Tree species diversity and community composition in a human-dominated tropical forest of Western Ghats biodiversity hotspot, India

Tree species diversity and community composition in a human-dominated tropical forest of Western Ghats biodiversity hotspot, India

Ecological Complexity 7 (2010) 217–224 Contents lists available at ScienceDirect Ecological Complexity journal homepage: www.elsevier.com/locate/eco...

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Ecological Complexity 7 (2010) 217–224

Contents lists available at ScienceDirect

Ecological Complexity journal homepage: www.elsevier.com/locate/ecocom

Tree species diversity and community composition in a human-dominated tropical forest of Western Ghats biodiversity hotspot, India K. Anitha a,b,*, Shijo Joseph a,c, Robert John Chandran d, E.V. Ramasamy a, S. Narendra Prasad b a

School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala 686560, India Division of Landscape Ecology, Salim Ali Centre for Ornithology and Natural History, Anaikatty P.O., Tamil Nadu 641108, India c Department of Natural Resources, International Institute for Geoinformation Science and Earth Observation (ITC), 7500 AA Enschede, The Netherlands d Ashoka Trust for Research in Ecology and Environment, Royal Enclave, Srirampura, Jakkur Post, Bangalore 560064, India b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 17 February 2009 Received in revised form 2 December 2009 Accepted 4 February 2010 Available online 3 March 2010

The structure, function, and ecosystem services of tropical forest depend on its species richness, diversity, dominance, and the patterns of changes in the assemblages of tree populations over time. Long-term data from permanent vegetation plots have yielded a wealth of data on the species diversity and dynamics of tree populations, but such studies have only rarely been undertaken in tropical forest landscapes that support large human populations. Thus, anthropogenic drivers and their impacts on species diversity and community structure of tropical forests are not well understood. Here we present data on species diversity, community composition, and regeneration status of tropical forests in a human-dominated landscape in the Western Ghats of southern India. Enumeration of 40 plots (50 m  20 m) results a total of 106 species of trees, 76 species of saplings and 79 species of seedlings. Detrended Correspondence Analysis ordination of the tree populations yielded five dominant groups, along disturbance and altitudinal gradients on the first and second axes respectively. Abundant species of the area such as Albizia amara, Nothopegia racemosa and Pleiospermum alatum had relatively few individuals in recruiting size classes. Our data indicate probable replacement of rare, localized, and oldgrowth ‘specialists’ by disturbance-adapted generalists, if the degradation is continuing at the present scale. ß 2010 Elsevier B.V. All rights reserved.

Keywords: Primary forest species Generalist species Detrended Correspondence Analysis Disturbances Anaikatty hills

1. Introduction Research on tropical forests has been going on for several decades and yet we do not precisely understand their ecology (Hubbell and Foster, 1992). Tropical forests contain the most diverse plant communities on earth, with up to 473 tree and liana species coexisting in a single hectare (Gentry, 1982; Hubbell and Foster, 1986; Phillips et al., 1994; Givnish, 1999), but the mechanisms that maintain such high levels of tree diversity are not well understood. Biotic factors such as density dependent effects on seed and seedling survivorship and recruitment are known to be important in maintaining tree diversity in tropical moist forest (Janzen, 1970; Connell, 1971). Niche differentiation among tree species with respect to the availability of light and soil resources also contributes to the maintenance of tree diversity (Grubb, 1977;

* Corresponding author at: School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala 686560, India. Tel.: +91 481 2732620. E-mail address: [email protected] (K. Anitha). 1476-945X/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ecocom.2010.02.005

Silvertown, 2004). Although such evidence for the influence of ecological factors on species diversity and community structure has accumulated over the years, much of this understanding has come from studies conducted in old-growth forest that have seen little human activity in the recent past. Historically, most tropical forests have experienced varying levels of human activity and tropical forests today are being increasingly affected by expanding human populations, exploitation, fragmentation, and climate change. How these rapidly changing factors impact species composition, structure, and function of tropical tree communities is not well known and remain a critical gap in developing conservation plans for tropical biodiversity. Among tropical forest ecosystems, tropical dry forests are particularly threatened because of relatively high population densities that have led to agricultural expansion and increased human dependence for fuelwood, non-timber forest products, and grazing of livestock. Although communities have depended on forest ecosystems for long, changing socioeconomic conditions and traditional approaches for conservation of biodiversity have drawn little attention to the long-term sustainability of this human dependence on forest ecosystems. Biodiversity conservation needs

