Species diversity and regeneration of native species in Pennisetum ciliare (buffelgrass) pastures from the thornscrub of Sonora,México

To examine the influence of buffelgrass land conversion and pasture management on native species diversity and regeneration patterns, we describe community attributes and population structure in four different active pastures in thornscrub vegetation from eastern Sonora, Mexico. We compare a relatively undisturbed thornscrub community with a contiguous five years old active pasture, to identify species able to regenerate under current management practices. Buffelgrass conversion has a significant influence on species diversity and other community attributes. Active pastures have lower species diversity, crown cover and basal area of native species than the studied native thornscrub. An active pasture subjected to heavy grazing and without management of the thorny legume, Acacia cochliacantha, showed the lower species diversity and an almost monospecific stand of this legume. It is likely that the reduction in species diversity is caused by the conversion process, inadequate management and regeneration barriers that limit seedling establishment in active pastures. Our data recorded eight native species (13%) that were able to regenerate in active pastures. However, the great majority of native species were unable to regenerate under pastures. This study shows that under current management, active buffelgrass pastures maintain only a small fraction of native species with regenerating populations in the thornscrub.     

Constancy of local spread rates for buffelgrass (Pennisetum ciliare L.) in the Arizona Upland of the Sonoran Desert

In North American deserts, grass invasions threaten native vegetation via competition and altered fire regimes. Accurate prediction and successful mitigation of these invasions hinge on estimation of spread rates and their degree of constancy in time and space. We used high-resolution aerial photographs from 11 sites in the Santa Catalina Mountains, southern Arizona to reconstruct the spread of buffelgrass (Pennisetum ciliare), a C₄ perennial bunchgrass, since 1980. The total area infested was fit to a logistic model and residuals of the model were compared to climatic factors of the corresponding and lagged time periods. Infestations grew from small colonizing patches in the 1980s to 66 ha in 2008, doubling every 2.26–7.04 years since 1988. Although buffelgrass germination, establishment and distribution are favored by wet summers and warm winters, climate variables did not predict spread rates. Buffelgrass has grown at a constant rate, at least since 1988, when much of its expansion took place. In the study area, minimum requirements are met almost every year for germination and reproduction, establishing a consistent baseline for spread that manifests as a constant spread rate.     

Demographic consequences of chronic anthropogenic disturbance on three populations of the endangered globose cactus Coryphantha werdermannii

Cacti are thought to be highly vulnerable to chronic anthropogenic disturbance (CAD). To assess its effects, we modeled the dynamics of three populations of the endangered cactus Coryphantha werdermannii exposed to different intensities of disturbance. Because no seedlings germinated and survived in the less-disturbed site, we analyzed two different scenarios: If the same, average germination probability was used for all sites, the population growth rates (λ) decreased with disturbance, but λ remained unchanged if a very low germination probability was assigned to the less-disturbed site and the observed probabilities were used for the remaining populations. Retrospective analysis showed that different demographic processes affected λ as a result of increasing disturbance: The unsuccessful establishment of seedlings in the preserved site diminished λ. The damage caused by livestock to reproductive structures in the site with intermediate disturbance was responsible for a reduction in λ. In the most disturbed site, the reduced individual growth rates that seemingly resulted from land degradation caused a decrease in λ. No simple management strategy can be proposed because different threats require attention depending on disturbance intensity. CAD had both positive and negative effects on λ, conferring this species with a certain degree of tolerance.     

What can the demography of Astrophytum ornatum tell us of its endangered status?

The Cactaceae are prominent members of national and international endangered species lists. This is true for even those that have not been studied in any significant detail, and given the need to assess these species there is still a general lack of information. Demographic studies in the Cactaceae have highlighted several threats some of which are clearly human induced (disturbance), and others that have a biological component (e.g. low survival rates of seedlings). We modelled the population dynamics of Astrophytum ornatum (the southernmost representative of Astrophytum) in one population in central Mexico, during a three year period. We constructed two size classified transition matrices and determined the growth rate (λ), as well as the stochastic log growth rate. We simulated changes in the matrix elements that correspond to the seed bank and the seed-seedling transition as these were the most important bottlenecks to population growth. In both years, the growth rate indicates a declining population, which will face serious problems in the next 2 to 3 decades. The simulations show that the seed bank is not as important as the seed-seedling transition. Any program that aims to restore A. ornatum populations needs to enhance seedling establishment.     

