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 m 3 ), 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.

Abstract:Proper knowledge about resources in forest management is fundamental. One of the most important parameters of forests is their size or spatial extension. By determining the area of treefall gaps inside the compartments, a more accurate yield can be calculated and the scheduling of forestry operations could be planned better. Several field-and remote sensing-based approaches are in use for mapping but they provide only static measurements at high cost. The Earth Observation satellite mission Sentinel-2 was put in orbit as part of the Copernicus programme. With the 10-m resolution bands, it is possible to observe small-scale forestry operations like treefall gaps. The spatial extension of these gaps is often less than 200 m 2 , thus their detection can only be done on sub-pixel level. Due to the higher temporal resolution of Sentinel-2, multiple observations are available in a year; therefore, a time series evaluation is possible. The modelling of illumination can increase the accuracy of classification in mountainous areas. The method was tested on three deciduous forest sites in the Börzsöny Mountains in Hungary. The area evaluation produced less than 10% overestimation with the best possible solutions on the sites. The presented work shows a low-cost method for mapping treefall gaps which delivers annual information about the gap area in a deciduous forest.

KivonatA szálalóerdők kialakítása során elengedhetetlen az erdő szerkezetében bekövetkező változások ismerete. Roth Gyula 1936-ban kezdett kísérletének területén, a Sopron 182 B szálaló üzemmódú erdőrészletben végeztünk részletes törzstér-képezést. Legfőbb célunk egy olyan adatbázis létrehozása volt, amely a későbbiek folyamán alapot szolgáltathat idősoros elemzésekhez. Mindehhez egy olyan felvételi eljárást dolgoztunk ki, amely megfelelő pontosságú törzstérkép készítésére alkalmas. A kapott adatbázist felhasználva 3D modellt készítettünk a felvett faegyedekről, majd vizsgáltuk az erdőállomány struktúráját. A kísérlet eltelt évtizedei során a fafaj-összetétel a bükk dominanciája felé tolódott el, a fényigényesebb fafajok koronái csak a felsőbb szintekben találhatók meg. Ezzel szemben az átmérő-és magasságeloszlás igen változatos, az erdőrészlet egyes részein már a szálalóerdők jellegzetességeit, míg máshol a differenciálódás kezdeti szakaszait mutatják.Kulcsszavak: szálaló üzemmód, szálalás, erdőszerkezet, törzstérkép INVESTIGATIONS ON STAND STRUCTURE IN THE ROTH MEMORIAL FOREST AbstractDuring transformation of even-aged forests to selection forests it is important to follow the changes in stand structure. Detailed forest mapping was made in Sopron 182 B experimental selection forest, where the research was started by Roth Gyula in 1936. The main purpose of the survey was to create a database which can be used for timeline analysis in the future. We developed a survey method which is accurate enough to generate spatial forest stand databases. We made a 3D model of the forest and examined it's structure. During the decades of the experiment beech became dominant, lightdemanding tree species withdrew to upper canopy regions. Diameter and height distribution is heterogeneous, in some areas it shows the characteristic of selection or structurally differentiated forests.