Dispersal and establishment of slender thistle, Carduus pycnocephalus L. as affected by ground cover

1985 ◽  
Vol 36 (6) ◽  
pp. 791 ◽  
Author(s):  
AR Harradine

After 3 years of spread from sown infestations, slender thistle density in spring was 0.12 and 4.67 plants m-2 for plots in which the ground cover was dominated by cocksfoot and annual grass species, respectively. On plots maintained free of plants other than slender thistle ('bare plots'), the corresponding density was 47.31 plants m-2. Slender thistle seed was dispersed at least 10 m from the parent plant in the first year of seeding and plants were evenly spread over the bare plots after 2 years. After 3 years, slender thistle ingress was still occurring on the other plots. The results indicate the importance of ground cover, either of living plants or of litter, in reducing seedling establishment and seed dispersal of slender thistle.

2002 ◽  
Vol 42 (8) ◽  
pp. 1033 ◽  
Author(s):  
A. M. Ridley ◽  
A. L. Avery ◽  
R. N. Oram ◽  
J. Hunter ◽  
J. B. Shovelton ◽  
...  

Persistence of an aluminium (Al)-tolerant phalaris F1 hybrid (Siro 1146 Phalaris aquatica × P.�arundinacea) was compared with that of 3 more Al-sensitive phalaris (P. aquatica L.) lines (cv. Australian and the progenitors of cvv. Sirosa and Sirolan) at 2 sites (Strathbogie and Baddaginnie) in north-eastern Victoria with strongly acidic soils 20 years after sowing. Soil pHCa and extractable aluminium (AlCa) were also measured to 1 m depth under Siro 1146 and annual grass pasture at each site. All grass treatments contained volunteer subclover. Siro 1146 persisted better than the other lines (P<0.05) at Strathbogie where the soil contained high AlCa concentrations down to 50 cm depth. Soils should be sampled and tested to at least this depth to determine their suitability for phalaris. At this site Australian phalaris persisted better than the progenitors of Sirosa and Sirolan (P<0.01), probably because Australian has more spreading ability and tolerance of set stocking than the winter active lines. At Baddaginnie, the soil contained lower concentrations of AlCa below 20 cm depth than at Strathbogie and persistence of the 3 Al sensitive phalaris lines was good despite the lower rainfall. The less drought-tolerant Siro�1146 persisted poorly at Baddaginnie, but had high ground cover due to high lateral spread of the survivors. At Strathbogie, the 10–20 cm layer of soil under Siro 1146 had a higher pHCa and lower AlCa than that under the other 4 phalaris and the annual grass treatments. Soil under Siro 1146 also had higher pHCa and lower AlCa down to 40�cm�depth compared with the annual grass treatment, the differences being significant in the 20–30 cm layer. These differences were reversed at 50–100 cm, but only the effect on Al was significant. Although soils were not sampled at the beginning of the experiment, adequate replication and randomisation of the grass treatments showed that it was statistically improbable for observed final differences to be due to initial soil differences. The final differences may be due to greater amounts of nitrate being taken up from the upper layers by Siro 1146 over its long growing season compared with the annual grasses, leading to greater nitrate leaching from the upper layers and greater nitrate uptake from lower layers under the annuals (i.e. spatial separation of acid generation and consumption processes within the profile). Another possible reason for the greater acidification below 50 cm by the perennial is that its roots may have taken up more cations in this zone. Because of rising concern in some sectors of the public about the off-site, environmental effects of agriculture, the future role of more acid-tolerant phalaris cultivars growing near native vegetation in the high rainfall zone is discussed.


