Elevation patterns of woody taxa richness in the evergreen Afromontane vegetation of Ethiopia

Abstract

Plant species distributions show patterns along elevation gradients. Regardless of the diverse Afromontane vegetation in Ethiopia (AFE), studies of elevation patterns of woody plants are limited and they are restricted to small areas or single/few Mountains. Moreover, there is no general consensus on the patterns of woody taxa distribution by elevation. The objectives of this study were to examine the elevation patterns of woody taxa richness and their relationship with elevation in the AFE. Data were collected and compiled from the Flora of Ethiopia and Eritrea (Vols. 1–7). About 5918 plant species of 243 families were examined and their elevational distributions were recorded. The distributional ranges of woody taxa were aggregated at 19 points (sites) at 100 m intervals starting from 1500 to 3400 m a.s.l. Single-factor analysis of variance (one-way ANOVA) was used to test the hypothesis that mean species richness of woody taxa decreases from the lower to the upper limit of AFE. Simple linear correlation and regression were used to show the relationships of woody taxa richness with elevation. We documented the presence of 505 woody taxa (441 species, 31 subspecies and 33 varieties) representing 267 genera and 90 families in the AFE. In terms of habit, 279 taxa are shrubs, 178 are trees and 48 are lianas. The distribution of woody taxa (trees, shrubs and lianas) showed a slight increase at the lower portion and a monotonic decline with increasing elevation. Species richness of trees, shrubs and lianas was negatively and significantly correlated with elevation (r = −0.985, −0.984, −0.981, respectively; all p < 0.001). Our hypothesis was accepted because mean richness significantly decreased from the lower to the upper limit of AFE (p < 0.001). Generally, monotonic patterns of decline in richness were observed for trees, shrubs and lianas. The contribution of shrubs to total richness increased with increasing elevation whereas that of trees and lianas decreased.

Keywords

Plant elevational distribution / Lianas / Shrubs / Trees

References

[1] Austin MP. Searching for a model for use in vegetation analysis. Vegetatio, 1980, 42(1): 11-21.

[2] Aynekulu E (2011) Forest diversity in fragmented landscapes of northern Ethiopia and implications for conservation. Ph.D. Dissertation University of Bonn, Bonn, pp 1–132

[3] Barry RG. Mountain weather and climate, 2008, Cambridge: Cambridge University 1 506

[4] Bekele T (1993) Vegetation ecology of remnant Afromontane forests on the central plateau of Shewa, Ethiopia. Ph.D. Dissertation, Uppsala University, Uppsala, pp 1–64

[5] Berhanu A. Endemic plant taxa within the Afromontane vegetation in Ethiopia: implications for plant biodiversity conservation, 2015, Addis Ababa: Addis Ababa University 1 22

[6] Brown JH, Lomolino MV. Biogeography (2nd edn), 1998, Sunderland: Courier Companies 1 704

[7] Cox CB, Moore PD. Biogeography: an ecological and evolutionary approach, 2005 7 Oxford: Blackwell 1 440

[8] Demissew S, Friis I (2009) Natural vegetation of the Flora Area. In: Hedberg I, Friis I, Persson E (eds) Flora of Ethiopia and Eritrea vol 8. General part and index to vols 1–7. The National Herbarium, Addis Ababa and Uppsala, pp 27–32

[9] Denu D (2006) Floristic composition and ecological study of Bibita forest (Gura Ferda), southwest Ethiopia. MSc. Thesis, Addis Ababa University, Addis Ababa, pp 1–83

[10] Edwards S, Tadesse M, Hedberg I (eds) (1995) Flora of Ethiopia and Eritrea. Cannelaceae to Euphorbiaceae, vols 2-2. The National Herbarium, Addis Ababa and Uppsala, pp 1–456

[11] Edwards S, Demissew S, Hedberg I. Flora of Ethiopia and Eritrea. Hydrocharitaceae to Arecaceae, 1997, Addis Ababa and Uppsala: The National Herbarium 1 586

[12] Edwards S, Demissew S, Tadesse M, Hedberg I (eds) (2000) Flora of Ethiopia and Eritrea. Magnoliaceae to Flacourtiaceae, vols 2-1. The National Herbarium, Addis Ababa and Uppsala, pp 1–532

[13] Friis I (1986) The forest vegetation of Ethiopia. Acta Universitatis Upsaliensis Symbolae Botanicae Upsaliensis XXVI:31–47

[14] Friis I. Forests and forest trees of northeast tropical Africa. Kew Bull Addit Ser, 1992, 15: 1-396.

