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Ancient and Famous Trees Risk Assessment in Changting Based with Multi-Level and Multi-Dimensional Indicator System

According to the results of the second census of ancient and famous trees and field investigation in Changting County, Through VTA method and AHP method, the multi-level and multi-dimensional evaluation index system of risk degree of ancient and famous trees was constructed. The results show that: The higher weight of growth factors are the main trunk diseases and insect pests, abnormal cracks in the main trunk, hollow trunk, branch diseases and insect pests, abnormal cracks in the branches, dangerous dead branches, root diseases and insect pests, leaf diseases and insect pests. The growth space of tree roots is the most important factor in environmental factors. Among the anthropogenic factors, the most important ones are the artificial dumping of pollutants and the lack of professional management. Hazard index of Taxus chinensis var. mairei is maximum, followed by Schima superba, Cinnamomum camphora and Liquidambar formosana. The most dangerous indicators are the professional level of managers, lack of professional management, V-angle trunk and plant parasitism. Through the risk assessment, this paper seeks for the key points of management and protection of ancient and famous trees, aims at solving problems and reducing the risk of ancient and famous trees, so as to promote the management and protection of ancient and famous trees.


Introduction
Ancient trees are the precious heritage delivered to us by nature, more is to bear the historical and cultural values. With the proposal of "Beautiful China", the construction of ecological civilization has been put in a prominent position, and the protection of ancient trees in urban and rural areas is becoming increasingly important. At present, the research on the degree of risk mainly includes Zhu Zhipeng [1] conducted research on risk degree assessment of ancient trees in Minhou county, Fu Weicong [2] and Cai Yuanyuan [3] respectively conducted risk degree assessment of the common green trees and common street trees in Fujian coastal villages, Zheng Ran [4]  2 the risk assessment of ancient trees, Liu Yu [5] and Xie Yuanyuan [6] conducted research on ancient trees health assessment. Most existing domestic research focus on the landscape evaluation of ancient trees [7][8][9], species diversity [10], protection countermeasure [11] and so on. Abroad, there are related researches on detecting the risk degree of trees through ultrasonic technology detection [12], biomechanical detection [13], comprehensive analysis method [14][15], etc. On the whole, the research on the danger degree, risk degree and the healthy degree of trees is still lacking. Thus, research on ancient trees risk in Changting county has great guiding significance to the research and protection for ancient trees in the province and even the whole country.
As a renowned historical and cultural city in China, Changting is also a key prevention and control area for soil erosion in southern China [16]. Protecting ancient trees is an essential part of the inheritance and promotion of Changting's history and culture, and it also has a guiding role in the management of soil erosion. However, global climate change has led to a significant increase in extreme weather disasters in recent years, with natural disasters such as heavy rains and seasonal frosts caused by typhoons, increasing the risk of some ancient trees. In addition, due to the acceleration of urban greening process. Inappropriate human management has also accelerated the process of aging and death of ancient trees. This study conducted a field statistical survey in Changting county, and through the establishment of a multi-level and multi-dimensional risk evaluation indicator system for ancient trees, the risk assessment of ancient trees in the area was conducted to find out the deficiencies of ancient trees management, and provide a scientific basis for the management and protection in Changting county.

Overview of the research area
Changting county is affiliated to Longyan City, and is situated on the west of Fujian Province, a total of 18 towns (townships) in the county, belonging to the mid-subtropical monsoon climate zone. The annual average temperature is 18.3℃; the average temperature in January is 7.5℃, the average temperature in July is 27.1℃; the extreme maximum temperature is 38.9℃, the extreme minimum temperature is -6.5℃; accumulative temperature≥10℃ is 6159.4℃, and the frost-free period is 262 days. The average annual precipitation is between 1173.9-2548.3mm, and the multi-year average precipitation is 1698.7mm. Changting county's soil types include red soil, yellow soil, purple soil, lime (rock) soil, meadow soil, tide soil, paddy soil, a total of 7 soil types, 16 subtypes, and 38 soil genera. Soil parent rock mainly includes sandy rock, mudstone, acid rock, etc., and its weathering material turns into red soil and yellow soil.

Plot survey
The survey based on the data of the second census from Changting Forestry Administration, the ancient trees were investigated one by one according to the existing basic data, and the data were further checked and updated. We took photos of ancient trees on site, and recorded the growth status of ancient trees with images and remarks.

