plant biodiversity inventory and conservation of two tropical dry...

Plant biodiversity inventory and conservationof two tropical dry evergreen forestson the Coromandel coast, south India

N. PARTHASARATHY and R. KARTHIKEYANSalim Ali School of Ecology and Environmental Sciences, Pondicherry University, Pondicherry 605 014, India

Received 4 September 1996; revised and accepted 9 December 1996

Species diversity, population structure, abundance and dispersion patterns of all woody plants

³10 cm gbh were inventoried in two 1-ha plots of tropical dry evergreen (sacred grove or temple)forests at Kuzhanthaikuppam (KK) and Thirumanikkuzhi (TM) on the Coromandel coast of southIndia. Site KK is a stunted forest (average tree height ca 6 m) and TM a tall forest (average tree

height ca 10 m). A total of 54 species (in 47 genera and 31 families) were recorded. Species richnessand stand density were 42 and 38 species and 1367 and 974 individuals ha)1 respectively for the sitesKK and TM. About 50% of the total species were common to both the sites. Site TM is twofold

more voluminous (basal area 29.48 m2 ha)1) than KK (basal area 15.44 m2 ha)1). Nearly one thirdof the individuals are multi-stemmed in the low-statured site KK whereas one fourth of the treedensity is multi-stemmed in TM. Species abundance pattern varied between the two sites. The

abundance of three species in KK and two species in TM is pronounced.Memecylon umbellatum, themost abundant species contributing to one third of total stand density in KK, is least represented inTM. Species richness, density and diversity indices decreased with increasing girth threshold. Mostspecies exhibited clumped dispersion of individuals both at 0.25 and 1-ha scales. Population struc-

ture for girth frequency is an expanding one for both the sites, except for basal area distribution inKK. Variations in plant diversity and abundance are related to site attributes and human impacts. Inthe light of habitat uniqueness, species richness and sacred grove status, the need for conservation is

emphasized.

Keywords: tropical forest; plant biodiversity; tree density; population structure; conservation.

Introduction

Many of the quantitative plant biodiversity inventories have been conducted in species-rich forests and data on species-poor forests are inadequate (Johnston and Gillman, 1995).Tropical dry evergreen forests are fairly ill-known forest types even within the country andare species-poor when compared to tropical wet forests. These unique, nearly two-layeredevergreen forests, occurring in drier areas experiencing about six dry months in a year,harbour largely evergreen species with a few deciduous and brevi-deciduous species. In theCoromandel-Circar (East coast of India) the remaining true tropical dry evergreen forests(those not degraded to thorny scrub types) occur presently in the form of sacred groves or`temple forests' i.e. patches of natural climax forests preserved as a result of religious beliefof the local people, such as that resource extraction from the grove would bring them thewrath of the deity. Although complete details on the total number of sacred groves are notavailable (Gadgil and Vartak, 1975), Mitra and Pal (1994) have prepared an account of thesacred groves of India. They occur chie¯y in Andhra Pradesh, Assam, Bihar, Karnataka,

0960-3115 Ó 1997 Chapman & Hall

Biodiversity and Conservation 6, 1063±1083 (1997)

Kerala, Madhya Pradesh, Maharashtra, Rajasthan and Tamil Nadu. Gokhale et al. (inpress) inventoried tree diversity and growth rates in selected sacred groves ofMaharashtra. Induchudhanan (1996) studied the ecology of sacred groves in Kerala.

The tranquil sacred groves of Tamil Nadu have not been studied for quantitativebiodiversity except for a few recent studies (Sethi, 1993; Visalakshi, 1995), and a fewqualitative ¯oristic surveys. Murphy and Lugo (1986) reviewed the climate variation,structure and functioning and human interaction in the dry tropical forests.

It is necessary to determine tree diversity and dispersion for conservation and man-agement of forest bioresources. The objectives of the present study were to investigate theextent of tree and liana species richness, density and their dispersion pattern in two dryevergreen forests which vary in their topographic features, forest stature and the extent ofhuman disturbance, with a view to generating baseline data of use to conservation.

Materials and methods

Study area

The present study was conducted in two tropical dry evergreen forests, namely Kuzh-anthaikuppam (KK) and Thirumanikkuzhi (TM) which are 6 km apart and located nearCuddalore town on the Coromandel coast of Tamil Nadu, south India. They occupy anarea of about 1.2 ha and 1.6 ha respectively. Site KK lies at 11°45¢N. Lat. and 79°38¢ E.Long. and TM at 11°43¢N. Lat. and 79°41¢E. Long. (Fig. 1). These forests are sacredgroves or temple forests. They encompass a primitive form of Ayyanar temple well withinthe forest. The granite idols of the presiding deities (surrounded by a brick hood-likestructure in site KK but open to sky in site TM with a surrounding knee-high wall), statuesof huge horses (varying in number from two to four) with their assistants and soldiers atthe entrance of the grove, are part of the temple. The local people worship at these`temples' mostly on Mondays, but peak seasons for visits include Mondays fromNovember to February and in June±July every year. Site KK is more heterogeneous interrain with a stream ¯owing within the plot (Fig. 1) while TM has a uniform level terrain.

