Composition and Distribution of Vascular Epiphytes in a Tropical Semideciduous Forest, Ghana

Composition and distribution of vascular epiphytes in a tropical semideciduous forest, Ghana

Patrick Addo-Fordjour*, Alexander Koﬁ Anning, Mathew Glover Addo and Margaret Frimpomaa Osei Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology, KNUST, Kumasi, Ghana

examine´, et l’on a note´ la pre´sence, l’emplacement et les Abstract formes vivantes de tous les e´piphytes. Vingt-neuf (29) es- The composition and distribution of vascular epiphytes pe`ces d’e´piphytes appartenant a` 14 genres et a` 11 familles were studied in two 1-ha plots in the KNUST Botanic ont e´te´ identifieés au cours de cette e´tude. Elles croissaient garden, Ghana. One-hectare plot each was randomly set sur 48 espe`ces d’arbres et se pre´sentaient sous trois formes up in secondary and cultivated forests for the identification vivantes, he´mi-e´piphytes (45%), e´piphytes opportunistes and enumeration of trees and shrubs (‡10 cm dbh), and (45%) et e´piphytes vrais (10%). Les espe`ces vasculaires epiphytes. Each tree was carefully examined, noting the d’e´piphytes repre´sentaient 25,7% de toutes les espe`ces presence, positions and life-forms of all epiphytes. Twenty- ve´ge´tales identifieés (a` l’exclusion des herbaceés et des nine epiphyte (29) species belonging to fourteen genera plantes grimpantes). Les espe`ces hoˆtes (P < 0,001), and eleven families were identified in the study. These were l’habitat (P = 0,001) et leur interaction (P < 0,001) ava- hosted by 48 tree species and occurred in three life-forms: ient un effet tre`s net sur la composition des e´piphytes dans hemi-epiphytes (45%), casual epiphytes (45%) and true les foreˆts. Les Moraceae e´taient la famille dominante epiphytes (10%). The vascular epiphyte species made up (44,8%) et Nephrolepis undulata J. Sm. et N. biserrata (Sw.) 25.7% of all the identified plant species (excluding herbs Scott e´taient les espe`ces d’e´piphytes les plus communes. En and climbers) encountered. Host species (P < 0.001), termes de distribution verticale, la plupart des e´piphytes se habitat (P = 0.001) and their interaction (P < 0.001) had situaient sur les troncs et quelques-uns croissaient dans la strong effects on epiphyte composition in the forests. canopeé. Moraceae was the most dominant family (44.8%), while Nephrolepis undulata J. Sm. and N. biserrata (Sw.) Scott. were the commonest species of epiphytes. In terms of vertical distribution, most epiphytes were located on the Introduction trunk, while a few occurred in the canopy. Epiphytes are plants that attach themselves to and grow on Key words: composition, distribution, hosts, vascular other plants occurring from the forest understorey to the epiphytes periphery of tree crowns (Benzing, 2000). The importance of vascular epiphytes to tropical biodiversity lies in their ability to provide habitats and food for many of the animals Re´sume´ inhabiting the rainforest canopies (Cruz-Angoń & Green- On a e´tudie´ la composition et la distribution d’e´piphytes berg, 2005). Epiphytes, as vulnerable as they are known to vasculaires dans deux parcelles d’un hectare, dans le Jar- be, can serve as a good indicator group of biodiversity that din botanique de la KNUST, au Ghana. Chaque parcelle can be monitored to assess the effects of forest disturbance d’un hectare fut creéé au hasard dans des foreˆts secondaire (Turner et al., 1994). Other important ecological functions et cultiveé pour y identifier et faire la liste des arbres et des played by epiphytes include regulating water balance and arbustes (‡10 cm dbh). Chaque arbre fut soigneusement nutrient cycling through the maintenance of high humidity levels and reduction of the potentially disruptive *Correspondence: E-mail: [email protected] ⁄ effects of torrential rains in the forest (Coxson & Nadkarni, [email protected] 1995).