[15] Friis I, Demissew S, Breugel PV (2010) Atlas of the potential vegetation of Ethiopia. The Royal Danish Academy of Sciences and Letters, Natural habitats, pp 1–307

[16] Gentry AH. Changes in plant community diversity and floristic composition on environmental and geographical gradients. Ann Mo Bot Gard, 1988, 75(1): 1-34.

[17] González AS, Lopez-Mata L. Plant species richness and diversity along an altitudinal gradient in the Sierra Nevada, Mexico. Divers Distrib, 2005, 11(6): 567-575.

[18] Grytnes JA, Vetaas OR. Species richness and altitude: a comparison between null models and interpolated plant species richness along the Himalayan altitudinal gradient, Nepal. Am Nat, 2002, 159(3): 294-304.

[19] Hedberg I. Hedberg I, Friis IB, Persson E. The Ethiopian flora project—an overview. Flora of Ethiopia and Eritrea, 2009, Addis Ababa and Uppsala: The National Herbarium 1 331

[20] Hedberg I, Edwards S. Flora of Ethiopia and Eritrea Pittosporaceae to Araliaceae, 1989, Addis Ababa and Uppsala: The National Herbarium 1 659

[21] Hedberg I, Edwards S, Nemomissa S (eds) (2003) Flora of Ethiopia and Eritrea. Apiaceae to Dipsacaceae vols 4-1. The National Herbarium, Addis Ababa and Uppsala, pp 1–352

[22] Hedberg I, Friis I, Edwards S (eds) (2004) Flora of Ethiopia and Eritrea. Asteraceae (Compositae), vols 4-2. The National Herbarium, Addis Ababa and Uppsala, pp 1–408

[23] Hedberg I, Kelbessa E, Edwards S, Demissew S, Persson E. Flora of Ethiopia and Eritrea. Gentianaceae to Cyclocheilaceae, 2006, Addis Ababa and Uppsala: The National Herbarium 1 690

[24] Hedberg I, Friis I, Persson E. (eds) (2009) Flora of Ethiopia and Eritrea vol 8. General part and index to Vols 1-7. The National Herbarium, Addis Ababa and Uppsala, pp 1–331

[25] Henrik BH, Jon M, Risto V, John-Arvid G, Lauri O, Anders A. Effects of altitude and topography on species richness of vascular plants, bryophytes and lichens in alpine communities. J Veg Sci, 2006, 17: 37-46.

[26] Jiménez-Castillo M, Wiser SK, Lusk C. Elevational parallels of latitudinal variation in the proportion of lianas in woody floras. J Biogeogr, 2006, 34(1): 163-168.

[27] Kebede M, Yirdaw E, Luukkanen O, Lemenih M. Plant community analysis and effect of environmental factors on the diversity of woody species in the moist Afromontane forest of Wondo Genet, south central Ethiopia. Biodiv Res Conserv, 2013, 29: 63-80.

[28] Kharkwal G, Mehrotra P, Rawat YS, Pangtey YPS. Phytodiversity and growth form in relation to altitudinal gradient in the central Himalayan (Kumaun) region of India. Curr Sci, 2007, 89(5): 873-878.

[29] Lomolino MV. Elevation gradients of species-density: historical and prospective views. Glob Ecol Biogeogr, 2001, 10: 3-13.