This part of the country is characterized by a hot, maritime climate experiencing anarrow daily range of temperature, humid weather and moderate rainfall. There is no cleardemarcation of seasons. The climate is tropical and dissymmetric with the bulk of rainfallreceived during October±November due to depressions and cyclones formed in the Bay ofBengal, and little rainfall during June to August. The mean annual rainfall during the 25year period 1971±1995 is 1258 mm and the mean number of rainy days for the same periodis 58. Dew is an important source of moisture from late October to March. October toNovember constitute the north-east monsoon period. December to February is mildly coldalthough there is no real winter. Summer lasts from March to May followed by south-westmonsoon up to September.

Soils are red ferralitic, belonging to the Cuddalore sandstone formation of the Mioceneperiod (Meher-Homji, 1974). It is red ferruginous to greyish brown in KK i.e. the ridgesharbour hard, compact, red ferruginous soil while greyish sandy soil with alluvial depositscovers the ¯at terrain. Soil in TM is more or less uniform alluvium overlying theCuddalore sandstone formation. The physico-chemical characteristics of soils are pro-vided in Table 1.

1064 Parthasarathy and Karthikeyan

Figure 1. Map indicating (a) the location of study sites near Cuddalore town in Tamil Nadu, south

India and (b) a crude toposheet of study sites Kuzhanthaikuppam (KK) and Thirumanikkuzhi (TM)dry evergreen forests.

Plant diversity in tropical dry evergreen forest 1065

The vegetation in this part is described as tropical dry evergreen forest (Champion andSeth, 1968; Meher-Homji, 1974; Rao and Meher-Homji, 1993), degraded to thorny scrubdue to anthropic activities in various areas. Our study areas harbour fairly intact tropicaldry evergreen forests and this type has been little studied (Champion and Seth, 1968).Understorey is comparatively denser in TM, composed mostly of the shrub Miliusamontana, the undergrowth is formed by Sanseveria roxburghiana, Theriophonum spp.,Selaginella sp. and thalli of Riccia sp., particularly following the monsoon, besides a fewephemerals. Site KK is relatively sparse in understorey and undergrowth. Many treesharbour epiphytic lichens on their boles, branches and twigs, and leaves bear epiphylls inTM. Site KK harbours a stunted forest with an average tree height of about 6 m whereasTM is comparatively tall forest with an average height of 10 m.

Among fauna, major vertebrates include babblers, bulbuls, cuckoos, doves, ¯ower-peckers, jungle crow, koel, treepie, parakeet, sunbird, warblers; mammals include bats,Indian hare, ®eld rats, jackal, mongoose, palm civet, small Indian civet, palm squirrels andwild cat, many of which are involved in seed dispersal. Both sites KK and TM are about 6km away from human habitation and surrounded at least on one side by agricultural landwith road on the other side. Fuelwood extraction, letting cattle inside the grove for grazingand browsing, and collection of edible fruits (Syzygium cumini, Glycosmis pentaphylla, etc.)during fruiting seasons are some of the human activities. Site TM is comparatively lessfrequented and thus less disturbed than KK.

Methods

Two 1-ha square plots were established, distributed one each in site KK and TM. Fieldwork on quantitative enumeration was carried out in May 1995. This was facilitatedthrough previous botanical exploration conducted from October 1993 to March 1995.

The 100 ´ 100 m plot was subgridded into 10 ´ 10 m as workable units. All living treesand lianas of ³10 cm gbh were identi®ed and their girth measured at 1.3 m from groundlevel. This girth threshold was chosen considering the low stature of the dry evergreenforest. For multi-stemmed trees, bole girths were measured separately, basal area calcu-lated and summed.

Table 1. Soil characteristics of Kuzhanthaikuppam (KK) and

Thirumanikkuzhi (TM) study sites on the Coromandel coast ofsouth India

Site

Variable KK TM

Water holding capacity (%) 36.33 28.65pH 5.0 5.8Organic carbon (%)a 2.33 2.03Total nitrogen (%)b 0.399 0.226

Total phosphorous (lg g)1)c 1016.0 405.0

Analytical methods:aKalembasa and Jenkinson (1973)bHesse (1971)cAllen et al. (1986)


Data analysis

For species diversity and evenness, Shannon-Weiner index (H0), Simpson's index (k), (as inMagurran, 1988), Hill diversity (Hill, 1973) and hierarchical richness index (HRI) (French,1994) were calculated.

Relative density, relative frequency, relative dominance and importance value index(IVI) were calculated according to the formulae of Cottam and Curtis (1956). Species±areacurve was plotted by sequential arrangement of 100 ´ 10 m2 subplots. Distributionalpatterns of species were determined based on quadrat count method using standardizedMorisita's index as per Krebs (1989).

