CHAPTER I THE SHRUBS

Transcription

1 CHAPTER I THE SHRUBS Understorey shrubs in the tropics have been poorly documented the world over. Regional and global trends in distribution of species, dominance of certain families and presence of endemics are important attributes that help in comparing the wet forest shrubs of Kakkachi with the rest of the tropics. For this chapter, the data on shrub community of Agastyamalai region, the Western Ghats and other parts of the tropics are complied from secondary sources and only some significant trends are presented and discussed. The detailed analyses is presented in Krishnan & Davidar. (1994). Manuscript. METHODS Analysis of Commoness and rarity Commoness and rarity was analysed by studying the patterns of the species occurence by laying quadrats. The method is described in detail in chapter II. A species is considered rare when it occurs infrequently or at low densities or both. RESULTS Western Ghats About 368 species belonging to 45 fam~lies have been listed from published sources on the evergreen forests of the Western Ghats. This list is not exhaustive and excludes weeds, exotics and ornamental plants. Rubiaceae is the largest family contributing to 23% of the species (881368). The other important families are Acanthaceae 16% (62/368), Fabaceae 8% (32/368), Euphorbiaceae 7% (291368), Lamiaceae 5% (20/368), and Melastomataceae 4% (171368). These seven families contribute up to 73% of the species ( ) (Nair & Henry, 1983; Henry eta/, 1987). The endemics comprise 81% ( ) of the species listed. The largest number of endemics are in Rubiaceae 24% (73/299), followed by Acanthaceae 19% (591299), Fabaceae 10% (301299), Asteraceae 8% (251299), Euphorbiaceae 6% (20/299), Labiatae 6% (191299) and Melastomataceae 5% (151299). Fifteen percent of the shrubs listed were rare

2 (571368) and 8% were endangered (321368) (Nair & Henry, 1983; Henry eta/, 1987). Agastyamalal reglon When the understorey shrubs are listed in the Agastyamalai range (Table 2, Appendix 3.1), there are at least 113 species, representing 29 families and 61 genera. Rubiaceae was the most common family with 24 (21.23%) species. Eleven families (38%) were represented by one species and 22 families (76%) had less than three species. An analysis of the species (Nair & Henry 1983; Henry et a/, 1987; Ahamedullah & Nair. 1986) in the region showed that 25% (281113) are endemics to the Westem Ghats, rare species accounted for 2.7% (3/113) and 17% (191113) were economically important. Species categorised as both endangered and rare accounted 5.31%(61113). Memecylon sisparense is reported as rare, endangered and endemic to the Agastyamalai region (Henry et a/. 1987). Kakkachi I recorded 59 shrubs from 20 families from both the primary and the disturbed forests. Some famiiies such as Chloranthaceae, Pittosporaceae and Proteacaae are represented by only one specles. Rubiaceae is the largest family with 26% (15159) of the species. Acanthaceae by 15% (9159) and Euphorbiaceae by 14% (8159) of the species. Eighty percent (16120) of the families had fewer than three species each. Rare species constituted 13.56% (8159) of which 9% (5159) were economically important. Endemic element in the flora was 34% (20159). In Rubiaceae, 8.5% (5159) of the species were endemic to the Western Ghats and 12% (7159) were rare. In Acanthaceae and Euphorbiaceae, the endemic elements were 7% (4159) and 8.5% (5159) respectively. They had negligible number of rare species in their composition. Background Information on aom of the study spacia8 Three genera Lasianthus, Psychotria and Hedyotis (family Rubiaceae) are represented by two species each. Taxonomic work has been done on Psychotria (Deb & Gangophadyay, 1983) and Hedyotis (Deb & Dutta,1985) but not on others. Acanthaceae is represented by several monocarpic genera with only Diotacanthus gmndis being poiycarpic. Few taxonomic studies exist on the family in India (Anderson,1867; Ellis 8 Swaminathan, 1975). In

