Grass Species Richness Research Articles

Effects of perennial aromatic grass species richness and microbial consortium on soil properties of marginal lands and on biomass production

AbstractThis study investigates the effects of perennial grass species richness levels and consortium of three bacteria on properties of a slightly alkaline soil and on biomass production of grasses. Four species of perennial aromatic grasses namely: vetiver (Vetiveria zizanioides), lemongrass (Cymbopogon citratus), palmarosa (Cymbopogon martinii), and citronella (Cymbopogon winterianus) were planted in all possible combinations at one, two, three, and four species richness levels in a randomized block design with three replications and two treatments, these were PGPR+ (with plant growth promoting rhizobacteria) and without (PGPR−). Species and richness level specific changes in soil physicochemical properties: electrical conductivity (EC); bulk density (BD); total soil organic carbon (TOC); available nitrogen (Nav), microbial colony forming unit (CFU); microbial biomass carbon (MBC), and enzymatic alkaline phosphatase (ALKP) and dehydrogenase activity (DHA) were observed. The highest reduction in soil pH and EC and increase in soil TOC, CFU, Nav, MBC, and enzymes activities were found at two species richness levels of vetiver and lemongrass in both PGPR+ and PGPR− plots followed by monoculture of vetiver. The highest annual total dry biomass 22.8 and 27.5 Mg ha−1 was produced by monoculture of vetiver in PGPR− and PGPR+ plots, respectively, with similar values at two species richness levels of vetiver and lemongrass in PGPR− and PGPR+ plots. The highest plant carbon was found in vetiver monoculture and two species richness levels of vetiver and lemongrass. The soil carbon sequestration potential was highest at two species mixtures of vetiver–lemongrass and lemongrass–palmarosa as well.

Direct and indirect effects of plant diversity and phenoxy herbicide application on the development and reproduction of a polyphagous herbivore

Widespread application of synthetic pesticides and loss of plant diversity are regarded as significant drivers of current global change. The effects of such phenomena on insect performance have been extensively studied separately, yet the interactions of these two drivers have been poorly explored. Here, we subjected the polyphagous grasshopper Pseudochorthippus parallelus (Zetterstedt, 1821) to a full-lifecycle field experiment with 50 cages containing experimental plant communities differing in grass species richness (2 vs. 8 grass species), half of them treated with a phenoxy herbicide commonly employed to control broadleaf plants in grasslands. We measured plant elemental content as a proxy for plant physiology, and a wide range of insect traits in both female and male grasshoppers. In females, grass diversity increased herbivory, insect nitrogen content and egg load, while herbicide reduced herbivory but increased the number of offspring, likely mediated by altered plant community composition. In males, grass diversity also increased herbivory, had positive effects on fat body, muscle volume and lifespan, and negative effects on body mass. Herbicide negatively affected herbivory in both females and males. Overall, plant diversity and herbicides may shift resource allocation in generalist terrestrial insect herbivores, indicating complex and unexpected effects of human-induced environmental change.

Can livestock exclusion affect understory plant community structure? An experimental study in the dry Chaco forest, Argentina