Results

Species richness, diversity and evenness

The 2-ha dry evergreen forest inventory yielded a total of 54 woody species of ³10 cm gbhwhich belonged to 47 genera and 31 plant families (Tables 2 and 3). Species richness was42 and 38 respectively for the sites KK and TM. Nearly 50% of the species (i.e. 26) werecommon to both the sites. The assemblage of evergreen species with only a few deciduousones is notable. Out of the 54 species only two tree species, namely Lannea coromandelica

Table 2. Consolidated details of quantitative plant biodiversity inven-

tory of a 2-ha sacred grove dry evergreen forest distributed 1 ha each inKuzhanthaikuppam (KK) and Thirumanikkuzhi (TM) sites on theCoromandel coast of south India

Parameter KK TM Total

Species richness 42 38 54Number of families 26 26 31Number of genera 37 35 47

Diversity indices(1) Shannon-Weiner 2.3564 2.5700(2) Simpson 0.1733 0.1251

(3) Hierarchical richness 6724 5507index

(4) Hill diversity 1 42 38

Hill diversity 2 10.5531 13.0658Hill diversity 3 5.7687 7.9960

(5) Evenness index 1 0.63045 0.70651Evenness index 2 0.25126 0.34384

Evenness index 3 0.23300 0.32610Evenness index 4 0.54660 0.61200Evenness index 5 0.49920 0.57980

Stand density (no. ha)1) 1367 974 2341Stand basal area (m2 ha)1) 15.44 29.48 44.93Number of liana species 16 13 20

Density of lianas 117 131 248Number of thorny species 9 11 14Number of species 430 232 662multi-stemmed


Table 3. Population density (site-wise and total) of woody plants (³10cm gbh) in KK and TM dry

evergreen forest sites, south India

Family and species KK TM Total

Anacardiaceae1. Lannea coromandelica (Houtt.) Merr. 1 1

Annonaceae2. Miliusa montana Gard. ex J. D. 13 9 22

Hook. & Thoms.

Arecaceae3. Borassus ¯abellifer L. 1 1Boraginaceae

4. Cordia obliqua Willd. 3 3Caesalpiniaceae5. Cassia ®stula L. 1 1

6. Pterolobium hexapetalum (Roth) 3 3Sant. & Wagh

Capparaceae7. Cadaba trifoliata (Roxb.) Wight 13 12 25

& Arn.8. Capparis brevispina DC. 7 10 179. C. sepiaria L. 2 2

10. C. zeylanica L. 3 9 12Celastraceae11. Maytenus emarginata (Willd.) 1 1

Ding Hou12. Reissantia indica (Willd.) Halle 3 7 1013. Salacia chinensis L. 3 3Clusiaceae

14. Garcinia spicata (Wight & Arn.) 65 21 86J.D. Hook

Combretaceae

15. Combretum albidum G. Don 51 57 108Convolvulaceae16. Ipomoea sp. 4 4

Ebenaceae17. Diospyros ebenum Koen. 103 17 12018. D. ferrea (Willd.) Bakh.

var. buxifolia (Rottb.) Bakh. 1 119. D. montana Roxb. 13 13Euphorbiaceae20. Euphorbia antiquorum L. 1 1

21. Mallotus rhamnifolius Muell.- Arg. 40 60 100Flacourtiaceae22. Flacourtia indica (Burm.f.) Merr. 8 67 75

Linaceae23. Hugonia mystax L. 2 2Loganiaceae

24. Strychnos minor Dennst. 2 5 7Melastomataceae25. Memecylon umbellatum Burm. f. 452 5 457


Table 3. (Continued )


Meliaceae26. Azadirachta indica A. Juss. 1 127. Walsura trifolia (A. Juss.) Harms 1 1

Mimosaceae28. Mimosa intsia L. 10 10Moraceae

29. Ficus amplissima J.E. Smith 2 230. F. benghalensis L. 3 16 1931. Plecospermum spinosum Trec. 1 1

Myrtaceae32. Syzygium cumini (L.) Skeels 4 4Oleaceae

33. Chionanthus zeylanica L. 14 1 15Opiliaceae34. Cansjera rheedii Gmel. 6 5 11Papilionaceae

35. Butea monosperma (Lam.) Taub. 9 936. Dalbergia paniculata Roxb. 1 137. Derris scandens (Roxb.) Benth. 22 1 23

38. Ormocarpum cochin-chinense 1 1(Lour.) Merr.

Rhamnaceae

39. Ventilago madraspatana Gaertn. 6 6Rubiaceae40. Benkara malabarica (Lam.) 1 1

Tiruvengadum

41. Canthium dicoccum (Gaertn.) 18 5 23Teijsm & Binn.

42. Ixora pavetta Andr. 5 2 7

43. Tricalysia sphaerocarpa (Dalz.) 295 243 538Gamble

Rutaceae

44. Atalantia monophylla (L.) Correa 32 70 10245. Glycosmis pentaphylla (Retz) DC. 3 9 1246. Pleiospermium alatum (Wall. ex Wight 1 57 58

& Arn.) SwingleSapindaceae47. Lepisanthes tetraphylla (Vahl) 44 189 233

Radlk.

Sterculiaceae48. Pterospermum canescens Roxb. 92 49 14149. P. xylocarpum (Gaertn.) Sant. 15 15

& WaghTiliaceae50. Grewia obtusa Wall. ex Dunn 1 1

51. G. rhamnifolia Heyne ex Roth 1 4 5


and Cassia ®stula and the liana Combretum albidum are deciduous, the rest are evergreenor a few, like Pterospermum spp., are brevi-deciduous.

