Stipa Tenacissima Research Articles

Effects of soil and vegetation on runoff along a catena in semi-arid Spain

Runoff and infiltration were investigated on abandoned fields of patchy vegetation in semi-arid Spain during 15 months of natural rainfall and by rainfall simulations. The aim was to ascertain sources and sinks of runoff and the effects of soils and plant cover. Soils of the catena developed from mica schists of the upper hillslopes, fan deposits of the lower hillslopes, and an alluvial terrace at the bottom. Runoff from natural events were from three sets of three pairs each of 10 × 2 m runoff plots. The pairs of each set had different densities of plant cover; the sets were vegetated with tussock grass, Stipa tenacissima, a shrub, Anthyllis cytisoides, and a bush, Retama sphaerocarpa. Nineteen natural rainfall events of intensities up to 18 mm/h produced 400 mm of rain during the study period. Because the rainfall threshold for runoff production was about 20 mm, only eight events produced runoff. The rainfall simulations used a sprinkler that produced 50 mm/h of rain for 30 minutes; runoff was recorded each minute in 0.24 m 2 bounded plots. The depth and structure of the soil mantle provide the main controls on runoff rates, which are lowest on the lower fan deposits and highest on the thin upslope soils. The river-bank terrace, with a surface covered by crusts and mosses, also yields relatively high runoff. In general, vegetation density varies inversely with runoff. Nevertheless, shrub and bush litter favor runoff, as does a particular spatial distribution of individual plants on the hillslope. Settling of the upper few centimeters of soils of the alluvial fan following cessation of cultivation 15 to 40 years ago has produced a near-surface compacted layer favoring shallow subsurface runoff. Apparently contradictory results between runoff plots and rainfall simulations are the result of differing processes.

Comparative Physiology and Growth of Two Perennial Tussock Grass Species in a Semi-Arid Environment

The physiology and growth of Lygeum spartumand Stipa tenacissima, two perennial tussock grasses which dominate wide areas of semi-arid south-eastern Spain, were compared at times of high and low availability of water, in autumn and summer respectively, to study the adaptation of this growth form to arid environments. The two species differed in morphological and physiological traits. Stipatussocks were larger and had opportunistic growth, and Stipaleaves had a smaller specific area and lower diffusive conductance to water vapour. The two grasses were similar in maximum photosynthetic rate, leaf nitrogen concentration, and in the response to high light conditions but had different tissue water relations. Stipawas better suited to cope with drought and erratic rainfall, because of its more effective control of water loss and its growth patterns. Lygeumseems to be adapted to less dry conditions and more saline soils. The tussock growth form provides an adaptive advantage in these infertile environments by reducing radiation absorbance.

Fluctuación estacional y dinámica microbiana en una catena afectada por el abandono del cultivo en la cuenca del

Soil biological activity is partly determined by human activity. Areas with Pinus halepensis , have the highest microbial carbon contents (1.200 μg C g -1 ), while soils situated between tussocks of Stipa tenacissima and the abandoned fields have values of 300 μg C g -1 . Alivays, cultivated soils have a very low or negligible microbial activity (< 150 μg C g -1 ). In every case, except in the ploughed field, an increase in microbial carbon biomass occurs between June and February. The aggregate stability shows a similar spatial distribution as the microbial biomass. Pinus halepensis has soils with more stable aggregates than elsewhere. The soil in the area between tussocks of Stipa tenacissima is slightly more stable than the cultivated soil. Abandoned areas show intermediate behaviour, although this varies from season to season. The soil aggregate stability shows a clear spatial correspondence with microbial carbon biomass. This occurs at different season, although there is a period of delay that maybe different for each soil type.

Interactions of plant growth and sediment movement on slopes in a semi-arid environment

The morphology, and architecture of the tussocks of alpha grass ( Stipa tenacissima) as well as its associated micro topography have been described in several sites on the south versant of the Filabres Range, in southern Spain. The annual rainfall of this area is between 225 and 275 mm, and plant cover ranges from 20 to 45%. The results show the formation of micro topographic mounds upslope of the tussocks which are interpreted as deposition bodies originating from the interception of downslope sediment movement by the vegetated patches. The tussock architecture shows an outer growing zone, a middle mature zone and a central senescent zone. The outward expansion of the tussock is performed by tillers in the growing zone which bend at the nodes and root when they come into contact with the soil surface. The mat of dead leaves inside the tussock may prevent the stems from bending and this factor plays a significant role in controlling tussock growth. A similar effect on slopes is produced by the mound of sediments which accumulate upslope of the tussock and press upon the growing stems. A simple simulation model has been built from the above field observations. The model is able to reproduce the tussock shapes found in nature and predicts that at low plant rates, the tussocks become unstable and collapse, while at higher levels of plant vigour and sediment movement rates, sedimentation occurs upslope of the tussock and erosion downslope. These foci of sedimentation and erosion are crescent shaped and their relative importance depends on the splash factor.