Livestock grazing can be a problem for forest conservation because it can generate heterogeneous and unpredictable changes in plant communities. Understanding these changes is important for generating management strategies that are compatible with long-term conservation of threatened forests. Livestock exclusion is a useful experimental approach used to evaluate grazing effects. However, the evidence showing the effects of grazing on forests is mixed and little in know about the responses of different plant life forms, especially in dry forests. In this study, we evaluated the effects of a 7–8 year of livestock exclusion experiment on understory plant community structure in the dry Chaco forest (Argentina). We categorized understory plant life forms as shrubs, succulents (Cactaceae family + Bromelia hieronymi), and herbs (forbs, grasses and vines). Then, we compared the plant community structure (richness, diversity, density and cover) and understory structure (soil hardness, bare soil and vegetation vertical and horizontal structure) between five excluded plots and five grazed plots, in a paired design. We found that livestock exclusion lead to an increase in grass species richness and grass cover as well as an increase in lower understory biomass (0–0.5 m) and a decrease in percentage of bare soil. On excluded plots, dominant herbs were Setaria nicorae (grass), Trichloris crinita (grass), and Justicia squarrosa (forb). Grass species that were recorded exclusively on excluded plots were Gouinia latifolia, T. crinita, and Pappophorum mucronulatum, all forage species preferred by livestock. In contrast, on grazed plots, the dominant species was Stenandrium dulce (forb), a species with resistance strategies to grazing. As for the other variables, we did not find strong differences between excluded and grazed plots. Livestock grazing did not modify the ensemble structure of shrubs and succulents nor did it change the horizontal vegetation structure or soil hardness. Our evidence suggests that the assemblage composed by shrubs and succulents seems to be tolerant to livestock grazing, and that the grass assemblage has the ability to quickly recover when grazing stops. Finally, the effectiveness of exclusion as a management tool will depend on which attribute of the plant community to be conserved or recovered. In dry Chaco forests after many years of grazing at moderate stocking rates, livestock exclusion could help recover grass cover, generate opportunities for the establishment of certain grass species that are sensitive to grazing, and increase ground cover.

Asymmetric responses of plant community structure and composition to precipitation variabilities in a semi-arid steppe.

Changing precipitation regimes can profoundly affect plant growth in terrestrial ecosystems, especially in arid and semi-arid regions. However, how changing precipitation, especially extreme precipitation events, alters plant diversity and community composition is still poorly understood. A 3-year field manipulative experiment with seven precipitation treatments, including - 60%, - 40%, - 20%, 0% (as a control), + 20%, + 40%, and + 60% of ambient growing-season precipitation, was conducted in a semi-arid steppe in the Mongolian Plateau. Results showed total plant community cover and forb cover were enhanced with increased precipitation and reduced under decreased precipitation, whereas grass cover was suppressed under the - 60% treatment only. Plant community and grass species richness were reduced by the - 60% treatment only. Moreover, our results demonstrated that total plant community cover was more sensitive to decreased than increased precipitation under normal and extreme precipitation change, and species richness was more sensitive to decreased than increased precipitation under extreme precipitation change. The community composition and low field water holding capacity may drive this asymmetric response. Accumulated changes in community cover may eventually lead to changes in species richness. However, compared to control, Shannon-Weiner index (H) did not respond to any precipitation treatment, and Pielou's evenness index (E) was reduced under the + 60% treatment across the 3year, but not in each year. Thus, the findings suggest that plant biodiversity in the semi-arid steppe may have a strong resistance to precipitation pattern changes through adjusting its composition in a short term.

Nitrogen addition decreases seed germination in a temperate steppe.

Seed germination and seedling establishment play an important role in driving the responses of plant community structure and function to global change. Nitrogen (N) deposition is one of the driving factors of global change, which often leads to a loss in species richness in grassland ecosystems. However, how seed germination responds to N addition remains unclear. A pot incubation test was conducted in a semi‐arid grassland in the Mongolian Plateau, Northern China, to investigate the effect of N addition (0, 5, 10, 20, 40, and 80 g N/m2) on seed germination from May to October 2016. Twenty species germinated under all treatments; however, the responses of the 20 species to N addition were different. The densities of Stipa krylovii, Leymus chinensis, and Artemisia frigida, which are the dominant species in this temperate steppe, decreased significantly as the amount of N addition. Moreover, N addition significantly suppressed seedling densities of the community, perennial forbs, perennial grasses, and annuals and biennials. Furthermore, species richness of the community, perennial forbs, and annuals and biennials decreased sharply with increasing N addition level, but perennial grass species richness did not change. The Shannon–Wiener diversity index also decreased as the amount of N addition increased. Our results suggest that N enrichment plays an important role in the seed germination stage and decreases supplements of seedlings to adult plants. These findings may help explain the causes of species loss by atmospheric N deposition in grassland ecosystems.

