Increase In Plant Cover Research Articles

Native prairie grasses and microbial community responses to reclamation of taconite iron ore tailing

The effect of reclamation treatments on seeded native grass cover and species composition, soil microbial biomass carbon, and populations of actinomycetes, fungi, free-living N2-fixing bacteria, and aerobic heterotrophic bacteria was compared in field plots in coarse taconite tailing. Reclamation treatments consisted of all possible combinations of three rates of composed yard waste, three rates of fertilizer, and inoculation with arbuscular mycorrhizal fungi. Composted yard waste increased plant cover, soil microbial biomass, and populations of all groups of microorganisms compared with unamended, non-inoculated control plots. Microbial populations and biomass in tailing plots were low compared with natural soils and were correlated with plant cover and available P. Mycorrhizal inoculation resulted in a 6% increase in plant cover, although this was not significant, and significantly enhanced N2-fixer populations in June but did not affect other groups of microorganisms. There were no differences between moderate and high rates of composted yard waste. We conclude that incorporation of a moderate rate of organic matter can ameliorate the stressful conditions of coarse taconite tailing and can enhance the initiation of a functional soil ecosystem able to support the establishment of seeded native prairie grasses and may provide a long-term solution to reclamation of taconite tailing. Key words: arbuscular mycorrhizal fungi, mine reclamation, soil microorganisms, composted yard waste.

Vegetation recovery patterns in early volcanic succession

Permanently plots were monitored from 1983 to the present on Mount Usu after the eruptions of 1977–78 which destroyed the pre-eruption vegetation by 1–3 m thick accumulations of ash and pumice in order to clarify the processes and mechanisms of succession. Until now, 163 species were recorded in the summit area. Most of these species were derived from vegetative reproduction throughout the volcanic deposits. Vegetative reproduction plays a major role on increases in cover. Although long-distance seed-dispersal species could immigrate to the crater basin, their cover increase was slow. Seedbank species only established in gullies where the original topsoil was exposed by erosion. Most annuais were supplied by the seedbank in the original topsoil and woody species originated via immigration, suggesting that the source greatly determines the species composition of establishing vegetation. Annual seedlings showed low survival, while overwintering perennial seedlings steadily established. Ground surface movements strongly restricted increases in plant cover and the distance from source vegetation was the principal determinant of plant density. Due to differences in disturbance intensity, successional rates were higher in the stable substrates outside gullies and lower on the exposed original topsoil in some gullies.

Diet selection of the plains vizcacha (Lagostomus maximus, family Chinchillidae) in relation to resource abundance in semi-arid scrub

The diet of the plains vizcacha (Lagostomus maximus) was studied in semi-arid scrub of central Argentina from November 1985 to May 1987 as a basis for understanding the effects of this herbivore on plant communities. Diet composition was documented with microhistological analyses. Fecal nitrogen, an index of diet quality, and vegetation cover were used as measures of resource abundance. Vizcachas consumed a wide variety of grasses, forbs, and shrubs. Grasses were observed in the feces significantly more than expected on the basis of plant cover in the field. Intensive foraging on grasses is consistent with observations of a lower abundance of grasses on colony sites than in the surrounding matrix. Diet quality and breadth of the grass–forb component of the diet were strongly correlated, and comparisons within a season between years showed that diet selectivity decreased with increasing plant cover. Our results contrast with many other studies of foraging strategies that have shown higher selectivity with increasing resources. The inverse relationship we observed could be related to constraints on diet selection due to low food availability.

Sea level and initiation of Predynastic culture in the Nile delta

PREDYNASTIC occupation of the Nile valley and delta, dating back to at least 5000 BC, has been attributed by most archaeologists to environmental factors, primarily regional climate change and fluctuating Nile flood stages1–5. Here we propose instead that initiation of farming settlements in the Nile delta was closely related to eustatic sea level. We present geological analyses of late Quaternary subsurface sections throughout the delta which reveal that the deceleration in sea-level rise that occurred at about 6500–5500 BC was a prime factor in the accumulation of Nile silt, and the creation of the widespread and fertile delta plain. As rising sea level reduced the gradient of the river course, a system of meandering Nile distributaries evolved, with increased overbank deposition burying the former (early Holocene), partially vegetated sandy plain. The broadening, seasonally flooded, fecund plain, with its increasing plant cover, provided a setting that was conducive to evolving agricultural activity and was therefore instrumental in the development of Predynastic communities in the Nile delta.

