Abstract
Open areas, along with their non-forest vegetation, are often threatened by secondary succession, which causes deterioration of biodiversity and the habitat’s conservation status. The knowledge about characteristics and dynamics of the secondary succession process is very important in the context of management and proper planning of active protection of the Natura 2000 habitats. This paper presents research on the evaluation of the possibility of using selected methods of textural analysis to determine the spatial extent of trees and shrubs based on archival aerial photographs, and consequently on the investigation of the secondary succession process. The research was carried out on imagery from six different dates, from 1971 to 2015. The images differed from each other in spectral resolution (panchromatic, in natural colors, color infrared), in original spatial resolution, as well as in radiometric quality. Two methods of textural analysis were chosen for the analysis: Gray level co-occurrence matrix (GLCM) and granulometric analysis, in a number of variants, depending on the selected parameters of these transformations. The choice of methods has been challenged by their reliability and ease of implementation in practice. The accuracy assessment was carried out using the results of visual photo interpretation of orthophotomaps from particular years as reference data. As a result of the conducted analyses, significant efficacy of the analyzed methods has been proved, with granulometric analysis as the method of generally better suitability and greater stability. The obtained results show the impact of individual image features on the classification efficiency. They also show greater stability and reliability of texture analysis based on granulometric/morphological operations.
Highlights
In Poland, since the 1990s, a gradual cessation of agricultural use, the secondary succession process, has been observed in some areas
The tested variants differed in many features: Type of spectral data (P, RGB, CIR), type of textural data, and in the quality of the source spectral data related to the type of images, original image scale, original spatial resolution, and general radiometric quality of photos
The analysis of the results shows that regardless of the archival data and the texture analysis method used, individual trees and shrubs are difficult to detect—only larger trees and shrubs are possible to detect with these methods
Summary
In Poland, since the 1990s, a gradual cessation of agricultural use, the secondary succession process, has been observed in some areas This is observed in valuable natural areas, including Natura 2000 habitats, and results in deterioration of biodiversity and the habitat’s conservation status. The course of succession is influenced by, e.g., the state of abandoned land (e.g., black fallow, mowed meadow, stubble), soil fertility in nutrients, recently grown plants, the location of the ground (including proximity to the forest), slope, and insolation [2,3,4] This knowledge plays an important role in proper planning of active protection of the Natura 2000 habitats. According to current research in this area [20], for the DIM technique to yield good quality results, archival data must meet several conditions: (1) The scale of images should not be less than 1:13 000 for analog photos, or GSD (Ground Sample Distance) should be smaller than 25 cm for digital photos; (2) the date of obtaining the photos should provide a picture of vegetation in full development; and (3) photos should have good radiometric quality, i.e., small image blur, adequate contrast, and no mechanical damage (in the case of analogue photos)
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