scholarly journals Changes in Herbaceous Species Composition in the Absence of Disturbance in aCenchrus biflorusRoxb. Invaded Area in Central Kalahari Game Reserve, Botswana

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Shimane W. Makhabu ◽  
Balisana Marotsi
Keyword(s):  
Species Composition ◽  
Human Activities ◽  
Grass Species ◽  
Herbaceous Species ◽  
High Tolerance ◽  
Perennial Species ◽  
The Third ◽  
Disturbed Areas ◽  
Game Reserve ◽  
Vegetation Characteristics

A-nine year study was carried out to investigate changes in herbaceous species composition in an area invaded byCenchrus biflorusRoxb, an exotic invader grass species. The study ensued termination of livestock and human activities in the area when residents of the area were relocated to another area. Vegetation characteristics from the disturbed sites (previous occupied areas) and undisturbed sites (previously unoccupied areas) were determined. The results show thatC. biflorushas high tolerance to disturbance. It comprised the larger proportion of grasses in disturbed sites at the inception of the study. However, it decreased in abundance with time in disturbed areas and was absent in the undisturbed areas, suggesting that its ability to invade undisturbed sites is limited. Perennial species successfully reestablished on the third year after termination of disturbance. The study reveals thatC. biflorusinvasion in the Kalahari ecosystem can be controlled by termination of disturbances.

scholarly journals Tree seedling establishment among C4 grasses

2016 ◽  
Author(s):  
Edmund C February ◽  
Joel R Lewis
Keyword(s):  
Species Composition ◽  
Plant Height ◽  
Root Length ◽  
Canopy Cover ◽  
Perennial Grasses ◽  
Rooting Depth ◽  
Grass Species ◽  
Tree Seedlings ◽  
Panicum Maximum ◽  
Perennial Species

The coexistence of leguminous trees and C4 grasses in African savanna remains poorly understood. Trees are able to establish among grasses despite grasses being competitively superior for below ground resources. Here we test the hypothesis that trees are only able to establish when grass biomass has been reduced. We do this at four locations in Limpopo Province South Africa where we locate young seedlings of Senegalia nigrescens. Where we found seedlings we determine grass species composition as well as grass percentage canopy cover, height above ground, and root length. We also make determinations of grass characteristics at two locations where we found no seedlings. For seedlings we determine rooting depth, plant height and stem diameter. To confirm that these are indeed young seedlings, less than a year old, we compare root length and plant height with that of seedlings germinated and grown for 77 days in a greenhouse. Our results show that where seedlings are present grasses are dominated by short-lived species such as Aristida congesta and Enneapogan cenchroides. These species are often found in disturbed soils and would increase with overgrazing. On those sites with no seedlings grass species composition is dominated by perennial species such as Panicum maximum, Panicum coloratum and Cenchrus ciliarus that would decrease with overgrazing and/or repeated burning. The perennial species have a 90-100% canopy cover while the short-lived species have a much lower canopy cover of less than 50%. Within 77 days of germinating tree seedlings are able to develop a root system that is deeper than the short-lived grasses but not deeper than the perennial grasses. These results demonstrate that tree seedlings are only able to establish among grasses if there are gaps in both grass canopy and root mass resulting from increased herbivory, frequent fire or extended drought.

scholarly journals Tree seedling establishment among C4 grasses

2016 ◽  
Author(s):  
Edmund C February ◽  
Joel R Lewis
Keyword(s):  
Species Composition ◽  
Plant Height ◽  
Root Length ◽  
Canopy Cover ◽  
Perennial Grasses ◽  
Rooting Depth ◽  
Grass Species ◽  
Tree Seedlings ◽  
Panicum Maximum ◽  
Perennial Species

The coexistence of leguminous trees and C4 grasses in African savanna remains poorly understood. Trees are able to establish among grasses despite grasses being competitively superior for below ground resources. Here we test the hypothesis that trees are only able to establish when grass biomass has been reduced. We do this at four locations in Limpopo Province South Africa where we locate young seedlings of Senegalia nigrescens. Where we found seedlings we determine grass species composition as well as grass percentage canopy cover, height above ground, and root length. We also make determinations of grass characteristics at two locations where we found no seedlings. For seedlings we determine rooting depth, plant height and stem diameter. To confirm that these are indeed young seedlings, less than a year old, we compare root length and plant height with that of seedlings germinated and grown for 77 days in a greenhouse. Our results show that where seedlings are present grasses are dominated by short-lived species such as Aristida congesta and Enneapogan cenchroides. These species are often found in disturbed soils and would increase with overgrazing. On those sites with no seedlings grass species composition is dominated by perennial species such as Panicum maximum, Panicum coloratum and Cenchrus ciliarus that would decrease with overgrazing and/or repeated burning. The perennial species have a 90-100% canopy cover while the short-lived species have a much lower canopy cover of less than 50%. Within 77 days of germinating tree seedlings are able to develop a root system that is deeper than the short-lived grasses but not deeper than the perennial grasses. These results demonstrate that tree seedlings are only able to establish among grasses if there are gaps in both grass canopy and root mass resulting from increased herbivory, frequent fire or extended drought.

