*3.4. Results of Detailed Dendrological Inventory*

We inventoried 15 trees in the church garden, among which two species dominated: *Acer pseudoplatanus* and *Tilia cordata* (Table 1). Additionally, there are two trees with significant trunk circumferences, registered in 1992 as natural monuments: a small-leaved linden (672 cm in circumference) and sycamore maple (370 cm in circumference).

**Table 1.** Species and quantity lists of trees around the church in Horostyta, 2020 (authors).


The Result of the Tomograph Examination

The fall of an entire tree or branch can cause significant damage to public infrastructure, personal property, and even human life [47]. Sometimes strong winds can also significantly affect the stability of a tree [48]. Aerodynamic drag on all surfaces of aboveground parts of trees—from individual leaves to entire tree crowns—significantly disrupts the airflow inside them [49,50]. The wind load affects the tree crown and generates significant bending moments on the trunk and its root. These are the primary sources of trunk damage and causes of uprooting. At the same time, it is worth noting that when branches move in the wind, they dissipate their energy, reducing the load transferred to the trunk and increasing the tree's mechanical stability. These features can be considered to be self-optimizing tree structures from evolutionary processes [51].

Safety in historic gardens with large trees is critical, and their preservation requires precise diagnostic techniques to detect structural damage to tree trunks caused, for example, by biological or physical factors. Visual tree assessment (VTA) is still the starting point for such studies. However, internal defects in tree trunks often remain out of sight of the arborist or botanist [52,53]. For many years, the Pressler auger was the only tool available for detailed assessment of the internal wood structure of a growing tree. However, this method requires mechanical intervention in the internal tissues of the tree. Its application in the

case of valuable historic trees is controversial. At the beginning of the 21st century, surveys of the health of urban stands were conducted using various survey methods (electrical tomography, acoustic, etc.) with varying degrees of success. Of the methods used, acoustic tomography proved to be the most effective tool for detecting the distribution of internal tissues, being the most accurate in locating anomalies and estimating their dimensions and shapes and being the least invasive [54,55]. Compared to other methods, examination by acoustic waves is efficient even in the early stages of wood decay [56,57]. Gilbert and Smiley (2004) estimated that the average accuracy of the device was 89% [29]. Rapidly preventing the degradation of a protected specimen and properly conducting arboricultural work to keep the tree in good condition contribute to preserving the rich biodiversity of parks and gardens.

Additionally, it should be clarified that tree decay is a normal process, not an illness, and belongs to a tree's life, and that there should be decaying parts in old trees. Decaying wood is an essential part of an old tree and it supports other species and biodiversity. Decay is not always a risk, and a professional must conclude by looking carefully at the structure based on VTA and studying the decay using non-invasive methods or microdrill resistance whether structural weaknesses exist and what to do about them.

Many factors can cause decay in trees. Here are some of them: *humidity*—humid conditions support the activity of fungi and bacteria that promote tooth decay. Trees located in places with high humidity, e.g., by a riverbank or pond, are more susceptible to decay; *mechanical damage*—mechanical wounds on tree trunks or branches are places where microorganisms can penetrate; *lack of ventilation and light*—trees that grow in too much density do not have enough light.

Disturbing features and grounds for thoroughly examining a given specimen include peeling bark, holes, cavities in the trunk or branches, dead branches, and mushroom fruiting bodies (Figure 10).

**Figure 10.** Senile tree. Designations: 1. dry branches under the tree; 2. suckers around the tree's crown; 3. early leaf fall; 4. bumps and mushrooms on the trunk; 5. hollow; 6. asymmetric crown; 7. broken top; 8. mistletoe.

The first thing an arborist may do is use a mallet to strike a tree's trunk and listen to the quality of the sound it makes. The sound of solid or decayed wood that has lost its structural strength sounds different. Next, an arborist may probe cavities with a metal rod to test how easily the cavity's interior gives way when pushed. Sound wood is hard and unyielding when poked, while decaying wood crumbles or allows a tool to pierce it.

