American Journal of Plant Biology
Volume 1, Issue 1, November 2016, Pages: 1-12

Undergrowth Species Composition of the Exotic and Indigenous Tree Plots in Deciduous Forest Area of Hoteya Forest Range of Tangail District, Bangladesh

Md. Mijanur Rahman1, *, Saleh Ahammad Khan1, Gazi Mosharof Hossain1, Md. Abdur Rahim2

1Department of Botany, Faculty of Biological Sciences, Jahangirnagar University, Savar, Dhaka, Bangladesh

2Plant Systematics and Biodiversity Laboratory, Department of Botany, Faculty of Biological Sciences, Jahangirnagar University, Savar, Dhaka, Bangladesh

Email address:

(Md. M. Rahman)

*Corresponding author

To cite this article:

Md. Mijanur Rahman, Saleh Ahammad Khan, Gazi Mosharof Hossain, Md. Abdur Rahim. Undergrowth Species Composition of the Exotic and Indigenous Tree Plots in Deciduous Forest Area of Hoteya Forest Range of Tangail District, Bangladesh. American Journal of Plant Biology. Vol. 1, No. 1, 2016, pp. 1-12. doi: 10.11648/j. ajpb.20160101.11

Received: September 29, 2016; Accepted: October 10, 2016; Published: November 3, 2016


Abstract: To assess the impacts of monoculture of exotic tree species on the species composition and status of undergrowths in relation to that of indigenous tree species and to provide the baseline data on the undergrowth species of the plantation forests of exotic and indigenous tree species that might be useful in biodiversity conservation through appropriate selection of tree species for massive plantation programs.This study reports 116 undergrowth species belonging to 97 genera and 52 families of vascular plants fromthe tree plotsof exotic Acacia auriculiformis and Eucalyptus camaldulensis and 150 undergrowth species under 122 genera and 56 families from that of indigenous Shorea robusta and Mangifera indica of Hoteya Forest Range of Tangail district. Most of the 182 undergrowth species, found in exotic and indigenous tree plots together, were Angiosperms (±95%) and only ±5% were Pteridophytes. 63.74% of these species were herbs, 25.82% trees and 10.44% shrubs. In exotic tree plots, the undergrowths of 86, 87 and 76 species, and in indigenous tree plots, the undergrowths of 118, 113 and 111 species were found in summer-, monsoon- and winter seasons, respectively. In S. robusta-, A. auriculiformis-, E. camaldulensis-, and M. indica tree plots, a total of 93,69, 61 and 42 species were found in summer; 90, 77, 55, and 46 species in monsoon; and 82, 68, 39 and 51 species in winter seasons, respectively. In exotic tree plots, Axonopus compressus was found in highest relative density and frequency and Cyperus iria in highest relative abundance, whereas, in indigenous tree plots, A. compressus was found in highest relative density and abundance, and C. infortunatum in highest relative frequency when all undergrowth species were considered. Species number and density were significantly different between A. auriculiformis- and S. robusta- and M. indica- or E. camaldulensis plots. Study conclude that, indigenous tree plots harbored the higher number of species (18.68%) than the exotic tree plots, considering all types of plant species and all seasons and the number of uncommon species was relatively higher in number in indigenous tree plots than that in exotic tree plots. It proves that plantations of indigenous tree species are relatively better in harboring better species richness and diversity. This study suggests preferring the indigenous species for plantation programs in forested and fertile land areas; and exotic species for that in the degraded or barren areas with strict maintenance of the natural condition.

Keywords: Undergrowth, Exotic, Indigenous, Acacia, Shorea, Plot


1. Background

Exotic species are the non-natives that grow outside their natural adapted ranges and dispersal potential (Randall, 1996). Many of the exotic tree species had been introduced to new habitats by humans (Ridenour and Callaway, 2001 and Dogra et al., 2010) due to economic reasons, especially commercial timber production (Hossain and Pasha, 2001; Bhagwat et al., 2012; Mukul et al., 2006), their efficient dispersal capacities, large reproductive output, and greater tolerance to a broad range of environmental conditions (Campbell, 2005). Indigenous species are those that grow in an area only naturally, i.e., without any human intervention since many years or over a geologic time. Such species growing in their natural adapted ranges and dispersal potential has the positive role on food security and in bringing economic, environmental and social benefits.

Both the exotic and indigenous timber yielding species are being used in creating the plantation forests or intensively managed forest stands artificially with the primary purpose of wood production (Evans, 1999). Various plantation or reforestation and afforestation programs with exotic tree species have shown success (Hossain and Pasha, 2001; Ara et al., 1989). In contrast, the exotic plant species can be invasive when they are deliberately or intentionally planted outside their natural range into new areas where they are able to establish themselves and quickly invade and out-compete native plant species for resources (Randall, 1996; Williamson, 1996 and Akter and Zuberi, 2009). Recent research has emphasized on the potential advantages of plantation with indigenous species instead of exotic species (Erskine et al., 2006; Hartley, 2002; Lambert et al., 2005; Piotto et al., 2010), however, there is a strong debate on the impacts of using exotic versus indigenous tree species in plantation programs.