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Epiphytes as a group may be prominent, accounting for of tree species as a whole in the composition of epiphyte a large proportion – or even most – of the vascular species flora. The findings of this study would help increase the of the forest (Kelly et al., 1994). They generally make up understanding of ecology of epiphytes in Africa. about 10% of the total vascular flora worldwide (Benzing, This study was conducted to determine the role of host 1990). Most of them are limited to tropical and subtropical tree species and habitat type on the composition of epi- forests, where they may be the most diverse life-form in phyte flora and their distribution in a semideciduous very humid formations (Gentry & Dodson, 1987). Their rainforest. composition in tropical forests is influenced by frequent disturbance and habitat patchiness (Benzing, 1990). Materials and methods As hosts, the type and nature of trees constitute important determinants of epiphyte composition in the Study area tropical forest (Burns & Dawson, 2005). Epiphyte distribution is also affected by conditions of the canopy The study was carried out in a tropical semideciduous including shortage of water and nutrients, and the modes rainforest of the Kwame Nkrumah University of Science of seed dispersal of epiphytes (Hamrick & Godt, 1996). Tree and Technology, KNUST, Kumasi, Ghana (latitude bark architecture has also been suggested as an important 635¢N–640¢N and longitude 130¢W–135¢W) (Fig. 1). factor in the distribution of epiphytes (Butler, 2005). The forest, which is located in an urban area, covers an Studies have shown that epiphyte diversity and composi- area of 12.9 ha, comprising two main habitat types tion often vary vertically along tree trunk and crown (Ter namely, secondary forest and cultivated forest. Most of Steege & Cornelissen, 1989; Dickinson, Mark & Dawkins, the plant species (both native and exotic) in the 1993), with most of them located in the canopy of rain- cultivated forest were intentionally introduced. Part of forests (Werneck & Espı´rito-Santos, 2002) compared to a this forest has also been developed for recreational few on the trunk (Schuettpelz & Trapnell, 2006). activities, resulting in increased pressure on the vegeta- Epiphyte studies in the tropics, though lagging behind tion. Human-induced disturbances from illegal felling of those of trees and shrubs, have gained much more atten- trees and hunting are also common in this part of the tion in recent times. However, literature on epiphytes in garden. This habitat thus experiences human distur- Ghana and Africa as a whole is scanty. While several bance from time to time. The secondary forest on the studies have suggested that tree size plays an important other hand has been free from human intervention in role in the composition of epiphytes in forests (Lyons, terms of cultivation. This portion of the garden is Nadkarni & North, 2000; Zotz & Vollrath, 2003; Burns & therefore characterized mostly by native species and less Dawson, 2005), only a few studies have examined the role disturbance.

Main Entrance

Cultivated Main Road forest

ver

Wiwi Ri

Farm Road Secondary forest

Unity Hall

Ayeduase R Fig 1 Map of a section of the KNUST showing the secondary and cultivated Paa joe Stadium oad forests of the Botanic garden

