Influences of Post-fires on Subsequent Population of Japanese Pine Sawyer Beetles, Monochamus alternatus Hope (Coleoptera: Cerambycidae) in Masson Pine Forests

PAN Youliang, CHANG Xiangqi, LI Qiang, LI Hongzheng, CHEN Yuansheng, LIU Xingping

Influences of Post-fires on Subsequent Population of Japanese Pine Sawyer Beetles,Hope (Coleoptera: Cerambycidae) in Masson Pine Forests

PAN Youliang1, CHANG Xiangqi2, LI Qiang3, LI Hongzheng4, CHEN Yuansheng5, LIU Xingping1*

(1. Key Laboratory of National Forestry and Grassland Administration on Forest Ecosystem Protection and Restoration in Poyang Lake Watershed, School of Forestry, Jiangxi Agricultural University, Nanchang 330045, China; 2. Forestry Bureau of Xinjian District, Nanchang, 330100, China; 3. Forestry Bureau of Wuning Country, Jiujiang 332300, China; 4. Jiangxi Forestry Harmful Organism Control and Quarantine Bureau, Nanchang 330077, China; 5. Jiangxi Environmental Engineering Vocational College, Ganzhou, Jiangxi 341000, China)

Both fire and insect outbreaks are considered as important natural disturbance factors in many forest ecosystems, yet few studies have addressed the effects of fires on subsequent insect outbreaks.In this paper, tree mortality, larval density and vertical distribution were measured through field investigation and sampling method toevaluate the short-term response of Japanese pine sawyer beetle,Hope to Masson pine,Lamb. in the second year after the fire in Jiangxi Province, China.compared with unburned Masson pine forest, burned Masson pine forest suffered from higher tree mortality and morepine trees were attacked by. Burned Masson pine tended to harbor much higher larval density further up along the trunk than unburned pine trees, and most individuals distributed in the middle section and middle-lower section of the trunk.The results confirmed that Masson pine forest after being damaged by non-lethal fires were more susceptible to attacks by Japanese pine sawyer beetles, displaying higher population density and higher vertical distribution position.The study will provide an important guideline for the managers of Masson pine forests suffering from fires and pest invaded areas.

population density; vertical distribution;Hope;forest; fire

1 Introduction

Forest ecosystem is the largest and most important natural ecosystem in terrestrial ecosystem. It is well known that various biotic and abiotic disturbance factors affect the integrity and resilience of forest ecosystems, such as habitat fragmentation, human exploitation, pest outbreaks, invasion from exotic species, overgrazing and forest fires, etc.[1]. Among these disturbance factors, Forest fires and pest outbreaks are considered as important natural disturbance factors in many forest ecosystems, affecting the succession, nutrient cycling and species composition[2-4]. In particular, forest fires can have severe impacts on ecological communities through the direct mortality of plants and animals during the fire, and also have indirect effects on the vegetation structure and species turnover in the post-fire period[5-6], while subcortical insects such as wood borers, can directly control the succession of many tree species by preferentially attacking old or weakened trees[7]. Although the direct effects of fires and insects on forest ecosystems have been evaluated, their interactions can be just as important[8-9].For example, insects may increase the forest susceptibility to fires by rapidly killing many trees or accumulating a large number of combustible substances[10-11], and conversely, forest fires may predispose surviving trees to be attacked by insects[12-13], producing cascading and unpredictable changes in forest ecosystems[2,9]. Thus, understanding the interaction between forest fires and pest outbreaks is an important goal for researchers and forest managers. In recent years much progress has been made in understanding the impacts of insect outbreaks on subsequent fires[8,11,14-16], few studies have addressed the effects of fires on subsequent insect outbreaks[2, 17, 18].