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to integrate the livelihoods of forest-dependent communities in a manner that does not erode biodiversity, but the mechanisms for achieving these twin objectives needs to be investigated and developed. In this paper we characterize the phytodiversity of the hills with special reference to species assemblages and regeneration status. We also address changes in compositional attributes of the tree community (species richness, diversity, assemblages and dominance of species), and evaluate regeneration status of the tree community by comparing the standing adult populations of tree species to the populations of recruiting seedlings and saplings. 2. Methods 2.1. Study site In this study we focus on tree diversity and community structure in a human-impacted tropical mixed dry deciduous forest landscape in the Nilgiri Biosphere Reserve (NBR) of the Western Ghats- Sri Lanka biodiversity hotspot in southern India. This region is recognized as one of the eight ‘hottest hotspots’ of biological diversity in the world (Myers et al., 2000) and among the 200 globally most important ecoregions (Olson and Dinerstien, 1998). The Western Ghats faces severe threats from human disturbance due to deforestation, developmental activities, conversion to plantations, and habitat fragmentation (Nair, 1991). Menon and Bawa (1997) estimated that between 1920 and 1990 forest cover in the Western Ghats declined by 40%, resulting in a four fold increase in the number of fragments and an 83% reduction in the size of forest patches. This is not surprising given that this region is having the highest human population density among the biodiversity hotspots (Cincotta et al., 2000) and one among four hotspots with high human population pressure (Shi et al., 2005). Anaikatty Reserve Forest (768390 to 768500 E and 11800 to 118310 N), an area of about 140 km2, is situated in the Coimbatore forest division of Tamil Nadu state, in southern India (Fig. 1) from an altitudinal range of 560–1600 m a.s.l. Anaikatty hills or reserve forest (administratively in Tamil Nadu state), situated at the foothills of the Nilgiri Biosphere Reserve and consists of southern dry mixed deciduous forest according to Champion and Seth’s (1968) classification of Indian forests. The Reserve Forest is

surrounded by the Palghat Forest division of Kerala state to the west, agricultural plains in the east, Palghat gap (35 km wide gap in the Western Ghats) in the south and Sathyamangalam and Nilgiri Forest Divisions in the north. The terrain is undulating with seasonal waterfalls and is the watershed of the River Bhavani. The climate of the area is semi-arid as it is located in the rain shadow part of the Western Ghats. The average rainfall was 668 mm per year and maximum temperature varied from 29 to 37 8C for a period of 1996–2006 (Mukherjee, 2007). The Northeast monsoon contributes more than half of the total annual rainfall of the Anaikatty Hills. Monthly mean relative humidity fluctuated between 32% and 92% (Eswaran, 2006). Anaikatty Hills is comprised of largely rocks of Archean origin. In most parts soil comprised hard gravel and in some places it is red loamy. In plains soil is reddish brown soil and clay. Soil is generally devoid of humus (Mukherjee, 2007). This area, which was under different royalties till the 19th century, had dense forests where the economically backward people practiced shifting cultivation and the well to do people indulged in hunting. Timber extraction (selective logging) began on a commercial scale in some parts of the hills in late 20th century and the extraction of non-timber forest products (NTFP) too increased. Even though, selective logging has been prohibited in early 1970s, human activities from the surrounding socioeconomically backward population continued to impact the area. (As per the 2001 census, the average per capita income of respondents was less than one third of the state) (Purushothaman, 2004). Anitha et al. (2007, 2009) pointed out high level of disturbances from the surrounding population such as cattle grazing, collection of leaves and branches for livestock, timber extraction and NTFP collection. 2.2. Data collection We collected data from forty randomly selected plots of 50 m  20 m size. In each of these 0.1 ha plots, all woody plants with 20 cm Girth at Breast Height (GBH) (1.3 m) were identified at species level, counted, and measured for height (hypsometer) and GBH using a tape measure. Four sub plots of 5 m  5 m were laid in a zig-zag pattern (Fig. 2) within each 50 m  20 m plot for recording saplings (individuals with 10 to <20 cm GBH). Nine plots

Fig. 1. Location of Anaikatty Reserve Forest in Tamil Nadu state, India.