Genotypic diversity among pasture and roadside populations of the invasive buffelgrass (Pennisetum ciliare L. Link) in north-western Mexico

Buffelgrass (Pennisetum ciliare L. Link) is an African agamospermous grass that has been widely introduced into arid regions of the world to improve rangelands for cattle production and as a result, it has invaded adjacent habitats. In this study, ISSR markers were employed to assess genotypic variation in populations of P. ciliare from north-western Mexico. We sampled plants from pasture and from colonizing roadside populations in order to explore if invasion success is associated with greater levels of genotypic diversity. Three ISSRs primers produced 27 reproducible bands that were used to screen 480 plants from sixteen populations. Mean values of the proportion of distinguishable genotypes (G/N) were 0.29, Nei's genotypic diversity was 0.75 and multilocus evenness (E) was 0.50. Sixty-seven multilocus genotypes were detected among 480 plants, with 46 (69%) restricted to single populations and 21 (31%) found in two or more populations. Our results showed no significant differences in genotypic diversity between pasture and roadside populations, suggesting that in P. ciliare invasion success is not directly associated with greater levels of genotypic variation. Probably, other factors such as phenotypic plasticity and propagule pressure could be major determinants of the invasion success of buffelgrass in this region of Mexico.     

Grazing itineraries and forage selection of goats in the Al Jabal al Akhdar mountain range of northern Oman

In view of the repeatedly reported overstocking of the high-altitude pastures on Al Jabal al Akhdar, northern Oman, plant species abundance, cover and frequency, and herbaceous mass yield were studied in ungrazed versus heavily grazed areas of this mountain range. In addition, plant species selection by goats along a gradient of 1000–2000 m and spatial extent of pasture areas were investigated after abundant rainfall and a subsequent 6-months dry spell by means of manual observation and GPS/GIS tools.The substantially higher species diversity and herbaceous mass yield in the ungrazed area illustrate the production potential of these mountain pastures or, respectively, the biodiversity and productivity loss resulting from continuous grazing. The concentration of goats' selection on only a dozen herbaceous and ligneous species favours pasture encroachment with poisonous shrubs such as Nerium mascatense in the lower and Dodonaea viscosa in the higher altitudes. Given the spatially limited extent of pasture areas, these are exposed to high stocking rates. Therefore, grazing and feeding schemes need to be developed which reduce livestock pressure on the pastures, taking into account local property rights, herding skills and the recovery potential of the vegetation, which heavily depends on unpredictable rainfall events.     

Agricultural land use dynamics in the Brazilian Amazon based on remote sensing and census data

The potential impact of deforestation in the Brazilian Amazon on greenhouse gas emissions to the atmosphere calls for policies that take account of changes in forest cover. Although much research has focused on the location and effects of deforestation, little is known about the distribution and reasons for the agricultural uses that replace forest cover. We used Landsat TM-based deforestation and agricultural census data to generate maps of the distribution and proportion of four major agricultural land uses throughout the Brazilian Amazon in 1997 and 2007. We built linear and spatial regression models to assess the determinant factors of deforestation and those major agricultural land uses - pasture, temporary agriculture and permanent agriculture - for the states of Pará, Rondônia, and Mato Grosso. The data include 30 determinant factors that were grouped into two years (1996 and 2006) and in four categories: accessibility to markets, public policies, agrarian structure, and environment. We found an overall expansion of the total agricultural area between 1997 and 2007, and notable differences between the states of Pará, Rondônia, and Mato Grosso in land use changes during this period. Regression models for deforestation and pasture indicated that determinant factors such as distance to roads were more influential in 1997 than in 2007. The number of settled families played an important role in the deforestation and pasture, the effect was stronger in 2007 than 1997. Indigenous lands were significant in preventing deforestation in high-pressure areas in 2007. For temporary and permanent agricultures, our results show that in 1997 the effect of small farms was stronger than in 2007. The mapped land use time series and the models explain empirically the effects of land use changes across the region over one decade.     