In Bangladesh, two exotic species, A. auriculiformis and E. camaldulensis, are most commonly used in various reforestation and afforestation programs because of their fast growing characteristics and production of high volumes of biomass within a short time frame, short rotation, non-palatability to grazing animals and ability to thrive in poor soils. In this country, plantation programs with exotic tree species are getting priority in both public and private sectors. But, the choice of the species is still under debate. Some public opinions have also been raised against the cultivation of exotic species like A. auriculiformis and E. camaldulensis in plantation programs claiming that these species have a damaging impact on the ecosystems, though such opinion is not backed by sufficient scientific information and research or field experiments (Hossain, 2003). Some studies on the growth performance and impacts of the exotic species have been conducted by different authors (Chowdhury, 1982; Das, 1982; Hossain et al., 1998; Hoque, 1977; Davidson and Das, 1985; Amin et al., 1995 and Elahi, 2006 and 2008). However, the existing research on exotic species in Bangladesh is still very limited in terms of detailed investigations of their effects on native ecosystems (Akter and Zuberi, 2009; Barua et al., 2001; Hossain and Pasha, 2001; Hossain, 2003 and Islam et al., 2003). Detailed and quantitative investigations of exotics in biogeographic and ecological aspects, including their impacts on formation of the understories, are still scarce (Biswas et al., 2007, 2012; Islam et al., 1999).

On the other hand, though much of the biodiversity harbored in the forests resides in undergrowth vegetation and data on undergrowth species ofthe forests help us to have an idea on the actual species richness and diversity existing under their canopy cover, studies on undergrowth species in forested areas and impacts of plantations with exotic versus indigenous tree species on the undergrowths are still scarce, especially in Bangladesh. Some studies on undergrowth species composition in different areas of this country (Ahmed; 1996; Al-Amin et al., 2004; Malaker et al., 2010) including the deciduous ‘Sal’ (S. robusta) forest areas of Modhupur-Mymensingh-Gazipur region (Green, 1981; Rahman, 2001, 2009; Khan et al., 2007) have been conducted. However, no study included anintegrated and comparative inventory on the composition of undergrowth species in exotic and indigenous tree plots of this country.

The study area Hoteya Forest Range of Tangail district, one of the forest areas that harbor the typical deciduous forests of S. robusta as well as the massive plantations of exotic tree species, is an appropriate area for conducting a comparative study on undergrowth composition in exotic and indigenous tree plots. The objectives of this study were to assess the impacts of monoculture of exotic tree species on the species composition and status of undergrowths in relation to that of indigenous tree species and to provide the baseline data on the undergrowth species of the plantation forests of exotic and indigenous tree species that might be useful in biodiversity conservation through appropriate selection of tree species for massive plantation programs.

2. Methods

Study area: The study area Hoteya Forest Range, located in between 24°11´and 24°26´ north latitudes and 90°04´ and 90°18´ east longitudes, is situatedin Sakhipur forest area (191 sq. Km.) under the Tangail Forest Division, 80 Km north from Dhaka. This area is a part of Madhupur tract of ‘Sal’ forest. The floristic composition, wildlife and forest characteristics of this area are almost similar to that of other parts of Madhupur ‘Sal’ forests. 70% to 75% trees of this forest area belong to S. robusta which is associated with other tree species, such as Terminalia bellirica (Gaertn.) Roxb., Albizia procera (Roxb.) Benth., Lagerstroemia speciosa (L.) Pers. and Ficus spp. The study area was selected following the information of Forest Department and field reconnaissance survey.

Specimen collection and identification: Field data and representative plant specimens were collected over a period of two years, ranging from April 2010 to November 2011, and in three seasons, viz., a hot, humid summer from March to June, a less hot, rainy monsoon season from June to October; and a cool and dry winter from October to March.The quadrat method (Braun-Blanquet, 1932; Raunkiaer, 1934) following the determination of the standard size of the quadrat (4m x 4m) by the ‘Species Area Curve’ (Cain, 1938; Braun-Blanquet, 1964) was applied in collecting the field data and plant specimens. Following the standard herbarium techniques (Hyland, 1972; Jain and Raw, 1977), the freshly collected representative specimens were processed and pressed in the field station and dried and preserved in Jahangirnagar University Herbarium (JUH). Besides the author’s own collections, the herbarium specimens previously collected from Bhawal-Madhupur tract of Bangladesh by different collectors and deposited at Jahangirnagar University Herbarium (JUH) and Bangladesh National Herbarium (DACB) were also examined.

Identification of all plant specimens was confirmed throughconsultation with the experienced Plant Taxonomists of JUH and DACB, matching the specimens with authentically identified herbarium specimens housed at DACB, JUH and Dhaka University Salar Khan Herbarium (DUSH), clear type images available in the websites of different international herbaria, and taxonomic descriptions and keys available in standard taxonomic literatures (e.g., Hooker, 1872-1897; Prain,1903; Nasir and Ali, 1980-2005; Wu, et al., 1995-2013; Watson et al., 2011; Flora of North America Editorial Committee, 1993-2014). The original and updated nomenclatural information was incorporated following Index Kewensis, recent taxonomic publications and the nomenclatural data bases (e.g., IPNI, 2008 and TROPICOS, 2010).

Data analysis: Data were analyzed using SPSS software (version 16.0). One way ANOVA (DMRT) was used to test the significant differences (P<0.05) for marginal means of variables. Density, relative density, frequency, relative frequency, abundance and relative abundance of the plant species were estimated calculating the relevant formulae available in Mueller-Dombois and Ellenberg (1974) and Shukla and Chandal (1980).