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3. Results 3.1. Floristic structure, species abundance, and species diversity

Fig. 2. Sampling method adopted for trees (50 m  20 m), saplings (5 m  5 m) and seedlings (1 m  1 m). A zig-zag pattern of sampling scheme was implemented for saplings and seedlings for representing spatial heterogeneity of large plot.

(1 m  1 m) were laid on the corners of sub plots and also one at the centre for recording seedlings (individuals with 30 cm height). The seedlings <30 cm height were considered ephemeral and not counted. Herbarium specimens of trees were prepared and identified with the help of floras and confirmed with Botanical survey of India. The spatial location (latitude, longitude and altitude) of each plot was measured using a Global Positioning System (GPS) having an accuracy of 10 m. In addition, indicators of disturbance such as cutting, lopping, cattle grazing, nearness to human habitation, and collection of non-woody forest products were also noted.

A total of 40 plots were analysed for trees, 160 plots for saplings, and 360 plots for seedlings. In total, 2255 individuals (20 cm GBH) belonging to 106 tree species (78 genus and 31 families) were recorded from 40 plots. In the tree database, Pleiospermum alatum accounted for the maximum number of individuals (n = 230, 10.3%) followed by Albizia amara (n = 211, 9.45%) and Nothopegia racemosa (n = 121, 5.42%). Out of 106 tree species, 27 species were occurred in only one plot and 12 species were observed in two plots. Fourteen species were represented by single individuals (singletons) while another 12 species had only two individuals in all plots studied. 3.2. Species accumulation curve and sampling We obtained a species accumulation curve for tree species by computing the cumulative number of species encountered with increase in the number of plots (or total area) sampled. We laid plots randomly and repeated this procedure 50 times to obtain the 95% confidence intervals of species numbers as a function of sampled area. The computed curve approached an asymptotic value within 40 plots, which suggests adequate sampling within the study region (Fig. 3). 3.3. Tree species assemblages

2.3. Data analysis Species richness, species diversity (Shannon–Wiener diversity index) and dominance (Simpson index) were calculated as per Magurran (1988). Population structure of the tree species (GBH  20 cm) was characterised as the size distribution using GBH classes. Detrended Correspondence Analysis (DCA) was used on the tree species database for identifying the major species assemblages in the area. We also computed the Importance Value Index (IVI) for each species, which is expressed as the sum of relative density, relative dominance and relative frequency of the species in and among plots (Curtis, 1959). Based on the IVI values, we identified species associations within these assemblages and characterized each community by these species associations. Regeneration status of the forest was examined by comparing different attributes (species richness, diversity and assemblages) of present tree populations (large trees) with the regenerating populations (seedlings and saplings) of tree species. All the analyses were carried out using the packages EstimateS (Colwell, 2005), Species Diversity and Richness (Henderson and Seaby, 2001), PC-ORD (McCunne and Mefford, 1999), and Microcal (TM) Origin (R) (1999).

Detrended Correspondence Analysis ordination was performed on the tree database with a final data matrix of 106 species and 40 plots. The first DCA axis accounted for 39.5% of the variation in species composition among the plots and the second axis accounted for 27.2% of the variation. Together the first two axes accounted for over 2/3 of the variation in species composition among plots. The contributions of the third and greater axes declined rapidly, with the third DCA axis accounting for only 3.2% of the variation in species composition. Therefore we considered only the first two DCA axes in determining species assemblages. The first and second DCA axes were strongly correlated with the disturbance and elevation gradients respectively, and five dominant groups of species were identified along these gradients (Fig. 4). These species assemblages were identified based on species composition and on Champion and Seth’s (1968) classification of vegetation types. Further, we identified the top three dominant species of each assemblage using the IVI and classified each species assemblage as a major association of these species. The five species assemblages or groups are the following: Group I: This species assemblage closely corresponds to the West Coast Tropical Semievergreen Forest (2A/C2) of Champion

Fig. 3. Species accumulation curve in Anaikatty reserve forest, India. The middle curve represents the actual number of species observed, the upper and lower curve represents 95% confidence intervals.