The food habits of goats on rangelands with different amounts of fourwing saltbush (Atriplex canescens) cover

Esophageally fistulated goats were released in a microphyll desert scrub habitat with 14.6% or 46.2% aerial cover of Atriplex canescens (induced by removal of all shrubs except A. canescens, with livestock grazing exclusion for 10 years) to determine the seasonal forage species selected by the goats. The shrub removal strongly influenced the goats’ feeding habits. The goats grazing the Atriplex-dominated site consumed 4.5 times more A. canescens than the goats on the untreated (control) pasture during all seasons. Shrubs were used heavily during all seasons by goats in both pastures, with higher percentages (75.5–82.8%) in the diets of goats grazing the control pasture than in the diets of goats grazing the Atriplex-dominated area (62.5–68.5%). No differences were found between seasons. The goats in the Atriplex-dominated pasture ate more grass than the goats grazing the control area and used more perennial graminoids during the summer (15.0%) and spring (18.3%) than the goats on the control area (6.0–7.0%). Forbs were an important component of diets. It was concluded that the successful revegetation of the treated pasture affected the goats’ feeding strategy, with an increase in the use of A. canescens, forbs and grasses in all seasons.     

An assessment of revegetation treatments following removal of invasive Pennisetum ciliare (buffelgrass)

In semi-arid regions of North America and Australia, Pennisetum ciliare (L.) Link (syn. Cenchrus ciliaris; buffelgrass) is highly invasive and has the potential to introduce fire to fire-intolerant ecosystems. Major efforts to remove P. ciliare continue and it is essential that P. ciliare be prevented from recolonizing. This study investigated potential methods to revegetate with native herbaceous plants: sowing seeds; sowing seeds and mulching; sowing seeds and transplanting seedlings; and relying on natural revegetation from the seedbank. The treatments were applied in 2009 and 2010 at sites in the Sonoran Desert which had undergone P. ciliare removal. Monsoon precipitation was below average each year and seedling emergence and establishment rates were low. There are indications that soil disturbance associated with planting seedlings promoted P. ciliare emergence and increased mortality of brittlebush (Encelia farinosa A. Gray ex Torr.), a common native perennial forb. Addition of mulch may have promoted P. ciliare over native grasses, and seeding had no effect. We did not find competition between herbaceous seedlings. Rather, native and exotic grass seedling densities were positively correlated across sites. Under prevailing conditions, low precipitation appeared to limit herbaceous plant establishment and none of the treatments reduced P. ciliare abundance.     

腾格里沙漠东南缘不同生境油蒿种群的数量动态

对腾格里沙漠东南缘不同的生境条件（包括始建于1964年的人工植被区和天然植被区）下油蒿（Artemisia ordosica）种群调查取样,按照植株的体积大小分为7个龄级（Ⅰ,0~2 cm³;Ⅱ,2~5 cm³;Ⅲ,5~10 cm³;Ⅳ,10~15 cm³;Ⅴ,15~20 cm³;Ⅵ,20~30 cm³;Ⅶ,>30 cm³）,分析了种群的组成、静态生命表和存活曲线。结果表明：人工植被区油蒿种群的总体规模大于天然植被区,幼龄个体占有很高的比例;天然植被区油蒿的死亡率低于人工植被区,天然植被区Ⅰ和Ⅱ龄级油蒿种群的死亡率最高,人工植被区Ⅴ~Ⅶ龄级的油蒿种群死亡率最高;天然植被区油蒿种群的稳定性维持主要通过幼苗的更新,而人工植被区可通过幼苗的自我更新和大龄植株的自疏作用;Ⅴ龄级的油蒿个体是种群中的生存质量最佳的个体;两种生境下油蒿种群均符合Deevey Ⅱ型存活曲线。     

Pinus jeffreyi establishment along a forest-shrub ecotone in eastern California,USA

