Ograniczanie wyników

Czasopisma help
Autorzy help
Lata help
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 31

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  landscape structure
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
In Slovakia the agricultural use of the landscape represents 50% of the total area. Over last 100 years it has undergone many forms of development that has been reflected in its spatial and area structure. The landscape structure depends on intensification forms of the landscape use and the ownership relations. The changes in agricultural land are visible and differentiated in the period before and after the collectivization in the fifties of the 20th century. In this paper the landscape ecological structure is evaluated for three geoecological landscape types: lowland, basin and sub mountain. The lowland landscape type is ecologically most labile with average size of the agricultural land units of 50-250 ha where the woody vegetation constitutes only 2.0%. Many rare biotopes were removed from this type of the landscape and it is a relatively dry and ecologically unstable landscape. South slopes of the Malé Karpaty (The Low Carpathians) and Štiavnické vrchy (The Štiavnické Mountains) with a various mosaic of dominant vineyards, orchards, and elements of natural woody vegetation represent other evaluated, sub mountain landscape type. This type of the landscape is generally stabile and creates a characteristic landscape image of a high cultural and aesthetic value.
Former studies usually show a positive effect of landscape heterogeneity on different groups of animals occurring in crop fields but some controversies have been discovered. The aim of this study was to answer the question whether the introduction of mid-field tree belts can help to increase numbers of predatory carabids in crop fields. Distance and the direction of movements of individually marked carabids caught in traps in the shelterbelts and in the adjacent crop fields were measured during one week of July (in 2003 and 2004). Pitfall traps (N=360) were placed 2 meters apart in 30 parallel rows which formed a rectangle of 58 × 22 m divided into 5 strips (5 rows in each one). Strip A was located in the shelterbelt, the others (B-E) were placed in the field. Beetles (exclusively – Harpalus rufipes (Degeer, 1774) which predominated in both habitats) after being marked with fast drying paint (non-dissolving in water, not harmful, and using dot code) were released at the same spots where they were caught. Accordingly 1099 and 1683 individuals in both years were marked and the number of recaptured individuals was equal to 259 (24%) and 307 (18%). Proportion of recapture rate for individuals marked in particular strips ranged between 18 and 28%. Mobility of the beetles was similar in both years (15.9 m and 16.5 m; t = 0.59, df = 579, P> 0.5). Individuals marked within the shelterbelt (strip A) were in both years caught much further away (25 and 27 m) than the individuals marked in opposite strip E, located in crop field (15 and 17.5 m). Differences between the distance covered daily by insects marked in the field and in the shelterbelt were statistically significant whereas differences between distances covered within the field by insects marked in particular strips – were not significant. Only 8–9% of insects marked in the shelterbelt (strip A) was recaptured in the same strip while recapture rate for individuals marked in other strips was higher –16 to 32%. The proportion of insects marked in the field (strip B, C, D, E) and recaptured in the shelterbelt was very low (2–11%). The comparison of recapture rates between strips A and B also shows that insects move mostly from the shelterbelt to the field. As much as 30–34% of the insects marked in the shelterbelt were caught in the bordering field. Among the insects marked in the next strip B, adjacent to the shelterbelt, only 10–11% individuals were caught in the shelterbelt. Presented results indicate that dominating direction of the dispersal in the mosaic landscape is from the shelterbelt to the field.
