Tree Species Diversity and Spatial Distribution Patterns on Agricultural Landscapes in Sub-Humid Oromia, Ethiopia
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Tree species diversity and spatial distribution patterns on agricultural landscapes in sub-humid Oromia, Ethiopia Dawit Samuel, Abayneh Derero, Zerihun Kebebew & Kiros M. Hadgu Agroforestry Systems An International Journal incorporating Agroforestry Forum ISSN 0167-4366 Volume 93 Number 3 Agroforest Syst (2019) 93:1015-1029 DOI 10.1007/s10457-018-0197-7 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media B.V., part of Springer Nature. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Agroforest Syst (2019) 93:1015–1029 https://doi.org/10.1007/s10457-018-0197-7 (0123456789().,-volV)(0123456789().,-volV) Tree species diversity and spatial distribution patterns on agricultural landscapes in sub-humid Oromia, Ethiopia Dawit Samuel . Abayneh Derero . Zerihun Kebebew . Kiros M. Hadgu Received: 14 July 2016 / Accepted: 9 January 2018 / Published online: 18 January 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018 Abstract Trees are important components of agri- of 2.42, and Simpson index of 0.84. The density of cultural landscapes in different parts of Ethiopia, and trees among the tree communities in the four sites information on their type, diversity and distribution in varied from 133 in Bako Tibe to 476 in Jima Arjo, sub-humid agroecologies is essential for designing but not any one of the sites had more diverse tree interventions. A study was conducted to evaluate tree community as revealed by the Re`nyi diversity profiles diversity and their spatial patterns in agricultural analysis. The three dominant tree species in the landscapes under different land use categories in four agricultural landscapes were Eucalyptus camaldulen- selected sub-humid sites in Western Oromia, Ethio- sis, Vernonia amygdalina and Cordia africana. pia. Tree inventory was conducted on 100 Pearson correlation analysis showed that high tree homesteads (19 ha), 18 crop lands (35 ha) and 11 species density, richness and diversity had high grazing lands (5.5 ha) belonging to 100 randomly association with homesteads than with crop lands selected households. A total of 82 tree species were and grazing lands. It also revealed significant positive identified: 67 in the homesteads, 52 in the crop lands correlations between land size and evenness, and and 29 in the grazing lands. The density of trees latitude and evenness whereas there were significant varied from 68 trees per ha in crop lands to 801 trees negative correlations between family size and Shan- per ha in homesteads. Diversity indices revealed that non diversity index, and land size and tree density. homestead was the most diverse with Shannon index The majority (81.6%) of the trees were established through plantation and only 18.4% were regenerated naturally. The proportion of planted trees varied from D. Samuel 68% in Gobu Seyo to 94.1% in Guto Gida. The study Bako Agricultural Research Center, Oromia Agricultural showed that agricultural landscapes harbour high Research Institute, Bako, Ethiopia diversity of tree species with a spatial pattern, and A. Derero (&) increasing the tree cover with focus in the crop lands Ethiopian Environment and Forest Research Institute, is essential for improved resilience of the agricultural Addis Ababa, Ethiopia systems and for circa-situm conservation of e-mail: [email protected] biodiversity. Z. Kebebew Jimma University, Jimma, Ethiopia Keywords Crop land · Evenness · Grazing land · Homestead · Richness K. M. Hadgu World Agroforestry Centre, ICRAF Ethiopia, Addis Ababa, Ethiopia 123 Author's personal copy 1016 Agroforest Syst (2019) 93:1015–1029 Introduction Spatial pattern of tree diversity along ecological gradients and land use categories may give evidence- Ethiopia is endowed with ecosystems diversity and based information for making appropriate decisions natural vegetation which is categorized in twelve for improved conservation and management of bio- types (Friis et al. 2010). However, most of the natural diversity in different landscapes. Moreover, woody ecosystem has been under human influence, and the species diversity is essential for making sustainable landscape now comprises of mosaics of agricultural development in Ethiopia and other tropical countries fields (with and without trees), remnant and regen- (Shumba 2001). However, limited studies were erated natural vegetation and settlement areas. Such carried out so far on diversity of plant species in alteration of natural ecosystems and loss of biodiver- agricultural landscapes in Ethiopia (e.g. Asfaw and sity have significant impacts on ecosystem functions Hulten 2003; Abebe 2005; Endale et al. 2017). and reduce opportunities to avert production related