*2.1. Materials*

The Orthodox church and belfry, surrounded by centuries-old plantings, are located at the western end of the village of Horostyta (approximately 2100 sqm) (Figure 2). The building of the Orthodox church, together with the interior and exterior furnishings and belfry, is included in the list of monuments of Lubelskie province under No. A/143 [16]. A historic tree stand surrounds the church, which includes 15 trees of various ages and health, including two natural monuments. A brick wall and part of an old fence outline the area. Cast iron, stylized lanterns illuminate the whole area. Within the property's boundaries, along the fence and on the side of the municipal road, there are two wooden crosses and one metal cross. A wooden cross and a stone slab commemorating the January Uprising (1863) are on the church's northern side. A procession road runs around the church, and the temple dominates this small plot. Its architecture fits very well into the rural surroundings of the village, as does the free-standing bell tower. The parish house is on a separate plot north of the church.

**Figure 2.** Geographic location of the study area (https://polska.geoportal2.pl/map/www/mapa. php?mapa=polska, accessed on 1 February 2023 (by authors).

Gardens around religious buildings were often created in previously developed areas for cemeteries. However, these necropolises were mainly relocated outside temples in the 18th century for sanitary reasons, among others. The tendency to locate cemeteries within churches dates back to the 10th century, coinciding with concern for burials to occur on consecrated ground [17]. The location of the former church cemetery is also marked around the temple in Horostyta. Today, the burial place is on the south side of the church building, in the cemetery about 100 m from the church.

#### *2.2. Methods of Dendrological Measurements*

During the field research, we made a dendrological description of all trees in the study area. The dendrological research consisted of a general description of the tree, which included: inventory number, species name, and general metric data, i.e., trunk circumference at 1.3 m, trunk diameter at 1 m, bark thickness, total height of the tree, range of the tree crown, height of the base of the crown, height of the entire crown, as well as the approximate age, GPS coordinates, and health condition of the assessed tree with comments.

The overall health of the root system, trunk, and crown was important for visual inspection. The visual examination included the characteristics of the trunk's surroundings, the shape of the root neck, and changes and possible damage to the roots. The condition of the trunk essentially determines the health of the entire tree. In the case of fungal infections, the condition of the wood deteriorates, limiting the transport of nutrients and water. During the visual inspection of the trunk, we also considered the base of the crown, in terms of the way the branch fixing might affect the tree's static strength in the future. Assessing a tree's vitality also depends on the amount of downy growth, branch damage, crown asymmetry, or parasitic organisms such as fungi or mistletoe. To determine the vitality of the trees, it was also essential to assess the mechanical, physical, and biological damage (cavities, hollows, and sprouts; signs of insect feeding, fungal fruiting bodies, or exudates). We also paid attention to the leaning of the trunk and other external signs.

We examined trees from all sides, from roots to crown. Visual assessment is always qualitative and sometimes subject to errors depending on the assessor's experience, which should be considered when interpreting the results [18–20]. Of the 15 trees examined, we classified 10 as healthy with no visible damage. The remaining 5 specimens showed noticeable weakness (excessive branch drift, diminished leaves, and falling bark). Three specimens were subjected to detailed acoustic tomography examination for final confirmation of their health status.

We performed tree measurements using a measuring tape and mechanical caliper. The circumference of the trunks was measured using a measuring tape with an accuracy of 1 cm at 130 cm above the ground and the diameter was measured using the caliper at 100 cm above the ground. We measured the crown's reach using the Leica DISTO D5 rangefinder in two directions, N–S and E–W, and we averaged the obtained results. The height of the tree was measured using a Nikon Forestry Pro laser rangefinder. We performed photographic documentation using a NIKON D5300 camera. We also used specialized diagnostic equipment, such as the PiCUS 3 acoustic tomograph by Argus-Electronic GmbH.

The ages of the trees were estimated using several methods: age tables by Majdecki (1980–86) [21], age tables by Mydłowska (2014) [22], a tree age calculator [http://www. tree-guide.com/tree-age-calculator, accessed on 11 April 2023] [23], and a tree size guide [https://wdvta.org.uk/veteran\_trees.php, accessed on 11 April 2023] [24]. The additional file contains Majdecki's and Mydłowska's age tables. Significant deviations between methods are often visible when assessing the age of trees. However, there are no better non-invasive methods for determining the age of trees. A more accurate assessment of the age of standing trees can be made using a Pressler probe or a resistograph. However, these are invasive methods. It is worth noting that, in addition to differences in the calculation methodology, the result may be affected by many factors (environmental conditions, substrate abundance, soil moisture, growth rate, or genetic factors); therefore, plantings even from the same period may differ significantly in terms of measured age.