We classified 12 of the 15 trees growing around the church as healthy due to the lack of visible damage. The remaining three specimens showed weakness (downy, small leaves, and falling bark). We examined the trees using acoustic tomography (Table 2). Signs of

progressive decay were found inside their trunks, qualifying them for detailed observation for the time being but not immediate felling. This decision would depend on the wood's decay rate and the safety of the environment.

**Table 2.** Results of dendrological expertise (by authors).


Object 1—small-leaved linden (*Tilia cordata* Mill.)

The assessed tree grew on a slight elevation at a distance of 1.5 m from the fence separating the church from the cemetery. The distance from the walls of the church building was 14 m, and it was 1 m from the neighboring tree (Figure 11). In the tree's crown, the growth of small downy branches was estimated at 20%, with hanging branches and wilting leaves. Traces of the maintenance work carried out were visible, and the areas of cuts were well healed. Based on the tomographic results obtained, small foci characterized by weakened internal wood structures were estimated at 8%, located on the northern side of the trunk section. They did not significantly affect the mechanical strength of the trunk. Technically sound wood occupied 85% of the trunk cross-section, and the remaining part (7%) was so-called transitional wood with a slightly weakened structure but was not yet damaged. The recorded speed of sound inside the trunk ranged from 817 to 1150 m s−1, which suggested the tree was in good condition, especially since, according to the available literature, the average speed of sound waves in healthy linden wood is in the range between 940 and 1183 m s−<sup>1</sup> [58].

The red line illustrated the minimum wall thickness of 12.8 to 13.6 cm (average 13.2 cm), depending on the site, which indicated that the safety limit against trunk fracture was preserved on most of the cross-section. Destructive processes only went beyond this limit on the north side of the trunk.

Calculated for different directions, the trunk section's geometric moment of inertia, measured at the weakest point at the measurement height, ranged from 3.2% to 7.8% of the maximum strength relative to a trunk without defects or damage. The calculations themselves only took into account the trunk's geometry at the measurement level, while the properties of the wood itself may affect the final result of the measurement. Based on the results obtained, one could assume that the tree's mechanical strength and resistance to trunk bending were safe for the environment (Figure 12).

The minimum thickness of a healthy wall relevant to the preservation of tree statics, calculated by the Tree SA method, should be 6.6 cm on average (green line on the attached tomogram). Based on the measurement carried out at the height of 120 cm above ground level, we found that significant weakening of the wood structure occurred only at the height of the 1st and 2nd measurement points in the northern part of the trunk section, and the safety limit was still preserved.

As calculated by the Tree SA method, the wood in the solid trunk required a minimum residual strength of 38%. However, based on the tomographic survey, the percentage of entirely sound wood was 85%. This finding testified to the good statics of the tree (Figure 12).

According to the Roloff scale, the evaluated linden was in the exploration stage (grade 0) [59].

The tree grew very close to another tree, which may have resulted in insufficient sunlight. On the trunk and branches, there were traces of maintenance cuts that may have allowed the penetration of fungi that weakened the tree. The wilting leaves were also evidence of a slight weakening of the plant's vitality.

The project suggested leaving the tree and its surroundings unchanged, i.e., as lawn turf. Planting a floor of shrubs around the trunk or locating small architectural objects under the tree canopy were not planned. The project recommended removing dead branches, and that all work and care procedures should be performed following the rules of arboriculture by a team qualified to care for veteran trees. The condition of the tree should be monitored every 2 years.

**Figure 11.** General view of small-leaved linden (by M. Dudkiewicz, 2020).

Object 2—sycamore maple (*Acer pseudoplatanus* L.)

The tree grew 0.3 m from the fence wall in the eastern part of the property (Figure 13). The trunk had several cavities, mainly hollows of various sizes. The initially straight trunk from a height of 2.5 m sloped northward at an angle of 30◦ and revealed several breakages in the crown, resulting in hollows and branch ashes at a level of 15–20%. The topographic examination showed progressive destruction of the trunk's interior in the core, moving to the outer layers on the northeast side at the height of measuring points 7–8. At this point, the minimum wall thickness required to maintain the proper mechanical strength of the trunk, which should have an average thickness of 10.6 cm, was also not maintained. The recorded speed of sound traveling in the wood of the tested maple ranged from 818 m s−<sup>1</sup> between measurement points 7 and 2 to 1616 m s−<sup>1</sup> between sensors 4 and 3. Referring to the average speed of sound waves propagating in healthy maple wood, which is on average from 1006 to 1426 m s−<sup>1</sup> [58], one could conclude that the lower recorded value was slightly lower than the norm while the other was well above the accepted level.

