Hierarchical Cluster Groupings, Principal Component Analysis, Crown Shape and Trunk Surface Characteristics of Shea Trees in Savannah Woodlands of Nigeria

Abstract

Abstract A diversity study was conducted to look at Shea tree species relatedness in six states (Niger, Kwara, Oyo, Nasarawa, Kogi and Kebbi) of Nigeria. The states are located within the shea belts of Nigeria. A data form was designed based on International Plant Genetic Resources Institutes (IPGRI) descriptors for shea tree. Twenty-two data sets were collected that included trunk characteristics, leaf and fruit characters; non- morphometric characters that included crown shape, growth pattern and fruit taste. A total of 900 trees were studied, however, only 833 were used for analysis because of incomplete data. In each state, 150 trees were considered in three different locations based on Agricultural zones in the states and the total number of locations across the states was 18. Each location had 50 trees. The data collected were subjected to cluster and principal component analysis. Also, bar charts were constructed to define the number of trees in a location that has a particular crown shape and trunk surface characteristics. Results from the states and combined clustering showed that most trees across the states were of similar backgrounds. Trees from individual states showed a high level of similarity by clustering into one group. The percentage range from 50% (Kebbi state) to 96.6% (Oyo). When all the trees from across the states were combined; cluster one had 407 trees with smaller subgroups and were found in the states of Kogi, Kwara and Oyo; this represents about 50% of all the trees. There was a stand-alone tree in clusters 11 and 17 coming from Ilorin south and Nasarawa respectively. The principal component analysis delineated the parameters into five components. The first component explained 92.54% of the total variation among the characters studied. The crown shape characters were classified into six classes with most of the locations having various shapes except elliptical shape. Also, almost all the trees were either rough trunk surface or very rough. This result shows that shea trees in these states have a common origin and the spread might have arisen from a single center of diversity.