Based on the conducted dendrological inventory and literature review, we created a revalorization concept for the garden around the temple.

#### *2.3. Measurements with the PICUS 3 Acoustic Tomograph*

In recent years, the number of tools and methods used in tree surveys has steadily increased [25–27]. Non-destructive testing can be divided into global techniques (ultrasound waves, stress waves, and resonance) and local techniques (probing, coring, and drilling) [28]. Among the methods used here were mechanical acoustic waves [28–30] and several others [31–33]. Using modern examination techniques based on acoustic tomography gives promising results compared to basic visual assessments [34–36]. Qiu

et al. developed a tomographic technique using mechanical waves (i.e., stress and acoustic waves) and electromagnetic waves (i.e., laser beams) to evaluate tree trunk defects. In their experimental work, they used the tomographic technique to inspect a tree trunk with an air hole fabricated at the centric position and air gaps made at 5–50 mm near the surface. The results indicated that the internal air hole and air gaps at 5–20 mm below the tree surface could be effectively detected and quantified. Compared to the results using conventional sonic tomography, the presented tomographic technique achieved more accurate and reliable detection of internal defects in tree systems, especially if the internal defects were close to the free surface (i.e., critical defects associated with bending failure) [37].

In addition to the accuracy of the results, the measurement time is also essential. The Balas team evaluated the time needed for measurement and proposed an optimal workflow in 2020 [38]. The results of their work suggested that the scanning of one average-difficulty tree by SoT and ERT resistance tomography took an average of approximately 52 min when one operator measured one scan and approx. 37 min when two operators measured a queue of trees. Working in a two-person team was moderately more efficient. Typically, the overall cost of one scan is approximately EUR 25–30, depending on many variables.

Sonic tomography is a technique broadly applied for detecting defects and voids within several kinds of elements. Sonic pulse velocity tests (SPV tests) are widely applied for detecting the morphology, hidden defects, and voids within structural elements. This technique, broadly applied because it is non-invasive and easy to perform, is remarkably adaptable to ancient buildings, in which no damage is tolerated due to historic preservation requirements. Moreover, SPV tests were recently applied with tomography technology to obtain images of sonic speeds from which it was possible to rapidly reconstruct the morphology of the internal elements [39].

Camassa et al. (2019) proposed some improvements to ultrasonic tomography for masonry constructions, based on the implementation of advanced inversion algorithms, the use of information about wave attenuation (attenuation tomography), and acoustic wave time-of-flight measurements, and enhancements to the experimental setup concerning the coupling between probes and masonry [40].

The topographic measuring apparatus comprised a central unit, sensors deployed around the trunk, and specialized software (Figure 3). Before deploying the sensors, the trunk was tapped with a rubber mallet to pick up deafening noises, suggesting potential changes inside the trunk's internal structure. Only then was the correct measurement level established, and pins were placed around the trunk, at equal distances. Then, the pins were shallowly driven into the bark, on which the sensors receiving the acoustic waves were then attached.

**Figure 3.** Acoustic tomograph CT scanner on a tree trunk (photo by M. Dudkiewicz).

The number of sensors installed depended on the circumference and shape of the trunk mapped using a specialized PiCUS caliper (Figure 4).

**Figure 4.** Measuring the geometry of the tree trunk using the PiCUS caliper (photo by M. Dudkiewicz).

The first measurement point was always located on the north side to facilitate the interpretation of the results.

Acoustic tomography is based on measuring sound waves passing through the tree trunk between installed sensors. The sound waves are excited by tapping the individual sensors with an electronic hammer. The measurement process results in a color tomogram illustrating the sound velocity distribution over a trunk cross-section. The default color code for interpreting the results obtained using the included software is as follows: brown and black areas indicate high sound wave velocities corresponding to healthy wood; green corresponds to medium velocities, indicating a transition area between solid and nonsolid wood, but in some cases, it can also suggest problems inside the trunk; and purple, blue, and white areas indicate low sound velocities, characteristic of damage or voids inside the trunk. The processed sound velocity map (tomogram) can be used as a basis for making a scientific and knowledge-based decision on the viability of a tree without felling it. Yellow lines on the cross-section of the trunk suggest the occurrence of internal cracks, which often do not give apparent external symptoms. The thicker the line, the greater the risk of such an occurrence. In contrast, a red line on the tomogram indicates the limiting wall thickness, which allows the determination of the minimum mechanical strength of the tree trunk [41].

#### **3. Results**