Trunk circumference at the height of 1.3 m: 293cm Height: 17 m Crown range: 11.5 m Approximate age: 121years, 121years, 202years, 97years

Instructions: 1. Tree to keep. 2. Dry branches should be removed following the rules of arboriculture by a team qualified to care for veteran trees. 3. Health monitoring every 2 years.

**Figure 12.** Tomogram of the interior of small-leaved linden trunk inv. no. 4 (by W. Durlak) [21–24].

Damaged wood on the cross-section of the trunk occupied 30% of the area, and healthy wood occupied 62%. The remaining area was transitional wood (Figure 14). It was most likely that the destructive processes that had begun would worsen in the future. Therefore, monitoring the tree was recommended for the time being in order to prevent possible felling.

The minimum wall thickness indicated by the red line on the tomogram, considered the safety limit before stem fracture, was between 9 and 12.1 cm (average 10.6 cm), depending on the site. It was preserved in most of the cross-section. Destructive processes only went beyond this limit on the northeast side of the trunk (Figure 14).

Calculated for different directions, the geometric moment of inertia for this section of the trunk, measured at the weakest points at the height of the measurement, ranged from 51.3% to 56.7% of the maximum strength compared to a trunk without defects or damage. Based on the results, one could assume that the tree's mechanical strength and resistance to trunk bending were safe for the environment.

The minimum thickness of a healthy wall relevant to the preservation of tree statics, calculated by the Tree SA method, should be 7.15 cm on average (green line on the attached tomogram). Based on the measurement carried out at 80 cm above ground level, significant weakening of the wood structure occurred only in a small area around the 8th measurement point in the northeastern part of the trunk section. In the remaining area, the safety limit was preserved in excess.

As calculated by the Tree SA method, the required minimum residual strength of the solid wood of the trunk of this tree was 48%. On the other hand, based on the tomographic survey, the percentage of utterly sound wood was 62%, which confirmed the good statics of the tree.

According to the Roloff scale, the evaluated linden was in the exploration stage—light degeneration (grade 0–1) [59].

The tree grew close to another tree and right next to a brick fence, which may have resulted in insufficient sunlight. There were hollows in the trunk, broken branches, and deadwood in the crown. The tree's strength was probably weakened by the low amount of light and humid conditions in which the tree grew (by the old brick fence), which resulted in the decay of the trunk.

The project suggested planting low turf vegetation around the tree. Locating small architectural objects under the tree crown was not planned. The project suggested removing the dead branches, and that all work and care procedures should be performed following the rules of arboriculture by a team qualified to care for veteran trees. The condition of the tree should be monitored every 2 years.

**Figure 13.** General view of sycamore maple (by M. Dudkiewicz, 2020).

Object 3—small-leafed linden (*Tilia cordata* Mill.)

A small-leaved linden grew near the main gate on the northern side of the church (Figure 15). It was characterized by its considerable size and quite downy solid growth in the upper parts of the crown. The crown showed traces of broken branches, and the surgical cuts were partially healed. Numerous heavily leafy outgrowths appeared on the trunk. The crown was asymmetrical, facing north. At the base of the trunk, large root intakes had developed. Traces of insect activity were also visible. The upper part of the tree trunk had numerous hollows. The root system was strongly developed, pushing slightly against the fence's foundation. The CT scan made it possible to determine the health of the trunk's interior (Figure 16). Linden trees are characterized by wood susceptible to biocorrosion; hence, the destruction visible on the tomogram in the core part of the trunk was a common phenomenon. We calculated the limiting wall thickness considered safe for this trunk's mechanical strength to be 16.9 cm on average.