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Fig. 4. Tree species assemblages in Anaikatty reserve forest derived from Detrended Correspondence Analysis. Five groups were identified based on the disturbance in the first axis and elevation on the second axis.

and Seth’s classification (1968). In our study area, it is dominated by the N. racemosa–Maba neilgherrensis–Syzygium densiflorum species association (IVI—13.82, 5.83 and 5.11 respectively). The other major species in this group are Syzygium cumini, Neolitsea scrobiculata, Glycoptalum lawsonii, Goniothalamus sp., Mimosops elangi, Mallotus philippensis, Acacia sinuata, Dalbergia sissoids, Limonia acidissima, Cordia obliqua, Manilkara roxburgiana, Clausena dentata, Diospyros ovalifolia, Lannea coromandalica, Loeseneriella obtusifolia and Clausena heptaphylla. Typically, the West Coast Tropical Semievergreen Forest occurs in relatively undisturbed areas at an altitudinal range of 950–1500 m a.s.l. Climatically these forests are characterized by high humidity and relatively low temperatures and characterized by scanty shrub layer, lower forest gaps and dense leaf litter. Geographically, the area can be distinguished by steep slopes and mountain folds and they form the catchment area for major rivulets. Group II: The second group corresponds to Southern Moist Mixed Deciduous Forest (3B/C2) as per Champion and Seth’s Classification and is characterized by the presence of Tectona grandis, Anogeissus latifolia, Terminalia chebula, Bridelia retusa, Ficus bengalensis, Semecarpus anacardium, Pterocarpus marsupium, and Santalum album. The area is dominated by A. latifolia–P. marsupium–S. anacardium associations (IVI—7.46, 5.93 and 1.23 respectively). The topography is typically characterized by gentle slopes with good canopy cover at an altitude of 800– 950 m a.s.l. Group III: This formation is distinguished by species such as Premna tomentosa, Dalbergia paniculata, Acacia leucopholea, Acacia sp., Bauhinia racemosa, Ixora pavetta, Strychnos potatorum, Maytenus emarginata and Ficus religiosa, and corresponds to Southern Dry Mixed Deciduous Forest (5A/C3). The area is characterized by B. racemosa–I. pavetta–P. tomentosa (IVI—9.26,

4.21 and 2.22 respectively). This is found on altitudinal range of 700–800 m and experiences a strong dry season. Group IV: This group is characterized by the presence of species such as Atlantia racemosa, Celtis philippensis, Pachygone ovata, Bombax ceiba, Cansjera rhedii, Phyllanthus polyphyllus and Euphorbia antiquorum and match up with Champion and Seth’s Dry Deciduous Scrub (5A/DS1). This forest is a dominant association of P. polyphyllus–A. racemosa–C. philippensis species (IVI values of 7.95, 7.57 and 2.71 respectively). Group V: This group is mainly a composition of thorny shrub species such as Randia dumetorum, Dichrostachys cinera, Acacia planifrons, Acacia canescens, Flacourtia indica, Grewia flavescens, Pleiospermium alatum, Mundulea sericea, Premna latifolia, Maba buxifolia, Tamarindus indica, Chloroxylon swietenia, A. amara, Zizhyphus oenoplia, Z. mauritiana, Capparis sepiaria, Ehretia ovalifolia and Capparis grandis and it corresponds to Southern Thorn Scrub (6A/DS1) of Champion and Seth’s classification. This is a major habitat in the area, which occurs at low altitudes and experiences high levels of disturbance due to grazing by livestock and collection of fuelwood by local communities. The major species association is A. amara–P. alatum–Mab buxifolia (IVI values of 29.08, 17.59 and 7.58 respectively). Thorny evergreen shrubs constitute the major growth form and although dense patches can be found, the formation is mostly open. 3.4. Tree regeneration 3.4.1. Population structure of the regenerating classes We found a total of 117 woody species from the study site. Of these 106 species were found among trees (20 cm GBH), 76 species were found among saplings and 79 species among seedlings. Thus many species were not encountered in the sapling

