Article

Is long-term protection useful for the regeneration of disturbed plant communities in dry areas?

Authors:
  • Food & Agriculture Organization of the United Nations
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

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.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... In the literature, there are conflicting results. While certain studies conducted in arid environments suggest that species composition and diversity increase with short-term protection, others suggest that long-term benefits are reduced [10,17,18]. ...
Article
Full-text available
Citation: Louhaichi, M.; Gamoun, M.; Ben Salem, F.; Ouled Belgacem, A. Rangeland Biodiversity and Climate Variability: Supporting the Need for Flexible Grazing Management. Sustainability 2021, 13, 7124. https:// Abstract: Resting or grazing exclusion is an effective practice widely adopted to restore degraded, arid rangelands. To understand its effect on plant diversity, we studied Hill's diversity indices during two growing seasons (2017-2019). The experiment consisted of a three-level factorial design with four plant communities subjected to different resting durations (one, two, and three years) compared to continuously grazed areas (control). The results showed that rainfall plays an important role in arid rangeland restoration. Under favorable conditions, one-year grazing exclusion considerably enhanced species richness and evenness diversity compared to longer resting durations under dry to average rainfall conditions. The decision to how long livestock grazing exclusion would last should not be decided upfront as it depends on the climatic and the site-specific conditions. The findings of this study will have vital management implications for development agencies. Knowing that short grazing exclusion with adequate rainfall amount and distribution could be enough and offers a cost-effective technical option to ensure the sustainable restoration of arid rangeland. This flexible grazing management would also be more acceptable by the pastoral communities. Longer resting periods could have detrimental effects on arid rangeland vegetation, in addition to adding more pressure on the remaining rangeland areas open to grazing.
... In the face of the degradation of natural resources and the progress of desertification, maintenance of biodiversity through active management has recently become an important challenge for biodiversity conservation [12]. Restoration efforts for natural rangelands are important and result in high species diversity [13][14][15][16][17]. Some efforts have been implemented to restore rangelands functions, and resting is the most widely and successfully used practice in arid rangelands restoration and represents an ideal still applied in rangelands management. ...
Article
Full-text available
Natural rangelands occupy about 5.5 million hectares of Tunisia’s landmass, and 38% of this area is in Tataouine governorate. Although efforts towards natural restoration are increasing rapidly as a result of restoration projects, the area of degraded rangelands has continued to expand and the severity of desertification has continued to intensify. Any damage caused by disturbances, such as grazing and recurrent drought, may be masked by a return of favorable rainfall conditions. In this work, conducted during March 2018, we surveyed the botanical composition and species diversity of natural rangelands in Tataouine in southern Tunisia. The flora comprised about 279 species belonging to 58 families, with 54% annuals and 46% perennials. The Asteraceae family had the greatest richness of species, followed by Poaceae, Fabaceae, Amaranthaceae, Brassicaceae, Boraginaceae, Caryophyllaceae, Lamiaceae, Apiaceae, and Cistaceae. Therophytes made the highest contribution, followed by chamaephytes and hemicryptophytes. Of all these species, 40% were palatable to highly palatable and more than 13% are used in both traditional and modern medicine.
... However, it is of note that long-term exclusion can also have a detrimental impact on rangeland health. Livestock hoofs break up the hard-crusted soils common to arid rangelands, allowing rainwater infiltration in the soil and seedlings emergence; and in the case of perennial grasses, grazing removes oxidised plant material that would otherwise remain on the top of plants and prevent photosynthesis, causing plant death after several years (Holechek 2006;Tarhouni et al. 2017). Natural establishment of vegetation by reseeding may be assisted by human intervention through soil scarification that increased the vegetation cover by 12-20%, compared with control plots during the dry season of 2017/2018. ...
Article
Full-text available
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.
... Short-term exclusion was proven to increase the richness and diversity of plant species (Zhang and Zhao, 2015;Ebrahimi et al., 2016;Liu et al., 2019), plant cover and density (Tang et al., 2016;Sigcha et al., 2018), and affects plant community composition (Korkanç, 2014;Sigcha et al., 2018). On the other hand, some studies have suggested that grazing exclusion either does not affect vegetation cover (Kakinuma et al., 2017) or have negative effects on plant diversity (Tarhouni et al., 2017a(Tarhouni et al., , 2017bYao et al., 2019). Thus, the response of plant communities to grazing exclusion in arid rangelands and other water-limited environments is inconsistent and hotly debated (Frank et al., 2014;Sigcha et al., 2018). ...