Prospection caryologique de la famille desPoaceaeen Tunisie steppique

Summary The chromosome numbers of twenty five Poaceae species in the arid Tunisian flora have been determined. Sixteen of these taxa are polyploids: three hexaploids, twelve tetraploids and one triploid. Six new chromosomes numbers have been found: Aristida obtusa Del. (n = 22), Panicum turgidum Forsk. (n = 27), Pennisetum dichotomum Del. (n = 27), Pennisetum setaceum Desf. (n = 18), Oryzopsis miliacea L. (n = 18) and Stipa tenacissima L. (n = 33).

Influence des conditions stationnelles sur la production de l’Alfa (Stipa tenacissima L.)

The phytomass and production of Alfa (Stipa tenacissima L.) are studied in three experimental stations located along a climatic gradient, during three years (1987-1989). Important differences are appeared by the results. In the more arid station, aerial phytomass and production are low. But the quotient, primary production by pluviosity, twice as important, prove a best rainfall efficiency for the production.

Reconstitution de la végétation à la suite de mesures de protection des sols en terrains montagneux de Tunisie centrale

Recover of vegetation after soil conservation measures in mountain areas of central Tunisia. Sampling sites with a similar soil type, slope and degree of exposure, within areas were selected along the mountain ridge Djebel Kbar in central Tunisia, gouvemorate Sidi Bouzid. Five of the sites had been subjected to various types of soil conservation treatments (e.g. construction of long banks, terraces and pits ; grazing protection, pine plantation establishment) between 5 and 35 years earlier, and another five sites had not been conservateci except grazing protection for the same time période, i.e. from 5 to 35 years. All species of vascular plants were identified, and the number of individuals of each species was counted in each of 9 plots (1 m²) at each sampling site (5 soil conservation areas and four control areas). Biomass of the 25 most frequent species was estimated. Ground cover in % of alfa grass (Stipa tenacissima) was estimated in large plots (10 m x 10 m). The recovery of the plant cover over time was described in terms of character species representing four important stages of succession. About 50 species were identified in the small plots. About 60 plant individuals were present in each small plot. However, plants were much more abundant in the more recently treated areas (about 140) owing to the high frequency of annuals (50-70 % vs 20-40 % in the older ones). The mean biomass per plant was 6,3 g and the range was 0,2-28 g. Approximately 10 species accounted for 80 % of the total biomass, which was 250 g/m². The percent of the ground covered with the alfa grass was considerably higher in the older areas (30 %) than in the more recently established area (5 -10 %). Consequently herbs and grasses were less abundant in the older areas. As the sampling areas increased in age as concerns conservation and protection, plant succession resulted in gradual shift from ruderal, overgrazed vegetation with a high proportion of annuals over to a dwarf shrub -and herb -dominated vegetation type, toward a stage dominated by shrub vegetation. Apparently, these changes were more the result of grazing protection than of the technical conservation measures.

THE IDENTIFICATION OF NON-WOOD PAPER-MAKING FIBRES: PART 3

Describes source, preparation and fiber characteristics of manila hemp (musa textilis) and esparto (stipa tenacissima), both fibers used in papermaking. See also AATA 17-256 for Part I and 19-258 for Part II.

δ13C values of grass species collected in the northern Sahara desert.

δ13C values were measured for 45 Poaceae species collected in the northern Sahara desert, at the foot of the Saharan Atlas. The results indicate a clear relationship between carbon isotope discrimination and phytogeographical distribution of the grasses. Mediterranean species predominantly had δ13C values indicating the C3 pathway of photosynthesis. By contrast, nearly all species belonging to the Saharo-Arabian and /or Sudanian group showed a C4 like carbon isotope composition. Leaf material of two species, Lygeum spartum and Stipa tenacissima, had δ13C values in the region of-20‰, i.e. intermediate between the mean δ13C values of C3 and C4 plants. However, additional speciments of both these grasses obtained from a different source (herbarium of the Hebrew University, Jerusalem) yielded a C3 like carbon isotope composition.

AN EVALUATION OF 15 GRASS SPECIES AS FORAGE CROPS FOR SOUTHWESTERN SASKATCHEWAN

Fifteen grass species were evaluated for dry-matter yield, protein content, in vitro digestibility of cellulose, and winterhardiness. Of these species only Agropyron cristatum and Elymus junceus are used extensively as cultivated forage crops in the prairie area. E. excelsus, E. giganteus, E. sibiricus, and E. striatus appeared to possess fairly high forage-yielding potential as they produced nearly as much as A. cristatum in the first crop year. E. sabulosus and Stipa tenacissima lacked drought tolerance but may give satisfactory yields in moist areas. The other species yielded less forage, generally in the range of production typified by E. junceus. The cellulose digestibility of E. angustus was similar to that of E. akmolinensis and E. junceus. However, E. angustus contained less crude protein than these two species. S. viridula exhibited qualities between those of A. cristatum and E. junceus, and since its yielding capacity and drought resistance were quite good, this species should be reasonably useful for forage production. Of the 12 Elymus species, E. angustus showed the best possibilities of becoming a useful forage crop on dry land for late fall and winter grazing. After the severe drought of 1961, E. arenarius, E. excelsus, E. giganteus, E. sibiricus, E. striatus, and E. virginicus killed out completely and should therefore be considered of doubtful usefulness as cultivated forage crops in a semi-arid, cold climate despite other attributes they may possess.