Hence, it is vital to assess and evaluate stocking risks (Power and Flecker 2001). Moreover, popula- levels of tree plants diversity that are grown or tion growth and associated increasing demands are maintained in different niches. The present study, causing pronounced reductions in forest and tree thus, focused on characterization of tree diversity and covers. their spatial distribution patterns on agricultural Despite this, trees in most of the tropics remain landscapes in Western Oromia, Ethiopia. important elements in most of the human dominated agricultural landscapes for various goods and ser- vices. Empirical evidences also suggest that the Materials and methods diverse perennial vegetation in agricultural land- scapes has greater significance in nutrient cycling as Study site description compared to annual crops (Sharma 1997), and specifically trees provide a wide range of important The study was conducted in West Shewa and East products and service functions. The distribution Wollega administrative zones of Western Oromia pattern of various vegetation structures and the Regional State, Ethiopia. More specifically, there mixture with diverse tree-based farming are also were four study sites: (i) Oda Haro Kebele (the interesting features about floristic and eco-diversity at smallest unit of local government) in Bako Tibe a landscape level (Backes 2001). Woody species Woreda (equivalent to a district) in West Shewa diversity, thus, contributes to ecosystem productivity zone; and (ii) Wayu Kumba Kebele in Jimma Arjo and sustainability under conditions of heterogeneity Woreda (iii) Uke Badiya Kebele in Guto Gida in species traits and environmental characteristics in Woreda, and (iv) Ongobo Bakanisa Kebele in Gobu agricultural landscapes (Kindt et al. 2004). Further- Seyo Woreda of East Wollega (Fig. 1). Hereafter they more, the trees in landscape mosaics enhance are referred to as Bako Tibe, Jimma Arjo, Guto Gida ecological quality of landscapes as well as provide and Gobu Seyo site. The sampled Bako Tibe sites are habitat and greater landscape connectivity through located around 9°04′N and 37°2′E and between 1630 buffer zones, corridors, and stepping stones for and 1850 m a.s.l., Jima Arjo around 8°77′N and 36° dispersal of plant and animal species (Perfecto and 57′E and between 2030 and 2210 m a.s.l, Guto Gida Vandermeer 2002; Schroth et al. 2004). around 9°39′N and 36°54′E and between 1320 and Diversity of woody species in agricultural land- 1400 m a.s.l, and Gobu Seyo around 9°09′N and 36° scapes also plays an important role in conserving 99′E and between 1640 and 1900 m a.s.l. biodiversity (Harvey and Haber 1999). To enhance The study area is characterized by rugged land- multi-functionality and sustainable benefits (e.g., scapes with hills and valleys, and is dominated by ecological, socially and economic), it is important sub-humid areas, which are subdivided into warm to increase and manage diversity of tree species in the lowlands (‘Kola’) and tepid mid highlands (‘Woina- agricultural landscapes. In addition, decisions on land dega’). Some areas within river gorges have warmer use and land management, and their consequences on moist lowland climates, whereas areas towards higher agricultural landscapes play significant roles on altitudes have prevalent tepid humid/moist climates. biodiversity maintenance (Polasky et al. 2003). The annual rainfall in the study area follows 123 Author's personal copy Agroforest Syst (2019) 93:1015–1029 1017 Fig. 1 Location of the study areas in West Shewa and East Wollega Zones in Western Oromia, Ethiopia unimodal rainfall regime which is characterized by Acacia abyssinica. In addition, exotic woodlots, such one distinct rainfall peak (August- September) and as that of Eucalyptus camaldulensis are common in with the driest season observed between November the study area. and February. The mean annual rainfall is 2000 mm in Gobu Seyo and Bako Tibe 1320 mm, whereas it Sampling design ranges from 1400 to 2000 mm in Jimma Arjo, and from 1600 to 2000 mm in Guto Gida. The mean The tree inventory was nested on the farmland area annual temperature is greater than 15 °C in Guto Gida owned by households that were surveyed for socioe- but it ranges from 15 to 20 °C in Jimma Arjo, 15 to conomic characterization by Iiyama et al. (2017). We 20 °C in Gobu Seyo and 14.1 to 28.3 °C in Bako Tibe then selected randomly 25 households per each site (i. (http://www.oromiyaa.com). e., total of 100 households from the four sites). In Agriculture is the major livelihood source of the each site, five households were selected randomly for inhabitants in the study area. The farming system is a complete inventory of all existing trees in all the diverse and includes mixed (crop-livestock) farming land use categories owned by the households.