The Shannon-Weiner index, Hill diversity indices 2 and 3 and all evenness indices wereslightly greater for TM than KK whereas Simpson's diversity and HRI were greater forsite KK (Table 2). Habit-wise, of the 54 species, 34 were trees and 20 lianas. Nearly one-third of the total species in each of the sites were lianas (Table 2). The number of thornyspecies is slightly greater (10%) in TM than in KK. Nearly one-third of the total stems aremulti-stemmed in KK and one-fourth in TM.

Species±area curve

Species±area curves for both the sites nearly levelled o� at the 1-ha scale (Fig. 2). The rateof climb of species±area curve was nearly the same (3.4 and 3.3 respectively) for KK andTM. The area of forest itself gets almost saturated at one hectare in both the sites,particularly so in TM.

Stand density and basal area

A total density of 2143 stems were enumerated in the two 1-ha areas. The density was 1367stems ha)1 for KK and 964 ha)1 for TM (Tables 2 and 3). Although the forest stand

Table 3. (Continued )


Verbenaceae52. Premna tomentosa Willd. 2 13 1553. Vitex altissima L.f. 4 4

Vitaceae54. Cissus quadrangularis L. 7 7

Figure 2. Species±area curves for KK and TM dry evergreen forests.


density was lower in TM, trees were twice as voluminous, with a basal area of 29 m2 ha)1,than site KK (basal area 15.44 m2 ha)1). Fifteen species most important either in KK orTM sites contributed the bulk of total density, basal area and IVI (Table 4). Species suchas Garcinia spicata and Pterospermum canescens in both the sites, Ficus benghalensis (siteTM) and Memecylon umbellatum (site KK) contributed individually to greater than 10%of the sites' basal area (Table 4). These 15 species contributed 90% and 88% of the totalstand density in KK and TM respectively, the remaining 39 species contributed the rest.The basal area contribution by these 15 species was 87 and 96% for sites KK and TMwhereas IVI was 256 and 261 respectively.

Species density, dominance and rarity

The population density of di�erent woody species varied in the two sites (Table 3). Whenconsidered site-wise, a total of nine species in KK and eight species in TM were dominant,scoring an IVI exceeding 10 (Table 4). In site KK, six species were represented by >50individuals. They include overstorey species such as Garcinia spicata, Diospyros ebenumand Pterospermum canescens (these are poorly represented in TM) and understorey treeslike Memecylon umbellatum and Tricalysia sphaerocarpa and the liana Combretum al-bidum. On the other hand, in site TM, besides the last mentioned three species, thoserepresented by more than 50 individuals include Atalantia monophylla, Flacourtia indica,Lepisanthes tetraphylla, Mallotus rhamnifolius, and Pleiospermium alatum. Remarkably,

Table 4. Fifteen most important species and their contribution to density, frequency, basal area and

importance value index in the KK and TM sites on the Coromandel coast of India

KK TM

Species Density No.SU

BA IVI Density No.SU

BA IVI

Atalantia monophylla 32 21 0.514 10.05 70 34 0.717 16.81Canthium dicoccum 18 15 0.120 5.22 5 4 0.041 1.50Combretum albidum 51 25 0.240 10.49 57 28 0.265 12.67Derris scandens 22 13 0.280 6.13 1 1 0.002 0.32

Diospyros ebenum 103 40 0.630 19.95 17 15 0.755 7.48Flacourtia indica 8 7 0.174 3.17 67 43 6.801 39.03Ficus benghalensis 3 3 0.177 1.99 16 6 3.390 14.39

Garcinia spicata 65 26 1.720 21.33 21 11 1.260 8.75Lepisanthes tetraphylla 44 24 0.816 13.50 189 67 5.552 52.39Mallotus rhamnifolius 40 15 0.112 6.77 60 23 0.160 11.56

Memecylon umbellatum 452 70 2.356 62.90 5 5 0.084 1.85Pterospermum canescens 92 43 3.284 36.96 49 36 7.570 38.31Pterospermum xylocarpum 15 10 0.473 6.25 ± ± ± ±

Pleiospermium alatum 1 1 0.015 0.38 57 30 0.941 15.39Tricalysia sphaerocarpa 295 60 2.533 50.48 243 65 0.745 41.25

Subtotals (15 species) 1241 13.444 255.57 857 28.283 261.70Remaining 39 species 126 1.999 44.43 117 1.201 38.30Totals 1367 15.443 300.00 974 29.484 300.00

SU±sampling units; BA±Basal area; IVI±Importance value index.


Memecylon umbellatum and Diospyros ebenum are predominant in site KK whereas theyare poorly represented in TM. On the contrary, Lepisanthes tetraphylla and Pleiospermiumalatum, which are well represented in TM, are poorly represented in KK (Tables 3 and 4).

Species represented by one or two individuals were considered rare. Nearly 26% (11) ofthe total number of species in site KK are rare while in TM nearly 31% (12) are rarespecies. Of the total of 54 species nearly 30% (16) of species are rare when both sites areconsidered.

Plant families

Taxonomically the number of plant families was the same (26) in both the sites, but therewere ®ve families not represented in KK which were represented in TM and vice versa andthus 21 families were common to both the sites (Table 5). The number of genera was 37and 35 respectively for KK and TM. There were only one to three species represented ineach of the families in KK, while in TM there were one to four species. Fifteen families(nearly 30%) in KK and 18 families in TM were represented by one individual. Cap-paraceae, Ebenaceae, Papilionaceae, Rubiaceae and Rutaceae were the top ®ve mostspeciose and important families. When analysed density-wise for species, Capparaceae,Ebenaceae, Melastomataceae, Rubiaceae and Sterculiaceae ranked as abundant (Table 5).