Calculation method
This article uses visual tree assessment (VTA) [3] and analytic hierarchy process (AHP) to construct a multi-level and multi-dimensional system of ancient trees' risk assessment in Changting. By reviewing literature and consulting experts, constructed 3 first-level indexes for ancient trees, including growth factors, environmental factors, and human factors, 8 second-level indexes and 30 third-level indexes, invite experts to rate the importance of index, the weight of each index is shown in Table 1 [17]. Through a comprehensive investigation of ancient trees in various towns and townships in Changting, then determine whether the risk degree is serious according to the on-site situation [1][2][3] and get a score, and the risk degree score of the third-level index is multiplied by the weight to obtain the risk degree score of second-level index, the situation of managers and climate environment are provided by Since the scale in the judging matrix is determined by reference materials, expert advice and the local managers' experience after repeated study, it has a small randomness and consistency ratio indicate that the matrix maintains the consistency of judgment thinking, and the deviation caused by man-made is small.

Analysis of the composition of ancient trees in Changting
The results showed that the ancient trees in Changting included a total of 20 families, 26 genera and 32 species, with a total of 547 plants, of which 226 were scattered, a total of 321 plants in 5 ancient tree communities. According to the classification of ancient trees [18]: there are 37 ancient trees at the national first-class (tree age over 500 years), 27 ancient trees at the national second-class (300 to 499 years old), and 481 ancient trees at the national third-class (100 to 299 years old), 2 trees less than 100 years old. There are 47 ancient trees in the town and 500 ancient trees in the countryside. According to the results in Changting, the top 3 kinds of frequency ancient trees are Castanopsis nigrescens, Cinnamomum camphora, Taxus chinensis var. mairei, according to the second census conducted by local Forestry Administration and combined with on-site research, the frequency of ancient trees in Changting is shown in

Risk assessment of growth factors
Multiply the weight obtained in Table 1 by the points of the ancient trees, calculate the top 10 kinds of frequency trees (Table 3), the growth factor (0.432) is the index with the greatest impact on the risk of the ancient trees. The specific content includes the growth state of trunk, branch, root and leaf. Compared with environmental factors (A2) and human factors (A3), growth factors measure the health of ancient trees and affect their environmental affordability.

Trunk potential risk analysis.
Under the second-level index system, the weight of trunk risk (B1) is 0.306, which the experts believe that has the greatest impact on the risk of ancient trees, in addition to growth factors for ancient trees. Among the top 10 kinds of frequency trees, the prevalence indexes of trees are plant parasitism (C6), followed by v-angle trunks (C2) and unnaturally inclining trunk (C1). Taxus chinensis var. mairei, Schima superba, Celtis sinensis, Liquidambar formosana, Cinnamomum camphora, Castanopsis nigrescens, Castanopsis carlesii, Pinus massoniana, and Osmanthus sp all have trunk plant parasitism. The risk degree of Taxus chinensis var. mairei is 1.00 and the risk degree of Schima superba is 0.93. Taxus chinensis var. mairei, Schima superba and Celtis sinensis with more serious plant parasitism are located in the mountains and woods, with more plant species and higher density, thus providing better climbing conditions for various parasitic plants. The roots of parasitic plants will pierce into the ancient trees, and absorb nutrients from them, which will cause greater harm to the ancient trees.
The v-angle trunks are widespread in tree species such as Schima superba, Osmanthus sp, Platycladus orientalis, Celtis sinensis, Taxus chinensis var. mairei, Liquidambar formosana, Cinnamomum camphora. The highest risk degree of Schima superba is 0.79. Overall, the v-angle trunk is more common in evergreen broad-leaved trees, but the degree of the v-angle trunk is relatively slight.
The unnatural inclining trunk is more obvious on 3 tree species: Osmanthus sp, Celtis sinensis, and Liquidambar formosana. Osmanthus sp are mainly distributed in Changting, partly in towns. Most of the 3 species with unnaturally inclining trunks are adjacent to the building. Therefore, the first reason for the tilt may be that the growth space is restricted by the building, and the second may be that Osmanthus sp is a shade-intolerant tree species, so the uneven lighting caused by the building's blocking leads to the unnatural trunk tilt. The overall situation of trunk tilt is relatively slight, and some ancient trees with serious tilt should be given some support.
Abnormal trunk cracks of Taxus chinensis var. mairei, Schima superba are more obvious. The dangerous symptoms are mainly physical injuries to humans and animals, or wounds caused by extreme weather such as heavy rains and winds. The bacteria are easy to enter the trunk after years, resulting in a widening gap and increased decay symptoms. The risk of hollow trunk (C3) and trunk diseases and insect pests (C4) is low, such as the hollow trunk risk of Schima superba is 0.36. According to the on-site investigation, it can be known that one or two ancient trees exist the hollow trunk situation, should be repaired on the post-maintenance.