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species of Anaikatty hills has an importance value of 10.20% for trees, 16.59% for saplings and 17.44% for seedlings. In the tree population P. alatum (10.2%), A. amara (9.36%), N. racemosa (5.37%) were the species dominated where as in sapling population dominant species found to be A. canescens (16.59%), Pavetta indica (10.90%), Zizhyphus mauritiana (8.29%) and in case of seedlings A. canescens (17.44%), P. alatum (7. 07), and Bambusa bambos (6. 60%). In trees 50 species formed 90% of the population, 28 species each in the case of saplings and seedlings.

Fig. 5. Comparison of the dominance–diversity curves for trees, saplings and seedling of Anaikatty hills. Species rank plotted on the abscissa, and percentage of total abundance on the ordinate derived Fisher’s logarithmic series model.

or seedling stages. In total 80 species were present both adult and recruiting populations, while nine species were present only as juveniles, and 26 species were found only in adult size classes. 3.4.2. Dominance–diversity curve Dominance–diversity curve followed S-shaped log series model, which is characteristic of species-rich communities (Fig. 5). Different communities produce characteristic dominance–diversity curves when the species rank plotted on the abscissa, and percentage of relative abundance (log-transformed) on the ordinate. The rank-1

Table 1 Species richness and diversity indices of different regenerating classes in Anaikatty reserve forest, India. Regenerating classes

Species richness (2nd order Jackknife estimate)

Shannon index

Simpson index

Seedling Sapling Trees

111 109 198

3.36 3.32 3.84

16.22 15.92 28.09

3.4.3. Species diversity of the regenerating classes Since the sample sizes were different for trees, saplings and seedlings (though we tried to give spatial representation by implementing the zig-zag pattern sampling scheme), we have used a rarefaction based on a second-order Jackknife estimate to calculate the different diversity indices (Table 1). The highest values observed for trees followed by seedling and sapling. The One-Way ANOVA was carried out in species richness (F = 42.41851, p < 0.005) and Shannon index (F = 47.474, p < 0.005) and Simpson index (F = 538.003, p < 0.005) for all the three classes, which revealed that the means are significantly different at 95% confidence limits. The analysis showed that the future generation (recruiting class/sapling + seedling) may be less diverse than present generation. 3.4.4. Species assemblages of the regenerating population For identifying species assemblages in the regenerating populations, we carried out DCA ordination by pooling the saplings and seedlings together. The obtained ordination (Fig. 6) was poorer than the one obtained for trees (Fig. 4) and species assemblages were not as clearly identifiable as for the tree populations. The first DCA axis accounted for 18.4% of the variance in the dataset, while the second axis accounted for a small 1.1% of the variance in the data. Post-hoc correlations with environmental data reveal that the first axis essentially captures the disturbance gradient. Using only the first DCA axis, we identified two major groups and the rest of the groups showing no clear patterns: Group I: This group is a mixture of typical semievergreen species like C. obliqua, Goniothalamus sp., P. ovata, S. cumini, Albizia sp., Cassine paniculata with early-successional elements such as A. lebbeck, Capparis brevispina, D. ovalifolia, A. sinuata, and A. racemosa.

Fig. 6. Species assemblages of recruiting population in Anaikatty reserve forest derived from Detrended Correspondence Analysis. Two major groups and a few minor groups were observed.

