Abstract
Strong wind disturbances can affect large forested areas and often occur irregularly within a forest. Due to this, identifying damaged sites and estimating the extent of these losses are crucial for the harvesting management of salvage logging. Furthermore, the location should be surveyed as soon as possible after the disturbance to prevent the degradation of fallen trees. A fixed-wing type of unmanned aircraft system (UAS) with a compact digital camera was used in this study. The imagery was acquired on approximately 200 hectares where five large windthrow areas had occurred. The objective of the study was to determine the location of the windthrow areas using a semi-automatic approach based on the UAS imagery, and on the combination of UAS imagery with airborne laser scanning (ALS). The results were compared with reference data measured by global navigation satellite system (GNSS) devices. At the same time, windthrow areas were derived from Landsat imagery to investigate whether the UAS imagery would have significantly more accurate results. GNSS measurements and Landsat imagery are currently used in forestry on an operational level. The salvage logging was estimated for each forest stand based on the estimated areas and volume per hectare obtained from the forest management plan. The results from the UAS (25.09 ha) and the combined UAS/ALS (25.56 ha) methods were statistically similar to the reference GNSS measurements (25.39 ha). The result from Landsat, at 19.8 ha, was not statistically similar to the reference GNSS measurements or to the UAS and UAS/ALS methods. The estimate of salvage logging for the whole area, from UAS imagery and the forest management plan, overestimated the actual salvage logging measured by foresters by 4.93% (525 m3), when only the most represented tree species were considered. The UAS/ALS combination improved the preliminary results of determining windthrow areas which lead to decreased editing time for all operators. The UAS imagery shows potential for application to early-stage surveys of windthrow areas in forests. The advantages of this method are that it provides the ability to conduct flights immediately after the disturbance, the foresters do not need to walk within the affected areas which decreases the risk of injury, and allows flights to be conducted on cloudy days. The orthomosaic of the windthrow areas, as a by-product of data processing in combination with forest maps and forest road maps, can be used as a tool to plan salvage logging.
Highlights
Forest ecosystems have always been an inseparable part of human existence, as a source of food, shelter, fuel, etc. [1]
This study focuses on the capabilities of unmanned aircraft systems (UAS) to estimate the forest areas affected after windthrow and the volume of salvage logging
The windthrow areas were mapped by four different global navigation satellite system (GNSS) devices and was estimated using Landsat imagery
Summary
Forest ecosystems have always been an inseparable part of human existence, as a source of food, shelter, fuel, etc. [1]. Forest ecosystems have always been an inseparable part of human existence, as a source of food, shelter, fuel, etc. The wind is the most important damaging agent in European forest ecosystems [2]. Storms and strong winds have caused considerable economic losses in the forests of Central Eastern. Europe since 1990 [3,4]. Significantly affected the forests within the country. In many areas of Europe, future wind damage to forest stands is expected [7] because of climate change [8,9], and the changing ratio of autochthonous to non-autochthonous species composition [10], which has meant a shift from deciduous trees to unstable conifers, such as spruce [4]. Determining the extent of potential damage is necessary to plan the processing and marketing of wood to prevent its degradation [11]
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