Regeneration in Quercus Pyrenaica Ecosystems After Surface Fires

1991 ◽  
Vol 1 (4) ◽  
pp. 205 ◽  
Author(s):  
L Calvo ◽  
R Tarrega ◽  
E Luis
Keyword(s):  
Species Diversity ◽  
Spatial Heterogeneity ◽  
Structural Dynamics ◽  
First Year ◽  
Herbaceous Species ◽  
Quercus Pyrenaica ◽  
Perennial Species ◽  
The Third ◽  
Surface Fires ◽  
Second Year

Early post-fire structural dynamics in three Quercus pyrenaica communities after intense fires was studied. In the first year there is a marked domination of perennial species (herbaceous or woody); afterwards, herbaceous species tend to decrease in importance and ligneous species increase. Changes in species diversity were analysed as an indicator of recovery and stability in the communities. An increase was observed in the second year, and then diversity was maintained or reduced slightly in the third and fourth years. Spatial heterogeneity tends to diminish with time.

Species Composition and Biomass Production in Two Communal Coastal Rangelands of the Eastern Cape Province, South Africa

2020 ◽  
Vol 1 (1) ◽  
pp. 1-10
Author(s):  
S. Matshawule,
Keyword(s):  
Species Composition ◽  
Biomass Production ◽  
Management Practices ◽  
Ecological Status ◽  
Rangeland Management ◽  
Grass Species ◽  
Herbaceous Species ◽  
Eastern Cape ◽  
Frequency Occurrence ◽  
Study Sites

This study investigated species composition and biomass production of herbaceous plants in two communal rangelands surrounding homesteads areas. In each study area, the rangelands were divided based on the distance from homesteads into near (up to 1 km), middle (> 1–2 km) and far (> 2–3 km) sites. On each site a HVU of 50 m x 20 m was used and six 0.25 m2 quadrants were laid randomly on each HVU. Herbaceous species found within a quadrant were identified, counted and their height and tuft were measured. Herbaceous species were also harvested, bulked and placed into well labelled brown paper bags and oven-dried for 48 hours at 60 oC to determine biomass production. Herbaceous species were also classified according to their palatability ecological status and life form. Data were collected for two seasons over 2014/15 (winter and summer). A total of 20 herbaceous species were identified in the study areas. Of these 17 were grass species. The most common or dominant grass species were T. triandra, C. dactylon, E. capensis, E. plana and S. africanus. At Dyamdyam T. triandra showed the greatest frequency of occurrence at far site than middle and near homesteads sites. The frequency occurrence of S. africanus at Machibi was relatively similar in all the study sites. Density of herbaceous species was significantly lowest on near and bottom sites at Dyamdyam and Machibi, respectively. In both winter and summer, grazing site far and top from homestead had greatest (P <0.05) biomass production at Dyamdyam and Machibi respectively. The biomass production was significantly highest in the summer than the winter across the study sites in both study areas. It can be concluded that composition of herbaceous species and biomass production are significantly dependent on distance and topography from homesteads and seasons. Therefore, any rangeland management practices in communal grazing lands should consider these factors in to consideration during the planning of development progress.

Effect of fire regime on the grass community of the humid savanna of Lamto, Ivory Coast

2018 ◽  
Vol 35 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Kouamé Fulgence Koffi ◽  
Aya Brigitte N’Dri ◽  
Jean-Christophe Lata ◽  
Souleymane Konaté ◽  
Tharaniya Srikanthasamy ◽  
...  
Keyword(s):  
Relative Abundance ◽  
Ivory Coast ◽  
Fire Regime ◽  
Fire Regimes ◽  
Abundant Species ◽  
Grass Species ◽  
The Third ◽  
Humid Savanna ◽  
The Impact ◽  
Tussock Grasses

