Line thinning enhances diversity of Coleoptera in overstocked Cryptomeria japonica plantations in central Japan
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- Maleque, M.A., Ishii, H.T., Maeto, K. et al. Arthropod-Plant Interactions (2007) 1: 175. doi:10.1007/s11829-007-9016-1
We evaluated the effectiveness of line thinning, a new silvicultural technique, toward restoring diversity of Coleoptera in overstocked Cryptomeria japonica D. Don plantations in central Japan. We compared the abundance of some common Coleoptera families between line-thinned stands and adjacent unthinned stands in two plantations: low-elevation Sugi site (4 years since thinning) and high-elevation Kuchiotani site (6 years since thinning). Many bettle families comprising various functional groups such as plant feeders, wood borers, rotten wood feeders, root feeders, fungus feeders, dung feeders, and scavengers were more abundant in the line-thinned stands than in the unthinned stands. Furthermore, some important families were missing from the unthinned stands. There were strong positive relationships between Coleopteran abundance and understory vegetation. Our results suggest that line thinning may potentially increase biodiversity in overstocked C. japonica plantations by restoring important ecological processes such as food-web interactions (pollination, predation, herbivory, decomposition, parasitism, etc.), and habitat conditions.
KeywordsArthropodsBiodiversityEcosystem managementNew forestrySilviculture
Conservation and restoration of biodiversity has become an important objective of forest management in recent years (Lindenmayer et al. 1998; Lachat et al. 2006). Dobson et al. (2006) warn that losses of ‘trophic diversity’ cause ‘trophic collapse’ in nature, which ultimately cause losses of biodiversity and ecosystem services. Biodiversity conservation is especially important in areas where risks of species extinction are high (Burton et al.1992). Land areas covered by mono-specific plantation forests are increasing worldwide, where biodiversity may be declining owing to lack of habitat attributes needed to support many species (Lindenmayer and Franklin 2003; Ishii et al.2004). Sustainable silvicultural systems that also aim to restore biodiversity in plantation forests are being developed in many countries (Larsen 1995; Khom and Franklin 1997; Progar et al.1999; Halpern et al.1999; Kerr 1999; Aubry et al.2004; Nagaike 2006; Maleque et al.2006b). However, the effectiveness of these new silvicultural treatments toward biodiversity conservation is still to be tested (Halpern and McKenzie 2001; Nelson and Halpern 2005; Halpern et al.2005).
In Japan, more than 40% of the forested areas are plantations planted after the Second World War to meet the growing demand of the lumber industry (Ishiyama 1998). These even-aged commercial plantations mainly include Cryptomeria japonica D. Don (Japanese cedar), Chamaecyparis obtuse Endl. (Japanese cypress), and Larix kaempferi Lamb. (Japanese larch) trees, where C. japonica plantations alone constitute half of the plantation area. Most of these plantations have reached commercial harvesting age (40–60 years), but many have remained unmanaged for several years due to high labor costs and low wood value in the country. Lack of management has resulted in overstocked stands with very dark forest floor conditions, supporting low diversity of understory plants (Ito et al.2003, 2006).
The Japanese government recognizes that loss of biological diversity, more specifically loss of endemic plant and animal species from the mountainous regions is a major concern (Forestry Agency of Japan 2004). Recent studies have demonstrated that biodiversity can be restored in the plantations through adequate management (Nagaike 2002; Ito et al.2003, 2006; Kodani 2006). Most studies, however, investigated diversity of understory plants and did not consider diversity of other organisms. Recently, Maleque et al. (2006a) proposed that arthropod community structure reflects overall biodiversity conditions of forest ecosystems and thus, can be used to assess the effectiveness of various ecosystem management techniques. Abundance and diversity of plant-dwelling arthropods increase with increasing diversity of plant communities (Parmenter and MacMahon 1987; Parmenter et al.1991; Siemann et al.1999; Moir et al.2005; Inada et al. 2006). However, it is still unclear whether or not this has a cascading effect on overall biodiversity. In addition, important ecological processes that promote biodiversity in plantation forests after management applications are still to be explored (Nagaike 2000, 2006; Maleque et al. 2006a).