Article
Full-text available
Grazing exclusion has been proved to be an effective approach for naturally restoring degraded rangelands. Still, the effect of this management practice on plant community composition and structure is ambiguous, especially under prolonged and repeated drought events. Here, we investigated the responses of community composition (i.e. incidence-based) and structure (i.e. abundance-based) to short-term sheep grazing exclusion under severe drought episode in the arid steppes of Alfa-grass (Stipa tenacissima L.) with a long evolutionary history of grazing. Individual species responses were tested based on species occurrence and abundance in either grazed or grazing-excluded steppes. Besides, indicator species analysis was used to identify species indicative of grazing-excluded steppes. Likewise, incidence-based and abundance-based α-diversity, β-diversity and functional groups' diver-sities were quantified using Hill Numbers and compared between the two steppe managements types. Under severe drought conditions, sheep grazing exclusion allowed the apparition of a large number of increasers, colonizers, and native indicator plant species. It also improved the size of regional species pool and increased overall incidence-based and abundance-based α-diversity. Moreover, grazing exclusion decreased the abundance based β-diversity at local scale but increased it at landscape scale. The incidence-based β-diversity significantly decreased at the landscape scale. Grazing exclusion enabled a significant spatial structuration of abundance-based β-diversity components by maintaining high balanced variation in species abundance at large spatial scale and greater abundance-gradient at fine-scale. Our results suggest that the implementation of short-term grazing exclusion in arid steppes would be the appropriate management practice for vegetation and habitat during prolonged droughts since it permits the recovery of native plant species and affects positively the size of the regional species pool, the overall incidence-and abundance-based α-diversity as well as the abundance-based β-diversity (chiefly at landscape scale).
... 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.
... 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
Full-text available
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.
Article
en Over the second half of the past century, the Zloul Valley has undergone rapid and intense changes, such as deforestation and massive clearing as well as a grazing ban in olive plots since the introduction of olive cultivation approximately 30 years ago. The aim of this study was to explore these rapidly changing ecosystems. The floristic analysis revealed a more pronounced anthropozoic impact on the Chamaerops humilis and Ampelodesmos mauritanicus steppe group, which displayed the lowest floristic diversity, with a Shannon–Weaver index of 3.72, and a very high disturbance, of 68.85%. The grazing ban in olive plots had a positive effect on floristic richness and diversity, with the Shannon–Weaver index reaching a maximum value of 4.67. However, the floristic composition remained unbalanced, with an equitability index of 0.61 and a perturbation index of 70.8%. Therefore, these ecosystems have not been able to recover their initial equilibrium despite being under protection for long. The ecosystems of the Zloul Valley demonstrated alarming levels of degradation, especially on the southern slopes of Jbel Ikraa and Jnab Diss. Urgent measures must be taken to mitigate biodiversity loss and soil erosion as a matter of priority. Résumé fr La vallée de Zloul a connu au cours de la dernière moitié du siècle dernier des changements rapides et intenses. Des déforestations et des défrichements massifs ainsi qu’une mise en défens des parcelles oléicoles, depuis l’introduction de la culture d’olivier il y a une trentaine d’années. Cette étude a été consacrée à explorer ces écosystèmes en pleine mutation. L'analyse floristique a révélé un impact anthropozoïque plus accentué au niveau du groupe des steppes de Chamaerops humilis et Ampelodesmos mauritanicus, qui a enregistré la plus faible diversité floristique, avec un indice Shannon‐Weaver de 3,72 et une perturbation très élevée de 68,85%. L'interdiction de pâturage dans les parcelles oléicoles a eu un effet positif sur la richesse et la diversité floristique, l'indice Shannon‐Weaver a atteint une valeur maximale de 4,67. Cependant, la composition floristique est restée déséquilibrée, avec un indice d'équitabilité de 0,61 et un indice de perturbation de 70,8%. Par conséquent, il semble que ces écosystèmes n'ont pas pu retrouver leur équilibre initial malgré une longue période de mise en défens. Les écosystèmes de la vallée de Zloul ont montré des niveaux de dégradation alarmants, en particulier sur les versants sud de Jbel Ikraa et Jnab Diss. Des mesures urgentes doivent être prises pour atténuer en priorité l’érosion de la biodiversité et des sols.