Small‐Scale Wetland Restoration in the High Arctic: A Long‐Term Perspective

AbstractResults are presented using vegetative shoots and bryophyte sods to restore floristically impoverished high arctic wet sedge‐moss meadows that had suffered intense damage from vehicle activity during the period 1960–1967. Clonal transplants of Carex aquatilis var. stans, a native sedge, were planted with and without bryophyte sods in vehicle ruts in 1972. After nearly two decades, there was less Carex cover in the planted ruts with flowing water than in the contiguous controls. This pattern was slightly reversed in planted plots with standing water. Reinvasion of Eriophorum angustifolium occurred in treated ruts, but cover was less in both treatments than in controls in 1990. The unexpected recruitment of Eriophorum scheuchzeri from the seed bank in moss‐sodded plots is discussed in terms of its local and regional importance. Total plant cover in restored ruts was nearly equal to that of controls, but biomass was somewhat less than that in control plots. Plots with bryophytes were environmentally distinct, due primarily to increases in organic mat depth relative to controls. After 18 years, restoration efforts resulted in increased plant cover in treated ruts compared to naturally recovering ruts. The composition of no two patches of vegetation is precisely the same [and] neither are the seed banks. Successsion on different patches of disturebed ground in the same locality frequently proceeds quite differently because of such differences.—J. Miles, Vegetation Dynamics, 1979

Ecological correlates of small mammal community structure in the semi‐arid Karoo, South Africa

The understanding of the determinants of small mammal community structure in arid and semiarid ecosystems is of importance, both in the light of the role that small mammals play, and the impact of livestock grazing on the flora of these systems. In a study aimed at identifying these determinants, small mammal assemblages and environmental features were quantified at six localities (a gradient of floristic structure, with constant annual rainfall) across the southern Karoo, South Africa. Stepwise variable regression indicated that small mammal diversity was correlated with plant and rock cover, as well as plant cover and horizontal foliage diversity at intermediate heights (40–60 cm). Initially, small mammal diversity increased with increasing plant cover, but decreased at cover levels greater than 30%. This relationship is similar to that found in other desert systems, although the peak in diversity found here is at higher levels of plant cover than found previously. I suggest that this higher peak may be owing to the lack of reliance on granivory by these animals, which are relatively omnivorous. This model may therefore explain the conflicting reports on the impact of livestock grazing on desert small mammals, with small mammal diversity decreasing with grazing below the peak, and increasing with grazing above the peak.

Long-term patterns in soil moisture and revegetation after a clearcut of a Douglas-fir forest in Oregon

Soil moisture levels during 1960–1980 were compared for two areas within a 101 ha watershed in the Oregon Cascade Range. In winter 1962–1963, the old-growth Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) forest in one area was clearcut. The site was then lightly broadcast-burned in September 1963. An adjacent forested area was left undisturbed as a control. In summer 1963, the upper 120 cm of soil in the clearcut averaged over 10 cm more moisture than that in the forested control. By 1967 these surpluses in the clearcut had declined to become deficits of at least 2 cm less moisture than in the control. These deficits, which were presumably caused by a rapid increase in plant cover after the light slash burn, persisted in the upper 30 cm of soil throughout the rest of the study. The fluctuations in soil moisture in the treated area are extensive enough to influence forest regeneration and watershed hydrology.

The Effect of Sand Deposits on the Growth and Morphology of Ammophila Breviligulata

(1) The effects of sand deposition on the growth and morphology of Ammophila breviligulata were studied in the field. (2) Both belowand above-ground biomass increased as depth of sand-burial increased. On stable dunes compared with mobile ones, a greater below-ground biomass was supported by a relatively smaller above-ground biomass. (3) Leaf area was directly related to sand burial. Peak leaf area of 23.5 cm2 g-1 fresh weight occurred with 22 cm of sand burial. Plant height increased exponentially with increased sand burial and reached a maximum of 64.5 cm with 59 cm of sand. (4) The number of buds per tiller, the number of rhizomes per plant, the internode length on vertical rhizomes, and the number of horizontal rhizomes, all increased with increased sand burial. (5) The concentration of chlorophyll in leaves increased exponentially with increased burial. Maximum total chlorophyll (2-3 mg g-1 fresh weight) was found in plants buried to a depth of 23 cm. (6) Most increases in plant cover were found where sand accumulated, while most of the decreases were on stable sites. A multiple regression, in part based on sand burial, accounted for 57% of the variance associated with changes in cover.

The Effect of Human Trampling on a Sand Dune Ecosystem Dominated by Empetrum nigrum

(1) The influence of trampling was studied on the outer dune heath of Skallingen, southwest Jutland. The total number of passages and the period of time over which trampling occurred were varied independently, on areas that had either received fertilizer applications or were unfertilized. The depth and width of paths were measured and the relative cover of the vegetation and species frequency determined. (2) There was a linear relationship between the depth of the paths and the number of passages. 2560 passes lowered the soil surface by 28 mm. The width of paths increased with increasing numbers of passages. The paths were slightly deeper when trampled on a single day as opposed to the effect of trampling over a period of 4 months. (3) Relative cover was reduced with increasing numbers of passages; after 200 passages cover was only 50%. This low carrying capacity is suggested to be the consequence of reduced vigour of the dominant species Empetrum nigrum, although it is not reflected in frequency measurements of this species. The frequency of four species E. nigrum, Festuca rubra, Ammophila arenaria and Veronica officinalis was largely unaffected by 150 passages but only two species, Empetrum nigrum and Hypnum cupressiforme survived 2560 passages. (4) Addition of fertilizer only slightly increased plant cover on the paths but tended to produce a vegetation dominated by grasses. (5) It is emphasized that all the consequences of a management operation need to be considered before it is carried out.