Ecological functions of some common Coleoptera families used in this studya
Larvae predate on soft-bodied insects and adults feed on nectar and pollen
Larvae and adults predate on small insects and other animals
Wood borers/rotten wood feeders
Larvae bore into moist-wood, various species of trees and shrubs, and adults feed on nectar and pollen, sometimes foliage
Larvae feed on leaves, stems, and plant roots and adults feed on leaves, stems, and flowers
Larvae and adults feed on plant parts and seeds
Larvae feed on plant roots and adults feed on nectar
Larvae and adults feed on fungi
Larvae feed on bark and leaves, and adults feed on nectar, flower, and plants
Tumbling flower beetles
Plant/rotten wood feeders
Larvae feed on rotting wood, fungi, or the pith of stems, and adults feed on pollen
Larvae feed on fungi, corn ears, waste onion piles, food material in contact with the soil, and adults feed on cracked and damaged fruits
Pollen feeding beetles
Larvae feed on rootlets and fungal rhizomes, and adults feed on pollen
Scarabaeidae (Scarabaeinae and Aphodiinae)
Larvae and adults feed on carrion, dung, skin, and feathers
Scarabaeidae (excluding Scarabaeinae and Aphodiinae)
Plant/rotten wood feeders
Larvae feed on roots, rotting wood, and decaying organic material in the ground, and adults feed on leaves, pollen, and flowers
Larvae and adults bore into stressed or damaged plants
Larvae and adults predate on insects, and they feed on plants, fungi, and excrement
Larvae and adults feed on plant parts and stored grains
Materials and methods
The study was conducted in two C. japonica plantations located at two different elevations: ‘Sugi site’ in Kanzaki Town (low-elevation: 350 m asl, 35°24′N, 134°56′E) and ‘Kuchiotani site’ in Kami Town (high-elevation: 700 m asl, 35°47′N, 134°50′E). Both sites are located in northern Hyogo Prefecture, central Japan. Mean annual temperature and mean annual precipitation are, respectively, 16.3°C and 1,487 mm for Sugi and 14.5°C and 1,947 mm for Kuchiotani. Both sites experience monsoon climate with a rainy season from June to July with ∼20–25 rainy days. The surrounding landscape matrix of the two sites is very different. The Sugi area is dominated by plantation forests covering more than 80% of the forested landscape of Kanzaki Town. In contrast, the Kuchiotani area is dominated by natural forests comprising primary and secondary cool-temperate deciduous forests.
Research plots in the Sugi site are located on a southeast-facing slope (mean inclination = 25°). The stand was line-thinned in 2000, when the stand age had reached 35 years. The intensity of thinning was ∼25% of the total number of trees. Number of lines was twelve and thinning width was 3 m, with a length of 120 m each. Retention width was 9 m. Tower yarder was used for removing cut stems. The treatment plot (15 × 50 m2) included one line-thinned section and one retained section. The control plot (20 × 20 m2) was established in an adjacent unthinned stand on the same slope.
Research plots in the Kuchiotani site are located on a south-facing slope (mean inclination = 12°). The stand was line-thinned in 1998, when the stand age had reached 39 years. The intensity of thinning was ∼29% of the total number of trees. Number of lines was five and thinning width was 3.6 m, with a length of 65 m each. Retention width was 5.4 m. Swing yarder was used for removing cut stems. The treatment plot (20 × 30 m2) included two line-thinned sections and two retained sections. The control plot (20 × 30 m2) was established in an adjacent unthinned stand on the same slope. Maleque et al. (2007) give a detailed description of the study site and research plots.
Sampling, identification and grouping of Coleoptera
The study was carried out during April through October 2004. In April 2004, Townes-type white Malaise traps (height × width × length = 120 × 100 × 150 cm3, Morpho, Czech Republic) were set up in each stand to capture arthropods. In each site, eight traps were set up in the treatment plot (four each in the thinned and retained sections) and four traps were set up in the control plot. Traps were set up at random positions in each plot. Collection bottles (500 ml) were filled with propylene glycol for preserving trapped insect samples for each collection interval in the field. Arthropod samples were collected at 14–20-day intervals from mid-April through the first week of October. In Sugi site, sampling had to be discontinued after the third week of August due to typhoon damage.