Trunk circumference at the height of 1.3 m: 232 cm Height: 17 m Crown range: 18 m Approximate age: 132years, 132years, 133years, 62 years

Instructions:

1. Tree to keep.

2. Dead branches to be removed. All work and care procedures should follow the rules of arboriculture by a team qualified to care for veteran trees. 3. Health monitoring every 2 years

**Figure 14.** Tomogram of the interior of sycamore maple inv. no. 11 (by W. Durlak) [21–24].

The recorded speed of the sound wave in the wood of the evaluated linden ranged from 320 m s−<sup>1</sup> between measurement points 8 and 2 to 1245 m s−<sup>1</sup> between sensors 4 and 12. The recorded value was much lower than the average, influenced by the movement of sound through the damaged areas slowing down its speed. The upper value, on the other hand, was within the norm and even slightly exceeded it.

Damaged wood occupied an area equal to 26% of the cross-sectional area of the trunk, while healthy wood occupied 56%. The remaining 18% was transitional wood (Figure 16). Most likely, the destructive processes that had begun would worsen in the future, but it was unknown at what rate. Therefore, it was worth monitoring the tree and holding off on possible felling.

The minimum wall thickness marked on the tomogram with a red line, considered the safety limit against trunk fracture, was 16 to 17.8 cm (average 16.9 cm), depending on the location. This limit was preserved practically throughout the cross-section, indicating that the trunk's mechanical strength was still good.

The attached tomogram also shows two yellow lines indicating the possibility of internal cracks, the most likely one oriented to the northeast between measurement points 11 and 12.

Calculated for different directions, the geometric moment of inertia for this section of the trunk, measured at the weakest points at the height of the measurement, was 10.8% to 48.9% of the maximum strength compared to a trunk without defects or damage. Based on the results obtained, one could assume that the tree's mechanical strength and resistance to trunk bending were safe for the environment.

The minimum thickness of a healthy wall relevant to the preservation of tree statics, calculated by the Tree SA method, should average 5.8 cm (green line on the attached tomogram). Based on the measurement carried out at 130 cm above ground level, there was no significant weakening of the wood structure at this trunk section. The required safety limit was maintained in excess.

**Figure 15.** General view of small-leaved linden growing at the entrance of the property (by M. Dudkiewicz, 2020).

Trunk circumference at the height of 1.3 m: 367 cm Height: 17.8 m Crown range: 10 m Approximate age: 152years, 152years, 252years, 123years

Instructions:

1. Tree to keep.

2. Dead branches to be removed. All work and care procedures should follow the rules of arboriculture by a team qualified to care for veteran trees.

3. Modifying the foundation of the fence to allow root growth.

4. Health monitoring every year.

**Figure 16.** Tomogram of the interior of small-leaved linden inv. No. 15 (by W. Durlak) [21–24].

As calculated by the Tree SA method, the required minimum residual strength of the solid wood of the trunk of this tree was 23%. On the other hand, based on the tomographic survey, the percentage of entirely fine wood was 56%, which indicated good tree statics (Figure 16).

According to the Roloff scale, the evaluated linden was in a borderline stage between degeneration and stagnation (grade 1–2) [59].

The visual condition of the tree was disturbing. Traces of insect activity were visible on the trunk, and the crown was asymmetrical. There was a large dead branch, and the tree put out many root suckers. Modifying the fence's foundation was planned to allow root growth. The tree probably used to grow in a row of trees, and now it was a single object exposed to the wind. It was planned to plant two small trees on both sides of the linden. The project recommended removing the dead branches, and that all work and care procedures should be performed following the rules of arboriculture by a team qualified to care for veteran trees. The condition of the tree should be monitored every year.

The temple walls were shrub beds composed of, among other plants, *Juniperus chinensis* 'Stricta', *Thuja* 'Smaragd', *Spirea japonica*, and *Physocarpus opulifolius*. The selection of species primarily included species of foreign origin and characteristics mainly of home gardens rather than religious establishments. There was no reference to the plant symbolism crucial to the Christian faith.