Tree size class-wise richness and density

With increasing tree size classes, species richness, density and diversity, and richnessindices decreased drastically for both the study sites (Table 6). The lowest size class,10±30 cm, considered in this study contributed more than 50% of total tree density inboth the sites. The 30±60 cm size class accounted for three-quarters of species richness inKK while in TM nearly two-thirds of the species (30 out of the total 38) ®gured in thelowest (10±30 cm) girth class itself. HRI values are very low for 150±210 and >210 cm sizeclasses (Table 6).

Population structure of forest stand

The stand-level forest structure based on girth frequency of species is an expanding one inboth the sites with a greater number of individuals in lower girth classes, indicating thatthe stand harbours a growing and healthy population (Fig. 3). But the trends in basal areacontribution di�ered, site TM exhibiting a reversed J-shape curve whereas KK displayed aJ-shaped one.

Population structure of dominant species

The population structure of selected species dominant either in both the sites or in any oneof the sites, varied greatly (Figs 4 and 5). Flacourtia indica and Lepisanthes tetraphylla werewell represented with an expanding population in site TM while it exhibited a disturbedpopulation structure with poor representation in KK. Memecylon umbellatum, the pre-dominant and densely populated species in KK had an expanding population structure inKK while in TM it had a disturbed population with very low stem density. Tricalysiasphaerocarpa displayed a growing population in both the sites and attained larger girths insite KK than in TM. Pterospermum canescens and Garcinia spicata showed a growingpopulation in KK (although poorly represented in the lower girth class), while in TM girthfrequency was poor for both of the species but the basal area was greater in TM forPterospermum canescens.


Tree dispersion patterns

The majority of woody plants were clumped both at the 1-ha and 0.25-ha scales analysed,in both of the sites (Table 7). Species such as Cansjera rheedii, Diospyros montana andVentilago madraspatana in KK and Capparis zeylanica, Glycosmis pentaphylla andMiliusamontana in TM at the 1-ha scale were uniformly distributed. Pterospermum canescens isthe only species distributed uniformly at the 0.25 ha scale (in TM) whereas in KK at boththe scales it was clumped.

Table 5. Family-wise contribution to genera, species and density in the KK and TM study sites on

the Coromandel coast of India

KK TM

Family Genera Species Density Genera Species Density

Anacardiaceae ) ) ) 1 1 1

Annonaceae 1 1 13 1 1 9Arecaceae ) ) ) 1 1 1Boraginaceae ) ) ) 1 1 3Caesalpiniaceae 2 2 4 ) ) )Capparaceae 2 3 23 2 4 33Celastraceae 2 2 6 2 2 8Clusiaceae 1 1 65 1 1 21

Combretaceae 1 1 51 1 1 57Convolvulaceae 1 1 4 ) ) )Ebenaceae 1 3 117 1 1 17

Euphorbiaceae 1 1 40 2 2 61Flacourtiaceae 1 1 8 1 1 67Linaceae 1 1 2 ) ) )Loganiaceae 1 1 2 1 1 5Melastomataceae 1 1 452 1 1 5Meliaceae 1 1 1 1 1 1Mimosaceae ) ) ) 1 1 10

Moraceae 2 2 4 1 2 18Myrtaceae 1 1 4 ) ) )Oleaceae 1 1 14 1 1 1

Opiliaceae 1 1 6 1 1 5Papilionaceae 3 3 32 2 2 2Rhamnaceae 1 1 6 ) ) )Rubiaceae 3 3 318 4 4 251Rutaceae 3 3 36 3 3 136Sapindaceae 1 1 44 1 1 189Sterculiaceae 1 2 107 1 1 49

Tiliaceae 1 2 2 1 1 4Verbenaceae 2 2 6 1 1 13Vitaceae ) ) ) 1 1 7

Total 37 42 1367 35 38 974


Discussion

The total of 54 species enumerated on a 2-ha scale is closer to that of 51 species recordedon the same scale from Puthupet, another sacred grove dry evergreen forest located 45 kmnorth of the present study site in southern India (Sethi, 1993). Site-wise KK and TMharboured 42 and 38 species respectively. This is well within the range (35±90 species)reported for dry tropics (Murphy and Lugo, 1986). The slightly greater species richness(four species more) obtained in KK as compared to TM may be attributed to site heter-ogeneity in KK with a stream ¯owing within the site, with upland and ¯at terrains whileTM has a more or less uniform level terrain. The greater number and density of lianas inTM indicates that the site was disturbed some time ago particularly along the southeasternand southwestern portions of the grove. The occurrence of Mimosa intsia there indicatessuch past disturbance. In addition, currently, site KK experiences an intermediate level ofdisturbance which includes resource harvesting such as collection of fuelwood, and lettingcattle inside the grove for grazing and browsing, which occur only occasionally in TM.The species±area curve nearly levelled o� after the 1-ha area indicating species saturationon one hand; the real picture being that the area of the grove is also limiting. As far as ourobservation goes no new additional woody species were encountered beyond the 1-hastudy plots.