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Group II: The second group is a mosaic of typical moist deciduous species like T. grandis, A. latifolia, B. retusa, C. rhedii, Premna latifolia with dry deciduous species (B. ceiba, P. polyphyllus, I. pavetta, C. grandis, A. amara, Strebulus asper, M. sericea, C. swietenia, Cordia monoica, Gyrocarpus americanum) and scrub forest species (R. dumetorum, D. cinera, C. sepiaria, Z. oenoplia, P. alatum, A. canescens, M. buxifolia). 4. Discussion 4.1. Sampling scheme and methodology The primary aim of the study was to understand the structure of vegetation in a landscape where human disturbance is predominant. By considering the sampling efforts in an undulating terrain, first priority was given to optimize sampling scheme. Relatively large sample plots (0.1 ha) were implemented in tree population census. At the same time enumeration of saplings and seedlings in these plots were found cumbersome. Therefore, a zig-zag pattern of sampling scheme (for representing spatial heterogeneity in the large plot) which accounts 10% area for saplings and 1% area for seedlings were implemented (see Fig. 2). The next question to be addressed was whether the comparison of saplings and seedlings with trees is valid or not, though spatial representation was ensured in the sampling scheme. Therefore, a rarefaction (Jackniffe estimate) method which could reduce the uncertainty due to unequal sample size was employed for valid comparison of adult population with regenerating population. The selection of DCA for ordination analysis was also purposefully. The ability of DCA to efficiently order species along compositional gradients (Ejrnaes, 2000) was the major reason for selecting DCA. Moreover, the algorithm has the capability to resolve the artificial distortion (the so-called ‘arch-effect’) of the underlying correspondence analysis (CA) (McCunne and Mefford, 1999). NMS is another interesting ordination analysis which uses an iterative method that arranges entities into positions in which the rank order of their distances corresponds to the rank order of their similarities in real world (Clarke, 1993). Unlike DCA, its primary goal is not to reveal gradients in the data but to depict similarities. The direction of the NMS axes is arbitrary and they do not necessarily reflect any gradients of particular importance. In the present study, we were interested not only to derive the species similarities but also to identify the gradients in the floristic composition, which could be useful in implementing the management actions. 4.2. Tree regeneration DCA ordination and post-hoc analyses on environmental correlations uncovered the significant environmental determinants of plant community structure in our study region. We found that tree population assemblages were determined by both altitude and disturbance gradients, while species assemblages of the regenerating populations were primarily influenced by disturbance. We could identify only two groups in the regenerating tree populations, the first one mixture of semievergreen and earlysuccessional species, and the second, a mixture of deciduous and scrub species. The presence of scattered minor groups indicates the possibility of breaking up of continuous large habitats into smaller habitats. The probable effects involve the creation of an archipelago and thereby metapopulation of species. Subsequently, the persistence of species will be lower in this habitat (Diamond, 1976; Tilman, 1994) and is susceptible to demographic extinction pressure (Shaffer, 1981) and environmental stresses (Simberloff and Abele, 1976). The future community structure and composition could be indicated by the regeneration status of the tree species and the life