3 Euphorbiaceae, except for Agrostistachys (Balakrishnan, 1970) no other genera seems to have been taxonomically studied in Indian sub continent. Common and nrr apacirs The results on commonness and rarity suggest that 73% of the species belonging to families Celastraceae, Euphorbiaceae, Myrsinaceae and Rubiaceae are common, and, 26% species of families like Acanthaceae and Euphorbiaceae are rare. Acanthaceae had the largest number of rare species (Table 1). Some species declared rare for the Western ghats (like: Helicia nilagirica, Agalia indica) continued to be rare in the study area. However, for species like Octotropis travancorica, Saprosma corymbosum and Lasianthus clnereus, it did not hold true (Henry et at, 1987). Several genera such as Helicia and Sarcandra had disjunct geographic distributions with the former being found in the Western Ghats and Australia and the latter in old World forests and Pacific islands. Eaatrrn Ghats Evergreen forests in Eastern ghats are restricted to very small patches. Ecological studies have been undertaken In Biligirirangan hills of the Eastern ghats (Ramesh. 1989). Eleven families and 26 shrub species have been recorded from the area with Rubiaceae being dominant. Rubiaceae accounted for 38% of the species. Several species are shared with the Western Ghats (62 %) but with differences in abundances (Krishnan 8 Davidar Manuscript). North East Indh Several species are common to the Western Ghats. North East India and Sri Lanka. Based on this indirect evidence alone, it is possible to state that the shrubs are probably as rich and diverse as in the Western Ghats however no published information could be obtained.

4 * indicates the rarer species are infrequent or absent. Table 1 The rare and common shrub species in the primary forests of Kakltachi.

5 SH Lank. In the medium elevation rainforest of Sri Lanka, Strobilanthes, Hunteria zeylanica and Rauwolfia densiflora were dominant in the understorey. Kiioxia sp. and Dillenia sp. were more gap dwelling. Rubiaceae, was relatively less dominant as compared with the mid elevation forests in India (Abeysundere 8 Rosaryo, 1939; Mitchell & Tilaekratene, 1980; Dario de Franceschii, Pers.comm.). Other repons suggest that the forests were probably Rubiaceae dominant with Psychotrla nigra, Schumachaeria castanae, schizostigma hirsuta (Holmes, 1955). Other shrubs reported from the area include, Osbeckia walkerii, Urophyllum zeylanicum, Chassalia amblgna, Chimonombusa walkerina, Agrostistachys coriaceae and species of Strobilanthus (Rosaryo, 1958; Fonseka 8 Vinasithamby, 1971). Andaman 6 Nkobar Islands Rubiaceae was the common understorey shrub family, represented by 60 species, in the forests of Andaman archipelago. Genus Hedyotis is the largest representative with 17 species. lxora ranked second with 13 species, Psychotria ranked third with 10 species. However the locally abundant species were Homalonema aromaticum (Aroideae) and Amomum fenzlii (Scitaminae) (Kun. 1876; Vasudeva Rao. 1986). Representatives of families like: Acanthaceae, Apocyanaceae, Asteraceae, Celastraceae, Chloranthaceae, Euphorbiaceae, Fabaceae, Leeaceae, Melastomataceae, Myrsinaceae and Verbenaceae were also important. The second largest family is Acanthaceae, with 17 species. A total of 145 species from 12 families were recorded. Of which, the endemics were represented by 17 species. Usually, Psychotria sp. was dominant in the understorey (Soubadra devy, pers.comm). In the Nicobar archipelago, the common understorey family was Rubiaceae, represented by the genera: Hedyotis, Ixora, and Psychotria. Rubiaceae accounted for nearly 50% of the shrubs recorded from the area. Other families represented are: Acanthaceae, Apocyanaceae, Asteraceae, Annonaceae, Euphorbiaceae, Melastomataceae, Proteaceae and Symplocaceae (Project document 11, 1989). Most of these species have South-East Asian affinities (Chatterlee, 1939; Rao, 1986).