Comparing the effects of continuous grazing and long term exclosure on floristic composition and plant diversity in rangeland ecosystems of Saral, Iran

Continuous grazing as the most common land us in Kurdistan rangeland is practiced wildly. Along with continuous grazing, long term exclosure has been implemented in research site in Saral. The main objective of this study was to investigate the changes in plant diversity, floristic composition and plant groups of the major life forms in response to 40 years of continuous grazing and long terrm exclosure in Saral rangelands, Iran. This research was conducted in cold semi-arid rangeland of Baharestan located in Saral’s agricultural and natural resources station (including grazed and excluded sites). In total, six transects were sampled in both grazed and excluded sites and ten plots were randomly placed per transect to measure vegetation and plant characteristics. Sampling was carried out in late May to early June (peak biomass) in 2017. T test was used to compare the means of total plant material, and Shannon’s diversity index was used based on the total cover percentage in both grazed and exclosure sites. Our results indicated that long-term grazing exclosure significantly increased canopy covers and species richness of annuals, perennial grasses, perennial forbs and shrubs. Conversely, continuous grazing caused some species to disappear namely Ferula haussknechtii and Prangos ferulacea. There was statistically a significant difference between litter and total plant material in experimental sites (p < 0.001). Apart from palatability, exclosure increased floristic diversity by 17.8%. Our findings elucidated that exclosure in degraded vegetation is an effective strategy and management policy to recover and restore missing vegetation cover.

Species richness, productivity and quality assessment of grassland resources in hill agroecosystem of western Himalaya

Livestock contribution in agricultural economy is significantly higher in hilly regions of India. A detailed study was carried out to assess the productivity, species richness and diversity of grasses of the grasslands in different hill agro-ecosystems of Kangra district of Himachal Pradesh in western Himalaya. Saccharum spontaneum (low hills), Chrysopogon echinulatus (mid hills) and Festuca spp. (high hills) were observed as the most dominant species in hill agro-ecosystems. Productivity assessment was done at five locations, viz. open forest area; enclosed forest area; community land; farmers’ field; and wasteland in each hill zone. High species richness and diversity was observed in mid hill zone as compared to low and high hills. The mean production level was recorded highest in low hills closely followed by mid hills; much less in high hills. Amongst the land-use systems, highest biomass production was recorded at farmers’ field followed by community land and least in wasteland situation. The average herbage production obtained through six cuts at periodic intervals (March to December) was 3,202 DM kg/ha, while in single harvest it was 2,249 DM kg/ha (low-hill conditions); 2,893 and 1,924 DM kg/ha (mid-hill conditions) and 1,399 and 850 DM kg/ha (high-hill conditions), respectively. Averaged over the different locations, 6.01, 6.64 and 10.87% crude protein (CP) was observed (in multicut situation) in low, mid and high hills respectively. Average herbage production obtained through six cuts at periodical intervals (March-December) was consistently higher as compared to single harvest in all the three zones.

Site conditions determine a key native plant's contribution to invasion resistance in grasslands.

Many plant invasion studies in grasslands suggest that resident plants that share functional traits with invaders can reduce invasion by competing for limiting resources. However, since invasion studies often occur in highly controlled plots or microcosms, it is unclear how heterogeneous site conditions alter competitive interactions under realistic scenarios. To explore how landscape heterogeneity affects biotic resistance provided by competitive resident plants, we conducted a field-based experiment across four sites in California grasslands. Plots contained naturally occurring populations of native Hemizonia congesta, but differed in other characteristics, including litter cover, annual grass cover, soil moisture, and species richness. We invaded plots with the functionally similar nonnative Centaurea solstitalis (yellow starthistle) and, at one site, supplemented one-half of the established plots with water to test the effects of increasing a limiting resource. As in simplified plots and microcosms, increasing H.congesta abundance reduced starthistle biomass by competing for limited soil moisture, but only in plots with high starthistle germination. We conclude that higher abundances of native H.congesta can reduce starthistle invasion in heterogeneous grasslands, but competition is also affected by both abiotic (soil moisture) and biotic (starthistle germination number) conditions that vary across sites.