Reduced connectivity among local populations inhabiting a spatially heterogeneous landscape may restrict gene flow and thus contribute to diminished genetic variation within a population. The aim of this study was to determine the role of geographic distance and habitat barriers in developing genetic structure of a yellow-necked mouse Apodemus flavicollis (Melchior, 1834) population, taking into consideration the spatial organization of the landscape. A field study was carried out in two plots located in NE Poland that differed considerably in terms of the scale of habitat fragmentation: (1) a continuous forest complex, and (2) a mosaic of smaller forest habitats. The plots were separated by a water barrier comprised of a chain of lakes. DNA samples from a total of 654 individuals were examined by microsatellite analysis (5 loci). The results showed that the yellow-necked mouse population was characterized by a poorly pronounced genetic structure throughout the study area, although the statistical significance of F ST for most location pairs indicated that gene flow in the area was not free. The division of the mouse population into three genetically distinct groups clearly demonstrated the significant role of water bodies as a natural barrier effectively hindering free movement of animals and thus gene flow. Analysis of the genetic structure of the mouse population throughout the study area and also within the distinguished groups indicated that the entire study population may be considered as a single metapopulation. Our results suggest that geographic distance alone is not the predominant factor affecting the genetic structure of population, but in the mosaic landscape the relative isolation of individual forest fragments, and barriers hindering movements of individuals and limiting gene flow among local populations played a much more important role.
The agricultural landscape structure in relations between spatial units (forest edge, shrubberies, field borders and roadsides), its green cover and animal communities is studied. The share of parasitoid Hymenoptera of the Pimplinae subfamily in structural elements of agricultural landscape is presented. The relationships between species diversity and the abundance of Pimplinae communities and the complexity level of agricultural landscape are considered. For examining these dependences, multivariate statistical analysis, eg. principal component analysis is used.
According to the results of many studies construction of dams, their decommissioning, and sediment flushing from the reservoir have been associated with vegetation dynamics. However, factors governing the spatial changes of forestation in the floodplain below the dams have not been explored extensively. This study examined the interacting effects of dam, inflow and land-use patterns of catchment areas and other factors on downstream vegetation patterns along the downstream reaches of Southern African Rivers. A total of 105 segments of 15 rivers (16 dams) located in seven Southern African countries were studied. Areas of herbaceous and forest vegetation of river channels below a dam and land-use catchment area patterns were obtained by the Google area calculator and aerial image analysis. Forest development was the highest just below the dams, and the ratio of forest cover decreased with distance from the dam toward the river mouth. Forest coverage ratio was found to decrease with an increase in dyke distance, number as well as of inflows (r = −0.66, P <0.01) and water coverage ratio, and bare land in the river flood plain. However, a principal component analysis (PCA) showed that the proportion of bare land in the catchment area, the dyke distance of the river and the number of inflows or tributaries are the factors most associated with forestation among the studied parameters. Forestation progressively decreased following the entrance of free following tributaries below dams, which appeared to reduce the effects produced by dams on vegetation forestation by causing local deviation. The impact of different land use types, such as agriculture on forestation, was insignificant though in some cases, land use areas cause the forest area reduction.
The study focuses on the changes of Ortolan Bunting (Emberizia hortulana L.) habitats, which occurred during the last 20 years, and the implications of these changes for the presence of the species population in south-eastern Moravia, Czech Republic. The research was based on aerial photographs and field work. We have identified habitats that were favoured by Ortolan Bunting in the study area on the basis of expert knowledge and by spatial analysis. We found that these habitats experienced statistically significant decline in their area. The decline was steeper in the region where Ortolan Bunting occurred only in the 1990s and was smaller in the region where the bird was present from late 1990s till 2012. However, our analyses did not confirm direct relationship between the habitat changes and the decline of Ortolan Bunting population, i.e. we did not find that decline of favourable habitat significantly affected decline of the species population. The main reasons for the decrease of favourable habitats in the study area are changes in agricultural practices, especially spread of mechanisation that have caused an increase in the size of fields and a drastic reduction of groups of trees and solitary trees. Additionally, widespread grassing of vineyards and other plots as a result of integrated and organic farming contributed to the decrease of favourable habitats. Practices in the form of planting new trees and leaving parts of managed land bare to be used for mitigating the decline of the bird population were discussed.