Masson pine,Lamb., an important pioneer conifer species planted extensively in different parts of China for timber production and habitat restoration[19], it occupies 13.2 percent of all forested land in China, covering 14.2 million ha[20]. However, more than 90% of Masson pine forests have been managed in monoculture plantations often associated with ecosystem degradation, including the frequent occurrence of diseases and insect pests, and the high risk of fires[20-21]. Meanwhile, Masson pine in China is suffering from the lethal pine wilt disease (PWD) induced by the pinewood nematode,(Steiner et Buhrer) Nickle, and its insect vectorJapanese pine sawyer beetle,Hope (Coleoptera: Cerambycidae)[22-23]. This beetle is also an important xylophagous insect to genus[24]. Widespread tree mortality triggered by fires and pest outbreaks in pine forests in Southern China has caused concerns about forest health. During autumn of 2019, several fires burned a large area of Masson pine forests in Jiangxi Province in southern China, which offered a unique opportunity to study effects of fires in conifer stands on the subsequent insect outbreaks. In this study, it was investigated whether the direct weakening effects resulting from non-lethal fires on Masson pines were more susceptible to be attacked by.

The aim of this study was to investigate the response of the Japanese pine sawyer beetle to postfires in Masson pine forests. The main questions are: 1) Does the population density ofdecrease or increase in burned pine forests after single fire, comparing to the unburned forest? 2) Are there any differences in the vertical distribution ofon tree trunks between burned and unburned Masson pine? These results received from the study will provide an important guideline for the managers of Masson pine forests suffering in the fire and pest invaded areas.

2 Materials and methods

2.1 Study sites and investigated plots

Two sites we investigated for this study, which were located in Xingjian District and Wuning County, Jiangxi Province, China, respectively. These study sites were situated in the hilly and mountainous belt of the northern Jiangxi Province. The aspect was generally in the south with slopes of 0%-8%. Soils within the study sites was yellow soil and yellow-brown soil. Vegetation was a pure Masson pine pure stand. Masson pine in these sites ranged from 8.9 cm to 32.7 cm in diameter at breast height. In Xingjian County (28°24′N, 115°32′E, 78-102 m above sea level), lightning fire was ignited on 22 September 2019 and was burned until on 24 September 2019, with approximately 43.47 ha of Masson pine forest was burned. While in Wuning County (29°27′N, 115°11′E, 80-170 m above sea level), approximately 106.67 ha of pine forest was burned due to anthropogenic factor during September 23-25, 2019. The dominant tree species of all the sites was Masson pineLamb.

In each study site, three burned and three unburned plots were selected as the investigated plots based on the status of aboveground vegetation and trunk scorch levels. The plots without direct effects from fires were considered as unburned plots, while the plots which canopy trees had needles, with their stems scorched (leaf litter layer and herbs were charred), were considered as burned plots. All of the investigated plots were chosen on a south-facing slopes ranged from 23° to 29°. The area of each standard investigated plot was 20 m × 30 m. The groundcovers in each plot were(Labill.) Warb and(Thunb.) Berhn.

2.2 Investigation and sampling methods

2.2.1 Total pine mortality and mortality infested byField investigation was conducted in November 2020, thefirst year after the fire. In each standard investigation plot, the total number of Masson pine trees and dead trees with a diameter at breast height (DBH) more than 5 cm were counted respectively. Trees were recorded as dead if no green foliage was visible on the canopy. Dead trees damaged bywere also recorded by using their characteristics, including the loosed barks at the base of the trunk of Masson pine, a lot of sawdust seen in the cracks of the barks, and the entrance holes clearly visible after uncovering the barks. The tree mortality infested bywas assessed in each burned and unburned investigation plots.

2.2.2 Population density and vertical distribution ofTo examine the differences of population density and vertical distribution ofbetween burned and unburned investigation plots, three dead Masson pine trees damaged bywere chosen by the single diagonal method in each plot. These sampling trees in each plot were cut along the base of the trunk by using chain saw cutting tools. The height of each sampling tree was measured with steel tape. After removing branches, each sampling tree was cut into bole sections with 50 cm longfrom the base to top of trunk. Then boles were debarked and dissected into small pieces. The number of living larvae ofin each bole section were recorded.

2.3 Statistical analysis

All data in this study were analyzed by using SPSS version 24.0 for Windows (SPSS Inc., Chicago, IL, USA). Prior to statistical analysis, the assumptions of the normality of the distribution and homogeneity of variances of all data were examined by using Shapiro-Wilk tests, and the percentage data were arcsine transformed for the statistical analysis. Independent-Sample Student’s-test was used to compare the differences of the tree mortality infested byand the larval population density ofbetween burned and unburned plots. The vertical distribution ofin burned and unburned Masson pine trees were analyzed by using one-way ANOVA followed by Tukey’s HSD test, respectively.

