## 4 Discussion
During the first field collection, we noticed a non-significant trend of higher \(\alpha\)-pinene levels on the south side of the stem, despite the prevailing wind coming from the opposite direction. This was attributed to the tree's location near the forest edge, allowing for direct afternoon sunlight exposure during collection [17; 21]. The second collection, conducted later in the season, took place at a lower temperature of 22 \({}^{\circ}\)C. Interestingly, the highest abundance of monoterpenes was not observed at the lowest position, but rather at a height of 2.6 m, Additionally, it was not closest to the treestem, but rather 1 m away. Results were confirmed again by two collection methods, Solid-Phase Microextraction (SPME) and HayeSep-Q(r) Cartridge sampling, conducted at two different time intervals. This sampled tree, despite being in a similar stage of infestation as the first tree, was fully surrounded by other trees, including some broadleaf varieties in the vicinity, resulting in no direct irradiation of the stem. During this collection, we did not observe any significant influence of sunlight exposure or wind speed on the orientation of increased \(\alpha\)-pinene abundance. The temperature and humidity differences in altitude were recorded on the same experimental plot [9]. The highest temperatures were observed approximately \(1\) m above the ground with an upward gradient. This temperature variation may impact the higher abundance of \(\alpha\)-pinene at an altitude of 2.6 m compared to ground level due to the physical properties of pinene vapors. The variation in outcomes between the first and second field collections was attributed to differences in the surroundings of the measured trees, distinct parts of the season, and, primarily, variations in temperature and humidity conditions [36; 37]. In forest practices, our 3D distribution data of \(\alpha\)-pinene emitted by freshly infested spruces may serve as a foundation for scanning techniques, demonstrating promising potential for managing bark beetle populations by facilitating early attack detection. The most advanced technique for volatile scanning in situ can be based on field and portable Gas Chromatography-Mass Spectrometry (GC-MS) instruments, which are possible to mount on UAV. These instruments have the capability to separate, identify, and quantify VOC compounds in situ and collect data at short intervals. Existing instruments on the market have been tested for various analytes, primarily for military applications [58]. However, reliable devices for detecting terpenes and other infestation marker VOCs are still lacking. To specifically select markers of infestation by _Ips typographs_ and exclude infestations of different herbivores (as relevant bark species or defoliators) from the complex odor environment of a natural forest, such as bark beetle pheromomes and spruce host compounds, an olfactory perception system of the bark beetles, antennae can be used as a specific detector working via electroantennography principles [59; 60]. Ongoing research is exploring the application of this method in insect pest detection, with future directions aiming to target insect protein odorant receptors for specific compounds indicative of infestation [31]. However, the most potentially promising novel device is a non-specific electronic nose, designed for real-time chemical substance detection (e.g., detecting dangerous gas leaks or measuring concentrations near landfills, monitoring volcanic activity, etc.). We previously conducted tests to explore the feasibility of early-stage stress detection in forest stands using an electronic nose, specifically the Sniffer4D [9]. Due to limitations in measuring VOCs with non-specific sensors in forests, especially in areas with higher concentrations of compounds from fresh clearings, debris, and broken trees, an ideal approach would involve integrating environmental VOC scanning with other data collected through different scanning methods.