Temporary grazing exclusion promotes rapid recovery of species richness and productivity in a long‐term overgrazed Campos grassland

Moderate grazing intensity is considered the basic requirement to enhance ecosystem function in grasslands. Yet, deterioration by overgrazing is common in many biomes, including Campos grasslands in South America. Understanding how grazing management can lead to recovery of ecosystem function is essential to design and implement effective strategies for sustainable use of this resource. In a long‐term field experiment carried out in Southern Brazil, we studied the effects of temporal grazing exclusions (spring or fall) at moderate and severe livestock grazing intensities (maintained by adjusting contrasting forage allowances) on the species richness, botanical composition, forage mass, sward height, and photosynthetic active radiation intercepted. The experiment was arranged in a completely randomized design with three replications of grazing exclusions, applied simultaneously at moderate and severe grazing intensities. Moderate grazing intensity showed a bimodal structure of shorter and taller canopies, and high species richness. Severe grazing created a shorter and homogeneous sward structure characterized by less standing biomass and species loss. In response to grazing exclusions, sward height, standing biomass, and light interception recovered almost to the levels of moderate grazing. Further, within 2 years grass species richness increased and botanical composition changed toward grasses with erect habit prevailing in moderate grazing intensity. Our study confirms that (1) moderate grazing intensities allow the coexistence of high number of species and (2) spring grazing exclusions of long‐term overgrazed grasslands can lead to a quick start to recover the grass species richness, primary productivity, and species composition like that prevailing in well‐managed grasslands.

Effect of rangeland rehabilitation on the herbaceous species composition and diversity in Suswa catchment, Narok County, Kenya

IntroductionLand 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.MethodsTo 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.ResultsThe 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.ConclusionsIn 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.

Influence of solar energy and tree-crown closure on the species richness of grasses at the south of forest steppe

The perpendicularity of sunlight incidence on the land surface, called slope insolation, is calculated as the nonlinear function of steepness and exposure. This variable better describes the light and thermal regimes of slopes. We demonstrate that grass-cover insolation can be estimated based on the slope insolation and tree-crown closure. It is found for a terrain at the southern boundary of the forest steppe that species richness and green mass of grasses are closely related to topography and grass-cover insolation (R 2 = 0.77 and R 2 = 0.83, respectively), and crown closure is closely related to topography and slope insolation from the south (R 2 = 0.85). A critical level of crown closure (15%) is determined, so that the limiting factor for grasses is soil moisture below and light above this level. It is shown that grass-cover insolation close to its average value (400 W/m2) differentiates phytocenotic and soil characteristics into areas of increased and diminished values.

Phytosociology and ecology of treeline ecotone vegetation in Rolwaling Himal, Nepal

Questions: Species composition and ecology of treeline vegetation types in the Rolwaling Valley is largely unknown to date. The aim of this study is to differentiate plant communities along the elevational gradient in the treeline ecotone, and to identify site factors which cause the differentiation of the treeline ecotone vegetation. Study area: Rolwaling Valley (27 degrees 52' N;86 degrees 25' E) in the central Himalaya, Nepal. Methods: We included 91 phytosociological releves along three elevational transects in this analysis, ranging from 3745 to 4300 m a.s.l. Plant communities were differentiated and vegetation-environment relationships analysed using cluster analysis and ordination. For each community and higher ranked unit, we detected diagnostic species according to their fidelity index (phi coefficient). Ecological preferences of each community were examined using one-way analysis of variance (ANOVA). Results and conclusions: We identified five communities, belonging to two different classes: the Synotis alata-Abies spectabilis and Ribes glaciale-Abies spectabilis communities occupy the upper part of the subalpine forest zone, representing the uppermost forest stands below treeline. These communities are primarily comprised of Abies spectabilis and Betula utilis in the tree layer, with varying cover of several tree species and distinct differences within the herb layer. Above treeline, the mixed forest stands are replaced by the species-poor Boschniakia himalaica-Rhododendron campanulatum community, forming a dense krummholz belt. We assigned the forest and krummholz communities to the class Betula utilis-Abies spectabilis forests. In the alpine zone two communities were classified and assigned to the class Dasiphora arbuscula-Rhododendron anthopogon dwarf shrub heaths.The species-poor Pedicularis cf. micro calyx-Rho dodendron anthopogon community has a less developed herbaceous layer, whereas the Anaphalis royleana-Rhododendron anthopogon community is characterized by higher cover and higher species richness of herbs and grasses. Species composition of identified communities is mainly differentiated by soil temperature, nitrogen supply and availability, and soil moisture content.