3. Resultsand Discussion

Species composition: During this study, a total of 116 undergrowth species belonging to 97 genera and 52 families of vascular plants were found in the tree plots of exotic A. auriculiformis and E. camaldulensis, whereas, 150 undergrowth species belonging to 122 genera and 56 families in the tree plots of indigenous S. robusta and M. indica in the deciduous forest area of Hoteya Forest Range. Based on these results, this study reports the occurance of a relatively lower number of undergrowth species (18.68%) in the exotic tree plots of A. auriculiformis and E. camaldulensis in respect to that in the indigenous tree plots of S .robusta and M. indica in the study area in summer-, monsoon- and winter- seasons, whether considering all undergrowth species or the seedlings/saplings of the tree species (referred as ‘undergrowth tree species’ in this article) only (Table 2; Figure 1). The results of this study also indicate that the number of uncommon species was relatively lower in the exotic tree plots than that in the indigenous tree plots facing similar extent of ecological and anthropogenic stresses (Table 1). Moreover, the rare orchid species Gastrodia zeylanica and Geodorum densiflorum were found to grow in indigenous plots but no orchid was observed in exotic tree plots. These scenarios indicate that plantations of indigenous tree species are relatively better than that of the exotic tree species in harboring better richness of undergrowth species, consistent with Montagnini et al. (1995).

Among the tree plots of exotic and indigenous species, the S. robusta plots were found to harbor the maximum number of undergrowth species in each of the summer-, monsoon- and winter seasons, which was followed by that of A . auriculiformis, E. camaldulensis and M. indica, whether the undergrowths of all or only of tree species areconsidered (Figure 2).

Table 1. Checklist of undergrowth plant species recorded from the deciduous forest area of Hoteya Forest Range under Sakhipur upazila of Tangail district.

