Comparison of saproxylic insect diversity in three forest types of Rajiv Gandhi National Park, Nagarahole (Nilgiri Biosphere Reserve, India)

Transcription

1 Comparison of saproxylic insect diversity in three forest types of Rajiv Gandhi National Park, Nagarahole (Nilgiri Biosphere Reserve, India) P. Sarasija, O. K. Remadevi* and Y.B.Srinivasa Wood Bio degradation Division, Institute of Wood Science and Technology, 18 th Cross, Malleswaram, Bangalore, Karnataka, India *E- mail ABSTRACT Diversity of dead wood dependent (saproxylic) insects was studied in three different forest types of Rajiv Gandhi National Park (Nagarahole) during Out of the three forest types selected for study viz., moist deciduous, dry deciduous and teak plantations, dry deciduous forests observed to be most diverse with regard to the abundance and species richness of saproxylic insects, followed by moist deciduous. The teak plantations supported less number of insects. Many saproxylic species associated with moist deciduous and dry deciduous forests were absent or less abundant in plantations. The ecological preferences of these organisms will be useful as biotic indicators in monitoring forest degradation. The study also throws light upon the importance of species diversity of flora in conserving the faunal diversity. KEY WORDS: Diversity, Nagarahole, Nilgiri Biosphere Reserve, saproxylic insects INTRODUCTION The species richness and diversity among herbivores and carnivores is based on plants as primary producers (Hammond and Jeffrey, 1998). Since the diversity of flora varies in different regions there is a consequent change in organisms associated with it. The species composition and quality of the tree species differ according to the forest types and climatic conditions prevailing in the area. Differences between the stands may influence availability of microhabitats and niche assemblage of organisms associated (Siitonen, 2001). Many studies support the fact that the forest types influence general insect diversity. The stand characteristics of a particular forest type influence its dead wood dynamics, which in turn determines the saproxylic (wood dependent) insect diversity of that forest. Saproxylic insects form the largest and probably most vulnerable group supported by the dead wood. Saproxylic has been defined by Speight (1989) as those dependent, during some part of the life cycle, upon dead or dying wood or wood inhabiting fungi, or upon the presence of other saproxylic species. Saproxylic organisms are important components of forest ecosystems and play a vital role in decomposition of the wood and nutrient cycling (Samuelsson et al., 1994). Modern forest management practices like clear cutting, mono culture plantations, etc. adversely affect the saproxylic insect diversity, and many of the wood dependent species are now endangered. But only recently the research on saproxylic insects gained momentum. Most of the studies related to saproxylic insects have been carried out in boreal and temperate forests of Europe and America (Martikainen et al. 2000), and very little work is available from the tropical forests of the world. In tropical countries like India, 413