#### **4. The Problem of Protection of Senile Trees**

Old trees are witnesses to history [60,61]. They are not only picturesque elements of the cultural landscape (often painted, photographed, and described) but also a vital part of the natural world. They are the habitat of rich biological and microbial life. According to British data, more than 2000 species of invertebrates (6% of British invertebrate fauna) depend on the habitat of senile trees; therefore, removing such tree canopies seriously affects the biodiversity of cities and villages [62]. Dendroflora is also an essential biodiversity refuge with sometimes rich associated flora. Many species of lichens live on tree trunks, including rare and protected species. Branches are convenient places for bird nesting, and many species of birds (including legally protected birds) live in treetops, such as nightingales, nightjars, blackbirds, grackles, and kestrels.

Dangerous trees pose a significant risk to landowners and those who care for them. It is worth mentioning in this context that the ISA (International Society of Arboriculture) has created a so-called qualification to define the risk assessment of trees (Tree Risk Assessment Qualification—TRAQ). This qualification promotes people's and property's safety by providing a standardized and systematic process for assessing tree risks. The results can provide tree owners and risk managers with information to help them make informed decisions to increase the benefits, health, and longevity of trees [63].

Tree dieback begins with crown thinning, yellowing, and other symptoms on the leaves, a morbid appearance, and the top drying out. Tree branches begin to die from top to bottom. External features include spiral rings in the tree trunk, thin or balding bark, loss of apical dominance, crown dieback, and crowns with few large branches [64]. Pederson described six typical external features of old angiosperm trees. These features include: (1) smooth-textured bark; (2) a reduction in the tree's growth strength; (3) high waviness of shoots; (4) crowns composed of few, thick, and twisted branches; (5) low crown volume; and (6) a low ratio of leaf area to trunk volume [60].

Here, it is worth noting that tree death is a normal process, not a disease, and is part of the tree's life cycle. Decay is one of the crucial processes in old trees and decaying wood supports other species and biodiversity. Decay itself is not always a risk, and the professional must draw conclusions based on proper observations (VTA) and decay testing using non-invasive methods in order to assess whether there is structural weakness and what to do about it.

#### *4.1. Threats Related to the Felling of Ancient Trees*

An old-growth tree is a valuable element of tall greenery in urban and rural areas, and, despite its advanced age or significant damage, it is an invaluable element of biodiversity. Any overly hasty decision to remove an aged tree is a considerable loss to the environment, both image-wise, nature-wise, and often historically. In Poland, trees around historic churches are protected as greenery growing on a property entered in the register of monuments. Under this assumption, removing, destroying, or damaging a tree is a crime under Article 108 of the Monuments Act [65]. Unfortunately, we often witness illegal felling or improper care of senior trees (Figures 17–20). Most often, it is topping, i.e., removing the top part of the tree to slow down the growth of the tree, lower the center of gravity, or reduce the size of the crown. "Topping" leads to the destruction of the crown and is a mistake. Due to inefficient tree care, municipalities or parishes have to pay multi-million fines. We must sensitize society and the authorities (secular and ecclesiastical) so that the surroundings of churches are cared for and respected in order to preserve our cultural heritage and their natural value. This research is an example of how carefully each case of a veteran tree should be considered.

**Figure 17.** Destruction of trees around the Church of St. Marcin Wincenty in Skórzewo near Pozna ´n (Greater Poland Voivodeship) (photo M. Dudkiewicz, 2022).

**Figure 18.** Destruction of trees around the Church of St. Marcin Wincenty in Skórzewo near Pozna ´n (Greater Poland Voivodeship) (photo M. Dudkiewicz, 2022).

**Figure 19.** Destruction of trees around the church in Zajezierze near D ˛eblin (Lubelskie Voivodeship) (photo M. Dudkiewicz, 2022).

**Figure 20.** Destruction of trees around the church in Zajezierze near D ˛eblin (Lubelskie Voivodeship) (photo M. Dudkiewicz, 2022).