Scientific name Familyname Habit Plant group* Exoticplot Indigenous plot Voucher Specimen
Acacia auriculiformis Benth. Leguminosae Tree D MR-1
Aegle marmelos L. Rutaceae Tree D MR-54
Ageratum conyzoides (L.) L. Compositae Herb D   MR-54
Albizia lebbeck (L.) Benth. Leguminosae Tree D MR-179
Albizia procera (Roxb.) Benth. Mimosaceae Tree D MR-56
Alstonia scholaris (L.) R. Br. Apocynaceae Tree D MR-43
Alternanthera sessilis (L.) R. Br. ex DC. Amaranthaceae Herb D MR-89
Ampelocissus barbata (Wall.) Planch. Vitaceae Herb D MR-154
Ampelocissus latifolia (Roxb.) Planch. Vitaceae Herb D   MR-41
Andrographis paniculata (Burm. f.) Wall. ex Nees Acanthaceae Herb D MR-80
Anisomeles indica (L.) Kuntze. Lamiaceae Herb D   MR-49
Antidesma acidum Retz. Euphorbiaceae Tree D MR-52
Antidesma ghaesembilla Gaertn. Euphorbiaceae Tree D MR-31
Artocarpus chama Buch.-Ham. Moracerae Tree D MR-148
Artocarpus heterophyllus Lam. Moraceae Tree D MR-58
Axonopus compressus (Sw.) P. Beauv. Poaceae Herb M MR-5
Azadirachta indica A. Juss. Meliaceae Tree D MR-59
Bambusa balcooa Roxb. Poaceae Shrub D   MR-180
Bauhinia racemosa Lamk. Caesalpiniaceae Tree D   MR-147
Blumea flava DC. Asteraceae Herb D   MR-111
Blumea lacera (Burm. f.) DC. Asteraceae Herb D   MR-40
Bombax ceiba L. Bombacaceae Tree D MR-84
Borassus flabellifer L. Arecaceae Tree M MR-7
Bridelia retusa (L.) A. juss. Euphorbiaceae Tree D MR-108
Butea monosperma (Lam.) Taub. Caesalpiniaceae Tree D MR-86
Calamus guruba Buch.-Ham. ex Mart. Arecaceae Shrub D   MR-44
Canscora decussata (Roxb.) Roem.&Schult Gentiaceae Herb D   MR-94
Careya arborea Roxb. Lythraceae Tree D MR-11
Careya herbacea Roxb. Lythraceae Herb D   MR-112
Cassia fistula L. Caesalpiniaceae Tree D   MR-113
Catunaregam spinosa (Thunb.) Tirveng. Rubiaceae Shrub D   MR-2
Centella asiatica (L.) Urb. Apiaceae Herb D MR-71
Centrosema pubescens Benth. Leguminosae Herb D   MR-114
Cheilanthes belangeri (Bory) C. Chr. Sinopteridaceae Fern P MR-4
Cheilanthes tenuifolia (Burm. f.) Sw. Sinopteridaceae Fern P   MR-171
Chloris virgata Sw. Poaceae Herb M     MR-153
Chrysopogon aciculatus (Retz.) Trin. Poaceae Herb D   MR-79
Clerodendrum infortunatum L. Lamiaceae Herb D MR-6
Coccinia grandis (L.) Voigt Cucurbitaceae Herb D MR-105
Colocasia esculenta (L.) Schott Araceae Herb M MR-92
Commelina erecta L. Commelinaceae Herb M MR-115
Commelina nudiflora L. Commelinaceae Herb M   MR-34
Corchorus capsularis L. Tiliaceae Herb D   MR-149
Crinum latifolium L. Liliaceae Herb M   MR-168
Curculigo orchioides Gaertn. Hypoxidaceae Herb M MR-33
Curcuma caesia Roxb. Zizingiberaceae Herb M MR-142
Curcuma domestica Valeton Zizingiberaceae Herb M   MR-172
Curcuma zedoaria (Christm.) Roscoe Zinzigiberaceae Herb M MR-32
Cynodon dactylon (L.) Pers. Poaceae Herb M MR-73
Cyperus haspan L. Cyperaceae Herb M   MR-155
Cyperus iria L. Cyperaceae Herb M MR-116
Cyperus rotundus L. Cyperaceae Herb M MR-27
Dentella repens (L.) J.R. Forst. & G. Forst. Rubiaceae Herb D   MR-119
Derris trifoliata Lour. Fabaceae Herb D   MR-157
Desmodium gangeticum (L.) DC. Fabaceae Herb D   MR-165
Desmodium gyroides (Roxb. ex Link) DC. Fabaceae Herb D MR-117
Desmodium motorium (Houtt.) Merr. Fabaceae Herb D   MR-87
Desmodium pulchellum (L). Benth. Fabaceae Shrub D MR-118
Desmodium triflorum (L.) DC. Fabaceae Herb D MR-20
Digitaria sanguinalis (L.) Scop. Poaceae Herb M MR-162
Dillenia pentagyna Roxb. Dilleniaceae Tree D   MR-109
Dioscorea belophylla (Prain) Voigt ex Heines Dioscoreaceae Herb M MR-35
Dioscorea bulbifera L. Dioscoreaceae Herb M MR-169
Dioscorea hamiltonii Hook. f. Dioscoreaceae Herb M MR-19
Dioscorea pentaphylla L. Dioscoreaceae Herb M MR-67
Dioscorea triphylla L. Dioscoreaceae Herb M MR-120
Dysolobium pilosum (J.G. Klein ex Willd.) Maréchal Fabaceae Herb D   MR-167
Echinochloa colonum (L.) Link. Poacaeae Herb D   MR-159
Eclipta prostrata (L.) L. Asteraceae Herb D   MR-46
Elephantopus scaber L. Asteraceae Herb D MR-78
Eleusine indica (L.) Gaertn. Poaceae Herb M   MR-182
Eragrostis tenella (L.) P. Beauv. ex Roem. & Schult. Poacaeae Herb M MR-102
Eragrostis unioloides (Retz.) Nees ex Steud. Poaceae Herb M   MR-121
Eriocaulon sexangulare L. Eriocaulaceae Herb M MR-122
Eucalyptus camaldulensis Dehnh. Myrtaceae Tree D   MR-76
Eupatorium odoratum L. Asteraceae Shrub D MR-3
Euphorbia hirta L. Euphorbiaceae Herb D   MR-166
Evolvulus nummularius (L.) L. Convolvulaceae Herb D MR-62
Ficus hispida L. f. Moraceae Tree D MR-66
Ficus religiosa L. Moraceae Tree D   MR-106
Fimbristylis miliacea (L.) Vahl Cyperaceae Herb D   MR-181
Flacourtia indica (Burm. f.) Merr. Flacourtiaceae Shrub D   MR-12
Flemingia strobilifera (L.) R. Br. Fabaceae Herb D   MR-124
Fleurya interrupta (L.) Gaudich. Urticaceae Herb D     MR-150
Floscopa scandens Lour. Commelinaceae Herb M   MR-82
Garuga pinnata Roxb. Burseracerae Tree D   MR-125
Gastrodia zeylanica Schltr. Orchidaceae Herb M   MR-128
Geodorum densiflorum (Lamk.) Schltr. Orchidaceae Herb M   MR-81
Glochidion heyneanum (Wight & Arn.) Wight Euphorbiaceae Shrub D   MR-156
Glycosmis pentaphylla (Retz.) A. DC. Rutaceae Shrub D   MR-173
Gmelina arborea Roxb. ex Sm. Verbenaceae Tree D   MR-75