histories of the dominant regenerating populations. Community structure data show that overstory species such as A. amara, N. racemosa, P. alatum are being replaced by scrub forest species such as Pterolobium hexapetalum, A. canescens and G. flavescens primarily due to disturbances. Lower regeneration of most of the species might be due to the cumulative effects of disruption of key ecological processes such as pollination and seed dispersal in association with human induced disturbances (see Appendix A for checklist of trees, recruiting class and its regeneration ratio). Our previous studies indicated that the tree species diversity has a negative correlation with disturbance factors (see Anitha et al., 2009). The major disturbance parameters were cutting and illicit felling, grazing, lopping and fuel wood collection and extraction of non-timber forest products. Landscapes exposed to erratic and large-scale disturbances harbor a high proportion of wind-dispersed seeds (Grime, 2001). Autochrous plants such as P. hexapetalum, A. canescens showed higher recruitment in Anaikatty Reserve Forest, supporting of this argument. In dry tropical forest free-range grazing is detrimental to seedling recruitment of most species and could potentially shift the composition of soil seed bank in favour of weedy grasses and herbs (Khurana and Singh, 2001). Seedling establishment has been low in Phyllanthus emblica, a species which is sensitive to shade, while survival and growth of seedlings of P. marsupium and T. chebula appear to be adversely affected by grazing (Nair, 2000). Extensive collection of fruits of the species such as A. sinuata, T. chebula, Phyllanthes emblica, Sappindus emarginata, C. grandis were observed from Anaikatty reserve forest (Rajasekaran, 2000). Many studies pointed out that low seedling and sapling densities in intensively harvested areas compared to other areas where harvesting pressure is minimum (Shaankar et al., 2001; Shahabuddin and Prasad, 2004). Habitat modifications by anthropogenic activities could result in the disruption of key ecological processes such as pollination and seed dispersal (Howe, 1984; Hamilton, 1999). Recent experiments have shown that the functional diversity of pollinators can affect diversity in plant communities (Biesmeijer et al., 2006). During our plant community monitoring programme we encountered mass flowering of Strobilanthes spp. and Stenosiphonium cordifolium during 2004 through 2006 (see Anitha and Prasad, 2007). The major floral visitors of these species were bees. Low recruitment of bee-pollinated species such as A. amara, Acacia chundra, A. leucopholea, C. obliqua, T. chebula, Diospyros montana, P. emblica, B. racemosa, Lannea coromandelica, S. anacardium, Cassia fistula, P. marsupium, S. potatorum, Gmelina arborea, and P. tomentosa could be explained by the pollinator deficiency followed by mass flowering. Ganesh and Devy (2000) also reported the reduced fruit setting of certain tree species because of pollinator deficit followed by mass flowering. Raju and Rao (2006) observed that in absence of Xylocopa bees (large carpenter bees); most of the plant species adapted to pollination by Xylocopa bees such as B. racemosa, C. fistula do not fruit. At same time, P. hexapetalum which is a bee-pollinated species, found to be flowering in April-June, has shown good regeneration due to its temporal difference in flowering from other species, which might be helping it to escape from pollinator deficiency. The lower regeneration success of species like A. amara, A. chundra, A. leucopholea, B. retusa, C. obliqua, D. montana, P. emblica, B. racemosa, Ficus microcarpa, F. bengalensis, Ficus virens, S. anacardium, C. fistula, P. marsupium, S. potatorum, G. arborea, T. chebula, P. tomentosa, S. cumini, I. pavetta, and Zizyphus mauritiana could possibly due to the lack of or due to reduced numbers of key animal species in the study area as these species depend on specialized vectors for their seed dispersal (Murali and Sukumar, 1994; Balasubramanian and Bole, 1993). It was noted that animal movements i.e., small and large frugivores mammals such as bears and civets were rare in the study area due to prevalent human

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presence in the area. Statistics shows that more than 75% of the woody plants in tropical forests are characterized by animal dispersal (Janzen and Vazquez-Yanes, 1991; Eilu and Obua, 2005) and dispersal limitation has adverse effect on seedling distribution (Dalling et al., 1998). In comparison to species dispersed by ‘specialised vectors’, pioneer species showed good regeneration as they are dispersed by ‘generalised vectors’ in the area. Also, higher regenerating ratio was observed for P. hexapetalum i.e., 1:37 followed by A. canescens i.e., 1:26, both with autochrous dispersal i.e., explosive- dispersed mechanism where the dehiscing pod releases the seeds. 5. Conclusion Results pointed out that regeneration was affected in Anaikatty Hills by various processes. It would be envisaged that rare, localized, and old-growth ‘specialists’ may face ‘local extinction’ or replacement by disturbance-adapted generalists i.e., pioneer or secondary species, if the human disturbance is continuing at the present level. This may gradually lead to the transformation of five distinguished vegetation types into two major types and a few minor types in which the species composition would be a mixture of all five types i.e., a mosaic of different successional stages. Species with higher number of individuals in the recruiting class expected to be dominant in the near future. This structural degradation and species loss may affect the functional qualities of the habitats, if it is not reversed. Therefore, the paper calls for an urgent conservation plan to avoid further erosion of biological diversity. Acknowledgment We express thanks to Dr. A. P. Thomas, Director, School of Environmental Sciences, Mahatma Gandhi University for extending his support and encouragement. We sincerely thankful to Director, SACON for permission to carry out the work and Lalitha Vijayan, P. Balasubramanian and Liza S. Comitha for beneficial discussions, Murugan for identifying the specimens and Muragavel for the assistance in the field. Doctoral fellowship (KSCSTE research fellowship) by Kerala State Council for Science, Technology and Environment, Government of Kerala to first author is greatly acknowledged.