3 Results

3.1 Total pine mortality and mortality infested by M. alternatus

Through field investigation, it was found that the tree mortality in the burned Masson pine forest was significantly higher (77.61%) than that in the unburned forest (19.59%) (=9.041,=10,=0.000<0.001, Fig.1A). Among these dead pine trees, 62.34% of them damaged byin the burned Masson pine forest, while only 35.27% in the unburned forest, showing a significant difference (=10.803,=10,=0.000<0.001, Fig.1B).

Fig.1 Total pine mortality (A) and mortality infested by Monochamus alternatus (B) in burned and unburned Masson pine forest (Independent sample t-test, **: P<0.01)

3.2 Population density of M. alternatus

There was no difference in the average height of sampling pine trees, with 7.78±0.33 m in burned pines and 7.70±0.36 m in unburned pines (= 0.170,= 40,=0.866). However, the larval density ofwas significantly influenced by fires. Burned Masson pine tended to harbor much higher larval density further up along the trunk compared with that of unburned trees. The average larval density in burned pines (36.96±2.79 larvae/tree)significantly was higher than that in unburned pines (19.72 ± 2.41 larvae/tree) (= 4.48,= 40,= 0.000 0<0.001, Fig. 2).

The different lowercase letter above the bars represents differ significantly (Independent sample t-test, P<0.01)

Tab.1 Vertical distribution of larvae Monochamus alternatus in the trunk of dead Masson pine trees

Means followed by the different capital letters within the same column are significantly different (One way ANOVA,<0.05), and means followed by the different lowercase letters within the same row are significantly different (Independent sample t-test,<0.05)

3.3 Vertical distribution of M. alternatus

Larvae ofdistributed all parts of the trunk, however, the vertical distribution of larval individuals showed a significant variation (Table 1). For unburned pines, 46.21% of individuals distributed in the middle-lower section of the trunk, followed by the middle and base sections of the trunk (22.95% and 17.48%, respectively), and the lowest distribution existed in the middle-upper and upper sections of the trunk.A significant difference in the vertical distribution of larvae was found in unburned pines (ANOVA:= 34.756;= 4,85;= 0.000<0.001, Table 1). A similar trend was found in burned pines, but the proportion of larvae in the middle andmiddle-lower sections of the trunk was significantlyhigher than that in other bole sections (= 90.74;=4,115;=0.000<0.001, Table 1). There was significant difference in the vertical distribution of larvaebelow the middle section of the trunk when further comparison was conducted on the larval densities between burned pines and unburned pines, exhibiting the middle section of the trunk had higher proportion of larvae in burned pines than that in unburned pines (=4.63;=40;=0.000<0.001), but the base section of the trunk had lower proportion of larvae in burned pines than that in unburned pines (=-2.70;=40;=0.014).

4 Discussion

In this study, the short-term response of Japanese pine sawyer beetles,, to pure Masson pine forests in first year after the fire. Three important findings arose from the investigation. Firstly, the proportion of dead pine trees infested byin burned forest was significantly higher than that in unburned forests. Secondly, the larvae ofwere more numerous in burned pines compared to that of unburned pines. Finally, in terms of the vertical distribution, larvae ofmainly distributed in the middle and middle-lower sections of the trunk in burned pines, while larvae beetles mainly focused on the middle-lower section of the trunk in unburned pines. Present results demonstrate that Masson pine forests after non-lethal fires apparently attract Japanese pine sawyer beetles andthe distribution position of larvae tends to move upward of the trunk.

There is increasing recognition that forest fires and insect outbreaks do not function in isolation, which often interact with each other and influence forest ecosystems together[8]. A large body of studies have been performed to explore effects of insect outbreaks on subsequent fires. However, the results of data have been mixed, with evidence of positive[13,16,25], negative[26], and neutral[27]effects of insects on the subsequent fire likelihood, behaviors, or severity. In ecological communities, insects are regarded as bioindicators of fire disturbance due to their sensitivity to environmental changes and habitat requirements[28-31]. Thus, understanding the effects of fires on subsequent insect outbreaks are also important, because insect outbreaks followed by fires can also effectively disrupt or redirect the succession in forest systems[2,17].