6 REGIONAL COMPARISONS South-bat Asla In the medium eievation rainforests of Java, Rubiaceae is the most dominant family represented by approximately 75 species. Hedyotis (30 species) and Lasianthus (29 species) are the most common genera. Acanthaceae is the next, represented by 67 species and followed by Euphorbiaceae with 80 species (Backer B Bakhuizen van den brink, 1983). In the rainforests of Malayasia, 20 families of shrubs, representing 52 genera and 130 species have been recorded (Henderson, 1974). Rubiaceae is the most dominant family represented by 12 genera and 19 species. In the understorey of the medium elevation evergreen forests ( m) of ViBt-nPm, Lasianthus chevalirii, L. pierrei, Psychotria lecometei, Chassalia curviflora, Prismatomeris sub sessilis, (all Rubiaceae) are dominant. Myrsinaceae was represented by Ardisia racemosa and Ardisia crisps. Representatives of Acanthaceae included Paragoldfussia poilanei, Strobilanthes saltensis and Tetraglochin hirsutum. Other families found in the understorey are Annonaceae, Euphorbiaceae, Dichapetalaceae and Sapindaceae (Schmid, 1974). GLOBAL COMPARISONS Afrlca and Madagascar Comparative studies in Africa indicate that genus Sabicea (Rubiaceae) is represented by 82 species, while Debenoya (Acanthaceae) is represented by 35 species (Thorne, 1978). Reports from Madagascar (800-1,300 m) suggests that in the primary forests, the dominant understorey families are Asteraceae, Rubiaceae, Lauraceae, Araliaceae and Ericaceae (Koechiin, 1972). Australia and Papua MW Guinaa The Australian rainforests are reported to be predominantly lndo Malaysian in their affinities. In the medium low elevation rain forests of Papua New Guinea (lower montane zone forests of m), understorey is represented by the families, Rubiceae, Myrsinaceae, Melastomataceae and Piperaceae. Eurya, Cydantra, Saurauia are some of the genera present (Paijmans. 1976).

7 Neotroplos In the transition forests of La Selva, Melastomataceae and Piperaceae were the most dominant families. Rubiaceae was the third having 40 species of shrubs (Hammel, 1990). In the Neotropical lowland rainforests of Panama in the Panama Canal, Rubiaceae is the dominant family (Foster and Hubbell, 1990). In the mid altitude forests of the Central Amazon, the understorey is reported to be composed of thirteen families. Rubiaceae is ranked fifth in this study based on the order of abundance (Klinge et al, 1975). DISCUSSION Due to lack of information on the alpha diversity of shrubs in other regions of India and of the tropics it is difficult to make local and regional comparisons. However it is evident that the Western Ghats are a rich habitat for shrubs with 81% be~ng endemic. This figure is similar to the levels of endernism in the trees (60%) of the Western Ghats (Ramesh & Pascal. 1991). The dominant family in Kakkachi and possibly in the rest of the Western Ghats was Rubiaceae. In Kakkachi the dominant shrubs were Lasianthus cinereus and Saprosma corymbosum. These species are reported rare in other parts of Western Ghats as they are endemic to the Southern Western Ghats. At the generic level Psychotria, Hedyotis and lxora are common (Appendix 3.1, Table 2). When local comparisons are made, Acanthaceae has the largest number of rare specres although they might be the largest contributor in terms of the density (Bawa et a/ ms). Other common families are Euphorbiaceae and Myrsinaceae. When the shrub fiora is compared between low elevation Dipterocarp forests, high montane sholas (i.e; ~1400 m), and the medium elevation evergreen forests, it becomes evident that the richest shrub fiora might be present in the medium elevation evergreen forests of the Cullenia- Mesua- Palaquium type. Th~s type is common and widely distributed in the Western Ghats. At a regional level, shrubs in the evergreen forests of Sri Lanka, Malaysia and Vietnam are dominated by Rubiaceae. The patterns in Australia and Papua New Guinea might be similar to that of Indo-Malaysia. The shrub fiora of parts of tropical Africa and Madagascar is composed of Asteraceae, Rubiaceae, Melastomataceae and Araiiaceae among others.

8 The understorey shrubs of the neotropical wet forests do not seem to be dominated by Rubiaceae as is the case with the Old World tropics.