Article
Question We ask whether 11‐year mowing patterns and presence of fencing influence plant community diversity and functional assemblage in urban vacant lots. Location This study took place in 34 vacant lots on the south and west sides of Chicago, IL, USA. Urban vacant lots are an excellent study system in which to investigate the effects of management in cities: they are ubiquitous in many cities and they experience a range of management, particularly mowing and fencing. Methods We used municipal data to classify infrequent and intensive mowing regimes and assessed presence or absence of fencing in situ. In our sites, these management strategies are independent. We used individual permutational analysis of variance (PERMANOVA) models to assess the effects of these management strategies on plant community composition. We then assessed species richness of plants with various traits using six individual two‐way ANOVA models with interaction terms. Our predictor variables included management strategies (mowing intensity and fencing) and three plant traits (growth form [graminoid, forb, or woody], life duration (annual, biennial, or perennial), and biogeographic origin [native or introduced]). Results We found 120 plant species in the vacant lots. Most of these species were perennial, introduced forbs. We found no discernable effects of mowing intensity on plant community composition or richness of plants in the three functional groups. However, when we compared the species found along fences to those in lot interiors, we found significantly different plant communities. Fence line communities had significantly more native and woody species than lot interiors. Conclusions Plant communities differ at very fine spatial scales within an individual vacant lot, and this pattern is related to the presence of fences. Overall, vacant lots support diverse plant communities which can differentially contribute to wildlife habitat depending on management strategy.
Article
Full-text available
The restoration technique importance resides on the assessment of its impact on biodiversity. This assessment is possible by the use of some environmental indicators extracted from a diachronic study of land cover changes in protected areas. Our study is carried out with the evaluation of some indicators inside Sidi Toui national park. These indicators are measured on the one hand from a land cover map of 1988 (3 years before the creation of the park) and the map of 2007 on the other hand (16 years after the park creation). An important landscape heterogeneity, as a result of the progressive vegetation dynamic, was observed in 2007. This heterogeneity is indicated by an increasing of the Shannon diversity index under fencing impacts. The majority of 1988 vegetation units are replaced by new ones in 2007. The cover of all vegetation units is more important in 2007.
Article
Full-text available
The impact of community conservation management on a semi-arid savannah herbaceous vegetation and soil nutrient status was studied in the conservation and grazing zones of two community ranches in Laikipia County, Kenya. Land zoning was carried out in 1999 using participatory approaches to demarcate conservation areas excluded from livestock grazing, buffer areas for grazing, and high intensity use zones for both grazing and settlement. Collected data included cover, grass species composition, standing grass biomass and topsoil chemical characteristics using line transect and quadrant methods. The conservation zones had significantly higher herbaceous diversity, species richness, and relative abundance of both annual and perennial grasses, basal cover and herbage, and a lower percentage of bare ground compared to the continuously grazed zones. The conservation zones also had higher total organic carbon, organic nitrogen and exchangeable basic cations content, indicating improved soil nutrient status. The grazing zones exhibited loss of vegetation cover and reduction of forage production, with a decline in rangeland condition, whereas the conservation zones showed recovery and improvement of the rangeland condition. Long-term implementation of NRM programme in community wildlife conservancies seems to drive the semi-arid savannahs to exist in two steady states and transitions under the influence of grazing. We recommend long-term monitoring of the impact of the community conservation model on the rangeland and timely incorporation of remedial measures such as shifting bomas (cattle corrals) across the grazing zones, aggressive rangeland rehabilitation of severely degraded areas through reseeding and random grass seed broadcast along stock routes. This article is protected by copyright. All rights reserved.
Article
Full-text available
This study aimed to evaluate the impact of climate change on the geographical distribution of selected native species from two areas from West Asia and North Africa. Three species representing two genera were selected for assessment of their vulnerability to climate change. The first species was Salsola vermiculata L. which is common to both study areas. The second genus was represented by two species, Haloxylon salicornicum (Moq.) Bunge from the Syrian rangelands and H. schmittianum Pomel from southern Tunisia. To assess the vulnerability of these species to climate change we used ecological-based models. The data inputs were composed of the species occurrence data and the environmental data which included eight climatic layers, three soil property layers in addition to an altitude layer. Since environmental parameters only enable assessing the sensitivity of target species to climate change, a grazing pressure layer was used to assess the species vulnerability. Only climatic parameters were considered as changing across three periods; current situation, 2020 and 2050. The main results indicated that threatened range species, such as S. vermiculata which were subjected to continuous grazing pressure, showed high vulnerability to climate change as expressed by the predicted decrease in the areas of their distribution. However, species with low palatability and broad ecological niches (i.e. H. salicornicum and H. schmittianum) had an advantage due to the reduced competition for water and nutrients. An adaptation strategy to increase the resilience of the most vulnerable species should involve management of grazing pressure and the establishment of other mitigation measures.