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The garden is endowed with diverse species that include and habitat were used as factors, while the number of tropical palms, timber species, bamboo species and other epiphyte species on the host was used as the variate. Epi- species of medicinal value, with up to 68% of all species phyte species numbers at the various positions along the being native (Anning et al., 2008). The annual rainfall in hosts were compared using a t-test. All analyses were the area ranges between 931 and 1120 mm, while the conducted with the 10th edition of the GENSTAT Software average annual monthly temperature ranges between (VSN International Ltd, Hemel Hempstead, UK) at a sig- 21.6 and 32.1C (The KNUST Meteorological Department, nificance level of 5%. unpublished data). Results Sampling Composition of epiphytes The study was carried out between February and May 2007 in two 1-ha plots. One-hectare plot each was set A total of 29 epiphyte species belonging to fourteen genera up in the secondary and cultivated forests. Each plot was and eleven families were recorded during the study. The subdivided into sixteen 25 m · 25 m quadrats to ensure family Moraceae contributed most of the vascular epiphyte accurate enumeration of all species. All trees and shrubs flora (44.8%) followed by Nephrolepidaceae (10.3%). The (‡10 cm diameter at breast height, dbh) were enumer- families Orchidaceae, Polypodiaceae, Rubiaceae and Aster- ated in each quadrat. The trees were then carefully aceae contributed equally (6.9%) to the epiphyte flora examined for the presence and relative positions of epi- (Table 1). Species richness was greater in the secondary phytes. The canopies of very tall trees were accessed forest (24 species) than in the cultivated forest (fourteen using single-rope climbing techniques (Perry, 1978). The species). life-forms of the epiphytes were described according to The vascular epiphytes were characterized by three Bogh (1992), which included true epiphytes (T) – species life-forms (Table 1) namely, casual epiphytes (45%), hemi- that normally spend their entire lifespan as epiphytes; epiphytes (45%) and true epiphytes (10%). The hemi- hemi-epiphytes (H) – species that germinate on trees and epiphytes were represented by one family (Moraceae), later establish root contact with the ground; casual whereas the true epiphytes and the casual epiphytes were epiphytes (C) – species that can complete their life cycles represented by three and nine families respectively. either as terrestrials or as epiphytes. Identification of the A total of 558 trees representing 65 species, 59 genera plant species was carried out by plant taxonomists and and 29 families were identified in the study, of which 62% with reference to local manuals and Floras (Hawthorne, hosted epiphytes. More host species occurred in the 1990; Arbonnier, 2004; Poorter et al., 2004). Voucher cultivated forest than in the secondary forest (Table 2). specimens were deposited at the KNUST herbarium, Fabaceae was the most dominant host family recording six Kumasi. species, followed by Arecaceae (five species), Moraceae Horizontal distribution of species was determined using (four species), Euphorbaceae (three species) and Apocyn- their frequencies of occurrence (% FO) (Munõzet al., 2003) aceae (three species) (Table 2). Elaeis guineensis Jacq. hos- computed as follows: ted the highest number of epiphyte species (sixteen) Ni followed by Anthocleista vogelii Planch., Howea spp. and %FO ¼ 100% N Amphimas pterocarpoides Harms hosting nine, eight and seven species respectively. where Ni = number of trees on which epiphyte species i Host species (F = 17.28; df = 45; P < 0.001), habitat was recorded. N = total number of trees sampled within (F = 11.39; df = 1; P = 0.001) and their interaction the quadrat. (F = 23.48; df = 45; P < 0.001) had significant effects on the composition of vascular epiphytes in the forest. Vari- ation in the composition of epiphytes was explained more Data analysis by host species (40%) than the habitat (6%). Half of the Analysis of variance (ANOVA) was performed to determine variation in the vascular epiphyte composition (50%) the effects of host species, habitat and their interaction on could be explained by the interaction between host species the composition of epiphytes in the forests. Host species and habitat.

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Table 1 Composition and distribution of epiphytes in the KNUST Botanic Garden

Epiphyte species Family Life-form Relative frequency (%)

Acridocarpus sp. Orchidaceae C 1.2 Calyptrochilum emarginatum Schltr. Orchidaceae T 1.2 Ceiba sp. Bombacaceae C 2.4 Chromolaena odorata (L.) R.M.King & H.Rob. Asteraceae C 2.4 Combretum sp. Combretaceae C 1.2 Commelina benghalensis L. Commelinaceae C 2.4 Elaeis guineensis Jacq. Arecaceae C 1.2 Emilia sanchifolia (L.) DC. Asteraceae C 3.6 Ficus ottoniifolia (Miq.) Miq. Moraceae H 1.2 Ficus ovata Vahl Moraceae H 1.2 Ficus polita Vahl Moraceae H 7.1 Ficus saussureana D.C. Moraceae H 2.4 Ficus sp. 1 Moraceae H 1.2 Ficus sp. 2 Moraceae H 3.6 Ficus sp. 3 Moraceae H 3.6 Ficus tessellata Warb. Moraceae H 2.4 Ficus thonningii Blume Moraceae H 1.2 Ficus trichopoda Baker Moraceae H 4.8 Ficus umbellata Vahl Moraceae H 1.2 Ficus vogelii Miq. Moraceae H 6 Ficus vogelii var. pubicarpa Mildbraed & Burret Moraceae H 3.6 Microsorum punctatum (L.) Copel. Polypodiaceae T 2.4 Microsorum scolopendria Copel. Polypodiaceae T 3.6 Nephrolepis biserrata (Sw.) Schott Nephrolepidaceae C 9.5 Nephrolepis exaltata (L.) Schott Nephrolepidaceae C 2.4 Nephrolepis undulata J.Sm. Nephrolepidaceae C 22.6 Pavetta corymbosa (DC.) F.N. Williams Rubiaceae C 1.2 Psydrax subcordata (DC.) Bridson Rubiaceae C 1.2 Tabebuia spectabilis Nichols. Bignoniaceae C 2.4

T, true epiphyte; H, hemi-epiphytes; C, casual epiphytes.