The woody species richness in the tropical dry evergreen forests is low when comparedto many other tropical evergreen forests of palaeotropical and neotropical regions. But thepresent extent of species richness can be attributed to the protected sacred grove status ofthe forest. The diversity of tropical forest plant communities is strongly correlated withprecipitation (Gentry, 1982). The species diversity doubles from dry to moist forest(Holdridge, 1967) and triples from dry to wet forest. But dry forest diversity in turn ismore than double that of several similar samples of temperate forest (Gentry, 1982). Thusthe species richness in the present 2-ha study was more than that obtained for severaltemperate forests but lower than many tropical moist and wet forests.

This observation is supported by the dissymmetric rainfall regime of the east coast ofIndia with a long (average of 6 months) dry season from January to June (Blasco andLegris, 1973). But during the dry period, dew is an important source of moisture and in the

Table 6. Frequency of species distributed girth class-wise and its Shannon-Weiner (H¢) and

hierarchical richness index (HRI) in sites KK and TM

KK TM

Girth class(cm)

Richness Density H¢ HRI Richness Density H¢ HRI

10±30 27 744 2.199 3319 30 591 2.401 793830±60 28 412 2.261 1797 19 172 2.250 143160±90 16 135 2.130 514 17 83 2.215 41490±120 12 39 2.200 194 11 40 1.946 130

120±150 8 21 1.806 105 7 25 1.576 57150±180 5 7 1.550 18 8 22 1.770 96180±210 3 5 1.055 10 5 18 1.353 50

>210 3 4 1.039 7 6 23 1.519 73


present study site even in the dry month of May, when this study was undertaken, dewcould be observed in the morning. However, the role of dew in forests is poorly known.

The density of woody species is greater in both the sites because this study consid-ered ³10 cm girth threshold. Of the two sites the greater density but lower basal area ofindividuals in KK than in TM, could be related to the low-statured condition of the forestwhile in TM a comparatively tall stature and less disturbed condition of the forest, withexpanding canopy and voluminous trees could account for low density and greater basalarea. Tree density in tropical forests varies from 245 to 859 for trees of ³30 cm gbh(Richards, 1952; Ashton, 1964; Campbell et al., 1992).

The density of 623 and 383 stems ha)1 for the girth threshold ³30 cm gbh obtained inour study is well within the limit reported for tropical forests. The density of 1367 stemsha)1 in KK (974 for TM) for trees ³10 cm gbh in the present study site is comparable to

Figure 3. Population structure of woody species based on girth-frequency and basal area in various

size classes in the KK and TM sites.


that of nearby Puthupet dry evergreen forest wherein an average of 1388 stem ha)1 wasenumerated (Sethi, 1993) for the same girth threshold. Evidently, the density of the plantpopulation may be governed by a circular steady state in suitable niche loci, survival ofseedling to reproductive stage as a�ected by predation and environmental ¯uctuations inrelation to relative favourableness of loci and the density of seeds that the population ofmature plants produce (Whittaker, 1969).

The basal area for KK and TM sites was 15.4 and 29.5 m2 ha)1 for ³10 cm girththreshold, while it was 13.2 and 28.1 m2 ha)1 when worked out for ³30 cm gbh threshold.The nearby Puthupet dry evergreen forest had a basal area of 38 and 27.6 m2 ha)1

for ³10 cm girth and it was 35.6 and 26 m2 ha)1 for ³30 cm girths. Average basal areavalues being 22.45 m2 ha)1 for the present study sites and 30.86 m2 ha)1 for Puthupet. Thisis well within the range of 17±40 m2 ha)1 reported for dry tropics (Murphy and Lugo,1986), but lower than the pantropical average of 32 m2 ha)1 (Dawkins, 1959) as well asthat reported in the other tropical works notably of Poore (1968) in Malaysia (24.2 m2

ha)1); Paijmans (1970) in Costa Rica (29 to 56.7 m2 ha)1); Rai and Proctor (1986) for foursites in Karnataka, India (33.74 to 48.6 m2 ha)1); Campbell et al. (1986) in terra ®rme (27.6to 32 m2 ha)1) and varzea sites (25.5 to 27); Campbell et al. (1992) in Brazilian Amazon;Lieberman and Lieberman (1987) in Costa Rica (27.8); Je�re and Veillon (1990) in NewCaledonia (47 for alluvium and 49.5 for slope forests); Parthasarathy et al. (1992) in

Figure 4. Comparative population structure of Flacourtia and Lepisanthes in the KK and TM sites.


Kalakad, southern Western Ghats, India (53.3 to 94.6) and Nadkarni et al. (1995) inMonteverde, Costa Rica (62 m2 ha)1).