Article
Full-text available
The present study deals with the assessment of the effects of drought on the natural plant cover of two natural regions of Southern Tunisia. Several parameters and indicators have been used to describe the evolution of plant communities and their fate under the different constraints and disturbances effect. The main achieved results show that relations between soil and climatic conditions and plant cover are strongly influenced by the human activities impact. The highest specific flora richness has been recorded at the experimental stations of the Jeffara (sandy steppe). The impact of drought on plant cover was more important in the experimental stations presenting higher plant density mainly Artemisia herba-alba , Gymnocarpos decander and Hammada scoparia which are considered as key species of some ecosystems.
Article
Full-text available
In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects-particularly those caused by mortality-largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and pinon-juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.
Article
Seed size has been advanced as a key factor that influences the dynamics of plant communities, but there are few empirical or theoretical predictions of how community dynamics progress based on seed size patterns. Information on the abundance of adults, seedlings, soil seed banks, seed rains, and the seed mass of 96 species was collected in alpine meadows of the Qinghai-Tibetan Plateau (China), which had different levels of grazing disturbance. The relationships between seed-mass-abundance patterns for adults, seedlings, the soil seed bank, and seed rain in the plant community were evaluated using regression models. Results showed that grazing levels affected the relationship between seed size and abundance properties of adult species, seedlings, and the soil seed bank, suggesting that there is a shift in seed-size--species-abundance relationships as a response to the grazing gradient. Grazing had no effect on the pattern of seed-size-seed-rain-abundance at four grazing levels. Grazing also had little effect on the pattern of seed-size--species-abundance and pattern of seed-size--soil-seed-bank-abundance in meadows with no grazing, light grazing, and moderate grazing), but there was a significant negative effect in meadows with heavy grazing. Grazing had little effect on the pattern of seed-size--seedling-abundance with no grazing, but had significant negative effects with light, moderate, and heavy grazing, and the |r| values increased with grazing levels. This indicated that increasing grazing pressure enhanced the advantage of smaller-seeded species in terms of the abundances of adult species, seedlings, and soil seed banks, whereas only the light grazing level promoted the seed rain abundance of larger-seeded species in the plant communities. This study suggests that grazing disturbances are favorable for increasing the species abundance for smaller-seeded species but not for the larger-seeded species in an alpine meadow community. Hence, there is a clear advantage of the smaller-seeded species over the larger-seeded species with increases in the grazing level.
Article
Grazing intensity and bush encroachment are disturbance factors that may alter the floristic composition of herbaceous species. This paper investigates impacts of grazing (intensity) and bush encroachment on herbaceous species and rangeland conditions in Borana, southern Ethiopia. Herbaceous species richness and the abundance of each species were greater in the light- and moderate-grazed areas than heavy-grazed sampling plots. Similarly, herbaceous species richness was highest at an intermediate level of biomass and seems to decline as biomass increases. Among a total of 40 herbaceous species recorded, 20 per cent were tolerant of grazing, whereas the remaining 80 per cent were highly susceptible to heavy grazing. In both encroached and non-encroached sampling plots, species richness varied from three to six species 0·25 m−2. Overall, herbaceous species richness and abundance, in relation to grazing gradient, might disclose a better picture of the effect of grazing on individual herbaceous species. As species richness seems to decline under heavy grazing intensity, low to intermediate grazing levels may promote and conserve key forage species in savanna grazing lands. Copyright © 2012 John Wiley & Sons, Ltd.
Article
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.
Article
Grazing has been identified as the main cause of land degradation in Patagonia. However, land degradation is highly variable among areas, even within the same paddock. This strongly suggests that different plant communities differ in their resistance to land degradation. In this study we have evaluated soil erosion at both microsite and community scales in coexisting plant communities subject to sheep grazing in NE Patagonia. Three plant communities coexist in the area: two shrub steppes dominated by Chuquiraga avellanedae Lorentz and Nassauvia ulicina (Hook. f.) Macloskie, and a grass steppe dominated by Nassella tenuis (Phil.) Barkworth. At a community scale, our results indicate that shrub steppes generally experienced soil erosion whereas the grass steppe commonly did not show signs of soil erosion/deposition. At a microsite scale, non-vegetated soil surface types and degraded mounds never accumulated sediments, regardless of plant community. In contrast, we found that in some sites the intact mounds and grasses entrapped sediments, but in other sites soil erosion prevailed. Our results highlight the fact that soil erosion measurements are scale dependent, since results at microsite and community scales often differ. When comparing amongst communities, grass steppe is more intensely grazed, but at the same time it shows less evidence of past and present erosion. In contrast, the N. ulicina community showed a direct relationship between grazing and soil erosion. Finally, soil erosion was not related to grazing in the C. avellanedae community. Our results demonstrate that the grass steppe is more resistant to land degradation than shrub steppes. This article is protected by copyright. All rights reserved.