1991 ◽  
Vol 71 (3) ◽  
pp. 771-782 ◽  
Author(s):  
Léonie B. Nadeau ◽  
Jane R. King

The importance of seeds to the establishment and spread of Linaria vulgaris infestations in Alberta was assessed in 1988 and 1989. Stands were established on 17 May 1988. One 10-cm-long root piece with a 10-cm-tall shoot was planted in the centre of each of nine plots on fallow land and of nine plots in a barley crop. Over 90% of seeds in 1988, and over 80% in 1989 fell within a 0.5-m radius of the parent plants with very few seeds falling outside a 1.5-m radius. Seed deposition vs. distance followed a negative polynomial function. It was estimated that over 210 000 seeds m−2 fell less than 0.5 m away from the parent plant over the 1988 growing season. The presence of Gymnaetron sp. and Brachypterolus sp. in 1989 reduced seed deposition to a total of 1410 seeds m−2 within 0.5 m of the parent plant. The few seedlings that were established occurred in clumps, with densities varying from 1.3 to 7.0 seedlings cm−2 in May and from 0.8 to 7.8 seedlings cm−2 in June 1989. In 1988, total seedling emergence per plot varied between 0.13 and 0.23%. Seed viability and dormancy were major factors influencing seedling establishment. Seed viability was as low as 40% (tetrazolium test), and germination was maximized in the laboratory following a wet stratification at 5 °C for a period of at least 8 wk. Key words: Toadflax, Linaria vulgaris, seed dispersal, seedling establishment, seedling distribution


1985 ◽  
Vol 63 (1) ◽  
pp. 125-132 ◽  
Author(s):  
Irene L. Westelaken ◽  
M. A. Maun

Studies on spatial pattern and seed dispersal of Lithospermum caroliniense (Walt.) MacMill. on Lake Huron sand dunes revealed that the ratio of pin to thrum plants was approximately 1: 1 on the south slope of the first dune ridge and slack. However, thrum plants had a higher proportion than pin plants on the crest of the dune ridge. The density of plants was highest on the south slope as compared with the other topographical zones. The spatial pattern of plants was nonrandom and plants were clustered in each of the three topographical zones. Most dispersed seeds of L. caroliniense remained within 1 m of the parent plant. The seed dispersal was not radially symmetrical around the parent plant. The steepness of the dune slope affected the dispersal distance of some propagules. Some seeds were retained on the parent, but few of these seeds were normal. About 40 to 64% of the recovered seeds contained holes in the seed coat. Eight months after marking, about one-third of the original marked seeds were still intact.


Weed Science ◽  
1985 ◽  
Vol 33 (1) ◽  
pp. 50-56 ◽  
Author(s):  
Stephen C. Weller ◽  
Walter A. Skroch ◽  
Thomas J. Monaco

Field experiments conducted over a 2-yr period demonstrated that common bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] inhibited growth of newly planted peach (Prunus persica L. ‘Norman’) trees. Common bermudagrass densities of 100, 75, 50, and 25% ground cover reduced tree fresh weight by 86, 64, 43, and 19%, respectively, the first year (1978) and 87, 62, 44, and 28%, respectively, the second year (1979) after planting. Tree trunk diameter relative growth rate (RGR) was reduced by 75 and 100% common bermudagrass ground cover densities at all measurement dates only in 1978. Tree leaf N and K were reduced in both years by common bermudagrass; however, only at the 100% common bermudagrass density in 1978 was N at a deficient level. Leaf chlorophyll was reduced in trees grown in all densities of common bermudagrass only in 1978. Reduced tree growth cannot be explained entirely by competition for essential nutrients; thus an allelopathic effect of the bermudagrass on young peach roots is suspected.


1987 ◽  
Vol 14 (2) ◽  
pp. 163 ◽  
Author(s):  
D. Lunney ◽  
B. Cullis ◽  
P. Eby

