Ograniczanie wyników

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

Znaleziono wyników: 143

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 8 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  lesistosc
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 8 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
Praca przedstawia wyniki badań nad modelowaniem, w systemie informacji przestrzennej PA ARC-INFO, optymalnej struktury rozmieszczenia lasów w Polsce. Na podstawie analizy 25 czynników przedstawiono trzy warianty zwiększenia lesistości kraju, uwzględniające potrzeby zagospodarowania gruntów marginalnych dla rolnictwa, wykorzystanie środowiskowych funkcji lasów w ograniczaniu degradacji powierzchni ziemi oraz aspekty polityki ekologicznej i społecznej.
The aim of this work was to present changes in the fragmentation of forest area characterised by a two−fold increase in forest cover during the last century. The Forest Area Density (FAD) indicator was utilised in order to determine the forest fragmentation for the raster analysis of numeric maps. Its calculation was made using GuidosToolbox software. The research covered 1862 km² of a predominantly post−glacial area of the Ińsko Lakeland, located in the north−western part of Poland. At the end of the 19th century, forests occupied 273.0 km² of this area, while at the beginning of the 21st century their area coverage increased to 612.5 km². The observed increase in the forest cover was associated with changes in forest fragmentation, which was analysed using the FAD. When comparing the two surveyed periods on the synthetic result maps obtained by utilising the FAD method, visible changes can be seen in individual forest categories, which indicate a decrease in the fragmentation of forest areas. The use of fragmentation measures is justified because according to the data found in the literature, the recently observed increase in forest coverage in many areas of Europe does not always determine the decrease in their fragmentation. This verifies the legitimacy of using the FAD indicator in the context of ecological and economic assessments.
Training dataset for modelling of forest cover was created after classification of multispectral satellite imagery IKONOS−2 with spatial resolution 3.2 m (acquisition date – 12.08.2011). As a result, we created binary forest cover map with 2 categories: ‘forest’ and ‘not−forest’. That allowed us to compute the tree canopy cover for each pixel of Landsat 8 OLI, using vector grid with cell size of 30×30 m. Classification model was developed using training dataset that included 17,000 observations, 10,000 of them represented results of IKONOS−2 classification. Aiming to avoid errors of agricultural lands inclusion into forest mask because of lack of data, additionally we collected about 7000 random observations with canopy cover 0% that had been evenly distributed within unforested area. Random Forest (RF) model we developed allowed us to create continuous map of forests within study area that represents in each pixel value of tree canopy closeness (0−100%). To convert it into a discrete map, we recoded all values less than 30% as ‘no data’ and values from 30 to 100% as 1. Forest mask for two selected administrative districts of Chernihiv region (NE Ukraine) was created after screening map from small pixel groups that covered area less than 0.5 ha. Obtained results were compared with Global Forest Change (GFC) map and proved that GFC data can be used for forest mapping with tree canopy closeness threshold 40%. On considerable areas of abandoned agricultural lands in the analysed regions of Ukraine, forest stands are formed by Scots pine, silver birch, black alder and aspen. Existence of such forests substantially increases (on 6−8%) the forested area of Gorodnya and Snovsk districts of Chernihiv region – comparing to official forest inventory data. However, such stands are not protected and have high risks to be severed by wildfires, illegal cuttings with aim to renew the agricultural production, by diseases, insects and other natural disturbances.
Excessive deforestation and agricultural use of sandy soils, in particular of those in the middle basins of Wisła and Warta rivers, constitutes a significant factor for degradation of ecological structure in Poland. This problem was analyzed since a long time and efforts were undertaken to arrange the forest reclamation of non-effective arable land. The acreage of non-effective arable land is increasing along with advances of agrotechnology. Increasing awareness of the necessity for ecological revitalisation of excessively deforested land, laid the basis for resolution of the act on setting agricultural grounds aside for afforestation purpose [19], andin particular the grounds of VI and V classes. Undoubtedly this will help to promote the afforestation of non-effective agricultural land and intensify research in this field.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 8 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.