Article
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.
Data
In the northern highlands of Ethiopia, establishment of exclosures to restore degraded communal grazing lands has been practiced for the past three decades. However, empirical data on the effectiveness of exclosures in restoring degraded soils are lacking. We investigated the inu-ence of exclosure age on degree of restoration of degraded soil and identied easily measurable biophysical and management-related factors that can be used to predict soil nutrient restoration. We selected replicated (n = 3) 5-, 10-, 15-, and 20-year-old exclosures and paired each exclosure with samples from adjacent communal grazing lands. All exclosures showed higher total soil nitrogen (N), available phosphorus (P), and cation exchange capacity than the communal grazing lands. The differences varied between 2Á4 (AE0Á61) and 6Á9 (AE1Á85) Mg ha À1 for the total N stock and from 17 (AE3) to 39 (AE7) kg ha À1 for the available P stock. The differences in N and P increased with exclosure age. In exclosures, much of the variability in soil N (R 2 = 0Á64) and P (R 2 = 0Á71) stocks were explained by a combination of annual average precipitation, woody biomass, and exclosure age. Precipitation and vegetation canopy cover also explained much of the variability in soil N (R 2 = 0Á74) and P (R 2 = 0Á52) stocks in communal grazing lands. Converting degraded communal grazing lands into exclosures is a viable option to restore degraded soils. Our results also conrm that the possibility to predict the changes in soil nutrient content after exclosure establishment using regression models is based on eld measurements.
Article
Climate and grazing are the main drivers of plant community composition and species richness in arid environments. This study aimed to examine the vegetation response to a spatial precipitation gradient, interannual rainfall variability, and grazing pressure in Mongolia. To examine the effect of a spatial precipitation gradient, we compared species richness among six sites. To investigate the effects of interannual rainfall variability and grazing pressure, we compared species richness for 2 years at two sites, in desert-steppe and steppe areas. The regional gradient in annual precipitation showed positive and negative relationships with grass richness and shrub richness, respectively, although total species richness did not vary significantly. The proportions of the different functional groups were affected by grazing pressure and rainfall variability in both zones. In the desert-steppe zone, species richness was lower in the drier year but did not vary with grazing pressure. In the steppe zone, species richness varied significantly with grazing pressure but did not vary between years. Precipitation would be more important than grazing pressure on vegetation changes in drier areas with high rainfall variability.
Article
Species diversity influences plant community structure and function. This paper examines the patterns and dynamics of species diversity along a chronosequence of vegetation recovery on sand dunes in a semi-arid region to assess the probability of vegetation recovery via succession, and provides some implications for revegetation practices in this region. Species richness and diversity indices gradually increased with succession, except for a decline in the community of 18 years, which is attributed to the strong dominance of Artemisia halodendron. In each stage of the restoration process, there was a dominant species with particular life history traits which contribute to the dominance of this species. Species replacement and habitat changes were the main drivers of succession, while plant species and community succession drove the process of vegetation recovery. Results showed that restoration via succession holds promise for vegetation recovery and desertification control within protected, fenced enclosures.
Article
A 60-year chronosequence study of semi-arid old-fields indicates that abandonment age, litter depth, organic carbon soil content, carbonate content and soil moisture are related to vegetation ordination. The species turnover could be high in the recent abandoned fields. Species richness varies, holding a non-linear relation with time as a result of the coexistence of different functional groups. Land use history determines the ordination of communities and previous cropping influences the pathway of succession. Plant functional group and dispersal type richness and cover show significant differences between old-field age groups. The facilitation pathway of crop trees on bird-dispersed shrub species could promote the development of vegetation under these stressful conditions.
