Proportion Of Bare Ground Research Articles

Estimating surface erosion using137Cs at a semi‐arid site in Central Otago, New Zealand

Many authors have indicated significant erosion in conjunction with grazing of sheep and rabbits in the semi‐arid lands of Central Otago. Observations, however, have generally been based on subjective assessments influenced by vegetation depletion and proportions of bare ground. This paper quantifies net soil losses over the past 40 years using the radionuclide tracer caesium‐137 (137Cs). The study area was a ridge near Earnscleugh showing field evidence of surface erosion. Compared with a 137Cs input of 275 Bq/m2, analyses indicated a reduction in soil depth by 3.4 cm over 40 years from the sunny upper sideslope site. This corresponds approximately to an annual loss of 10.2 t/ha. The loss rate indicates that past land use was unsustainable. Net losses up to this value have affected approximately 24% of the local landscape. Conversely, there was net soil deposition on the shady upper sideslope and the sunny and shady footslope sites. Estimated gains in soil depth over 40 years range from 0.3 to 0.6 cm whi...

Effects of reindeer grazing on understorey vegetation in dry Pinus sylvestris forests

Abstract. Data on floristic composition and environmental variables were collected in floristically homogeneous oligotrophic pine (Pinus sylvestris) forests with heath‐like under‐ storey vegetation in eastern Fennoscandia, and ordinated by non‐linear multidimensional scaling (NMDS) in order to study the effect of lichen grazing by reindeer on the understorey vegetation. The study sites included areas with varying grazing pressure, as well as 50‐yr old grazing exclosures. Sites rich in respectively bryophytes and lichens were placed at opposite ends of the ordination axes, and heavily grazed sites were placed in between them. Reindeer grazing increased the abundance of bryophytes, especially Dicranum spp. and Pleurozium schreberi. Grazing changed the vegetation to the extent that it resembled more mesotrophic sites, but this did not show any relationship with tree volume or other site productivity indicators. This was observed both in the ordination and, in a more compelling way, when exclosures with adjacent grazed areas were compared. No such signs were evident at ungrazed sites, where especially Cladina spp. spatially replace Cladonia spp. and tiny bryophytes like Barbilophozia spp., Polytrichum spp. and Pohlia nutans during succession. Cladina stellaris had almost disappeared from the most intensively grazed sites.The soil at ungrazed sites was characterized by high Al and Fe concentrations and bryophyte‐rich sites by high Mn concentrations. Shannon's diversity index, depth of humus layer and proportion of bare ground also increased in sites getting richer in bryophytes.

Influence of successional stage of Eucalyptus regnans (mountain ash) on habitat use by reptiles in the Central Highlands, Victoria

Abstract Eleven sites, representing different successional stages of Eucalyptus regnans‐dominated forest in the Central Highlands of Victoria, were selected to identify potentially important habitat variables for heliothermic reptiles, three species (Eulamprus tympanum, Niveoscincus coventryi, Pseudemoia spenceri) of which were common at these sites. Analyses reveal that many forest attributes are strongly correlated with stand age and that some are significant habitat variables for some of these species. ‘One‐at‐a‐time’ modelling of habitat variables reveals that counts of E. tympanum are most strongly correlated with the proportion of grass as substrate (−ve), moss cover of logs (−ve) and litter depth (+ ve); N. coventryi counts are most significantly related to litter depth (−ve), numbers of logs (−ve), log diameter (−ve), the proportion of bare ground as substrate (−ve) and length of sunny patches (+ ve); P. spenceri counts are most significantly related to the number of sunny patches (−ve) and moss cover of logs (−ve). The total reptile count is most significantly correlated with stag diameter (−ve) and log diameter (−ve). Predictive equations for each of the common species are also presented, using measured habitat variables, and these, along with ‘one‐at‐a‐time’ models, indicate that a number of factors determine reptile occurrence or abundance and that no single predictor variable is apparent.

Distribution of seedlings and saplings of Quercus robur in a grazed deciduous forest

AbstractSeedling and sapling distribution of the deciduous tree Quercus robur was, studied in a grazed, partly open forest, ca. 20 km S of Linkoping, Sweden. Numbers of seedlings and saplings were compared between open and shaded parts of the forest. Cover values for the shrub and tree layers, proportion of bare ground and of stones and soil water content were determined. Q. robur was shown to germinate equally well in open and shaded parts of the forest; however, most saplings were found in the shade. No correlation was found between seedlings or saplings and cover of shrub layer or proportion of stones in the soil surface or with soil water content.

Effects of cattle grazing, sheep grazing, cutting and sward height on a grass-white clover sward

SUMMARYThirteen defoliation treatments were applied to a grass-white clover sward for 2 years to study some effects on the sward of cattle grazing compared with sheep grazing compared with various cutting treatments and to study the effect of height of defoliation.Sheep actively sought out the clover in preference to grass whereas the cattle did not. The response of the clover to sheep grazing was a large reduction in the amount of stolon, shorter internodes, petioles and leaflets, and thinner stolon closer to the ground. Reducing the height of defoliation from 8 to 4 cm above ground level also reduced the dimensions of white clover. The clover, however, appeared to recover quickly and completely from the effects both of sheep grazing and of reducing the height of defoliation when these treatments were discontinued. In plots cut for hay the clover disappeared from the sward suddenly and completely in dry conditions following the 2nd-year hay cut. The effect of cattle grazing on white clover was similar to the effect of comparable cutting treatments. Cattle grazing, however, reduced the number of tillers of grass andincreased the proportion of bare ground, compared with cutting or sheep grazing. Grazing rather than cutting tended to encourage perennial ryegrass and to discourageHolcus. Cutting for hay encouragedBromus mollis. Reducing the height of defoliation reduced leaf sheath and blade length and the rate of production of new blade per tiller in perennial ryegrass, but increased the numbers of tillers of grasses.

Selection of Breeding Habitat by the Thrush Nightingale Luscinia luscinia and Its Position in Bird Communities

Certain factors which appear to be decisive in habitat selection by breeding Thrush Nightingales are set out. This species favours deciduous coppices which are usually low and shady. Some dense thickets providing good shelter are always present in the territories. A proportion of bare ground without field vegatation is also important because the species feeds mostly on the ground. The small coppices where territories are established occur in open environments, near water or fields; this improves the audibility of the birds song. The position of the Thrush Nightingale in the bird community is also presented. It belongs to the guild of ground feeders, but unilke most other species of this guild is strongly adapted for foraging inside woodlands. On the other hand, it is also partly able to utilize other zones of vegatation. It can sometimes forage in field vegetation, on branches and boughs of trees, or even in the air. Its main diet consists of insects, mostly Lepidopteran larvae. In terms of habitat requirements and morphological similarities, the Thrush Nightingale has only two potential competitors, the Robin Erithacus rubecula L. and the Redwing Turdus iliacus L. However, the competition between these species seems usually to be weak. The effect of man on habitats is presumably the most important reason for population fluctuations of the Thrush Nightingale in Finland.

Bunch spear grass dominance in burnt pastures in South-Eastern Queensland

The results are reported of a study of the effect of annual burning, in the absence of grazing, on the botanical composition of a native pasture in south-eastern Queensland. The main effect of burning was to give dominance of Heteropogon contortus (L.) Beauv. ex R. & S. This appeared to be due to three main causes: established plants were resistant to fire; fire favoured the germination of seed; and fire reduced the basal ground cover of other species. The effects on other species and on the proportion of bare ground are reported. The significance of the results in relation to the present distribution of H. contortus-dominant pastures is discussed.