We examined large-scale climatic and small-scale biotic and abiotic factors affecting Pinus jeffreyi (Pinaceae) seedling establishment at its low-elevation boundary along the conifer forest-sagebrush steppe ecotone in eastern California, USA. In three successive growing seasons, P. jeffreyi seedlings were planted in three microhabitats (under Artemisia tridentata or Purshia tridentata canopies, and in open intershrub spaces) at a site within the ecotone (2300 m) and at a lower-elevation site (2200 m). We measured Photosynthetically Active Radiation (PAR; 400–700 nm), soil moisture and temperature, and air temperature in the three microhabitats, and monitored seedling survival, drought stress, and herbivory. At both sites, soil moisture decreased two- to six-fold between May and August of each summer. Maximum and minimum daily air temperatures were higher and lower, respectively, in intershrub areas, as were maximum daily soil temperatures and maximum daily PAR. At the ecotone site, mean P. jeffreyi seedling survival was longest following a very wet winter and shortest following a dry winter. For both elevations, seedlings had shorter survival times in intershrub microsites as compared to shrub microsites. Drought and herbivory both influenced seedling mortality within each microhabitat, but drought was the major determinant of seedling mortality by the end of each summer.     

近30年延安市耕地变化的政策背景及其作用机理

建立健全生态保护的长效机制以巩固现有生态退耕成果,是目前和未来中国生态建设需要解决的一个重要问题。针对这一问题,本文以最早开始退耕试点的延安市为研究区,利用统计资料,分析了延安市近30年耕地变化过程、耕地变化的政策背景及其作用机理。研究发现,面积逐步减少是延安市1978年以后耕地变化的长期趋势,减少的耕地主要流向果园、林地和草地;政策措施对退耕过程虽具有显著的加速作用,但在市场经济条件下,耕地的长期流向最终决定于各种用途间的比较效益和农户的生产投入能力。研究结果表明,要形成生态保护的长效机制,必须改变退耕土地的比较效益和农户的生产投入能力。     

Are Fabiana imbricata shrublands advancing over northwestern Patagonian grasslands? A population dynamics study involving fire and precipitation

Shrub encroachment is the advance of woody plants over grasslands. For some shrub species this process is favoured by fire and high precipitation. In northwestern Patagonia spring precipitation is related with the El Niño Southern Oscillation (ENSO). Over the past years, ENSO has shown an increase in both amplitude and frequency. Our study focuses on the population dynamics of the shrub Fabiana imbricata Ruiz & Pav. (Solanaceae) using stochastic models which involve different fire frequencies and variations in spring precipitation. Our results indicate that F. imbricata's population grows at a wide range of fire frequencies, reaching its maximum every 6–10 years. The elasticity analysis show that, as fire frequency diminishes, population growth rate depends almost exclusively on adult survival, recruitment events are rare and the presence of seedlings or juveniles is seldom observed. In this case, the landscape would be formed by mature F. imbricata shrublands, and population persistence would depend on adult survival, seed production and their accumulation in the soil bank. However, in the case of very high fire frequencies, more recurrent recruitment pulses would be observed, with a landscape dominated by young shrublands composed of individuals of different ages and reproductive status.     

Optimising seed broadcasting and greenstock planting for restoration in the Australian arid zone

Vegetation within some parts of Western Australia has been degraded by resource extraction, and ecological restoration is necessary to prevent erosion and reinstate plant biodiversity. Two restoration approaches, seed broadcasting and planting of seedlings, were tested with plant species (Acacia tetragonophylla F. Muell., Atriplex bunburyana F. Muell. and Solanum orbiculatum Poir.) known to have been dominant prior to mining activities in the World Heritage Area at Shark Bay. For broadcast seeding, soil raking and/or ripping increased seedling emergence, but only after sufficient rainfall. Survival of A. bunburyana seedlings (≤92%) was higher than A. tetragonophylla (≤13%) almost two years after planting and soil ripping partly alleviated soil impedance and resulted in increased seedling survival. Shoot pruning, fertiliser and moisture retaining gel had a reduced or detrimental effect on survival. Seedling survival differed between the three experimental sites, with electrical conductivity being the most noted soil difference between the sites. Restoration in the arid environs of the World Heritage Area at Shark Bay in Western Australia is challenging, but this study shows that seedling establishment is technically feasible and provides methodology useful to other arid restoration projects.     