Article
In this paper, we studied the spatial variability of soil organic C (SOC), inorganic N (SIN) and extractable P (Pextr) in a grazed Mediterranean-type formation. Sampling was conductedwithin a Northern Greek gentle slope. The grazing pressure was evenly distributed over the experimental area with the exception of an overgrazed passage zone 200–300m from the foothills. Soil samples, from the upper 10 cm, were collected every 10m along four replicate lines (400m length with a distance of 10m between them). Sampling took place twice (October and February). Data were analysed by geostatistical tools, and spherical models were significantly fitted to the semivariograms. SOC in both samplings and SIN in the first one displayed moderate spatial dependence which indicates the non-random distribution of their concentration. On the contrary, Pextr and SIN in winter exhibited weak spatial dependence, whereas Pextr in autumn showed spatial independence. For the parameters exhibiting spatial pattern, two scales of dependence were revealed: a fine scale within distances shorter than 10m and a coarse scale varying between 80 and 130m. The coarse distribution of SOC, SIN and Pextr invoked interplay among more predictable (composition of vegetation) and unpredictable (leaching, runoff) extrinsic factors, occurring at the landscape level. Specifically, SOC as a storage agent exhibited uniform spatial pattern in both samplings. By contrast, SIN by being susceptible to leaching exhibited time-specific dependence, whereas Pextr which was affected rather by surface runoff displayed limited or even spatial independence.
Article
Entropies such as the Shannon–Wiener and Gini–Simpson indices are not themselves diversities. Conversion of these to effective number of species is the key to a unified and intuitive interpretation of diversity. Effective numbers of species derived from standard diversity indices share a common set of intuitive mathematical properties and behave as one would expect of a diversity, while raw indices do not. Contrary to Keylock, the lack of concavity of effective numbers of species is irrelevant as long as they are used as transformations of concave alpha, beta, and gamma entropies. The practical importance of this transformation is demonstrated by applying it to a popular community similarity measure based on raw diversity indices or entropies. The standard similarity measure based on untransformed indices is shown to give misleading results, but transforming the indices or entropies to effective numbers of species produces a stable, easily interpreted, sensitive general similarity measure. General overlap measures derived from this transformed similarity measure yield the Jaccard index, Sørensen index, Horn index of overlap, and the Morisita–Horn index as special cases.
Article
Stipa tenacissima L., which has long been recognised as the typical dominant perennial plant in the North-African arid rangelands is currently going into extinction in the steppic High Plains of Algeria. The vegetation and soil dynamics were analyzed at an initially dense stand. The trend between 1976 and 2006 was investigated using five reference years. Sampling was performed along a grazing gradient including a grazed steppe and an exclosure. Between 1976 and 1993, the perennial cover and soil organic matter decreased outside the exclosure, while the composition of the dominant species remained unchanged. From 1993 to 2006, the plant cover, species composition and soil showed major changes both inside and outside the exclosure and S. tenacissima disappeared completely in 2006. These changes were primarily attributed to overgrazing by sheep. More frequent and intensive droughts exacerbated the grazing intensity in a context of common and uncontrolled land use. The exclosure, implemented as a remedy, temporarily played a positive role regarding vegetation and soil conservation. In addition to severe drought, the vegetation and soil degradation and sand encroachment even inside the exclosure, created conditions that were no longer able to support the pre-existing alfa-grass ecosystem.
Article
a b s t r a c t To understand the effects of grazing on grassland plants sexual and clonal recruitment, we conducted a demographic field investigation of species recruitment along a grazing gradient in the Tibetan alpine grassland. Grazing intensity had significant effects on quantity and diversity of sexual and clonal recruit-ment. Sexual recruitment increased significantly, but clonal offspring production decreased significantly with increased grazing intensity. Grazing intensity had different, significant effects on offspring recruit-ment of the various functional groups in the community, grasses (GG), sedges (SG), legumes (LG) and forbs (FG). Higher grazing intensity reduced offspring recruitment of GG and SG; it increased offspring recruit-ment of LG and FG. Seedlings were significantly more abundant in lightly grazed, moderately grazed and heavily grazed meadows than in non-grazed grasslands. Offspring diversity from sexual recruitment was significantly higher than that from clonal recruitment in grazed than in non-grazed grasslands. Our studies indicate that moderate grazing had positive effects on seedling recruitment and offspring diver-sity, but heavy gazing may alter community succession by affecting recruitment patterns among the four plant functional groups.