Hedyotis scabra Wall. ex Kurz Rubiaceae Herb D MR-126
Hemidesmus indicus (L.) R. Br. Asclepiadaceae Herb D MR-30
Holarrhena pubescens Wall. ex G. Don Apocynaceae Tree D MR-8
Hymenodictyon excelsum (Roxb.) DC. Rubiaceae Tree D   MR-37
Hyptis suaveolens (L.) Poit. Lamiaceae Herb D MR-129
Ichnocarpus frutescens (L.) W.T. Aiton Apocynaceae Herb D MR-21
Imperata cylindrica var. major (Nees) C.E. Hubb. Poaceae Herb M MR-22
Jasminum scandens (Retz.) Vahl Oleaceae Shrub D   MR-163
Justicia diffusa Willd. Acanthaceae Herb D MR-132
Kyllinga nemoralis (J.R. Forst. & G. Forst.) Dandy ex Hutch. & Dalziel Cyperaceae Herb M MR-90
Lannea coromandelica (Houtt.) Merr. Anacardiaceae Tree D MR-45
Leucas aspera (Willd.) Link. Lamiaceae Herb D MR-133
Leucas indica (L.) R. Br. ex Sm. Lamiaceae Herb D MR-70
Lindernia ciliata (Colsm.) Pennell Scrophulariaceae Herb D MR-130
Lindernia crustacea (L.) F. Muell. Scrophulariaceae Herb D MR-25
Litsea atrata S.K. Lee Lauraceae Tree D   MR-174
Litsea glutinosa (Lour.) C.B.Rob. Lauraceae Tree D MR-14
Ludwigia hyssopifolia (G. Don) Exell Onagraceae Herb D MR-136
Lygodium flexuosum (L.) Sw. Lygodiaceae Herb P MR-16
Lygodium yunnanense Ching Lygodiaceae Herb P MR-135
Mangifera indica L. Anacardiaceae Tree D   MR-101
Melia azedarach L. Meliaceae Tree D MR-74
Melocanna bambusoides Trin. Sterculiaceae Shrub M   MR-134
Microcos paniculata L. Tiliaceae Tree D   MR-127
Microlepia strigosa (Thunb.) C. Presl Dennstaedtiaceae Fern P   MR-137
Mikania cordata (Burm. f.) B.L. Rob. Asteraceae Herb D MR-61
Miliusa velutina (Dunal) Hook. f. & Thomson Annonaceae Tree D MR-50
Mimosa himalayna Gamble Mimosaceae Shrub D MR-85
Mimosa pudica L. Mimosaceae Herb D MR-23
Modhica trilobata Roxb. Cucurbitaceae Herb D MR-175
Mucuna pruriens (L.) DC. Fabaceae Herb D MR-104
Mukia maderaspatana (L.) M. Roem. Cucurbitaceae Herb D   MR-97
Murdannia edulis (Stokes) Faden Commelinaceae Herb M   MR-99
Nelsonia canescens (Lamk.) Spreng. Acanthaceae Herb D   MR-107
Neolamarckia cadamba (Roxb.) Bosser Rubiaceae Tree D MR-143
Neonauclea sessilifolia (Roxb.) Merr. Rubiaceae Tree D   MR-51
Ocimum gratissimum L. Lamiaceae Shrub D   MR-145
Oldenlandia corymbosa L. Rubiaceae Herb D   MR-151
Oplismenus compositus (L.) P. Beauv. Poaceae Herb M   MR-158
Panicum vicinus F. M. Bailey Poaceae Herb M MR-26
Paspalidum punctatum (Brum) A. Camus Poaceae Herb D   MR-139
Paspalum scrobiculatum L. Poaceae Herb D   MR-15
Phaseolus aconitifolius Jacq. Fabaceae Herb D   MR-176
Phaulopsis imbricata (Forssk.) Sweet Hort. Acanthaceae Herb D MR-60
Phoenix acaulis Roxb. Arecaceae Shrub M MR-36
Phoenix sylvestris Roxb. Arecaceae Tree M   MR-96
Phyllanthus embelica L. Euphorbiaceae Tree D MR-55
Phyllanthus reticulatus Poir. Euphorbiaceae Shrub D MR-13
Phyllanthus urinaria L. Euphorbiaceae Herb D MR-103
Pogostemon auricularius (L.) Hassk. Lamiaceae Herb D   MR-164
Polygala chinensis L. Polygalaceae Herb D   MR-131
Pteris ensiformis Burm. f. Pteridaceae Fern P MR-144
Pterygota alata (Roxb.) R. Br. Sterculiaceae Tree D   MR-64
Pueraria phaseoloides (Roxb.) Benth. Leguminosae Herb D MR-146
Randia uliginosa (Retz.)Poir. Rubiaceae Tree D MR-42
Rhaphidophora hookeri Schott Araceae Herb M   MR-63
Riedlea corchorifolia (L.) DC. Sterculiaceae Herb D   MR-138
Rungia pectinata (L.) Nees Acanthaceae Herb D MR-17
Sarcolobus sp. R. Br. Asclepiadaceae Herb D   MR-68
Scleria levis Retz. Cyperaceae Herb M   MR-48
Scoparia dulcis L. Cyperaceae Herb D MR-95
Selaginella ciliaris (Retz.) Spring Selaginellaceae Fern P MR-88
Selaginellavaginata Spring Selaginellaceae Fern P   MR-177
Semecarpus anacardium L. f. Anacardiaceae Tree D   MR-57
Senna sophera (L.) Roxb. Caesalpiniaceae Herb D   MR-98
Senna tora (L.) Roxb. Caesalpiniaceae Herb D   MR-178
Shorea robusta Roxb. Dipterocarpaceae Tree D MR-10
Sida acuta Burm. f. Malvaceae Shrub D   MR-100
Sida rhombifolia L. Malvaceae Herb D   MR-152
Smilax ovalifolia Roxb. Smilaceae Herb D MR-38
Spatholobus roxburghii Benth. Fabaceae Herb D   MR-29
Spermacoce articularis L. f. Rubiaceae Herb D MR-69
Spilanthes acmella (L.) L. Asteraceae Herb D   MR-161
Sporobolus diandrus (Retz.) P. Beauv. Poaceae Herb M   MR-72
Sterculia villosa Roxb. Sterculiaceae Tree D   MR-140
Streblus asper Lour. Moraceae Tree D MR-9
Synedrella nodiflora (L.) Gaertn. Asteraceae Herb D MR-123
Syzygium fruticosum DC. Myrtaceae Tree D MR-47
Tamarindus indica L. Caesalpiniaceae Tree D   MR-160
Terminalia bellirica (Gaertn.) Roxb. Combretaceae Tree D MR-24
Thespesia lampas (Cav.) Dalzell & A. Gibson Malvaceae Shrub D   MR-83
Triumfetta rhomboidea Jacq. Tiliaceae Shrub D MR-65
Typhonium trilobatum (L.) Schott Araceae Herb M MR-91
Uraria lagopodioides (L.) DC. Fabaceae Herb D   MR-141
Urena lobata L. Malvaceae Herb D MR-77
Vangueria spinosa Roxb. Rubiaceae Shrub D MR-110
Vernonia cinerea (L.) Less. Asteraceae Herb D MR-39
Vitex peduncularis Wall. ex Schauer in A. DC. Vitaceae Tree D   MR-170
Zanthoxylum rhetsa (Roxb.) DC. Rutaceae Tree D MR-28
Zehneria japonica (Thunb.) H.Y. Liu Cucurbitaceae Herb D   MR-53
Ziziphus rugosa Lam. Rhamnaceae Shrub D MR-18

