A synthesis of differnt models for assessing the balance between vegetation and livestock numbers in grazing lands may help policy-makers integrate human and ecosystem needs.
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