many reports of the significant contribution of epiphytes Distribution of vascular epiphytes in tropical forests (Gentry & Dodson, 1987; Kelly et al., The commonest species in all the studied plots were Neph- 1994; Schneider, 2001). Consistent with the work of rolepis undulata J.Sm. (22.6%) and N. biserrata (Sw.) Schott Mucunguzi (2007), there were three life-forms of (9.5%) (Table 1). The epiphytes were vertically distributed in vascular epiphytes in the study, with the hemi-epiphytes five positions along the host trees (Fig. 2). While most of the being represented by only the family Moraceae. The species were located on the middle trunk (33.3%) and lower true epiphytes were the rarest life-form of vascular trunk (32.6%), the least number of species occurred in the epiphytes in this study unlike in Mucunguzi (2007) upper canopy (0.7%). The diversity of epiphytes at the var- where it was the commonest life-form. The family ious positions on the hosts differed significantly (P = 0.002). Orchidaceae did not contribute much to the epiphytic flora unlike in other studies, where orchids predominated Discussion the epiphytic flora (Schuettpelz & Trapnell, 2006; Mucunguzi, 2007). Contrary to the findings of Nieder, Engwald & Barthlott (1999), orchids were more promi- Composition of epiphytes nent in the secondary forest than in the cultivated forest, The relatively high proportion of vascular plant species which has seen relatively higher levels of human inter- identified as epiphytes in this study (25.7%) confirms the ference.

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Table 2 Abundance of host species sampled and number hosting epiphytes in the secondary forest (SF) and cultivated forest (CF)

No. of individuals hosting No. of individuals sampled epiphyte

Species Family SF CF Overall SF CF Overall

Albizia adianthifolia (Schumach.) W.F. Wight Fabaceae 0 6 6 0 6 6 Albizia zygia (DC.) Macbr. Fabaceae 2 2 4 2 2 4 Alstonia boonei De Wild. Apocynaceae 2 2 4 2 2 4 Amphimas pterocarpoides Harms Fabaceae 4 26 30 4 22 26 Anthocleista nobilis G.Don. Loganiaceae 2 0 2 2 0 2 Anthocleista vogelii Planch. Loganiaceae 2 10 12 2 10 12 Anogeissus leiocarpus (DC.) Guill Pern Combretaceae 2 0 2 2 0 2 Antiaris africana Engl. Moraceae 2 0 2 2 0 2 Antiaris toxicaria (Pers.) Lesch. Moraceae 0 4 4 0 4 4 Arecaceae sp. Arecaceae 0 34 34 0 24 24 Artocarpus nobilis Thw. Moraceae 2 0 2 2 0 2 Baphia nitida Lodd. Fabaceae 8 0 8 4 0 4 Blighia sapida Koenig. Sapindaceae 0 12 12 0 12 12 Callitris cupressiformis Vent. Cupressaceae 6 4 10 2 4 6 Carapa procera DC. Meliaceae 10 0 10 2 0 2 Ceiba pentandra (L.) Gaertn. Bombaceae 0 2 2 0 2 2 Cinnamomum camphora (L.) J. Presl Lauraceae 4 0 4 2 0 2 Citrus sinensis (L.) Osbeck Rutaceae 4 4 8 4 4 8 Cola millenii K.Schum. Sterculiaceae 0 2 2 0 2 2 Croton sp. Euphorbiaceae 2 0 2 2 0 2 Daniellia oliveri (Rolfe) Hutch. & Dalz. Fabaceae 0 20 20 0 16 16 Elaeis guineensis Jacq. Arecaceae 44 4 48 38 4 42 Encephalartos barteri Carruth.ex Miq. Cycadaceae 2 0 2 2 0 2 Funtumia elastica (Preuss) Stapf Apocynaceae 2 0 2 2 0 2 Funtumia africana (Benth.) Stapf Apocynaceae 22 2 24 20 2 22 Gmelina arborea Roxb. Verbenaceae 6 0 6 2 0 2 Howea sp. Arecaceae 0 30 30 0 22 22 Lannea welwitschii (Hiern) Engl. Anacardiaceae 0 2 2 0 2 2 Maesopsis eminii Engl. Rhamnaceae 0 4 4 0 4 4 Mangifera indica L. Anacardiaceae 4 0 4 4 0 4 Mareya micrantha (Benth.) Muell. Arg. Euphorbiaceae 0 4 4 0 4 4 Margaritaria discoidea (Baill.) Webster Euphorbiaceae 0 2 2 0 2 2 Martinezia corallina Mart. Arecaceae 4 0 4 4 0 4 Martinezia sp. Arecaceae 20 0 20 20 0 20 Morinda lucida Benth. Rubiaceae 4 8 12 2 8 10 Myrianthus arboreus P.Beauv. Moraceae 0 10 10 0 10 10 Petersianthus macrocarpus (P.Beauv.) Liben Lecythidaceae 0 2 2 0 2 2 Pinus montezumae Lamb. Pinaceae 4 0 4 4 0 4 Prosopis africana Taub. Fabaceae 6 10 10 0 8 8 Spathodea campanulata Beauv. Bignoniaceae 0 8 8 0 8 8 Sterculia tragacantha Lindl. Sterculiaceae 0 4 4 0 4 4 Tabebuia rosea DC. Bignoniaceae 0 2 2 0 2 2 Tabebuia spectabilis Nichols. Bignoniaceae 0 2 2 0 2 2 Terminalia prunioides Lawson Combretaceae 4 0 4 4 0 4 Theobroma cacao L. Sterculiaceae 4 0 4 4 0 4 Vitex doniana Sweet Verbenaceae 2 0 2 2 0 2 Total 180 222 402 148 194 342