*D=Dycotyledon; M=Monocotyledon; P=Pteridophyta

The potential reasons of finding the better species richness in S. robusta plots include less human interferences and more wildness condition. The finding of relatively less number of species in E. camaldulensis plots in respect to that of S. robusta and A. auriculiformis might be due to less humus cover and more human interferences there. The reasons of occurrence of less number of undergrowth species in M. indica plots include deeper shade under most of the canopy of profusely branched trees and frequent human disturbances etc. in contrast to relatively light shade under the mostly dispersed or narrow canopies and less human interferences in other tree plots.

Figure 1. Species composition in exotic and indigenous plots in summer-, monsoon- and winter seasons.

In A. auriculiformis plots, the maximum number of undergrowth species was recorded during monsoon season, in E. camaldulensis- and S. robusta plots, during summer season, whereas, in M. indica plots, in winter season (Figure 2), which indicate the seasonal variation in growth performance and diversification of the undergrowth species in these tree plots. The occurrence of herbaceous plant species, especially grasses and sedges, was found to fluctuate along with the seasonal changes in a year. This phenemenon is desirable, since the availability of soil moisture, precipitation and temperature etc. plays a major role on the development and sustenance of the associated vegetation in the tree plots.

During summer season, the herbaceous species A. conyzoides, A. compressus, Chromelaena odorata, C. dactylon, C. rotundus, D. triflorum, C. odorata, C. infortunatum, D. triflorum and D. hamiltonii etc. were found to dominate in the exotic and indigenous tree plots. During moonson season, C. zedoarea, C. dactylon, S. articularis, P. vicinus, E. nummularius, I. frutescens, L. ciliate, L. hyssopifolia, R. pectinata and X. spinosaetc. And during winter season, A. compressus, C. infortunatum, C. rotundus, D. triflorum, D. belophylla, C. orchioides, C. zedoaria, C. dactylon, E. nummularius and H. scabra etc. were recorded as the dominating herbaceous undergrowth species in the tree plots studied. The habit categories of the undergrowths of the study area show that the herbs were highest in number and percentage than trees and shrubs (Table 2) in exotic and indigenous plots. The same status of habit categories was found when the undergrowths of all research plots were calculated.

Figure 2. Species composition in different tree plots in summer, monsoon and winter seasons.

During this study, altogether 182 species under 150 genera belonging to 56 families of vascular plant were found as undergrowths in the tree plots of exotic A. auriculiformis and E. camaldulensis and indigenous S. robusta and M. indica of the study area (Table 1 & 2). Out of these species, 133 were dycotyledons, 41 were monocotyledons and the rest eight were pteridophytes. These taxonomic enumeration of the undergrowth species occurring in the study area seems higher in respect to that reported by Uddin and Rahman (1999), Rashid and Mia (2001), Uddin (2002) and Malaker et al. (2010) etc. considering the size of area.

Table 2. Habit categories of the plant species found in exotic and indigenous plots.

Habit Species in exotic plots Species in indigenous plots Species in all plots
Tree 32 (45%) 42 (28%) 47 (26%)
Shrub 11 (9%) 18 (12%) 19 (11%)
Herb 73 (46%) 90 (60%) 116 (63%)
Total 116 (100%) 150 (100%) 182 (100%)

On the otherhand, irrespective of the size of area, it seems lower to that reported by Uddin and Rahman (1999), Uddin (2002), Uddin and Hassan (2010), Arefin et al. (2011), and Uddin and Hassan (2012) etc. and consistent to that reported by Malaker et al. (2010), Rahman and Hassan (1995) and Rahman and Uddin (1997) etc., though a realistic comparision in species enumeration between two or more floristic areas requires homogeneity in size and type of the areas, sampling, strategy and procedure of specimens collection and frequency and intensiveness of the field visits etc.