[30] McCain CM. Could temperature and water availability drive elevational species richness patterns? A global case study for bats. Glob Ecol Biogeogr, 2007, 16: 1-13.

[31] McCain CM, Grytnes JA (2010) Elevational gradients in species richness. In: Encyclopedia of life sciences (ELS). Wiley, Chichester. doi: 10.1002/9780470015902

[32] Pinokiyo A, Singh KP, Singh JS. Diversity and distribution of Lichens in relation to altitude within a protected biodiversity hot spot, north-east India. Lichenologist, 2008, 40(1): 47-62.

[33] Rahbek C. The role of spatial scale and the perception of large-scale species-richness patterns. Ecol Lett, 2005, 8: 224-239.

[34] Ren H, Niu S, Zhang L, Ma K. Distribution of vascular plant species richness along an elevational gradient in the Dongling Mountains, Beijing, China. J Integr Plant Biol, 2007, 48(2): 153-160.

[35] Rowe RJ, Lidgard S. Elevational gradients and species richness: do methods change pattern perception. Glob Ecol Biogeogr, 2008, 18: 163-177.

[36] Rutten G, Ensslin A, Hemp A, Fischer M. Vertical and horizontal vegetation structure across natural and modified habitat types at Mount Kilimanjaro. PLoS ONE, 2015, 10(9): 1-15.

[37] Sanders NJ, Rahbek S. The patterns and causes of elevational diversity gradients. Ecography, 2012, 35: 1-3.

[38] Sanders NJ, Moss J, Wagner D. Patterns of ant species richness along elevational gradients in an arid ecosystem. Glob Ecol Biogeogr, 2003, 12: 93-102.

[39] Schmitt CB, Denich M, Demissew S, Friis I, Boehmer HJ. Floristic diversity in fragmented Afromontane rainforests: altitudinal variation and conservation importance. Appl Veg Sci, 2009, 13: 291-304.

[40] Sharma CM, Suyal S, Gairola S, Ghildiyal SK. Species richness and diversity along an altitudinal gradient in moist temperate forest of Garhwal Himalaya. J Am Sci, 2009, 5(5): 119-128.

[41] Shimono A, Zhou H, Shen H, Hirota M, Ohtsuka T, Tang Y. Patterns of plant diversity at high altitudes on the Qinghai-Tibetan Plateau. J Plant Ecol, 2010, 3(1): 1-7.

[42] R Core Team (2015) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna. http://www.R-project.org

[43] Teketay D, Bekele T. Floristic composition of Wof-Washa natural forest, central Ethiopia: implications for the conservation of biodiversity. Feddes Repert, 1995, 106: 127-147.

[44] Toledo-Garibaldi M, Williams-Linera G. Tree diversity patterns in successive vegetation types along an elevation gradient in the mountains of eastern Mexico. Ecol Res, 2014, 29(6): 1097-1104.

[45] Tu W, Gao X, Wu N, Liu S. Altitudinal patterns of vascular plant richness in high mountains: applying of generative additive model. Pol J Ecol, 2010, 58(2): 231-240.

[46] Wana D (2009) Plant species and functional diversity along altitudinal gradients, southwest Ethiopian highlands. Ph.D. Dissertation, Bayreuth University, Bayreuth, pp 1–139

[47] Woldu Z. Edwards S, Demissie A, Bekele T, Haase G. Forests in the vegetation types of Ethiopia and their status in the geographical context. Forest genetic resources conservation: principles, strategies and actions. Proceedings of the national forest genetic resources conservation strategy development workshop, 1999, Addis Ababa: Institute of Biodiversity Conservation and Research 1 38

[48] Yoda K. A preliminary survey of the forest vegetation of eastern Nepal. II. General description, structure and floristic composition of sample plots chosen from different vegetation zones. J Coll Arts Sci, 1967, 5: 99-140.

[49] Yu H, Saprunoff M. Distribution of plant species richness along elevation gradient in Hubei Province, China, 2012, Nanjing: International Institute for Earth System Science, Nanjing University 378 386