This study of the effects of logging on small mammals in Mumbulla State Forest on the south coast of New South Wales included the effects of a fire in November 1980 and a drought throughout the study period from June 1980 to June 1983. Rattus fuscipes was sensitive to change: logging had a significant impact on its numbers, response to ground cover, and recapture rate; fire had a more severe effect, and drought retarded the post-fire recovery of the population. The three species of dasyurid marsupials differed markedly in their response to ground cover, canopy cover, logging and fire. Antechinus stuartii was distributed evenly through all habitats and was not affected by logging, but fire had an immediate and adverse effect which was sustained by the intense drought. A. swainsonii markedly preferred the regenerating forest, and was not seen again after the fire, the failure of the population being attributed to its dependence on dense ground cover. Sminthopsis leucopus was found in low numbers, appeared to prefer forest with sparse ground cover, and showed no immediate response to logging or fire; its disappearance by the third year post-fire suggests that regenerating forest is inimical to the survival of this species. Mus musculus showed no response to logging. In the first year following the fire its numbers were still very low, but in the next year there was a short-lived plague which coincided with the only respite in the 3-year drought and, importantly, occurred in the intensely burnt parts of the forest. The options for managing this forest for the conservation of small mammals include minimising fire, retaining unlogged forest, extending the time over which alternate coupes are logged and minimising disturbance from heavy machinery.


2000 ◽  
Vol 6 ◽  
pp. 171-182 ◽  
Author(s):  
Ben A. LePage ◽  
Hermann W. Pfefferkorn

When one hears the term “ground cover,” one immediately thinks of “grasses.” This perception is so deep-seated that paleobotanists even have been overheard to proclaim that “there was no ground cover before grasses.” Today grasses are so predominant in many environments that this perception is perpetuated easily. On the other hand, it is difficult to imagine the absence or lack of ground cover prior to the mid-Tertiary. We tested the hypothesis that different forms of ground cover existed in the past against examples from the Recent and the fossil record (Table 1). The Recent data were obtained from a large number of sources including those in the ecological, horticultural, and microbiological literature. Other data were derived from our knowledge of Precambrian life, sedimentology and paleosols, and the plant fossil record, especially in situ floras and fossil “monocultures.” Some of the data are original observations, but many others are from the literature. A detailed account of these results will be presented elsewhere (Pfefferkorn and LePage, in preparation).


1994 ◽  
Vol 70 (2) ◽  
pp. 151-158 ◽  
Author(s):  
R. L. Fleming ◽  
D. S. Mossa

A series of spot seeding experiments was set out on coarse-textured upland sites in northwestern Ontario to investigate how black spruce (Picea mariana [Mill.] B.S.P.) seedling establishment and growth could be improved by site selection and seedbed preparation. Virtually all germination occurred within the first growing season. Annual seedling mortality rates were greatest during the first year, then declined steadily and stabilized at low levels (<10%) after the third year. The highest fifth-year establishment ratios (seedlings/viable seed sown) were found on seedbeds derived from materials near the mineral soil/humus interface. On wetter sites (i.e., higher Soil Moisture Regimes) the best seedbeds occurred closer to the soil surface. Mean fifth year establishment ratios for the best seedbeds were 0.032 on moderately fresh to fresh sites, 0.146 on very fresh to moderately moist sites, and 0.082 on moist to very moist sites. On adjacent lowland sites, slow-growing, compact Sphagnum mosses had a mean establishment ratio of 0.179. Mean fifth-year seedling heights on upland sites ranged from 12 to 14 cm, and were not strongly correlated with site or seedbed type. Key words: direct seeding, black spruce, seedbed, seedling establishment, site type and germination