Density and relative density: The highest average value of undergrowth density was found in M. indica plots (387052±106848 per ha), which was followed by E. camaldulensis (342135±145009 per ha), A. auriculiformis (222465±102954 per ha) and S. robusta (68429±8872 per ha) plots, when all undergrowth species were considered (Figure 3). In M. indica plots, the individual number of few species, especially of grasses and sedges, was higher in respect to that of other plots, whereas, in the tree plots of A. auriculiformis and S. robusta, the individual number of undergrowth tree seedlings and saplings were higher than that of M. indica and E. camaldulensis tree plots. On the other hand, the tree plots of A. auriculiformis were found to house relatively more individuals of herbs, especially of grasses and sedges, and undergrowth tree species in respect to those of S. robusta plots. As the consequence, the average value of undergrowth density in exotic tree plots (262292±117188 per ha) was found to be higher than that (174583±41384 per ha) recorded for indigenous tree plots and A. auriculiformis plots housed relatively higher density of the undergrowths than S. robusta plots, considering all undergrowth species (Figure 3). During this study most of the exotic tree plots were found to be dominated by the individuals of small herbaceous species, especially of grasses and sedges,in respect to the indigenous plots due to whichrelatively more plant individuals were found inexotic plots. The occurrence of lower density of undergrowth species in S. robusta plots in each season in relation to other tree plotsis consistent with Sapkota et al. (2009). The data on plant density in the 14 year old Acacia and Eucalyptus plots recorded by Thapliyal (2002) seem much higher than that recorded by this study, which might be possible because higher number of individuals of herbaceous species like those of grasses and sedgescan occur per hectare land.

Figure 3. Status of undergrowth density per hectare in different tree plots.

Among three seasons, the highest value of density (485271 per ha) was found during winter in E. camaldulensis plots and the lowest value during summer in S. robusta plots (59536 per ha), when all undergrowth species were considered (Figure 4). In case of undergrowth tree species only, the highest density was found in winter (30958 per ha) in A. auriculiformis plots and the lowest in summer in M. indica (1479 per ha) plots (Figure 4). The records of this study on the density of all undergrowth species including the seedlings and saplings of tree species are much lower than that reported by Islam (2004) from S. robusta forests of Madhupur protected area. On the other hand, the data on undergrowth tree species are higher than Rahman (2009)’s record on the density of woody undergrowth species in S. robusta forests of Gazipur. It is notable that the S. robusta forests of Gazipur and the study area are not protected like that of Madhupur where better wild conditions exist and conservation measures were functional.

Figure 4. Status of undergrowth density per hectare in different tree plots in summer, monsoon and winter seasons.

Figure 5. Status of undergrowth density per hectare in exotic and indigenous tree plots in summer, monsoon and winter seasons.

Considering all undergrowth species including the undergrowth tree species it can be concluded that the average undergrowth plant density was higher in exotic tree plots than that in indigenous plots (Figure 5). The highest value (21875 per ha) was found during winter season in exotic tree plots and the lowest (10625 per ha) during summer season in indigenous tree plots (Figure 5).

The highest relative density in exotic tree plots was found for A. compressus (23.35%), which was followed by S. articularis, D. triflorum, C. odorata and A. auriculiformis etc. and in indigenous tree plots,it was recorded also for A. compressus (16.33%), but followed by D. triflorum, S. articularis, C. dactylon and C. rotundus etc., when all undergrowth species were considered. When only the undergrowth tree species were considered, the relative density in exotic plots were found to be highest for A. auriculiformis (77.17%), followed by S. robusta, A. indica, H. antidysentarica and L. glutinosa etc. In indigenous plots, it was found to be highest for S. Robusta (54.28%), followed by A. ghaesembilla, A. auriculiformis, L. glutinosa and H. antidysenterica etc. The seedlings and saplings of A. auriculiformis and S. robusta in some undisturbed tree plots were found to form a dense layer of vegetation that might be the potential reason of finding higher relative density for these two tree species. The finding of relative density for S. robusta and L. glutinosa in S. robusta tree plots is consistent with Islam (2004).

The results of DMRT (Duncan's Multiple Range Test) analysis showed that species number and density were significantly different between the tree plots of A. auriculiformis, S. robusta and M. indica or E. camaldulensis but not significantly different when only the M. indica- and E. camaldulensis plots were considered. These parameters were significantly different when only the tree plots of two indigenous or two exotic species were considered (Table 3).

Table 3. The results of DMRT analysis on different parameters of species composition and density in four types of research plots in Sakhipur, Tangail.

Plot type No. of species Density
A. auriculiformis 71.3333b 355.6667ab
E. camaldulensis 51.6667a 547.3333c
S. robusta 88.3333c 109.6667a
M. indica 46.3333a 619.0000c

Note: Values in the same column that do not share common letters are significantly different at 5% (α = 0.05) level among the plots after DMRT.

Frequency and Relative Frequency: In case of all undergrowth species, A. compressus was found in highest frequency and relative frequency (70.74%; 7.46%), which was followed by S. articularis, A. auriculiformis, C. infortunatum and C. odorata etc. in exotic tree plots, whereas, in indigenous tree plots, C. infortunatum was found in highest frequency and relative frequency (64.07%; 5.02%), which was followed by S. robusta, C. zedoaria, I. frutescens and D. hamiltonii etc. The finding of relative frequency for C. infortunatum and I. frutescens is in consistent with Islam (2004). In exotic tree plots, the value of frequency and relative frequency recorded for C. pubescens, C. iria, F. miliacea, M. trilobata and P. ensiformis etc, and in indigenous tree plots, for M. azadirach, M. trilobata, R. hookeri, Sarcolobus sp. and Z. japonica etc. were comparatively lower.