Analysis of potential risk of branch.
The potential risks of the branch are mainly concentrated in three items: plant parasitism (C13), water sprout (C12) and dangerous deadwood (C9). Plant parasitism of the branch is related to the plant parasitism of the trunk. Most of the climbing plants that are attached to the trunk will grow from the trunk to the branches. Therefore, parasitic plants on the trunk should be removed in time. In ancient trees, water sprout mainly occurs in weak backbone branches or below the irritated areas. Taxus chinensis var. mairei, Osmanthus sp, and Schima superba are more likely to have water sprout. Among them, high risk of abnormal trunk cracks of Taxus chinensis var. mairei and Schima superba also showed, physical injury of trunk may cause damage and irritation to the trunk bark, which promotes the appearance of water sprout. The water sprout should be pruned in time to balance the tree skeleton and prevent nutrient waste. For tree species with dangerous deadwood: Taxus chinensis var. mairei, Schima superba, Celtis sinensis and Castanopsis nigrescens, the dangerous deadwood should be pruned in time, avoid affecting the growth of other trunks or endangering to pedestrians.

Analysis of potential risk of root.
The survey and evaluation results show that the root risk of ancient trees in Changting is relatively low. No root diseases and insect pests were found in the trees, and root damage only appeared in a few bare roots. The most obvious manifestation of tree root nudity is Liquidambar formosana, with a risk of 0.38, followed by Pinus massoniana at 0.24, and Taxus chinensis var. mairei at 0.23. There is a correlation between root nudity and whether the roots have 8 enough room to grow, and the risk of the 3 tree species whether the roots have enough room to grow are 0.31, 0.29 and 0.62. The bare roots also increase the risk of root damage and affect the stability of the root system. Therefore, corresponding to Liquidambar formosana with the highest risk of exposed roots, the risk of instable root system is also the highest at 0.23.

Analysis of the potential risk of leaves.
The potential risk of leaves is measured by the degree of leaf denseness (C18) and leaf diseases and insect pests (C19). Tree species with denser canopies are more susceptible to extreme weather such as typhoons and rainstorms, resulting in abnormal fallen leaves and broken branches. Trees with a higher risk on this index are Taxus chinensis var. mairei, Pinus massoniana and Castanopsis nigrescens. These species should be pruned appropriately and timely to improve the resistance to extreme weather. While the situation of leaf diseases and insect pests only slightly exists on Schima superba and Liquidambar formosana, the management staff shall diagnosis and treat diseases and insect pests timely to avoid the expansion of the damaged area.

Analysis of potential risk of surroundings and climate
The environmental risk weight of ancient trees is 0.347, second only to the growth factor, of which the surroundings is 0.578 and the climate is 0.422. The poor growth of many ancient trees is influenced by the surrounding environment. The surroundings (B5) include the ground hardening degree (C20), growth space for root (C21), and growth space for branches (C22). 3 tree species with a higher risk of ground hardening are Osmanthus sp (0.57), Cinnamomum camphora (0.40) and Liquidambar formosana (0.38). Overall, the ground hardening degree is low, but there are still some hardened ground areas around ancient trees, for this kind of trees, we should observe their growth status, to prevent the danger in time. The 4 tree species with higher risk of root growth space are Taxus chinensis var. mairei (0.62), Cinnamomum camphora (0.60), Osmanthus sp (0.57), Platycladus orientalis (0.57), the main reasons are two, one is hardened road surface, the tree pool space is too small; the second is that the trees grow too dense. The tree species with high growth space risk are Schima superba (0.64), Castanopsis carlesii (0.50), Taxus chinensis var. mairei (0.46), Cinnamomum camphora (0.45), engineering facilities such as wires and some buildings that are too close also affect the growth space for branch. Climate (B6) includes 4 indexes: typhoon (C23), frost (C24), heavy rain (C25), drought (C26). Changting county is situated on the west of Fujian Province, near the interior, is less affected by the typhoon, Schima superba has the highest risk of 0.36. The highest risk of frost is Castanopsis nigrescens. The impact of frost is mainly showed in higher altitude areas, and winter is not only frost, but also often accompanied by snow. In addition, Changting is in the subtropical monsoon climate zone, the bigger amount of rainfall may cause flooding every summer, which may harm the growth of ancient trees. The drought risk is 0, indicating that the potential risk of drought is very low.