Appendix A. Details of tree, recruiting class and the ratio observed in Anaikatty reserve forest, India. Species Pterolobium hexapetalum Acacia canescens Grewia flavescens Opilia amantacea Clausena dentata Maytenus emarginata Pavetta indica Capparis sepiaria Santhalum album Premna latifolia Grewia bracteata Clausena heptaphylla Ixora pavetta Cansjera rheedii Litsea deccansis Phyllanthus polyphyllus Memecylon edule Stereospermum personatum Cordia obliqua Clerodendron seratum

Tree 2 32 5 2 8 5 65 8 10 1 11 51 34 9 1 69 26 25 1 1

Recruiting class

Ratio

73 821 112 32 63 32 409 44 52 5 52 237 155 39 4 271 98 90 3 3

1:37 1:26 1:22 1:16 1:8 1:6 1:6 1:6 1:5 1:5 1:5 1:5 1:5 1:4 1:4 1:4 1:4 1:4 1:3 1:3

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Appendix A (Continued ) Species

Tree

Recruiting class

Ratio

Goniothalamus sp Murraya paniculata Unidentified 1 Mundulea sericea Randia dumetorum Acacia sinuata Ehretia ovalifolia Atlantia racemosa Acacia sp Loeseneriella obtusifolia Zizhypus oenoplia Neolitsea scrobiculata Gmelina arborea Pachygone ovata Cassine paniculata Maba buxifolia Flacourtia indica Nothopegia racemosa Pleiospermum alatum Canthium dicoccum Albizia sp Bridelia retusa Capparis brevispina Diospyros ovalifolia Grewia orbiculata Tectona grandis Randia malabarica Terminalia chebula Dalbergia paniculata Euphorbia antiquorum Unidentified 2 Gyrocarpus amaericanus Maba neilgherrensis Albizia lebbeck Sappindus emarginatus Commiphora caudata Bombax ceiba Dichrostachus cinera Ficus religiosa Unidentified 3 Syzygium cumini Cordia monoica Unidentified 3 Unidentified 4 Alphonsea sclerocarpa Chloroxylon swietenia Syzygium densiflorum Cassine glauca Manilkara roxburghiana Bauhinia racemosa Unidentified 4 Glyptopatalum lawsonii Mallotus philippensis Premna tomentosa Diospyros montana Pterocarpus marsupium Ceiltis philippensis Anogeissus latifolia Cassia fistula Unidentified 5 Crateva religiosa Dalbergia latifolia Dalbergia sissoides Unidentified 6 Ficus bengalensis Ficus microcarpa Ficus talbotii Ficus virens Phyllanthus emblica Plerostylia oppositifolia Tamarindus indicus Unidentified 7 Semecarpus anacardium Unidentified 8 Strichnos potatorum Zizhyphus mauritiana Zizhyphus xylopyrus

11 20 26 10 8 12 10 71 4 3 41 17 7 4 7 82 15 121 230 81 8 4 8 39 4 2 27 9 11 9 3 20 64 5 51 13 2 4 2 2 6 69 14 7 39 20 41 18 9 68 15 5 19 22 10 39 14 70 2 1 1 3 1 4 2 4 3 1 1 1 2 3 9 1 12 2 11

31 55 77 24 19 28 21 144 8 6 80 32 13 7 12 132 24 158 294 97 8 4 8 39 4 2 21 7 8 6 2 13 41 3 29 7 1 2 1 1 3 33 4 2 11 5 10 4 2 15 3 1 3 3 1 3 1 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1:3 1:3 1:3 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:2 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 1:1 – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

K. Anitha et al. / Ecological Complexity 7 (2010) 217–224

224 Appendix A (Continued ) Species

Tree

Acacia chundra Acacia leucopholea Acacia planifrons Albizia amara Canthium parviflorum Cycas circinalis Capparis grandis Helictrose isora Lannea coromandalina Limonia acidiccima Litsea laevigata Mimosops elengi Unidentified 9 Ochna wightiana Unidentified 10 Securinega leucopyrus Sterebulus asper Unidentified 11

1 7 3 211 0 0 40 0 1 2 0 7 1 0 0 0 0 0

Recruiting class 0 0 0 70 3 3 14 26 0 0 2 0 0 1 3 95 5 2

Ratio – – – – – – – – – – – – – – – – – –

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