Our survey was carried out in two study sites of approximately 3.3 ha each located in the Suwałki Lake District in NE Poland in the year 2008. Earthworms and soil samples were collected during two campaigns (spring and autumn) from 25 × 25 cm and 30 cm deep sampling points. The complex arable landscape (CAL) supported higher earthworm diversity, density and biomass than the similarly managed but homogeneous arable landscape (HAL). The spring and autumn earthworm sampling campaigns revealed very different patterns, and we conclude that autumn sampling is the most adequate for biomonitoring. On the other hand, the spring collections were significantly correlated to soil physical parameters, thus spring sampling is more suitable for studying such correlations. Significant correlations occurred almost exclusively for CAL and the soil parameters significantly relating with earthworm community were: soil moisture, nitrogen and organic carbon contents. The possible reason for it is the presence of numerous refuges for lumbricids offered by field margins, balks, woodlots and meadows in the CAL and lack of them in the HAL.
The relationships between the density of brown hare Lepus europaeus Pallas, 1778 and landscape structure were analysed on the basis of data collected for 11 study areas between 1991 and 1994, and hunting reports from all the 49 provinces of Poland covering the period 1981-1995. The average autumn density of hares in study areas (8-28 ind/km2, estimated by strip census) decreased with the number of forest edges and increased with the number of permanent cover areas per km of transects. In the provinces of the country, the hare abundance index (hunting bag, ranging from 0.07 to 5.18 ind/km2) decreased with both the proportion of large fields and forests in all the years. The negative effects of large fields and forests on the hare abundance index increased in the study period.
Habitat management should be an important part of the brown hare (Lepus europaeus) conservation, but the habitat requirements of this species are not fully recognised. The aim of our research was to estimate these requirements by analysing the effect of various agricultural landscape structure features on the distribution of hares in five agricultural areas in Germany and Poland. The local density of hares was assessed in the spring and autumn of 2006 by using the method of spotlight–strip counts on 9–15 subareas in each research region. The structure of agricultural landscape has been described for each subarea: the share of grain, other crops and grasses as well as the density of crop edges and uncultivated places with wild vegetation. The density of hares was considerably higher in Germany than in Poland (18.8–48.4 vs. 4.1–9.5 indiv./km2). The hare density was positively correlated with non-grain crops in an area, with crop edges in two areas and with wild vegetation without trees in two areas, and negatively correlated with grassfields in two areas. The occurrence of wild vegetation without trees affected the hare density only in the study areas, where this habitat was relatively rare (<3 km/km2). It was suggested that proper projects aimed at habitat management for brown hares should be elastic, i.e. the projects should be modified depending on the structure of local landscapes. Moreover, the protection and creation of structures with wild vegetation among cropland seem to be considerable methods of brown hare or generally wildlife conservation; therefore, such measures should be an important part of agro-environmental packages.
The study was carried out in central and north-eastern Poland in order to assess bat occurrence in small winter roosts located in house-cellars, in relation to the share of the surrounding landscape taken by forest cover and the distance separating the different sites from forests of at least 1 km². Data from single checks in 2243 cellars in 1990–2007 revealed a positive relationship (R² = 0.33, P <0.001) between the percentage of cellars occupied by bats and the forest cover (range: 2–58%) in sections of surrounding landscape covering between 30 and 220 km². Forest cover in the landscape within 1 km of the cellar appeared to have a slight influence on the number of species and species diversity (Simpson’s index; respectively R² = 0.14, P = 0.006 and R² = 0.13, P = 0.011). Both number of species and species diversity were progressively lower with increasing distance from the nearest forest covering an area of 1 km² or more (for both R² = 0.15, P = 0.005). Myotis nattereri (Kuhl, 1817) and Barbastella barbastellus (Schreber, 1774) were significantly more likely to colonise the cellars surrounded by landscape with a higher level of forest cover (P = 0.001 and 0.031), while M. nattereri was also more likely to be found in those at shorter distances from forests (P = 0.005). No such relationships were reported for either Plecotus auritus (Linnaeus, 1758) or Myotis daubentonii (Kuhl, 1817).
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.