Analysis of the potential risk of man-made destruction and artificial management
Many ancient trees were destroyed due to man-made destruction, such as the fire caused by worship, which caused the ancient trees to be burned. Artificial management is also a major problem in the management of ancient trees, ancient trees are scattered, which makes it hard to find risk factors in time. The weight of human factors is 0.221, of which the weight of man-made destruction is 0.431, and the weight of artificial management is 0.569. Man-made destruction (B7) includes engineering facilities (C27) and artificial dumping pollutants (C28), the 3 tree species with higher risk in the engineering facilities are Cinnamomum camphora (0.45), Castanopsis carlesii (0.17), and Taxus chinensis var. mairei (0.08). Cinnamomum camphora is generally used as street tree in Changting, often have many wires passing by the tree, so the risk is higher. The phenomenon of artificial dumping pollutants is rare, only next to Cinnamomum camphora (0.1) and Liquidambar formosana (0.08), indicating that the residents have higher awareness of environmental and ancient trees protection, but there are some individual damage phenomenon requires the government to take relevant measures. Artificial management (B8) includes lack professional management (C29) and managerial

Conclusion and discussion
The ancient trees in Changting include 20 families, 26 genera and 32 species, with a total number of 547 trees. The top 10 kinds of frequency trees accounted for 89.9% of the total number of trees, represent most of the ancient trees in Changting, so it has a certain representative significance to monitor and survey the top10 kinds of frequency trees. According to the final risk assessment results of green tree species in village, the risk ranking of the selected tree species from high to low is: Taxus chinensis var. mairei, Schima superba, Cinnamomum camphora, Liquidambar formosana, Osmanthus sp, Castanopsis carlesii, Pinus massoniana, Celtis sinensis, Platycladus orientalis and Castanopsis nigrescens. The risks of top 3 tree species are mainly concentrated in 3 indexes: the trunk in growth factors, surroundings in environmental factors, and man-made destruction in human factors. This plays a great guiding role in the protection and management of ancient trees in Changting. The risk of Castanopsis nigrescens is lowest, only at 0.09. Ancient trees of Castanopsis nigrescens mainly exists in the Zhonghuang Nature Reserve, less affected by humans, has a stable ecological environment and more professional managers. Maximum age of Platycladus orientalis is about 1,200 years old, has highly historical and cultural value. Ancient trees are mainly distributed in the county town, which are better managed. Some ancient trees are in the villages far away from the county seat, especially in some backward villages, the phenomenon of dumping garbage by the ancient trees occasionally occurs, and there are common problems such as management difficulties and insufficient professionalism of managers. Through this investigation found that the protection unit (individual) on the disposal of ancient trees are more arbitrary. The reasons for decrease are that ancient trees are personal property, the original 2 Osmanthus sp at No. 45, Chehou lane, Tingzhou town, were excavated by their owners during the reconstruction of the old house. Locals worship the ancient trees as gods to serve, incense and candle burning, causing some ancient trees on the brink of death. The locals build arbitrarily on ancient trees can also cause damage, such as trunks' abnormal cracks (0.92) and branches' growth space (0.62) of Taxus chinensis in the Guilongshan Nature Reserve, protective measures should be taken. The local forestry administration has supported the ancient trees with serious trunk v-angle by brackets, but some ancient trees have no nameplate or the nameplates have been damaged, which needs to be resolved.
Managers should pay attention to protecting the health of ancient trees and reducing the risk in the process of management and protection. (1) Some of Taxus chinensis var. mairei, Schima superba and Cinnamomum camphora are relatively remote, for a long time, due to the lack of corresponding management and protection measures for ancient trees in remote areas, and the weak protection awareness of locals, there are situations such as soil borrowing, accumulation of straw and waste, and dumping of waste water. In response to this situation, should arrange worker to clean up the debris under the tree, and guard the ancient trees to provide good growth space. (2) For the trunks and branches, which are vulnerable to get plant parasitism and physical damage, should be under timely protection to minimize the risk. (3) The assessment results show that man-made factors have led to the increase of risk degree of ancient trees. In this regard, we should popularize the knowledge of ancient trees and to improve people's awareness of protection. (4) A responsibility tracing system should be implemented, provides certain punishments for malicious destruction of ancient and famous trees. ( Lightning rods should be erected on tall ancient trees to prevent lightning strikes, and communicate with the electric power department in time to avoid erecting high-voltage wires set up in the crowns of ancient trees. (6) Hollow trunks should be scraped and disinfected as soon as possible, and then filled with bricks, cement or other materials, and the inclining branches should be fixed by supporting brackets or by pulling wires [19]. (7) For the phenomenon of high degree of the ground hardening around ancient trees, managers should set up fences around ancient trees to isolate visitors, avoid trampling, and minimize cement pavement around ancient trees.
Compared with previous scholars' research on ancient trees [1][2][3][4][5][6], the innovation of this research lies in the establishment of a multi-level and multi-dimensional risk indicator system for ancient trees, combined with the VTA method and the AHP method, and taking Changting county as an example to explore. Compared with the south and east of Fujian, Changting is less affected by typhoons, and Changting is a famous city of national history and culture, so the research has certain typical characteristics. Later, we will be prepared to study the differences in the risk of ancient trees in various regions of Fujian, and combine the differences in climate and temperature in various regions, to provide better management strategies for the ancient trees in Fujian.