Non-host species have been omitted from the table.

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Proportion of individuals (%) 5

0 Middle trunk Lower trunk Upper trunk Lower canopy Buttress root Upper canopy Fig 2 Vertical distribution of vascular Postion on host epiphytes on host species

Epiphyte species richness varied significantly among the most abundant host species. This suggests that the host species (P < 0.001), as found in other studies (Zap- abundance of host species may influence the distribution of fack et al., 1996; Diaz-Santos, 2000). This generally indi- epiphytes, which have affinity with them. The leaf bases of cated some degree of influence of host trees on epiphytes’ E. guineensis are effective in collecting organic debris and composition, although not strong enough to suggest host humus (Mucunguzi, 2007) and thus may explain the fre- tree–epiphyte specificity. Usually, trees with rough and quent use of this plant as host by ferns. The light nature of coarse bark serve as preferred hosts for most epiphytes fern spores also enables them to be carried easily by wind (Munõz et al., 2003). This may account for the high to many places. number of epiphyte species on Elaeis guineensis, Anthocleista Like other studies (Ter Steege & Cornelissen, 1989; vogelii and Amphimas pterocarpoides. Dickinson et al., 1993), the composition and diversity of Habitat type played a significant role in determining epiphytes significantly varied vertically along trees epiphyte composition in this study. There were (P = 0.002), which is suggestive of vertical gradients in significantly more epiphyte species (P = 0.001) in the humidity, amount of organic matter and light intensity secondary forest than in the cultivated forest, reflecting the (Ter Steege & Cornelissen, 1989). More epiphyte species varying degrees of disturbance in the habitats. Increased occurred on the trunk than in the canopy. This trend habitat disturbance affects epiphyte diversity, abundance contrasts with those reported in Brazil (Werneck & Espı´- (Barthlott et al., 2001) and composition in general rito-Santos, 2002) and Costa Rica (Schuettpelz & Trapnell, (Schuettpelz & Trapnell, 2006). Open vegetations created 2006), where most epiphyte stands occurred in the can- by disturbances are characterized by intense light irradi- opy. It is interesting to note that a few epiphyte species ance and low humidity (Munõz et al., 2003), which to a were distributed on the buttress roots of some hosts, which large extent reduce the abundance and richness of epi- has not been recorded in many studies. phyte species (Ter Steege & Cornelissen, 1989). Although Although the location of the forest within the city is likely there were fewer individual trees hosting epiphytes in the to influence the findings of the study, the diversity of species secondary forest compared with the cultivated forest, more obtained in the study could be a reflection of the general epiphyte species occurred in the secondary forest. This diversity of epiphytes in Ghana, considering the fact that suggests that on an average, individual trees in the sec- studies (Addo-Fordjour et al., 2008; Anning et al., 2008) ondary forest hosted more epiphytes. have shown that the diversity of other growth forms (trees, shrubs, herbs, climbers) in the garden is similar to that of other forests in the country. While the forest studied seems Distribution of vascular epiphytes isolated, making dispersal by birds, rodents and other nat- The fern species, Nephrolepis undulata and N. biserrata, were ural agents appear less likely, it is possible for propagules of the commonest vascular epiphyte species identified in the epiphytes to be carried over long or short distances by hu- study area. Almost all individuals of the two species were mans and some migratory birds. Essentially, the forest could hosted by E. guineensis, which incidentally happened to be serve as seed source of epiphytes to other forests.

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