Impacts of grazing intensity and increased precipitation on a grasshopper assemblage (Orthoptera: Acrididae) in a meadow steppe

1. Grasshoppers are dominant herbivores in grassland ecosystems, and many studies have examined how grazing by large herbivores and precipitation patterns individually influence the dynamics of grassland grasshopper assemblages, but their combined effects are largely unknown.2. In this study, grazing intensities (ungrazed, moderate, and heavy) were manipulated and precipitation (ambient and increased amount of rainfall) altered in a field experiment to test the effects of grazing and altered precipitation on a grasshopper community in a meadow steppe in northeastern China.3. It was found that grasshopper species richness did not change according to different grazing intensities under ambient precipitation, but was significantly higher (by 38.1%) in moderate grazing intensities under increased precipitation. Grasshopper abundance increased considerably with increasing grazing intensities in ambient precipitation treatments; however, grasshopper abundance in heavy grazing intensities was significantly lower (by 32.9%) than in the other two grazing intensities under increased precipitation. Moreover, the responses of grasshopper abundance to grazing under altered precipitation were species‐specific.4. Grazing effects on grasshopper species diversity were mediated through the species richness and biomass of grasses (food resources), but the effects on grasshopper abundance were mediated through plant height (vegetation structure) under altered precipitation.5. These results suggest that appropriate grazing by large herbivores would be considered as beneficial management practices for maintaining grasshopper diversity and abundance under conditions of increased precipitation in grassland ecosystems. Additionally, greater attention should be paid to the population dynamics of different grasshopper species to better understand the responses of grasslands to grazing and altered precipitation.

Effectiveness of Burning, Herbicide, and Seeding Toward Restoring Rangelands in Southeastern North Dakota

Many rangelands in southeastern North Dakota are invaded by Kentucky bluegrass (Poa pratensis L.) and/or smooth brome (Bromus inermis Leyss.). It may be especially difficult for native species to reestablish in rangelands dominated by Kentucky bluegrass and/or smooth brome due to these species’ competitive advantages. Relatively few studies have specifically compared the effectiveness of methods intended to reduce competition from Kentucky bluegrass and/or smooth brome before seeding with native species in southeastern North Dakota. In our current study, we evaluated the effects of five restoration treatments: 1) control (no seeding or competition-reduction treatments), 2) interseed (native seeds drilled into the existing plant community), 3) spring burn before drill seeding native species, 4) glyphosate application before drill seeding native species, and 5) spring burn plus glyphosate application before drill seeding native species on a degraded rangeland plant community. We installed the five treatments in fifteen 40 × 100 m plots in 2010. In 2015, we sampled the vegetation within each plot to determine whether the restoration methods increased total and/or native warm-season grass biomass, reduced Kentucky bluegrass and/or smooth brome biomass, or increased grass species richness. Although none of our restoration treatments impacted Kentucky bluegrass biomass, each of our restoration treatments increased grass species richness over the control. Including a glyphosate application before seeding with natives also increased total biomass, reduced smooth brome biomass, and increased native warm-season grass species richness. Thus, we suggest that the glyphosate application was a worthwhile addition at this location because it resulted in additional improvements to the invasive-dominated plant community.