From the field investigations, it was found that Masson pine tree mortalities damaged byin burned Masson pine forests were significantly higher than that in unburned forests. In addition, the larvae density ofin burned Masson pine forests was obviously higher than that in unburned forests. These results revealed that forest fires apparently attractedfor the oviposition, leding to both increases in the tree mortality ofand the population density of. Similar results also have been reported in Buprestid beetles[2], Carabids beetles[32], and Cerambycid beetles[33]. Earlier studies onbeetles showed that some species, such asand, were attracted to burnt pine trees, which may result in increased progeny[30-31,34-35]. Possible reasons for burned forests attracting to insects are: 1) the burned forests may provide an easily accessible source of nutrients, or competition is low or absent, and temperature and moisture regimes are different and often more favorable than that of the surrounding unburned forests[2]. 2) a variety of cues may have mediated insect attraction to burn plots. Physical and chemical products of combustion, such as heat, smoke, and the odors of charred plant materials are attractive to some fire-associated forest insects[36]. In fact, manybeetles are easily attracted by weakened tree, and they may infest partially the burned conifers immediately after a fire, sometimes even when the burned trees are still smoking[33].

Previous studies have confirmed that the larvae of Japanese pine sawyer settled in all sections of the trunk mainly distributed in 2-4 m on the trunk of[37]. Similar findings were found in the vertical larval densities ofandon burnt black spruce ((Mill.) B.S.P.) and jack pine (Lamb.) in boreal forests[31]. In our observations, it was also found that the larvae ofsettled in all sections of the trunk. However, the vertical distribution of larval individuals showed a significant variation between burned pine trees and unburned pine trees. Larvae in unburned pine trees mainly settled in the middle-lower section, while those in burned pine trees focused on the middle section and the middle-lower section.This result indicated that the position of larval living in burned pine trees has moved upward than in unburned pine trees.Several mechanisms by which forest fires could influence the vertical distribution of insects were also proposed. Numerous studies demonstrated that the bark thickness, tree diameter, moisture contents, tree ages and vigor before death could all influence the adult oviposition and larval survivorship of insects[31,34,38]. For, the bark thickness and water contents in the middle-lower section of the trunk could be suitable for the adult oviposition and larval development. However, in burned pines, most of the bark in this section were scorched. Thus, more adultstended to lay their eggs on the middle section of the buck. In addition, Cadorette-Breton et al. identified that the bark thickness might be an indicator of the food quality for longhorned beetles[31]. Charred bark with lower nutrition and water contents on the tree trunkmaybe harmful to the larval growth.

Taken together, the current work highlights the fact that non-lethal firescan increase susceptibility of Masson pine to the occurrence of, which might lead to population outbreaks under appropriate circumstances. Thus, fire-affected Masson pine may act as vectors for the spread ofand the pinewood nematode. From our results, forest policy makers need to consider that it is necessary to put a large amount effort into the removal of dead trees ofin burned forests, especially adjacent to PWD-invaded areas. This paper, however, did not distinguish the severity of the fire, and the effects of fire severity on the growth and development of this beetle are still unclear. So, it still needs to further examine the life history traits ofon burnedwith different fire severities.

Acknowledgement

The authors would like to thank editors and anonymous referees for their constructive comments to improve the manuscript. Special thanks are also extended to Peng Yuyang and Gu Hangmin for their help in rearing the insects. This work was partly funded by the Research Project of Jiangxi Forestry Bureau (No. 201910) and the National Natural Science Foundation of China (No. 31760106).

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PAN Y L, CHANG X Q, LI Q, et al. Influences of post-fires on subsequent population of Japanese pine sawyer beetles,Hope (Coleoptera: Cerambycidae) in Masson pine forests[J]. Biological disaster science, 2021, 44(2): 183-189.

2021-04-30

2021-05-28

Project supported by Research Project of Jiangxi Forestry Bureau (No. 201910) and National Natural Science Foundation of China (No. 31760106)

Pan Youliang (1996—), graduate, engaged in forest entomology, 1649034597@qq.com; *Corres000ponding author: LIU Xingping, Professor, engaged in forest entomology, xpliu@jxau.edu.cn.

S763.38

A

2095-3704（2021）02-0183-07