After each collection, the arthropod samples were carried to the laboratory and preserved in 70% ethanol solution. We extracted all Coleoptera from the arthropod samples and identified common Coleoptera families based on identification keys (Kurosawa et al.1998; Lawrence et al.1999; Uéno et al.1999; Hayashi et al.2002). We assigned each family to functional groups based on larval feeding habits (Table 1). Because the feeding habit of dung-feeding Scarabaeidae (Scarabaeinae and Aphodiinae) is different from that of other Scarabaeidae, dung-feeding Scarabaeidae was considered separately.
Biomass and species richness of understory plants
In order to determine the biomass and species richness of understory plants, we harvested the aboveground parts of all vascular plants in 2 × 2 m2 quadrats near each Malaise trap in September, 2004. We took care to cause minimal disturbance to vegetation surrounding the Malaise trap so as not to affect subsequent insect sampling. We chose to collect plant samples in September after growth of most annual plants had been completed and plant biomass was at its maximum, although some early senescing plants may have been missed.
The harvested plant samples were brought to the laboratory for identification and biomass determination. After sorting to species, the plant samples were oven-dried to constant weight to determine dry mass. Biomass (dry mass) and species richness (total number of species) of understory plants were determined for the thinned and retained sections of the treatment plot as well as for the control plot as the average of the four quadrats.
Abundance of Coleoptera and biomass and species richness of understory plants showed positively skewed distributions. Therefore, the data were log transformed to normalize the variance. The total number of Coleoptera captured during the study period was compared among treatments (thinned section, retained section and control) using one-way ANOVA considering each trap as replicate samples within each treatment. The seasonal abundance pattern of common families was compared among treatments using two-way ANOVA with treatment and collection date as the two main effects. Multiple comparisons among the means were evaluated by Tukey’s test.
The total number of Coleoptera captured during the study period was analyzed in relation to biomass and species richness of understory plants using regression analysis. Similarly, the total number of Coleopteran functional groups (i.e., plant feeders, plant/rotten wood feeders, wood borers, and predators) captured during the study period was analyzed in relation to biomass and species richness of understory plants using regression analysis.
The experimental unit of this study is the forest stand, of which we have only two replicates due to logistical reasons. As a consequence, we were only able to conduct statistical tests comparing treatment versus control within each stand by considering traps as replicates. Thus, our results should be interpreted with caution when drawing conclusions regarding the effects of line thinning on Coleopteran abundance.
Response of Coleoptera and understory vegetation to line thinning
Abundance of important beetles (Coleoptera) in the line-thinned stand and unthinned stand of two Cryptomeria japonica plantations in northern Hyogo Prefecture, central Japan
Number per trap (mean ± SD)
Difference with control (%)
170.0 (±128.2) a
189.8 (±107.4) a
83.0 (±41.0) a
405.7 (±69.8) a
337.3 (±64.9) a
175.8 (±32.2) b
Response of Coleopteran families to line thinning
Abundance (number of individuals captured per trap) of some common Coleopteran families in Sugi
Number of individuals per trap (±SD)a
8.3 (±5.4) a
5.0 (±0.8) ab
1.5 (±1.3) b
18.5 (±19.1) ab
20.5 (±17.0) a
7.3 (±6.4) b
6.5 (±6.5) ab
10.0 (±6.2) a
2.3 (±3.9) b
18.5 (±15.3) a
27.3 (±17.5) a
11.3 (±6.2) b
21.3 (±14.5) ab
25.8 (±17.0) a
13.3 (±10.5) b
18.8 (±15.6) a
16.0 (±6.1) ab
6.5 (±3.7) b
34.3 (±32.1) a
27.3 (±19.6) a
22.5 (±4.9) a
13.0 (±10.4) a
6.3 (±5.9) ab
3.8 (±3.5) b