2 there has been no systematic quantification or documentation of the life forms that unlock elements from dead trees. The works of Beeson (1941) and Stebbing (1914) on forest insects of India is valuable in many aspects, but does not cover the quantitative estimation of the saproxylic insects or their ecological role. Literature on these aspects is restricted only to the temperate regions of the world. Tropics, which contain more than half of the estimated 10 million species, have been grossly neglected. India s Biosphere reserves where dead tree extraction is legally prohibited, may be acting as reservoir of enormous amount of diversity. Unless quantified and documented, what is conserved will remain a mystery. Keeping this in mind the present study was carried out to explore the diversity of saproxylic insects in Rajiv gandhi National Park (Nagarahole, Nilgiri Biosphere Reserve, India). A comparison of saproxylic insect fauna associated with different forest types was also carried out, which gives insight in to the relative abundance, species richness, and survival status of different insects species. This information will be very much useful in conservation strategies to be followed in Biosphere Reserves, including the extraction of dead wood. MATERIALS AND METHODS Study area : Nilgiri Biosphere Reserve (NBR) is the first among the thirteen biosphere reserves established in India. Rajiv Gandhi National Park of NBR is selected as the study area. Rajiv Gandhi National Park, which spans from the foothills of Brahmagiri range in west to the Deccan Plateau on the east, is a significant part of the 5520 sq. km. Nilgiri Biosphere Reserve. It lies in both the districts of Kodagu and Mysore of Karnataka state and falls between the geo-coordinates 11?50 to 12?15 North latitude and 76? and 76?15 East longitude. The total area of the park is sq. km. It occupies a pre-eminent position in the forested landscape with ecological continuity extending to Bramhagiri, Bandipur and Wynad wildlife sanctuaries. The park is divided into 7 ranges Kalhalla, Veeranahosahalli, Anechowkur, Nagarahole, D. B. Kuppe, Mitikuppe and Antharasanthe. The study was carried out during wherein sampling was done thrice in each year. Vegetation types of the park include dry deciduous forests, moist deciduous forests and teak plantations. The dry deciduous forests are characterized by Tectona grandis, Pterocarpus marsupium, Anogeissus latifolia, Terminalia tomentosa, Terminalia paniculata, Terminalia bellerica, Terminalia chebula, Grewia arborea, Bombax ceiba, Careya arborea, Odina wodier, Lannea coramandaliea, Dendrocalamus spp. etc. These forests have been subjected to severe fires during summer due to leaf fall and dry grass. The moist deciduous forests are characterized by Tectona grandis, Dalbergia latifolia, Ptercarpus marsupium, Lagerstroemia lanceolata, Terminalia tomentosa, Toona ciliata, Albizzia spp., Bambusa bamboos and Dendrocalamus strictus etc. Selection of logs The fallen logs of different species and decay stages in different forest types were selected randomly for the study. The identity of the log species was confirmed in the field itself. Some logs that were in their later stages of decay could not be identified and hence noted as unidentified in analysis. Since the recruitment of log is irregular in space and time and is often highly episodic, it was difficult to get same species and equal number of trees in different forest types for comparative studies. So the total surface area of the dead wood sampled and the insect diversity harboured by it in different forest types is compared. Sampling of insects Insects were collected by direct search method. logs were first visually inspected for insects. Those found sitting or walking on the logs and those visible were collected using brush, forceps, aspirator or 414

3 by hand. At first the log sampled was divided into 3 equal portions - lower, middle and upper according to its length cm 2 area (100 cm x 30 cm) was marked in each portion randomly and each was searched for 15 minutes. Totally an area of 9000 cm 2 was sampled in each log. Loose bark was pulled off, and sample specimen of the adult insects, larvae and pupae were collected. Number of individuals of different species was counted or, if more individuals were found estimated appropriately. The bark was removed from the surface of log and the logs were cut open whenever possible. Some groups like Dipteran larvae, bark beetles like Brenthidae, Platypodidae, termites, wood ants etc. had very high populations in certain logs and they were counted by semi quantitative methods (Jones 1994). This method involved splitting open the dead wood with a chisal and visually estimating the number of individuals by counting in nits of 10s, 100s or 1000s. The young stages were reared in the laboratory in controlled environments. The abundance of insects sampled in the cases of direct searching was compared with respect to the surface area of the wood sampled. Statistical analysis: Diversity was measured and compared through various indices like Margalef s richness index, Menhinick s richness index, Pielou s evenness index, Simpson s diversity index, Shannon s diversity index, Jaccard s similarity index etc. T test was also conducted to compare the insect fauna associated with different forest types. RESULTS AND DISCUSSION A total of 132 logs were sampled in three forest types. Since the recruitment of log is irregular in space and time, the number of logs sampled varied in different forest types. All the measures of species diversity, abundance and species richness were expressed in terms of the area of the log sampled (9000 cm x 30cm = 27,000cm /log = 118 square abundance and number of morphospecies, the absolute values were weighted by the number of sampled logs in each forest types. A total of 12,449 insects belonging to 10 orders and 315 morpho species were collected by direct search method. The assemblages of saproxylic insects differed across the forest types. Coleoptera dominated in abundance and species richness in all the forest types, while the assemblages of all the other groups differed drastically (Fig 1). The proportional abundance of Coleoptera was highest in plantations, followed by dry deciduous forests and moist deciduous forests, while Hymenoptera and Isoptera dominated in moist deciduous forests. The abundance of Coleoptera in plantations was mainly due to the high abundance of primary colonizers of family Platypodidae, which is attracted by the freshly fallen logs in plantations knocked down by the elephants. Families like Brenthidae, Nitidulidae, Pselaphidae etc. contributed the abundance of Coleoptera in dry deciduous forests which is usually associated with rotting bark and sap wood. In all the forest types Coleoptera dominated in species richness followed by Hymenoptera and Diptera. Trophic levels of saproxylic insects shows a relative abundance of primary xylophagous forms in plantations followed by dry deciduous and moist deciduous forests, while secondary xylophagous forms dominated in moist deciduous forests. Termites, ants and fungivores were also dominant in moist deciduous forests. This trend is seemed to be because of the large number of freshly fallen logs in plantations and higher proportion of logs in later stages of decay in moist deciduous forests. The logs in later stages of decay also supported termits, ants and fungivores in addition to secondary wood borers, which were dominant in moist deciduous forests (Fig. 2). The mean number of individuals/log sampled was highest for dry deciduous forests (100 indiv./log), followed by moist deciduous forests (96 indiv./log) and was least for meter/ log). For comparing the insect 415