AbstractThis study assesses the impact of four fire treatments applied yearly over 3 y, i.e. early fire, mid-season fire, late fire and no fire treatments, on the grass communities of Lamto savanna, Ivory Coast. We describe communities of perennial tussock grasses on three replicated 5 × 5-m or 10 × 5-m plots of each fire treatment. Tussock density did not vary with fire treatment. The relative abundance of grass species, the circumference of grass tussocks and the probability of having a tussock with a central die-back, varied with fire treatment. Mid-season fire had the highest proportion of tussocks with a central die-back while the late fire had the smallest tussocks. Tussock density, circumference, relative abundance and probability of having a central die-back varied with species. Andropogon canaliculatus and Hyparrhenia diplandra were the most abundant of the nine grass species. They had the largest tussocks and the highest proportion of tussock with a central die-back. Loudetia simplex was the third most abundant species but was very rare in no fire plots. The distribution of tussock circumferences was right skewed and dominated by small tussocks. The proportion of the tussocks with a central die-back strongly increased with circumference, which could lead to tussock fragmentation. Taken together, this study suggests that fire regimes impact grass demography and that this impact depends on grass species and tussock size.

The germinable soil seedbank of Eucalyptus victrix grassy woodlands at Roy Hill station, Pilbara district, Western Australia

2004 ◽  
Vol 26 (1) ◽  
pp. 17 ◽  
Author(s):  
R. A. Graham ◽  
S. K. Florentine ◽  
J. E. D. Fox ◽  
T. M. Luong
Keyword(s):  
Species Composition ◽  
Western Australia ◽  
Perennial Grass ◽  
Summer Rainfall ◽  
Distribution Patterns ◽  
Grass Species ◽  
Surface Areas ◽  
Hill Station ◽  
Soil Seedbank ◽  
Germinable Seed

The paper reports soil seedbank species composition, of Eucalyptus victrix grassy woodlands, of the upper Fortescue River in the Pilbara District, Western Australia. In this study, our objectives were to investigate germinable soil seedbanks and species composition in response to three simulated seasons, using emergence. Variation in seed density from three depths was tested. Four field sites were sampled. Thirty samples were collected in late spring, after seed rain and before summer rainfall. From each sample spot, three soil depths (surface, 1–5, and 6–10 cm) were segregated from beneath surface areas of 100 cm2. Samples were later incubated in a glasshouse to simulate three different seasonal conditions (autumn, winter and spring). Germinating seedlings were recorded on emergence and grown until identified. Forty-one species germinated, comprising 11 grasses (7 annuals and 4 perennials), 25 annual herbs and 5 perennial herbs. Distribution patterns of germinable seed in both the important annual grass Eragrostis japonica and the perennial Eragrostis setifolia (a preferred cattle fodder species), suggest that seedbank accumulation differs among species and between sites. In part, this may be associated with the absence of grazing. Species with most total germinable seed were E. japonica (Poaceae; 603/m2), and the annual herbs Calotis multicaulis (Asteraceae; 346/m2), and Mimulus gracilis (Scrophulariaceae; 168/m2). Perennial grass seed was sparse. Spring simulation gave most germination (1059), followed by autumn (892) and winter (376) sets. Greatest species diversity was produced from the spring simulation (33 species), followed by autumn (26), and winter (22). Of the total germination, 92% came from 17 species that were represented in all three simulations. Of the 1227 grass seedlings counted, most were recruited from the surface soil (735), followed by the 5 (310) and 10 (182) cm depths. Marginally more grass seedlings germinated from the spring simulation (558) than the autumn set (523). Only 11.9% of grass germinants came from the winter simulation. All grass species recruited from the soil seedbanks had a C4 photosynthetic pathway. Except for Cenchrus ciliaris all grass species are native to Australia. Of the four sites sampled, one fenced to exclude cattle five years earlier had significantly more germination than the three unfenced sites. Seedbank sampling produced several new records for plants in the areas sampled.