A Relationship between Competition and Sex Ratio of Shadscale

The sex ratio of shadscale populations within and outside grazing exclosures show significant departures from random expectations. Males are over represented within the ungrazed exclosures, while females are more prevalent in the grazed pastures. These unequal sex ratios could be the result of three factors: differences in genetic composition, differential grazing pressure on males and differences in water stress. Due to the increased plant cover within the ungrazed exclosures, we believe that plants inhabiting these sites are under greater water stress. Moreoever, it appears that females either tolerate water stress less well than males or change sex when stressed.

Atmospheric Emission and Plant Uptake of Mercury from Agricultural Soils near the Almadén Mercury Mine

AbstractSurface soils collected near the Almadén, Spain, mercury mine reflected increasing concentrations of mercury (Hg) with proximity to the mine due to weathered mineral deposits and to atmospheric deposition of Hg from the smelter. Extractions with NaHCO3 or NH4OAc removed small amounts of Hg from both control (20 km from the mine; total Hg = 2.3 µg/g) and mine site soils (1 km; total Hg = 97 µg/g). Density gradient centrifugation indicated a significant fraction of the Hg to be associated with a high‐density mineral fraction, presumably cinnabar. Accumulation of Hg by alfalfa suggested a dual mechanism of uptake; roots accumulated Hg in proportion to the soil levels, while aerial plant material absorbed Hg vapor directly from the atmosphere. Soil fertilization with and without liming significantly increased total Hg uptake, largely due to plant growth stimulation. Liming itself had no significant effect. The rate of volatilization of elemental Hg from both soils (∼0.13 and 0.33 µg/m2 per hour at 25°C, for control and mine site, respectively) exceeded reported background emission rates by factors of 4 to 10, increasing with surface temperature and Hg content and decreasing with increased plant cover.

Alpine and High Subalpine Plant Communities of the North Cascades Range, Washington and British Columbia

Community types were described from 209 stands in the alpine zone of the North Cascades Range. The maritime to continental climatic change from west to east has a profound effect on regional vegetation patterns. Most of the community types in the eastern North Cascades are closely related to those in the Rocky Mountains, southern Alaska and the southern Yukon whereas communities in the western North Cascades are more similar to communities in other west coast ranges. Soils in the region include Entisols, Inceptisols, and Spodosols. Physical properties are quite similar in most soils. Organic matter, total cation exchange capacity, and pH generally decrease from west to east while exchangeable cations and nutrient levels are low throughout the region. A fellfield—dry graminoid—mesic environmental gradient was examined on Grouse Ridge, Mt. Baker. High soil temperature and low soil moisture regimes were typical of the ridgetop fellfield. During drought periods, on the vegetated portion of the slope, soil temperatures decreased and soil moisture stress increased with distance downslope; a reflection of increased plant cover and greater evapotranspiration towards the base of the slope. Species at the base of the slope had reduced vigor and much lower leaf water potential than those upslope. Phenological patterns were closely related to date of snowmelt and early—season temperature regimes along the gradient.

Speculations Concerning Paleohydrologic Controls of Terrestrial Sedimentation

The relations that have been recorded among modern climatic, phytologic, and hydrologic data are used to speculate about the effects of evolving vegetation on the hydrologic cycle. At present the peak of erosion rates occurs in semiarid regions, whereas during prevegetation time erosion rates rose to a plateau, the magnitude of which depended upon the erodibility and weathering characteristics of the rocks. With the appearance of terrestrial vegetation and its colonization of the earth's surface, erosion rates decreased, as did runoff and flood peaks. A review of the relations existing between the morphologic and hydrologic characteristics of river channels demonstrates that fluvial sedimentary deposits are significantly different depending upon the nature of the sediment load moved through the channel. Combining the conclusions obtained from an analysis of hydrologic relations with conclusions concerning effects of type of sediment load upon river morphology, it is possible to speculate on the changing nature of the land phase of the hydrologic cycle before and during the colonization of the landscape by vegetation. During prevegetation time, bed-load channels moved coarse sediments from their sources and spread them as sheets on piedmont areas. With increased plant cover, alluvial deposits were stabilized, but large floods caused periodic flushing of sediment from the system, thereby creating cyclic sedimentary deposits. The influence of climate change on the volume and type of sediment moved from an erosional system became more pronounced as the effect of vegetation on the hydrologic cycle increased. Finally, with the appearance of grasses during the Cenozoic Era, the relations between climate, vegetation, erosion, and runoff became much as today except for the influence of man.