7.0 (±3.4) b
20.0 (±14.9) a
3.8 (±2.2) b
5.5 (±3.1) ab
7.0 (±5.3) a
1.8 (±2.4) b
11.3 (±8.1) a
11.8 (±5.3) a
3.5 (±2.1) b
Abundance (number of individuals captured per trap) of some common Coleopteran families in Kuchiotani
Number of individuals per trap (±SD)a
7.0 (±2.0) a
2.5 (±2.5) b
2.3 (±2.9) b
9.3 (±1.5) ab
11.3 (±4.8) a
3.8 (±3.4) b
16.3 (±13.7) a
11.3 (±4.4) ab
5.8 (±3.2) b
35.3 (±17.2) a
23.0 (±8.1) ab
14.0 (±3.7) b
64.0 (±18.2) a
57.5 (±11.9) ab
35.3 (±10.9) b
42.0 (±12.5) a
30.5 (±8.4) ab
15.0 (±4.3) b
8.0 (±2.6) a
5.5 (±3.1) a
0.8 (±1.0) b
21.0 (±17.3) a
16.8 (±7.5) ab
8.5 (±4.7) b
78.0 (±65.0) ab
84.5 (±36.4) a
37.3 (±28.2) b
13.0 (±1.7) a
10.5 (±2.6) ab
4.0 (±2.6) b
47.7 (±28.2) a
38.5 (±14.1) ab
18.0 (±7.9) b
8.0 (±6.6) a
2.3 (±1.9) a
5.8 (±7.5) a
34.0 (±19.2) a
22.3 (±9.1) a
11.8 (±6.8) b
20.0 (±9.5) a
20.0 (±5.0) a
13.3 (±6.3) a
Response of Coleoptera to understory vegetation
Our results show that line thinning increased the abundance and diversity of Coleoptera in the two C. japonica plantations. We found strong across-site positive relationships between abundance of Coleoptera and understory vegetation. Several studies have found positive associations between arthropod abundance and understory vegetation (e.g., Ohsawa 2004; Murray et al.2006). Thinning creates more sun-exposed understory conditions and can increase biomass, diversity, and cover of understory plants, if applied with sufficient time intervals to allow development of understory vegetation (e.g., Smith et al.1997; Kerr 1999; Thomas et al.1999; Griffis et al.2001; Clinton 2003). Arthropods respond relatively quickly to thinning and subsequent recovery of understory vegetation. For example, Ohsawa (2005) found higher abundance of Curculionidae in the middle-aged (21–45 years old) larch (L. kaempferi Lamb.) plantations only 1.5–2.5 years after thinning in the central mountainous region of Japan. Germain et al. (2005) found higher abundance of generalist carabid beetles only 2 years after logging in Canada. Our study sites were 4 and 6 years since thinning, which was shown to be sufficient for restoration of both plant and arthropod communities. Our estimates indicate that standing volume will recover to pre-thinning values in ca. 10 years (Maleque 2006). The results of this study suggest that this may be a good thinning interval for maintaining biodiversity in the plantation.
Many authors have used functional groups to evaluate arthropod diversity (e.g., Kennedy and Southwood 1984; Stork 1987; Memmott et al.2000; Vanderwel et al.2006). We evaluated the responses of Coleopteran families where each family represented one or more functional groups (Tables 3, 4). Most Coleopteran families increased in abundance in response to thinning. Plant-feeding Chrysomelidae, Curculionidae, root-feeding Elateridae, wood/plant feeding Lycidae, scavenger Tenebrionidae, wood-boring Cerambycidae, plant/rotten wood-feeding Scarabaeidae, all of which directly or indirectly depend on plants for food (Siemann 1998; Lawrence et al.1999; Weisser and Siemann 2004), increased in abundance in the thinned stands. The presence of more understory vegetation in the thinned stands may also have contributed to greater abundance of flower-visiting adults of Chrysomelidae, Curculionidae, Scarabaeidae, and Cerambycidae, which are attracted to floral fragrance (Maeto and Fukuyama 1995; Maeto et al.2002). Predatory Carabidae, which tend to be more abundant and diverse where herb and shrub cover contribute to increasing prey abundance (Magura et al.2000; Jukes et al.2001; Magura et al.2001, 2002), were more abundant in the line-thinned stand. The line-thinned stand also supported more individuals of predatory Staphylinidae. Although we believe that most of the insects captured in this study were resident in each stand, some may have been transient individuals moving through the stand. We contend that both resident and transient insects contribute to biodiversity because their presence reflects use of the stand by diverse insect groups.