4 plantations (86 indiv. /log). The difference between plantations and dry deciduous forests was significant. The total species richness was highest in moist deciduous forests (mean 6 spp./ log), followed by dry deciduous (5 spp./log) and was least for plantations (3 spp./log). Both diversity and richness indices were calculated for all the forest types. All the diversity indices calculated like Shannon and Simpson peaked for dry deciduous forests, showing higher diversity than the other two forest types. The abundance also peaked for dry deciduous forests. But the richness indices like Margalef s index and Menhinick s index were highest for moist deciduous forests. The evenness index was highest for dry deciduous forests (0.81) due to the large number of singleton and doubleton species in these forests (Table 1). T- test showed significant (p >0.001) differences between different forest types. Jaccard s similarity index (Table 2) shows low values across forest types, suggesting a unique insect fauna in all the forest types. There is more similarity between dry deciduous and moist deciduous forests (Jaccard s similarity index = 0.39), while plantation and moist deciduous (Jaccard s similarity index = 0.32) differed considerably. Results of ANOVA with number of individuals show that there is no significant difference (Fcrit = 3.07, Fcalc= 0.127, p >0.05) in the number of individuals between different forest types, but there was a significant difference in number of species. Dry deciduous forest has more number of species than the teak plantations and moist deciduous forests and dry deciduous forest significantly (Fcrit = 4.79, Fcalc= 7.035, p<0.01) differed from teak plantations (Table 3). This study has thrown light upon the impact of stand structure on the diversity of insects. The saproxylic insect diversity in plantations seem to be low compared to natural of primary xylophagous insects (which constitute bark beetles like Platypodids and Scolytids) in dry deciduous forests and plantations, but moist deciduous forests had very less abundance of these insects. The biological cause for the high population levels of bark beetles in plantations compared to the natural forests are high level of breeding material available in plantations mainly through windfalls, logging slash and timber piles provide suitable habitat for bark beetles. (Schlyter and Lundgren, 1993). These results gain support from similar studies of Martikainen and Kaila (2004) and Mathew et al. (1998) who argued that the monoculture plantations support less diversity than natural forests. The tree fall pattern in plantations of Nagarahole National Park is mainly controlled by the elephants, which knock down the trees of T. grandis and G. tiliaefolia of lower or medium diameters, since the bark of these trees are a preferable food for them. This half bark peeled trees attract many of the primary xylophagous forms like Platypoids, Bostrichids, Scolitids and their associated predators and parasites, resulting in their higher abundance in early stages of bark and sap wood deterioration in plantations. Since T.grandis, is a durable tree species, after sap wood decay it support only few species of secondary xylophagous forms. The number of freshly fallen logs was comparatively low in moist deciduous forests. This may be a reason for the low abundance of primary xylophagous forms in this forest type. But the secondary xylophagous forms showed a high abundance in moist deciduous forests, compared to plantations and dry deciduous forests. The shady and cold microclimatic conditions that prevail within dense natural forests, on contrary are not favorable for most primary bark beetles. It is also possible that higher population of predators and parasitoids are maintained within natural forests due to the abundance of secondary bark beetles which may keep the population level of bark beetles under control. Here the results agree well with forests. But there was a trend of high abundance 416