Article
In the northern highlands of Ethiopia, establishment of exclosures to restore degraded communal grazing lands has been practiced for the past three decades. However, empirical data on the effectiveness of exclosures in restoring degraded soils are lacking. We investigated the influence of exclosure age on degree of restoration of degraded soil and identified easily measurable biophysical and management-related factors that can be used to predict soil nutrient restoration. We selected replicated (n = 3) 5-, 10-, 15-, and 20-year-old exclosures and paired each exclosure with samples from adjacent communal grazing lands. All exclosures showed higher total soil nitrogen (N), available phosphorus (P), and cation exchange capacity than the communal grazing lands. The differences varied between 2·4 (±0·61) and 6·9 (±1·85) Mg ha−1 for the total N stock and from 17 (±3) to 39 (±7) kg ha−1 for the available P stock. The differences in N and P increased with exclosure age. In exclosures, much of the variability in soil N (R2 = 0·64) and P (R2 = 0·71) stocks were explained by a combination of annual average precipitation, woody biomass, and exclosure age. Precipitation and vegetation canopy cover also explained much of the variability in soil N (R2 = 0·74) and P (R2 = 0·52) stocks in communal grazing lands. Converting degraded communal grazing lands into exclosures is a viable option to restore degraded soils. Our results also confirm that the possibility to predict the changes in soil nutrient content after exclosure establishment using regression models is based on field measurements. Copyright © 2011 John Wiley & Sons, Ltd.
Article
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.
Article
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.
Article
Drought has become widespread in the Northern Hemisphere and has affected the specific Mongolian steppes both quantitatively and qualitatively. To simulate vegetation responses to drought, we conducted a drought experiment in the Mongolian steppe during a rainy summer growing season. A 30 × 30 m rain shelter excluded natural precipitation during the 2005-growing season, simulating a drought with a return interval of 60–80 years. We examined the effects of the drought on aboveground phytomass (AGP) of each species, total belowground phytomass (BGP), and soil water. The drought drastically reduced AGP and soil water but did not substantially affect BGP. AGP recovered quickly in the late summer of 2006, likely because BGP (which was several times AGP) was not severely damaged by the drought. However, the poorly resilient species did not recover to pre-drought levels, suggesting that the response time scales differed among species. Despite the intense drought, the large root system provided a basis for quick recovery of AGP to pre-drought levels without a shift to a drier equilibrium community. We propose new drought sensitivity and resiliency indices to measure the ecosystem's sustainability and identify species with low sensitivity (i.e., high drought tolerance) that form the baseline of AGP.
Article
Water points provide excellent sites for studying overgrazing effects on plant communities in dry areas. Distance from water can be considered like a surrogate of grazing pressure being high near the water and low away from it. The main aim of this study is to investigate overgrazing effects on acceptability of fodder plants along a grazing gradient around three natural watering points. To achieve this goal, we classified spontaneous plants according to their acceptability degree and we followed their cover, richness and density as well as the grazing value along a grazing gradient around these wells, using phyto-ecological studies during the spring 2004 and 2006. Main results show that very palatable plants (mainly constituted by annuals) are more dominant in both the closed and the more disturbed transect areas around wells. The unpalatable plants dominate sites with moderate disturbance around wells. Ligneous palatable species obviously have a lower degree of disturbance. During the studied seasons the grazing gradient around wells 1 and 2, the oldest ones, seemed to exert a feedback upon the grazing intensity.
Article
Future changes in precipitation regimes are likely to impact species richness in water-limited plant communities. Regional, spatial relationships between precipitation and richness could offer information about how altered rainfall will impact local communities, assuming that processes driving the regional relationship are also dominant at fine spatial and short temporal scales. To test this assumption, we compared spatial and temporal relationships between precipitation and both species richness and species turnover in central North American grasslands. Across a broad geographic gradient, mean plant species richness in 1m2 plots increased significantly with mean annual precipitation. In contrast, over a 36-yr period at one mixed-grass prairie in the center of the regional gradient, single-year precipitation and richness were poorly correlated, and consecutive wet years had little effect on richness. Instead, richness increased most in wet years that followed dry years. Geographically dispersed sites receiving different levels of mean annual precipitation displayed strong differences in species composition, whereas temporal variation in precipitation at one site was not related to compositional dissimilarity, indicating that species turnover plays a key role in generating the regional relationship. Analyses of individual species’ presence-absence suggest that the lagged temporal responses reflect environmental germination cues more than resource competition. These complex cues may dampen the initial impact of altered precipitation on diversity, but over the long term, turnover in species composition should lead to changes in richness, as in the regional, spatial relationship. How quickly this long-term response develops may depend on the colonization rates of species better adapted to the altered rainfall regime.
