Research Article Impacts of Different Tree Species of Different Sizes on Spatial Distribution of Herbaceous Plants in the Nigerian Guinea Savannah Ecological Zone Toma Buba Department of Biological Sciences, Faculty of Science, Abubakar Tafawa Balewa University, PMB 0248, Bauchi, Nigeria Correspondence should be addressed to Toma Buba; tomabuba@yahoo.com Received 19 June 2015; Revised 17 September 2015; Accepted 4 October 2015 Academic Editor: Artemi Cerda Copyright © 2015 Toma Buba. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. his study was aimed at inding the impacts of diferent tree species and individual trees of diferent sizes on species richness, diversity, and composition of the herbaceous layer. All the three tree species have greatly increased species richness and diversity both within and outside their crown zones compared with the open grassland. Both species richness and diversity were found to be higher under all the three tree species than outside their crowns, which was in turn higher than the open ield. Daniella oliveri has the highest species richness and diversity both within and outside its crown zone followed by Vitellaria paradoxa and then Parkia biglobosa. he result also revealed that the same tree species with diferent sizes leads to diferent herbaceous species richness, diversity, and composition under and around the trees’ crowns. P. biglobosa and V. paradoxa trees with smaller sizes showed higher species richness and diversity under their crowns than the bigger ones. he dissimilarity of species composition difers between the inside and outside crown zones of the individuals of the same tree species and among the diferent trees species and the open ield. 1. Introduction Vegetation with its biodiversity is a crucial part of the Earth Systems (soil, water, and atmosphere), ofering essential services to both the ecosystem and human societies [1]. Vegetation supports the functions of soil, which include decomposition, nutrient cycling, soil respiration, invasion resistance, and ecosystem stability. Soil biodiversity in turn provides many ecosystem services essential to mankind and the environment, such as the support of primary production, control of pests and diseases for man and his animals and crops, and the avoidance of environmental contamination through cycling of dead biomass. Also, soil biota plays a signiicant role in determining the soil physicochemical properties. Plants, in particular, play an important role in shaping soil proile with the diverse architecture of their root systems, being the center of soil-plant-microbial interactions [2]. Vegetation also contributes signiicantly to the control of soil erosion, which is a serious threat to ecosystem functioning in many parts of the world. It was reported that the magnitude of impact of plants in rendering ecosystem services, particularly in controlling soil erosion, depends on structural architecture of the plant’s morphologies (roots systems, crown shape and size, etc.), which in turn depends on the species [3–6]. Hence, diversity within vegetation has been shown to have remarkable efects on ecosystem functions and stability. More oten, increasing biodiversity enhanced ecosystem productiv- ity and stability. For example, Seitz et al. [6] report that tree monocultures in aforestation have only limited mitigation potential for soil losses and that there is growing evidence that higher species richness can reduce soil erosion. Vegetation is also of crucial beneits to the human societies. Many authors report the efectiveness of vegetation in protecting man-made structures like roads, embankments, man-made dams, and pastures that support a signiicant part of food production, and so forth [1, 7]. It is then of great importance to understand the consequences of the worldwide losses of plant species diversity for the ecosystem services in many parts of the world. Of fundamental importance Hindawi Publishing Corporation Scientifica Volume 2015, Article ID 106930, 8 pages http://dx.doi.org/10.1155/2015/106930