Grasses as invasive plants in South Africa revisited: Patterns, pathways and management

Background: In many countries around the world, the most damaging invasive plant species are grasses. However, the status of grass invasions in South Africa has not been documented recently. Objectives: To update Sue Milton’s 2004 review of grasses as invasive alien plants in South Africa, provide the first detailed species level inventory of alien grasses in South Africa and assess the invasion dynamics and management of the group. Method: We compiled the most comprehensive inventory of alien grasses in South Africa to date using recorded occurrences of alien grasses in the country from various literature and database sources. Using historical literature, we reviewed past efforts to introduce alien grasses into South Africa. We sourced information on the origins, uses, distributions and minimum residence times to investigate pathways and patterns of spatial extent. We identified alien grasses in South Africa that are having environmental and economic impacts and determined whether management options have been identified, and legislation created, for these species. Results: There are at least 256 alien grass species in the country, 37 of which have become invasive. Alien grass species richness increased most dramatically from the late 1800s to about 1940. Alien grass species that are not naturalised or invasive have much shorter residence times than those that have naturalised or become invasive. Most grasses were probably introduced for forage purposes, and a large number of alien grass species were trialled at pasture research stations. A large number of alien grass species in South Africa are of Eurasian origin, although more recent introductions include species from elsewhere in Africa and from Australasia. Alien grasses are most prevalent in the south-west of the country, and the Fynbos Biome has the most alien grasses and the most widespread species. We identified 11 species that have recorded environmental and economic impacts in the country. Few alien grasses have prescribed or researched management techniques. Moreover, current legislation neither adequately covers invasive species nor reflects the impacts and geographical extent of these species. Conclusion: South Africa has few invasive grass species, but there is much uncertainty regarding the identity, numbers of species, distributions, abundances and impacts of alien grasses. Although introductions of alien grasses have declined in recent decades, South Africa has a potentially large invasion debt. This highlights the need for continued monitoring and much greater investment in alien grass management, research and legislation.

Effects of Tanglehead Expansion on Bobwhite Habitat Use in South Texas

Usable space for northern bobwhite (Colinus virginianus) has been reduced across a large portion of South Texas rangelands due to the spread of non-native, invasive grasses. A native grass, tanglehead (Heteropogon contortus) has rapidly expanded its dominance in the western Sand Sheet of South Texas within the last 10-15 years. It has formed high-density monocultures, similar to non-native grasses, which are associated with losses of forb and grass diversity as well as bare ground, which are key components of bobwhite habitat. The objectives of our research were to 1) determine selection-avoidance of habitat features by bobwhites, and 2) determine the effects of tanglehead cover on vegetation characteristics. We detected 488 coveys across 20,103 ha on helicopter surveys conducted December 2014 in South Texas. We measured 6 vegetation characterstics (grass and forb species richness, vegetation height, woody-plant cover, tanglehead cover, and non-native grass cover) at all covey detections and an equal number of random locations. We developed continuous selection ratios based on probability density functions of used and random points derived using Simple Saddlepoint Approximations to determine habitat selection by bobwhites. We also used quantile regression at the 10th, 50th, and 90th quantiles to determine relationships between tanglehead and vegetation factors. Bobwhite avoided areas of high canopy cover (>20%) of all invasive grasses measured. Brush cover was selected for up to 47%, after which it was avoided. We found significant negative relationships between tanglehead cover and forb and grass species richness, bare ground, and shrub cover, and a positive relationship with vegetation height at all quantiles modeled. Our results demonstrate the negative effects of increased tanglehead cover on native rangeland habitats. Further expansion by tanglehead has the potential to significantly reduce usable space for bobwhites in South Texas.