5 Schlyter and Anderbrant (1993). Vaisanen et al. (1993) also documented a large turnover in species community of sub cortical beetles between different forest types, especially managed and primeval forests. The high abundance, diversity and species richness in dry deciduous and moist deciduous forests compared to plantations highlights the importance of species diversity of flora in conserving the faunal diversity. Many rare and specialized species require strict microhabitats, like large diameter trunks in advanced stages of decay (Jonsell et al. 1998). Their availability also seems to support varieties in species assemblages. The high species richness in moist deciduous forests, even though lower number of logs sampled reveals the forest health. The stand structure and age of this forest types was entirely different from others, with large logs from a variety of species and dense canopy cover. Since the number of logs on later decay stages is more, there was an abundance of fruiting bodies of wood decaying fungi and associated mycophagous (fungus feeding) insects. Here the results indicate that many species associated with moist deciduous and dry deciduous forests are absent or less abundant in plantations. For instance, families like Ciide, Passalidae Erotylidae, Ptynidae etc. were scarce or absent in our samples from plantations, but were frequently caught in moist deciduous forests. The difference between plantations and moist deciduous was pronounced in rare saproxylic species and in species that are mainly associated with advanced stages of wood decay. In older logs infestation by secondary borers like Passalidae, Blattidae and termites were noticed. These organisms preferred mostly rotting timber that was in relatively undisturbed forest floor where the logs remained moist. Plantations with open forest canopy where the required microclimatic conditions were not available, the occurrence of these organisms was found to be restricted. It seems that certain degree of microclimatic conditions is required for the survival of these insects. The ecological preferences of these organisms will be useful as biotic indicators for monitoring forest degradation (Mathew, 2004). CONCLUSION Fallen wood is an important component of forest ecosystem. It influences biological, physical and biochemical processes of a forest ecosystem. Above all, it provides habitat for a large variety of organisms like fungi, insects and birds. Saproxylic insects (dead wood dependent) form the largest and probably most vulnerable group supported by the dead wood, which is adversely affected by modern forestry practices. The present study assumes high significance in collecting about 12,449 insects belonging to 10 orders and 315 morpho species in different forest areas. The dry deciduous and moist deciduous forests supported a large number of insect fauna than plantations indicating higher diversity and abundance harbouring many important groups like Passalids and some rare group of fungivores insects. The three forest types surveyed differed in terms of diversity and species assemblages. ACKNOWLEDGEMENTS The authors thank the Ministry of Environment and Forests for the financial grants to carry out the studies. They also thank the officials of Karnataka Forest Dept., especially to the officials of Hunsur Forest Division and the Rajiv Gandhi National Park, Nagarahole for the help rendered to carry out the studies. Thanks are also due to the Director, Institute of Wood Science and Technology, Bangalore for providing the infrastructural facilities for the studies. All the Staff of Wood Bio degradation Division of IWST is kindly remembered at this occasion. 417