Productivity of restored grassland-steppe ecosystems

2019 ◽  
Author(s):  
Е. Пещанская ◽  
В. Кожевников
Keyword(s):  
Species Composition ◽  
Rare Species ◽  
Dominant Species ◽  
Civil Engineering ◽  
Botanical Garden ◽  
Grass Species ◽  
Anthropogenic Effect ◽  
Steppe Ecosystems ◽  
Stavropol Region ◽  
The One

Необходимость восстановления луговой степи центрального Ставрополья возникла ещё в середине прошлого столетия. Причиной тому послужило усиление воздействия антропогенных факторов на окружающую среду: распашка целины, промышленное и гражданское строительство, чрезмерный выпас скота, а также воздействие различного вида эрозий. В целях сохранения уникального природного комплекса степей с большим набором ценных и редких видов, а также в качестве опыта по восстановлению кормовых угодий в Ставропольском ботаническом саду в 1963 году были начаты исследования по интродукции дёрна. В период с 1963 по 1984 год на площади около 2 га были воссозданы фрагменты луговой степи. Изучение состояния искусственных ценозов, получение сравнительных данных в отношении видового состава, хозяйственно-ботанических групп, урожайности ценозов важнейшие компоненты исследования. В качестве эталонов обследовались территории естественных целинных степей (эталоны) (г. Бучинка, г. Стрижамент, урочище Новомарьевская поляна) с доминантами, сходными с доминантами изучаемых участков, восстановленных дёрном ( Бучинка , Стрижамент , Новомарьевская поляна ). Количество видов на эталонных участках составляет 6592, на восстановленных участках 83103. Видовой состав максимально представлен разнотравьем: от 44 до 72 видов. Во всех выборках проб преобладают злаки (31,9446,17) и разнотравье (29,4041,64), значительный удельный вес приходится на сухие остатки (старику) 7,6128,64. Масса бобовых колеблется в пределах от 0,85 до 11,01, осок от 0,1 до 13,83. Урожайность травостоя восстановленных ценозов сохраняется высокой 3,243,97 т/га. Показатели урожайности травостоя восстановленных формаций превышают показатели эталонов с разницей от 0,61 до 1,65 т/га. Restoration of grasslands became important in the Central Stavropol region in the middle of the last century. The reason was an increased anthropogenic effect: plowing, industrial and civil engineering, cattle grazing and erosion. Experiments on turf introduction got started at the Stavropol Botanical Garden in 1963 to preserve and restore the unique natural steppe area with a large number of valuable and rare species. Fragments of steppe were grown on 2 ha area from 1963 to 1984. The investigation focused on ecosystem conditions, species composition, botanical groups and yield. Natural steppes performed as controls (Buchinka, Strizhament, Novomaryevskaya Polyana) having similar dominant species as the trial areas. Control areas contained 6592 species, the restored ones 83103. There were 4472 different grass species grown. Proportions of gramineous averaged to 31.9446.17, grass mixtures 29.4041.64, grassland litter 7.6128.64. Contents of legumes varied within 0.8511.01, sedge 0.113.83. Grass productivity of the restored area was high 3.243.97 t ha-1. It exceeded the one of the natural areas by 0.611.65 t ha-1.

scholarly journals Testing for consistency in the impacts of a burrowing ecosystem engineer on soil and vegetation characteristics across biomes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
M. A. Louw ◽  
N. S. Haussmann ◽  
P. C. le Roux
Keyword(s):  
Species Composition ◽  
Ecosystem Engineer ◽  
Environmental Gradients ◽  
Plant Cover ◽  
Ecosystem Engineers ◽  
Conservation Strategies ◽  
Annual Rainfall ◽  
Mesic Grassland ◽  
Vegetation Characteristics ◽  
Semi Arid

AbstractThe impacts of ecosystem engineers may be expected to vary along environmental gradients. Due to some resources being more limited in arid than in mesic environments, disturbances created by burrowing mammals are expected to have a greater ameliorating effect in arid environments, with larger differences in microhabitat conditions expected between burrows and undisturbed areas. The aim of this study was to test if the impacts of a medium-sized burrowing mammal, the aardvark, on soil properties (soil temperature, moisture and compaction) and vegetation characteristics (plant cover, species richness and species composition) are consistent across three biomes that differ strongly in annual rainfall. Burrowing affected soil and vegetation attributes, but the direction and magnitude of these biogeomorphological impacts were not consistent across the different biomes. For example, plant species composition was altered by burrowing in the arid scrubland and in the mesic grassland, but not in the semi-arid savannah. Contrary to expectations, the difference in the impacts of burrowing between biomes were not related to rainfall, with burrowing having strong, albeit different, impacts in both the arid scrubland and the mesic grassland, but weaker effects in the semi-arid savannah. It appears, therefore, that the impacts of these biogeomorphic agents may be site-specific and that it may be difficult to predict variation in their biotic and abiotic effects across environmental gradients. As a result, forecasting the impacts of ecosystem engineers under different conditions remains a challenge to management, restoration and conservation strategies related to these types of species.