Effects of sand burial on dune plants: a review

Burial of different growth stages of plants （e.g., adult plants, seedlings and seeds） is frequent in dune ecosystems. The soil micro-environment, which differs from surface conditions, influences the survival and growth of dune plants. To sum up knowledge about the survival mechanisms of plants under sand burial and to promote practical rehabilitation of dune vegetation, we reviewed relevant published literature and concluded that： （1） Focus in recent years has been on impacts of sand burial on seed germination and seedling emergence. Generally, shallow burial increased seed germination and seedling emergence, but deeper burial was negative. Buried at the same depth, large seeds showed higher germination and seedling emergence rates, attributed to larger energy reserves. （2） Survival, growth and reproduction rates of dune plants show plasticity in response to sand burial. Long-term deep burial is fatal because it creates a physical barrier which overcomes the vertical growth of plants, reduces photosynthetic leaf area, and limits oxygen availability to roots. Modest burial, on the other hand, is advantageous for growth and reproduction of many dune plants, due to protection from excessive temperature and drought. （3） There are few reports concerning effects of sand burial on plant physiology, but a limited number of studies indicate that partial burial increases water use efficiency, chlorophyll content, transpiration rate and net photosynthetic rates. The antioxidant protective enzyme system and osmolyte balance were reported to be involved in the mechanisms of dune plant resistance to burial.     

Examining the reduction in potable water consumption by households in Catalonia (Spain): Structural and contingent factors

Water consumption by households is influenced by a host of factors, widely investigated in the literature. However, the effects of contingent situations like drought episodes and economic crises, which may strongly restrict direct water use in households, remain less explored, and especially a combination of both. Catalonia, a Mediterranean region, suffered the worst drought episode in the last 75 years in 2007 and 2008, followed immediately by the worst economic crisis also in several decades between 2009 and 2014 (though still fishtailing). Taking it as a case study and using metered water data for the household sector, we propose a generalized linear mixed model in which the influence of both the drought episode and the economic crisis on per capita water consumption by comarques (supra-municipal entities) is assessed using a drought index on one hand, and economic variables and the water price on the other hand. Likewise, demographic, territorial and climatic determinants, as well as environmental behaviour, are also evaluated. The dataset (N = 287) consists of panel data for the forty-one comarques of Catalonia covering the 2007 to 2013 period. Results confirm that the contingent factors analysed have contributed to further reduce per capita water consumption, being significant the drought index and water price. The proportion of elderly people, the household size and the proxy for environmental behaviour, also have a negative effect on consumption; whereas seasonal population has the expected positive effect. However, neither the climatic and economic variables analysed, nor urban density and the proportion of foreign population, are found to be significant. A better understanding of the factors influencing residential water consumption in a context of growing water scarcity and economic downturn may aid policy makers and water managers not only to improve the effectiveness and efficiency of demand-side management measures that affect households, but to address emerging social concerns such as water poverty.     

Analysis of vegetation seasonality in Sahelian environments using MODIS LAI,in association with land cover and rainfall

Present-day Sahelian vegetation in a highly anthropized semi-arid region is assessed from local to regional scales, through the joint analysis of MODIS LAI (1 km² and 8-day resolutions), daily rainfall, morphopedological and land cover datasets covering the period 2000–2008. The study area is located in northwest Senegal and consists of the “Niayes” and the northwestern “Peanut Basin” eco-regions, characterized by market gardening and rain-fed cultivated crops, respectively. The objectives are i) to analyse at pixel scale LAI time series and their relation to vegetation and soil types, ii) the estimation of phenological metrics (start of season SOS, end of season EOS, growing season length GSL) and their inter-annual variability, iii) to recognize the vegetation responses to rainfall trends (mean annual precipitation, MAP; frequency of rainy events, K; combination of MAP and K, called F).Pixel-scale analyses show that LAI time series 1) describe the actual phenology (agreeing with ground-truth AGHRYMET data), and thus can be used as a proxy for Sahelian vegetation dynamics, 2) are strongly dependent on soil types. Median maps of SOS and EOS suggest an increase of the GSL from Saint-Louis to Dakar, in agreement with both the North-South rainfall gradient and the intensification of agricultural practices around Dakar. Significant correlations (R: 0.64) between annual variation coefficient of LAI and MAP for both herbaceous crops and natural vegetation are highlighted; this correlation is reinforced (R: 0.7) using the rainfall distribution factors K and F. Rainfall thresholds allowing the SOS can be defined for each type of vegetation. These thresholds are estimated at 0–5 mm, 20 mm and 40 mm for natural herbs, herbaceous crops and shrublands, respectively.If previous works revealed the close link between the MAP and the SOS, our results highlight that LAI dynamics are also controlled by rainfall distribution during the Monsoon season. In this study, climatic indicators are proposed for estimating vegetation dynamics and monitoring SOS. Coupling Earth Observation data, such as MODIS LAI, with rainfall data, vegetation and soil information is found to be a reliable method for vegetation monitoring and for assessing the impact of human pressure on vegetation degradation.     