Effect of short-duration overnight cattle kraaling on grass production in a southern African savanna

Ranch owners in eastern and southern Africa have embraced a new rangeland management practice of keeping cattle overnight in temporary livestock corrals (hereafter referred to as kraals) within rangelands for short durations (for example, one week) to improve grass production. To better understand the influence of this practice on the grass community, we determined grass species diversity, richness, biomass and quality (crude protein, fibre, rumen fermentation and metabolisable energy) from a chronosequence consisting of kraals abandoned 1, 2, 3 and 4 years prior to the study and compared them to the surrounding vegetation. Grass species diversity, richness, biomass and quality were higher in abandoned kraals than the surrounding vegetation. Grass biomass increased five-fold in the first year of kraal abandonment and thereafter declined three-fold after four years. Metabolisable energy, a measure of grass nutritive value, increased from 8.92 to 11.90 MJ kg−1 with kraaling. The number of grass species also increased with kraaling. Palatable grass species, such as Urochloa mosambicensis and Panicum maximum, were more abundant in abandoned kraal sites than the surrounding vegetation. We conclude that short-duration overnight cattle kraaling improves grass quality and biomass.

Climate and the distribution of grasses in West Africa

AbstractQuestionsWhich environmental variables influence grass diversity in West Africa? What are the effects of climate and grass functional traits on the spatial patterns (richness and abundance) of the grass clades Andropogoneae, Paniceae and Chloridoideae?LocationWest Africa, demarcated by the Atlantic Ocean in the west and south (20° W and 4° N), the Sahara desert in the north (25° N) and the border between Niger and Chad in the east (20° E).MethodsBased on 38 912 georeferenced occurrence records, we modelled the distribution of 302 grass species (51% of West African grass diversity). We integrated species richness, abundance and functional traits (life cycle, photosynthetic type and height) to determine the contribution of the most speciose grass clades (Andropogoneae, Paniceae and Chloridoideae) to overall grass diversity in West Africa.ResultsPrecipitation is the variable most often influencing the species distribution models of grasses in West Africa. Richness and relative abundance of the tribe Andropogoneae show a centre of diversity in Sudanian savanna regions. The height of Andropogoneae species, generally &gt;150 cm, is driving this ecological dominance. Species richness of the tribe Paniceae is more dispersed and shows two main centres of abundance: The southern regions with higher mean annual precipitation and tree density are dominated by C3 Paniceae species. The Sahelian regions in the north are dominated by short Paniceae species with the C4 NAD‐ME photosynthetic subtype, as well as Chloridoideae possessing the same functional attributes.ConclusionsOur study provides insight into the environmental correlates of grass species richness in West Africa and contributes to the much‐needed research on tropical rangelands. Moreover, the integration of evolutionary history significantly improves our understanding of large‐scale biodiversity patterns.

Some ecological side-effects of chemical and physical bush clearing in a southern African rangeland ecosystem

Bush thickening is a major concern to farmers of arid and semi-arid rangelands; reactive intervention remains the norm. Here we compared some of the short-term ecological implications of chemical and physical removal of the bush encroacher Acacia mellifera in the central Highland savanna of Namibia. We selected 21 invaded sites, 7 had been chemically cleared, 7 had been physically cleared and 7 had never been cleared. From each site, we recorded grass species composition, as well as the densities of A. mellifera, the undesired perennial shrub Pechuel-loeschea leubnitziae and a non-targeted tree Acacia erioloba, 24–30months post-treatment. We fitted one-way ANOVA models to test for the effect of treatment on grass species richness and density of targeted and non-targeted tree species. A canonical correspondence analysis was used to determine how treatment affected grass species composition. While both treatments reduced the density of the bush encroacher, P. leubnitziae effectively replaced A. mellifera in chemically treated sites, where die-back presumably happened faster and nutrient and water competition decreased more rapidly. In such sites, perennial grass species were effectively outcompeted by P. leubnitiziae.

Effects of open grazing and livestock exclusion on floristic composition and diversity in natural ecosystem of Western Saudi Arabia

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.