In case of undergrowth tree species, the frequency and relative frequency in exotic tree plots was found to be highest for A. auriculiformis (65.37%; 37.24%), followed by S. robusta, L. glutinosa, A. indica and H. antidysentarica, whereas, in indigenous tree plots, it was recorded for S. robusta (63.15%; 20.48%), followed by A. ghaesembilla, L.glutinosa, C. arborea and H. excelsumetc. The relative frequency recorded here for S. robusta and L. glutinosa seems somewhat higher than the findings of Islam (2004). In exotic tree plots, B. ceiba, A. lebbeck, A. marmelos, A. scholaris and R. dumetorum etc., and in indigenous tree plots, M. azadirach, L. salicifolia, B. flabellifer, N. sessilifolia and M. paniculata etc. were found with less frequency and relative frequency.

Abundance and Relative Abundance: When all undergrowth plant species were considered, C. iria was found in highest abundance and relative abundance (329; 13.39%), which was followed by A. compressus, S. articularis, D. triflorum and C. dactylonetc. in exotic tree plots, whereas, in indigenous plots, A. compressus was found to be most abundant and in highest relative abundance, which was followed by D. triflorum, C. dactylon, S. articularis and A. conyzoides etc. In exotic tree plots, P. phascoloides, B. flabellifer, C. arborea, L. coromandelica and S. ovalifolia etc. and in indigenous plots, A. scholaris, D. pentagyna, G. pinnata, Z. japonica and N. cadamba etc. were found to occur in less abundance and relative abundance.

On the other hand, when only the undergrowth tree species were considered, A. auriculiformis was found in highest abundance and relative abundance (32; 19.78%), which was followed by A. indica, H. antidysentarica, P. emblica and E. camaldulensis etc. in exotic tree plots, whereas, in indigenous tree plots, S. robusta was found in highest abundance and relative abundance (18; 12.72%), which was followed by A. auriculiformis, P. emblica, H. antidysenterica and P. sylvestris etc. The data on relative abundance of S. robusta in Madhupur area recorded by Islam (2004) and Rahman (2009) are higher and that of P. emblica recorded by Islam (2004) is lower than the data of this study. In exotic tree plots, B. flabellifer, L. coromandelica, C. arborea, G. arborea and F. hispida etc., and in indigenous tree plots, D. pentagyna, A. scholaris, B. ceiba, B. monosperma and Z. rhetsa etc. were found in less abundance and relative abundance.

In the study area, some key factors were found to affect the occurrence and distribution of undergrowth species in the tree plots of exotic and indigenus species in different magnitudes. The undergrowth plant species, especially in most of the exotic tree plots, were found to be disturbed by the biotic factors like clear felling, fuel wood collcetion, leaf litter collection, cattle grazing, firing, and making pathways arbitrarily by the local people etc. and abiotic factors like shade, rainfall, temperature and soil moisture and humidity etc. Different management systems functional in the study area were also the important reasons for high internal variation in species richness in exotic and indigenous tree plots. Some tree growers weed out almost all seedlings of indigenous or associate species, but others allowed thier natural regeneration. In some cases fire was passed through the indigenous stands (S. robusta) as a weed control method, supported by Tyynela (2001).

4. Conclusions

This study concludes that the exotic tree plots of the study area harbored 18.68% less species in comparison to indigenous plots. The species composition of exotic tree plots was lower than that of indigenous plots in summer-, monsoon- and winter seasons. S. robusta tree plots were found to house highest number of undergrowth species and M. indica tree plots the lowest in all seasons. A. auriculiformis and S. robusta were found with highest relative density respectively in exotic and indigenous tree plots. The herbaceous species A. compressus and C. iria were found with highest relative frequency and highest relative abundance, respectively in exotic- and indigenous tree plots. The impacts of different key factors on the occurrence and distribution of undergrowth species in the tree plots of exotic and indigenousspecies were not uniform. This study provides an insight into the impacts of monoculture of exotic species on the status of undergrowths in a deciduous forest area of central Bangladesh. Further comparative studies involving more parameters are necessary to elucidate the exact impacts of massive monoculture of exotic tree species in this country. A. compressus was found in highest relative density and frequency and C. iria in highest relative abundance in exotic tree plots, whereas, in indigenous tree plots, A. compressus was found in highest relative density and abundance, and C. infortunatum in highest relative frequency. Species number and density were significantly different between A. auriculiformis and S. robusta- and M. indica or E. camaldulensis plots. This study suggests preferring the indigenous species for plantation programs in forested and fertile land areas and exotic species for that in the degraded or barren areas with strict maintenance of the natural condition.

Authors’ Contribution

All authors conceived the study and contributed to the interpretation and discussion of the results. All authors helped to analysed the field data and draft the manuscript. All authors read and approved the final manuscript.

Acknowledgements

The authors thank the Bangladesh Forest Department for granting permission to work in the forest of Tangail forest division and Bangladesh National Herbarium, Dhaka.


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