Fifteen most important species (IVI > 10) dominate the majority of space. Accordingto Keel and Prance (1979), dominance increases as a function of stress, while Jacobs (1987)holds that in tropical forests dominance by a single species often indicates past damage.However, disturbance is not the sole reason for dominance. In some undisturbed forestsdominance also occurs and is related to adverse conditions, poor drainage, etc. (Richards,1952). The IVI gives a total picture of the social structure of species in a community andcan be used to form an association of dominant species. Based on this in the present studyarea an association of Memecylon umbellatum and Tricalysia sphaerocarpa in KK andLepisanthes tetraphylla and Tricalysia sphaerocarpa in TM can be formed. Whereas in theallied Puthupet dry evergreen forest Flacourtia indica±Memecylon umbellatum±Canthiumdicoccum association was found (Sethi, 1993). For Marakkanam, a dry evergreen forestreduced to the stage of a thicket, Drypetes wightii±Strychnos colubrina±Memecylon um-bellatum association was found (Balasubramanian, 1977). In the light of these, the nameAlbizia amara community, proposed for the dry evergreen forest type by Meher-Homji(1973) for the vegetation of the Coromandel-Circar coast, is neither applicable to thicketnor to the dry evergreen forest of Puthupet, KK or TM.

Figure 5. Comparative population structure of Memecylon and Pterospermum in the KK and TMsites.


Melastomataceae, Rubiaceae, Ebenaceae and Sterculiaceae were the predominantfamilies in terms of density in KK while in TM Rubiaceae, Sapindaceae and Rutaceaewere the predominant families. In the nearby Puthupet dry evergreen forest, Me-lastomataceae, Rubiaceae and Flacourtiaceae constituted the predominant families basedon tree density. The species and family level similarity in the Puthupet, KK and TM sitescan be attributed to the nearness of the sites and a similar forest type. On the other handbetween-site di�erences may be attributed to site heterogeneity.

Rare species (those represented by <2 individuals) accounted for 26 and 31% in KKand TM respectively. This is greater than the value of 19.6% of rarity found in Puthupet(Sethi, 1993), but lesser than those obtained by Meijer (1959), where 50% were repre-sented by one individual; and by Paijmans (1970) wherein 217 of 392 species (55.4%) wererepresented by <2 individuals in New Guinea. These results are also lower than the valueof 59% of Ho et al., (1987) from Malaysia for <2 individuals; of Poore (1968) in

Table 7. Standardized Morisita's index values and the distributional patterns of species in the KK

and TM sites at 1±ha and 0.25±ha scales

KK TM

Species 1±ha 0.25±ha 1±ha 0.25±ha

Atalantia monophylla 0.5127 c 0.3233 c 0.5161 c 0.6958 c

Butea monosperma 0.2417 c ) ) )Cadaba trifoliata 0.5086 c 0.1953 c 0.3795 c )Chionanthus zeylanica 0.5001 c 0.1183 c ) )Combretum albidum 0.5110 c ) 0.5075 c 0.5372 c

Canthium dicoccum 0.2775 c 0.1790 c ) )Cansjera rheedii )0.0975 u ) ) )Capparis brevispina 0.5192 c ) 0.1869 c )Capparis zeylanica ) ) )0.1560 u )Cissus quadrangularis ) ) 0.3855 c )Diospyros ebenum 0.5071 c 0.5122 c 0.1279 c )Diospyros montana )0.2340 u ) ) )Derris scandens 0.5098 c ) ) )Flacourtia indica 0.3059 c ) 0.5005 c 0.1101 c

Ficus benghalensis ) ) 0.5792 c )Garcinia spicata 0.5119 c 0.5038 c 0.5337 c )Glycosmis pentaphylla ) ) )0.1560 u )Lepisanthes tetraphylla 0.5039 c 0.5031 c 0.5076 c 0.4142 c

Mallotus rhamnifolius 0.5283 c 0.5643 c 0.5239 c )Memecylon umbellatum 0.5058 c 0.5069 c ) )Miliusa montana 0.5153 c ) )0.1560 u )Mimosa intsia ) ) 0.5241 c )Pleiospermium alatum ) ) 0.5068 c 0.5344 cPterospermum canescens 0.5057 c 0.5032 c 0.2247 c )0.1724 uPterospermum xylocarpum 0.5134 c ) ) )Premna tomentosa ) ) 0.3190 c )Tricalysia sphaerocarpa 0.5049 c 0.5142 c 0.5054 c 0.5336 cVentilago maderaspatana )0.975 u ) ) )

u±uniformly distributed; c±clumped.


Malaysia wherein 38% were represented by a single individual; and 40% rarity (45 of atotal of 112 species with a maximum of 2 individuals) in Barro Colorado Island, Panama(Thorington et al., 1982). Manokaran and Kochummen (1987) found that in Malaysianforest ten common species accounted for 25% of total density while 35.8% (in 1947) and40.2% (in 1981) were represented by one individual. Sukumar et al. (1992) found that 12commonest species made up 90.6% while seven species were represented by only oneindividual in each plot. There is evidence that many widespread tropical species tend to belocally abundant in certain areas and relatively rare in others (Hubbell and Foster, 1983).It is exempli®ed by Memecylon umbellatum in our study site, which is abundant with anIVI of 62.9 in KK and an IVI of only 1.95 in TM.