scholarly journals Assessment of Anthropogenic Impact versus Climate Change on the Succession of the Diatom Community in Lugu Lake (Yunnan-Guizhou Plateau, China) Using the Sedimentary Record of Geochemical Elements

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 655 ◽  
Author(s):  
Yi Liu ◽  
Chuanhong Chen ◽  
Shao Yang
Keyword(s):  
Climate Change ◽  
Human Impact ◽  
Human Activities ◽  
Anthropogenic Sources ◽  
Diatom Community ◽  
The Third ◽  
The Past ◽  
Third Stage ◽  
Lugu Lake ◽  
Guizhou Plateau

The lake ecosystems on the Yunnan-Guizhou Plateau in China have degraded in recent decades under the effects of anthropogenic activities and climate change. The human impact on the oligotrophic Lugu Lake aquatic ecosystem was evaluated using the sediment records of metals, nitrogen isotopes (δ15N) and magnetic susceptibility over the past 200 years. Three periods were identified based on the trace metal and δ15N records. During the first stage (1816–1976 AD), the concentrations of metals, δ15N and magnetic susceptibility were low with small variations. The anthropogenic contributions to the inputs were also small, except for Ni, reflecting minor human activities in the watershed, and no significant change was observed in the sediment record of the diatom assemblage. During the second stage (1976–2001 AD), the concentrations of Zn and δ15N increased, as well as the anthropogenic contribution of Zn. However, no significant change was detected in the anthropogenic sources of the other metals. These results reflect the low-level use of chemical fertilizers. The major shift in the sediment diatom assemblage during this stage was mainly attributed to regional climate change. During the third stage (2001–2010 AD), the concentrations of the sedimentary metals (Ni, Cr, Mn, Cu, Hg and Al) increased rapidly, with the exception of As and Zn, and a similar increasing trend was observed in the changes by anthropogenic sources of Ni, Cr, Mn and Cu. RDA (Redundancy Analysis) and variance partitioning analysis showed that the human impact and climate proxies independently explained 31.59% and 4.26% of the change of diatom community, respectively, and the interaction between climate change and human impact accounted for 18.61% of the change of diatom community. Tourism-dominated human activities, which were reflected in the metals profiles, facilitated the dominance of eutrophic species and reduced that of oligotrophic species. The development of tourism was likely the main driving force for the succession of diatom assemblages in the third stage. In summary, the anthropogenic input of trace metals in Lugu Lake is still at a low level. However, the significant growth trend in metals over the past decade is significantly related to the change in the lake ecosystem. Therefore, the effects of human activities, especially tourism, on the watershed should be controlled for the protection of the oligotrophic Lugu Lake.

Correlations between environmental factors, the biomass of exotic annual grasses and the frequency of native perennial grasses

2006 ◽  
Vol 54 (7) ◽  
pp. 655 ◽  
Author(s):  
Tanja I. Lenz ◽  
José M. Facelli
Keyword(s):  
Species Composition ◽  
Soil Fertility ◽  
Perennial Grass ◽  
Perennial Grasses ◽  
Annual Rainfall ◽  
Grass Species ◽  
Soil Factors ◽  
Annual Grasses ◽  
Exotic Annual Grasses ◽  
Native Perennial Grass

The species composition of temperate grasslands in the mid-north of South Australia has been radically altered from a system dominated by native perennial grasses to a system dominated by Mediterranean annual grasses. This study investigated the importance of chemical and physical soil characteristics, topographical features and climatic variables on the abundance of native and exotic grass species in nine ungrazed grasslands. Overall, climatic and other abiotic factors were highly variable. In addition, past management practices and original species composition are generally unknown, leading to further unexplained variation in the data. On a large spatial scale (among sites), the abundance of exotic annual grasses was positively correlated with mean annual rainfall, and on any scale, with finer soil textures and higher soil organic carbon levels. The most abundant annual grass, Avena barbata (Pott ex Link), was generally associated with soil factors denoting higher soil fertility. The abundance of native perennial grass species was not correlated with any environmental variables at any scale. The various native perennial grass species did not show clear associations with soil factors, although they tended to be associated with factors denoting lower soil fertility. However, at small spatial scales (within some sites) and among sites, the abundances of exotic annual and native perennial grasses were strongly negatively correlated. The results suggest that at the present time, rainfall and soil properties are important variables determining the abundance of annual grasses. The driving variables for the abundance of perennial grasses are less clear. They may be controlled by other factors or extreme rainfall events, which were not surveyed. In addition, they are likely to be controlled by competitive interactions with the annual grasses.

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