1801 ◽  
Vol 91 ◽  
pp. 382-396 ◽  

Master W. the son of a respectable clergyman, at Castlecary, in Somersetshire, was born in the year 1793; and, for many months, appeared to be a healthy perfect child: his eyes, in particular, were large and rather prominent. When about six months old, he began to cut his teeth; which was attended with great pain, and frequently with violent convulsive fits. About the end of his first year, a number of persons passing in procession near his father's house, accompanied with music and flags, the child was taken to see them; but, instead of looking at the procession, it was observed that, though he was evidently much pleased with the music, his eyes were never directed to the place from whence the sound came. His mother, alarmed by this discovery, was naturally led to try whether he could see silver spoons, and other glaring objects, which she held before him at different distances; and she was soon convinced, that he was unable to perceive any of them. A surgeon in the country was consulted, who, on examining the child's eyes, discovered an opacity in the pupils, which was so considerable, that he did not hesitate to pronounce there was a complete cataract in each. A description of the child’s situation was then sent to me, with a request that I would point out those steps which its parents should pursue. The case was so evident, that I could not hesitate in saying, that the removal of the opaque crystalline humour, from the place it occupied behind the pupil, was the only method by which the child could obtain his sight; and, attached as I was, at that time, in all cases, to the operation of extracting the cataract, in preference to that of depressing it, I added, that I did not think he would be fit for the operation, until he was at least thirteen or fourteen years old. This advice being approved, all thoughts of assisting his sight were, for the present, relinquished. He soon discovered a great fondness for music; his memory was very retentive of the little stories that were read or recited to him; and, in every way, it became evident that he had a mind capable of receiving information. As soon as he could speak, it was also observed, that when an object was held close to his eyes, he was able to distinguish its colour, if strongly marked; but, on no occasion, did he ever notice its outline or figure. In November, 1800, his parents took him to Bristol; whither they went for the purpose of seeing the works carried on in the school for the indigent blind in that city, and in order that they might ascertain whether their son, who was then arrived to his seventh year, could be taught any thing that would be useful or amusing. Here he very quickly learnt the art of making laces. But his parents, having brought him so far from home, thought it adviseable to extend their plan, and make a visit to the metropolis, for the sake of giving me an opportunity of inspecting his eyes, and of hearing whether my opinion continued the same as that which I had written to them six years before. About a month previous to the time of their arrival, a Portuguese boy, fourteen years old, had been put under my care, who was in a similar situation; and, in this case, notwithstanding all the efforts I could use, I found it impossible to fix the eye, in order to extract the cataract, without employing a degree of force which might have been highly injurious. I therefore relinquished my intention of performing the operation in that way, and determined to make use of the couching needle; being prepared, either to depress the cataract with this instrument, if it was sufficiently solid for the purpose, or, if it was soft or fluid, (which I rather expected,) to puncture its capsule largely, so as to bring the opaque crystalline into free contact with the aqueous and vitreous humours. In order to fix the eye for this operation, I was not afraid to make use of a speculum oculi; since a pressure; which would have been highly dangerous in extracting the cataract, might be applied on the present occasion with perfect safety. Conformably to my expectation, the cataract was of a soft consistence; in consequence of which, I was not able to depress it, and contented myself with making a large aperture through the capsule, by means of which the crystalline was brought into contact with the other humours, a considerable part of it coming forwards, and shewing itself directly under the cornea.


2017 ◽  
Vol 7 (1) ◽  
pp. 173-179
Author(s):  
Elona Cera ◽  
Nevila Furxhiu

Abstract The entrepreneur aim is a very important factor, which is considered as a key element in youth employment and the development of the country's welfare. Literature suggests that same of factors which influence enterpreneurship intention are educatin programs, subjective norms and perceived behavioral control. This study was conducted based on an intentional sample, which consisted of master's student, respectively the first year Business Administration and Public Administration, in Economic Faculty of Tirana University. The sample is composed with 63 people. The empirical analysis is based in the main two elements: first, the use of a standardized instrument and secondly, statistical analysis, factor analysis, correlation and linear regression. The study shows that education programs and subjective norms don’t relate positively with the entrepreneur aim. On the other hand, it emerges that perceived behavioral control has a positive impact on the development of entrepreneurial goal.


Author(s):  
Johanna F. de Vos ◽  
Herbert Schriefers ◽  
Kristin Lemhöfer

Abstract We investigated whether the language of instruction (Dutch or English) influenced the study success of 614 Dutch and German first-year psychology students in the Netherlands. The Dutch students who were instructed in Dutch studied in their native language (L1), the other students in a second language (L2). In addition, only the Dutch students studied in their home country. Both these variables could potentially influence study success, operationalised as the number of European Credits (ECs) the students obtained, their grades, and drop-out rates. The L1 group outperformed the three L2 groups with respect to grades, but there were no significant differences in ECs and drop-out rates (although descriptively, the L1 group still performed best). In conclusion, this study shows an advantage of studying in the L1 when it comes to grades, and thereby contributes to the current debate in the Dutch media regarding the desirability of offering degrees taught in English.


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