People hastily remove trees because of the perception of trees as a problem, e.g., threats to the church building. This is primarily due to low social awareness of the importance of trees for biodiversity and ignorance about the principles of their proper care and protection [66]. The fundamental importance of solving the presented problem was to improve the administration and management system of trees in cities, following the example of similarly operating structures in European countries and in America (Table 3). In Germany, urban tree control is a safety assessment, the form of which is defined in the Baumkontrollrichtlinie (Tree Control Policy). The German Association of Landscape Experts (Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau) certifies tree care and assessment inspectors. The state registers street trees in a unified cadastral system, and trees over 40 years old are inspected twice a year for traffic hazards. Thanks to constant observation, we can assess how the tree copes with stress factors, whether it produces defense mechanisms, and how the observed defects and diseases progress. International institutions, such as the International Society of Arboriculture, also define standards.

**Table 3.** Ways of minimizing risk management related to ancient trees based on European and American programs.


#### *4.2. Research Limitations in Acoustic Tomography for Senile Trees*

It is also worth mentioning the research limitations, which included the sizes of the tree specimens under study. The distance between measuring points (electrodes) on the edges of the tree trunks under study was determined using the PiCUS electronic caliper. Unfortunately, the range of its arms was insufficient to examine trees with a considerable breast height. Therefore, determining the tree cross-section sometimes had to be performed by hand. After hitting the tree trunk with a hammer, an acoustic signal is generated in each electrode, the time is recorded, and the speed of passage of the acoustic waves between each sensor is calculated. In the case of a large internal cavity in a tree of considerable

size, some readings were not very precise and required several harder hammer blows. The measurement set consisted of 12 sensors and an electronic device, and a large tree specimen required rearranging the sensors and taking an additional measurement at another 12 points, which increased the time needed for the survey.

**Figure 21.** Senile tree in a historic garden—planted perennials can move traffic and benches are located beyond the projection of the tree crown (by M. Dudkiewicz).

**Figure 22.** Rubber band on the trunk with dendrometric data of the ancient tree and a request to be careful when parking under the tree crown, especially during a storm. Center for Contemporary Art Ujazdowski Castle in Warsaw (photo M. Dudkiewicz, 2022).

(**a**)

#### (**b**)

**Figure 23.** (**a**) Rubber band on the trunk with dendrometric data of the ancient tree. Center for Contemporary Art Ujazdowski Castle in Warsaw (photo M. Dudkiewicz, 2022). (**b**) Fencing off an ancient oak with a rope and placing signs warning about falling branches. Ujazdowski Park in Warsaw (photo M. Dudkiewicz, 2022).

**Figure 24.** A sign with the inscription: Area of an old stand. Danger of falling branches. Staying near old trees is associated with the risk of loss of life and health (photo M. Dudkiewicz, 2022).

Acoustic tomography also has other specific limitations. In some cases, the course of acoustic waves can be disturbed by the internal structure of the wood, such as reaction wood. Interpretation of the tomogram is also sometimes hampered by the presence of cracks or plugs, which tend to occupy a larger area on the tomogram than in reality. A particular case that makes it difficult to correctly read the information in the acoustic tomogram is the occurrence of so-called wet wood in some deciduous trees, mainly elm and poplar. The altered area in the central (core) part of the trunk is depicted on the tomogram in the same way as a cavity caused by rot, whereas the presence of wet wood in the trunk primarily makes the wood immune to rot fungi and has little effect on the stability of the tree. We can conclude that the device provides reliable information on wood density by determining the reason for the presence of low-density wood objects visible on the tomogram. The potential significance of these defects for tree stability and viability requires more profound dendrological knowledge [67].

**Figure 25.** Planned lack of foundations to protect an ancient linden tree (photo M. Dudkiewicz, 2018).

**Figure 26.** Planned cut-out in the wall to leave room for the development of ancient ash roots at St. Paul in Sandomierz (photo M. Dudkiewicz, 2020).

While advanced decay detection technologies are effective in quantifying internal decay, it is not clear how the additional information provided by these instruments impacts risk assessments concerning the likelihood of failure. Even the once commonly accepted arboricultural rule of thumb, t/R > 0.3–0.34 (where t is the radial thickness of sound wood, and R is the trunk radius; Mattheck and Breloer, 1994 [68], has not been spared from debate over its accuracy or widespread applicability [34,68].