The typical ÔL' shaped growing population in the frequency distribution curves (Fig. 3)for KK and TM forests revealed that at stand-level there is no girthclass-based selectivefelling but that voluminous trees, contributing to greater basal area in TM, can be at-tributed to its uniform terrain and also because TM remains relatively undistributedcompared to KK. Expanding population structure indicates that these sites are typicalmature stands with good regeneration and is also reported in Jengka forest reserve,Malaysia (Poore, 1968; Ho et al., 1987), Costa Rica (Lieberman et al., 1985), BrazilianAmazon (Swaine et al., 1987; Campbell et al., 1992), Sungei Menyala in Malaysia(Manokaran and Kochummen, 1987) in Mudumalai, India (Sukumar et al., 1992) and inMonteverde, Costa Rica (Nadkarni et al., 1995). Species-level di�erences in populationstructure may be attributed to species' preference in both the sites, site quality, topographyand forest stature. The trend of decreasing diversity with increasing girth class is similar tothat observed by Paijmans (1970) in New Guinea, Je�re and Veillon (1990) in New Cal-edonia and Newbery et al. (1992) in Malaysia.

Of the 28 species analysed for spatial patterns, the clumped dispersion obtained for mostspecies in both the study sites (Table 7) could arise due to reasons such as the limited area ofdry evergreen forest, only a few species composing the study site itself and the larger scalesconsidered for dispersion analysis in proportion to the whole study area. The predominanceof clumping is consistent with the results obtained by Ashton (1969), Whitmore (1975),Hubbell (1979), Forman and Hahn (1980) and Thorington et al. (1982). Uniform patternswere rare in our study sites. Armesto et al. (1986) stated that uniform dispersions are veryrare regardless of geographical location or forest type. Uniform distribution of species maybe the consequence of direct competition for water, or allelopathy (MacMahon andSchimpf, 1981), while clustering of trees may be brought about by seed dispersal. Many ofthe trees in both the KK and TM sites bear berries or drupes, thus vertebrate-dispersed anda few trees (Pterospermum spp.) and lianas (Combretum and Ventilago) with winged seeds/fruits are wind-dispersed. In the case of animal-dispersed trees, they will be concentrated ina pattern determined by the behaviour of the animal, which could result in clumping.However, dispersal is only one aspect, close to the trunk where many seeds fall, predationoccurs. But a noteworthy feature in the two small sacred grove dry evergreen forests is themovement of animals, particularly the mammals which could promote clumping of speciesin a limited area. In addition, every species has its own range of preferences with regard tosoil, topography, light requirement and various other basic conditions. Moreover, in allbiological systems di�erences tend to accumulate in the course of time. Finally, chanceplays a role not only in dispersal and germination but also in the natural dynamism of thecanopy with its randomly occurring centres of growth due to dismantling, natural death etc.(Jacobs, 1987) which facilitate growth of suppressed saplings.


Conclusion

Detailed biodiversity inventories of threatened tropical ecosystems such as the poorlyknown tropical dry evergreen forests, are needed to draw up management and conser-vation strategies. Increasing deforestation and forest fragmentation would call uponconservationists to preserve areas as diverse as possible. It calls for determining minimumcritical size (Lovejoy and Oren, 1981) required to maintain biodiversity, by studying theremnant patches in KK and TM sites that cover very small areas of about 1.2 and 1.6 harespectively. There are a few nearby tropical dry evergreen sacred grove forests which varyin their areal extent from approximately 0.5 ha to 3 ha or so within a radius of 4 km, andthe nearby 14-ha Puthupet dry evergreen forest 45 km north of the present study site TM.These patches would have once been a continuous tract of dry evergreen forest but humansettlements and changes in land use patterns have fragmented it. Isolated habitat frag-ments such as these sites, are exposed to a myriad of hazards, any or all of these canpotentially contribute to species loss (Janzen, 1986) and in the long run human activitiesadjacent to, but outside fragments, especially the smaller ones, may do more to acceleratethe species loss. The sacred groves in KK and TM are surrounded by agricultural ®eldsand roads on various sides. The grove edges are subjected to advancing agricultural lands.In such forests, pioneer species and weeds colonize (Lovejoy and Rankin, 1979) which willchange the forest composition. The shrinking area of sacred groves has a consequence ofreducing the e�ective population sizes of many of the included species, so demographicchange also in¯uences selection, mating system and the generation of novelty throughmutation. Low population density poses a danger for outbreeding forest species and willreduce reproductive output, as inbreeding chance of reproductive failure (Ledig, 1992).Barely 5% of the potential area under tropical dry evergreen forest type remains underforest cover (Meher-Homji, 1992). From the conservation perspective the crucial questionis the future of these forests which presently occur as islands. Being habitat islands thesewould not intrinsically be very speciose. Besides harbouring 54 woody species and theirgrowing population, these dry evergreen forests support a rich insect, bird, reptile andmammal life, many of which help in the functioning (pollination and seed dispersal etc.) oftropical dry evergreen forests. It is imperative that the remaining patches of this vegetationare preserved, involving the local people, too, because this area not only harbours asizeable proportion of this region's characteristic ¯ora, but also the rich cultural traditionassociated with it.

Acknowledgements

Thanks to the University Grants Commission, Govt of India for ®nancing this study. Wethank Dr G.T. Prance, Director, Royal Botanic Gardens, Kew; Dr V.M. Meher-Homjiand Dr J.P. Pascal, French Institute, Pondicherry for o�ering comments on the ®rst draftof this article.

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