6 MD 1 DD Plantation 0% 20% 40% 60% 80% 100% Co leo p t era H y m en o p t era D ip tera Iso p tera D erm ap t era Co llem bo la T h y san ura H em ip t era Lep ido p t era D y ctyop tera DD Dry deciduous, MD Moist deciduous Fig. 1: Proportion of abundance of insects belonging to different orders associated with different forest types MD DD Plantation 0% 20% 40% 60% 80% 100% P rim ary x y lo p h ago us Seco n dry x y lo p h ago us P arasito ids P redato rs D wellers Sap ro p h y tes Fun giv o res A n ts T erm ites Fig. 2: Proportion of abundance of insects belonging to different trophic levels associated with different forest types 418

7 Table 1: Diversity attributes of insects collected from different forest types Diversity Index Forest types Plantation Dry deciduous Moist deciduous S N DMg DMn J D H S Number of species, N - Abundance, DMg Margalef s richness index, DMn Menhinick s richness index, J Pielou s evenness index, D Simpson s diversity index, H Shannon s diversity index Table 2: Jaccard s similarity index computed for different host species Jaccard s similarity index Plantation Dry deciduous Moist Deciduous Plantation DD 0.39 MD Highest value is underlined Table 3: Results of ANOVA for comparing number of species found in different forest types Source df Sum of squares Mean Square F calc F crit Between ** 4.79 Groups Within Groups Total ** Significant at 1 % level of significance 419

8 REFERENCES Beeson, C.F.G The Ecology and Control of Forest Insects of India and Neighboring countries. Vasant Press, Dehradun. Hammond, P. C. and Jeffrey C. Miller Comparison of the biodiversity of Lepidoptera Within Three Forested Ecosystems. Conservation Biology and Biodiversity, 91:(1), Jones,C.G., Lawton, J.H.,Shachak,M Organisms as ecosystem engineers. Oikos 69: Jonsell, M., Weslien, & J.Ehnstrom,B Substrate requirements of red listed saproxylic invertebrates in Sweden. Biodiversity and conservation 7, Martikainen, P., Siitonin, J., Punttila, P., Kalia, L. and Josef Rahu Species richness of coleoptera in mature and oldgrowth boreal forests in southern Finland, Biological Conservation, 94: Martikainen, P. and Kaila, L Sampling saproxylic beetles: lessons from a tenyear monitoring study. Biologiacal Conservation, 120: Mathew, G., Rugmini, P. and Sudheendrakumar, V.V Insect biodiversity in disturbed and undisturbed forests in the Kerala part of Western Ghats, KFRI Res. Report, pp113. Mathew, G Documentation of forest insect diversity- Kerala scenario: An appraisal. Perspectives of Biosystematics and Biodiversity, T.C.Narendran Com. Volume Samuelsson, J., Gustafsson, L., Ingelog, T., Dying and dead trees a review of their importance for biodiversity. Swedish threatened species unit, Uppasala, Sweden, 109p. Schlyter, F. and Anderbrant, O Competition and niche separation between two bark beetles: existence and mechanisms, Oikos, 68: Siitonen, J Forest management, coarse woody debris and saproxylic organisms: Fennoscandian boreal forests as an example. Ecological Bulletins, 49: Speight, M.C.D Saproxylic invertebrates and their conservation. Nature and environment series No.42. Stratsbourg. Stebbling, F.G., Indian Forest Insects of Economic Importance. Clarendon Press, Oxford,pp Vaisanen, R., Bistrom, O. and Heliovaara, K Subcortical coleoptera in dead pines and spruces- is primeval species composition maintained in managed forests. Biodiversity and Conservation, 2: [MS received 18 December 2011; MS accepted 21 March 2012] Disclaimer: Statements, information, scientific names, spellings, inferences, products, style, etc. mentioned in Current Biotica are attributed to the authors and do in no way imply endorsement/concurrence by Current Biotica. Queries related to articles should be directed to authors and not to editorial board. 420