Article
Accumulating evidence points to an anthropogenic 'fingerprint' on the global climate change that has occurred in the last century. Climate change has, and will continue to have, profound effects on the structure and function of terrestrial ecosystems. As such, there is a critical need to continue to develop a sound scientific basis for national and international policies regulating carbon sequestration and greenhouse gas emissions. This paper reflects on the nature of current global change experiments, and provides recommendations for a unified multidisciplinary approach to future research in this dynamic field. These recommendations include: (1) better integration between experiments and models, and amongst experimental, monitoring, and space-for-time studies; (2) stable and increased support for long-term studies and multi-factor experiments; (3) explicit inclusion of biodiversity, disturbance, and extreme events in experiments and models; (4) consideration of timing vs intensity of global change factors in experiments and models; (5) evaluation of potential thresholds or ecosystem 'tipping points'; and (6) increased support for model-model and model-experiment comparisons. These recommendations, which reflect discussions within the TERACC international network of global change scientists, will facilitate the unraveling of the complex direct and indirect effects of global climate change on terrestrial ecosystems and their components.
People and rangelands: building the future D Eldridge D. Freudenberger The Congress Townsville
  • R M Callaway
  • C Tyler
Impact des variations climatiques et de la protection sur la dynamique du couvert végétal au sein du parc national de Sidi Toui
  • Ben Hmida
Ben Hmida, W. (2012) Impact des variations climatiques et de la protection sur la dynamique du couvert v eg etal au sein du parc national de Sidi Toui, Sud tunisien. Master de Recherche en Sciences de l'Environnement. Facult e des Sciences de Bizerte, Tunisie, 90 p.
Biodiversité et gestion pastorale en zones arides et semi-arides méditerranéennes du Nord de l'Afrique
  • Le Floc'h
Le Floc'h, E. (2001) Biodiversit e et gestion pastorale en zones arides et semi-arides m editerran eennes du Nord de l'Afrique. Bocconea 13, 223-237.
Relevés des transects et de la végétation des parcs nationaux de Bou-Hedma et de Sidi Toui 115
  • M Schönenberger
Cartographie des systèmes écologiques et évaluation de l'impact de la protection sur la dynamique du couvert végétal dans le parc national de Sidi Toui
  • A Lahdhiri
Lahdhiri, A. (2008) Cartographie des syst emes ecologiques et evaluation de l'impact de la protection sur la dynamique du couvert v eg etal dans le parc national de Sidi Toui. M emoire de mast ere, FLAHM. Tunis, 110 p.+Annexes.
Biodiversité et suivi de la dynamique des phytocénoses en Tunisie présaharienne: Cas des observatoires de Sidi Toui et de Oued Dekouk
  • Mohamed Ould Sidi
Indicateurs de biodiversit e et dynamique du couvert v eg etal naturel aux voisinages de trois points d'eau en zone aride tunisienne: cas des parcours collectifs d'El-Ouara
  • M Tarhouni
Tarhouni, M. (2008) Indicateurs de biodiversit e et dynamique du couvert v eg etal naturel aux voisinages de trois points d'eau en zone aride tunisienne: cas des parcours collectifs d'El-Ouara. Th ese de doctorat en Biologie. Univ. Tunis El-Manar. F.S.Tunis 168p.+annexes.
Flore analytique et synoptique de Tunisie: Cryptogames vasculaires, Gymnospermes et Monocotylédones
  • A. Cuénod
  • G. Pottier-Alapetite
  • A. Labre
Validation et comparaison de divers indicateurs des changements à long terme dans les écosystèmes Méditerranéens arides
  • S Jauffret
Jauffret, S. (2001) Validation et comparaison de divers indicateurs des changements a long terme dans les ecosyst emes M editerran eens arides. Th ese Doctorat. Univ de droit, d' economie et des sciences d'Aix-Marseille 328p.+Annexes.
Carte d'occupation des terres et des ressources pastorales d'El-Ouara
  • M Moussa
  • M Zaafouri
Moussa, M. & Zaafouri, M. (1988) Carte d'occupation des terres et des ressources pastorales d'El-Ouara. Projet: TUN 86/002 : cartographie des ressources pastorales dans les zones de mise en valeur de sud.
Variation de la richesse floristique en fonction du gradient de pâturage au voisinage de points d'eau en Tunisie pr esaharienne
  • M Tarhouni
  • F Ben Salem
  • A Ouled Belgacem
  • B Henchi
  • M Neffati
Tarhouni, M., Ben Salem, F., Ouled Belgacem, A., Henchi, B. & Neffati, M. (2007b) Variation de la richesse floristique en fonction du gradient de pâturage au voisinage de points d'eau en Tunisie pr esaharienne. S echeresse 18, 234-239.