In contrast to the thinned stands, the unthinned stands in both sites supported much lower abundance of beetle families. The lack of understory vegetation in the unthinned stands resulted in lack of palatable broad-leaf litter for decomposers. Magura et al. (2005) found that the distribution and abundance of Carabidae increased with increasing broad-leaf litter on the forest floor in the Norway spruce (Picea abies) plantations. In addition, organic acids produced by decomposing conifer litter may be deleterious to many plant and animal communities (Arnett Jr 2000; Kerr 1999).
Coleopteran abundance increased more markedly in response to biomass of understory plants than to species richness. In addition, most Coleopteran functional groups (excluding plant/rotten wood feeders) increased more markedly in response to biomass of understory plants than to species richness. The amount of understory vegetation is an important factor contributing to Coleopteran diversity, although plant species richness can be important for colonization by truly plant-feeding insects (Brown and Hyman 1986; Johnson and Agrawal 2006). Our results suggested that ‘structural diversity’ (sensu Southwood et al.1979) is more important for colonization by Coleoptera than ‘taxonomic diversity.’ Understory plants are the primary determinants of spatiotemporal heterogeneity on the forest floor (Clinton 2003). Because understory vegetation provides food and shelter for various arthropod species, arthropod abundance and diversity are correlated with abiotic and biotic factors created by understory vegetation (Nakamura et al.1970; Lattin 1993; Dabrowska-Prot 1999; Ikeda et al.2005). For example, favorable ground temperatures and higher abundance of foods provided by understory plants have positive impacts on the distribution and abundance of Carabidae (Magura et al.2004, 2005). In natural environments, temperatures exert great influence on developmental rates of insect communities, i.e., the higher the temperature the faster the developmental rates of insect communities within certain ranges (Pedigo 1996). In all types of habitats, the survival rate of immature insects is an important determinant of the abundance of insect communities (Ikeda et al.2005). We found that daytime temperatures were, on average, 1.8°C higher throughout the study period in the thinned stand than in the unthinned stand (Maleque 2006). In addition to greater availability of food and habitat attributes, higher temperatures in the thinned stand may have contributed to increasing growth rate and survival of immature insects (‘grubs’) of Coleoptera. We inferred that establishment of a structurally diverse understory plant community after line thinning provided heterogeneous understory conditions for arthropods in the thinned stands with respect to habitat, food sources and microclimate (Hammond and Miller 1998; Tanabe et al.2001; Oxbrough et al.2005; Ikeda et al.2005).
At a larger spatial scale, biodiversity conditions of managed forests and other human-influenced ecosystems are influenced by the surrounding landscape pattern (Kerr 1999; Hunter 2002; Nagaike 2002; Cook et al.2006; Kodani 2006; Sakai et al.2006). The Kuchiotani site, which included more natural forests in the surrounding landscape, supported more understory plants (Fig. 2) and twice the abundance of Coleoptera than the Sugi site (Table 2). Natural forests surrounding the Kuchiotani site are likely to function as seed sources for understory vegetation and source habitats for Coleoptera emmigration. Additional factors such as longer time since thinning, wider thinning width, and cooler, more humid climate probably contributed to increasing biodiversity in the Kuchiotani site. In contrast, the Sugi site may lack seed sources and source habitats due to the high percentage of plantation forests in the region. Our results suggested that spatiotemporal variations including landscape-level factors might potentially influence the success of biodiversity restoration.
This study suggests that, in addition to its economic viability (Taniguchi 2003), line thinning is a potentially effective ecosystem management technique for biodiversity restoration in overstocked C. japonica plantations. By creating heterogeneous understory conditions, line thinning increased understory plant biomass, which in turn contributed to enhancing arthropod diversity (Maleque et al.2007). Our results suggested that restoration of ecological processes, such as food-web interactions (pollination, predation, herbivory, decomposition, parasitism, etc.) and habitat preferences, is an important factor contributing to biodiversity of arthropod communities. Ecosystem management techniques should aim to enhance important ecological processes in order to restore biodiversity effectively.
We thank the students and faculty of the Laboratory of Forest Resources, Kobe University for their help with field work and discussion. We also thank the forestry unions of Kanzaki and Kami towns for permission to use the study sites. The Japanese Ministry of Education, Culture, Sports and Technology supported the first author and the Academic Research Grant of the Japan Forest Technology Assoc. supported this study. Voucher specimens from this study were deposited in a collection at the Hyogo Museum of Humans and Nature.