Arbuscular mycorrhizal fungi improve reestablishment of Leymus chinensis in bare saline-alkaline soil: Implication on vegetation restoration of extremely degraded land

Salinization and alkalinization are increasing problems in the world. Some land has been degraded to bare saline-alkaline soil where vegetation restoration is difficult because high toxic ionic content and pH are harmful to the survival of introduced plants. We grew Leymus chinensis with and without arbuscular mycorrhizal fungi (Glomus mosseae and G. geosporum) in either pots filled with soil from bare saline-alkaline land, or transplanted seedlings into field plots, to determine the influence of AM fungi on the reestablishment of this dominant grass species in bare degraded land. Association with AM fungi increased the absorption of N, P, K⁺, Ca²⁺, but decreased Mg²⁺, Na⁺ and Cl⁻ uptake under saline-alkaline stress. Therefore, higher K/Na, Ca/Na, P/Na, and P/Cl ratios were found in the inoculated plants. Plants inoculated with AM fungi accumulated significantly higher biomass, root/shoot ratio and tiller number than non-inoculated plants. AM fungi also significantly increased the survival of seedlings when they were transplanted into a bare saline-alkaline land in the field. The improvement of survival, growth and asexual reproduction of inoculated plants indicated that the plant-AM fungi mutualism could improve the reestablishment of vegetation in bare saline-alkaline soil, drive the vegetation restoration to a community dominated by original species.     

Seasonal dynamics of vegetation over the past 100 years inferred from tree rings and climate in Hulunbei'er steppe,northern China

The relationship between monthly vegetation cover anomalies and climate in the Hulunbei'er steppe were studied through analyzing the relationship between regional normalized difference vegetation index (NDVI) and climatic variables, and NDVI and tree-ring width during the growing season (May–October). The local moisture (dry/wet) and temperature (cold/warm) variations largely affected the vegetation cover and the radial growth of Mongolian pines (Pinus sylvestiris Linnaeus var. mongolica Litvinov) in the steppe. Monthly precipitation and Palmer drought severity index (PDSI) data from the previous to the current growing seasons were positively correlated to regional vegetation cover and radial growth of Mongolian pines; however, negative correlations were found between temperature and vegetation variables. A reconstruction of monthly vegetation cover dynamics for the growing season was created and spans 116 years (from 1891 to 2006). The results show that the total numbers of anomalies for dense and sparse seasonal vegetation cover is 22 years over the 116 year record; about 5–7 relatively dense or sparse periods; and ∼2–8 years significant periodicities (p < 0.05). Linkages to the Pacific Ocean and Arctic Ocean regimes were also detected.     

Spatial distribution and carbon stock of the Saxaul vegetation of the winter-cold deserts of Middle Asia

Carbon stocks and carbon accumulation in the earth's drylands have gained increasing attention. The winter-cold deserts of Middle Asia, i.e. in Kazakhstan, Uzbekistan, and Turkmenistan, cover an area of 2.5 million km². Within these deserts, the two Saxaul species White Saxaul (Haloxylon persicum Bunge ex Boiss. & Buhse) and Black Saxaul (Haloxylon aphyllum (Minkw.) Iljin) are dominant woody species with a potential distribution area of about 500,000 km². From the 1950s until today, the Saxaul vegetation has been degraded through logging and over-grazing. In this paper, we estimate the current and potential living above ground and below ground biomass of the Saxaul vegetation and its carbon stock. The living above ground biomass ranges between 1.5 t/ha and 3 t/ha. The potential carbon stocks above ground and below ground amount to 29.4–52.1 million t and 22–81.4 million t, respectively. Today, only 11%–28% of the potential biomass and carbon stock have remained. The carbon stock of the Saxaul vegetation is low compared to other ecosystems of the earth, but restoration and conservation of Saxaul vegetation is one way to sequester carbon through vegetation for Uzbekistan and Turkmenistan, which do not have much other woody vegetation.