Journal of Agriculture and Food Environment Volume 6(2): 1-5, 2019 Onilude, 2019 Short Communication Tree Density and Growth Rate of Nauclea diderrichii and Terminalia ivorensis in the Arboretum of Forestry Research Institute of Nigeria Onilude, Q.A. Forestry Research Institute of Nigeria, P.M.B 5054, Jericho Hill, Ibadan, Nigeria E-mails: [email protected]; [email protected] Received 28th April, 2019; Accepted 6th June, 2019; Corrected 30th June, 2019 Abstract Stands of Nauclea diderrichii and Terminalia ivorensis within the arboretum of Forestry Research Institute of Nigeria were assessed for stand density and diameter growth rates of the tree species. Total enumeration of all the trees for both species was carried out and their diameters at breast height (dbh) measured. Nauclea diderrichii stand had the highest density of 430 trees ha-1 and a total basal area of 4.32m2ha-1 while Terminalia ivorensis stand had a density of 400 trees ha-1 and a total basal area of 26.83m2ha-1. The diameter growth rates for the two species were determined by calculating their mean annual increments (MAIs) in DBH. Nauclea diderrichii had an average DBH of 10.98cm and a mean annual increment (MAI) of 1.10cmyr-1 while Terminalia ivorensis had an average DBH of 24.31cm and MAI of 2.43cmyr-1. This study showed that Mean annual increment generally increased with reduction in stand density. Permanent sample plots (PSP) should be established in the arboretum for continuous inventory to provide data for academic and research activities; and also for sustainable management of the tree resources. Keywords: Stand density, tree growth rate, Mean annual increment, Nauclea diderrichii, Terminalia ivorensis Introduction Due to the abundant and invaluable economic, social and environmental benefits forests provide, they are very important to mankind. The diversity of forest resources and their natural ability to renew themselves offer man a very great opportunity to tap these resources for his greatest benefits in perpetuity (Etigale et al., 2013). Due to the renewable natural ability of these forests, man has a great opportunity to use these resources to meet his immediate agroforestry needs. This calls for a sound forest management strategy that would ensure the sustainability of the resources and their benefits According to Higman et al. (2000), the basic requirement of a sound forest management strategy is thea vailability of reliable database that provides adequate information on the extent, state and potentials of the resources. Copyright © 2019 by The Faculty of Agriculture, Delta State University, Abraka, Nigeria This work is under Open Access within the terms of the Creative Commons Attribution 4.0 International License JAFE 6(2): 1-5, 2019 1 Journal of Agriculture and Food Environment Volume 6(2): 1-5, 2019 Onilude, 2019 Relevant information about forest resources provide forest managers with the necessary guides for rational decision making (Akindele, 2001) and management planning as well as its implementation. Stand density determines the amount of growing space available for individual trees growing on a site and the level of competition among them for light, soil moisture and nutrients while the growth rates of trees determine the yield of forest stands and the rate of returns on forest investments. Therefore, sound forest practices for a sustainable management cannot be successful without reliable data and information on tree growth rate and their stand density. Such information guides the resource manager in determination, valuation and allocation of forest areas. In timber production, estimates of the growing stock are often expressed in terms of timber volume, which can be estimated from easily measured dimensions of the tree (Husch et al., 2003; Akindele and LaMeay, 2006). However, since the establishment of Nauclea diderrichii and Terminalia ivorensis stands in the arboretum of the Forestry Research Institute of Nigeria (FRIN), the stand density and growth rates of the tree species have not been assessed. Thus, there had been no data on the stand densities of these stands and the growth rates of the trees for decision making, and for possible sustainable management. The objective of this study was to assess the stand density and mean annual diameter growth rates of these species in the arboretum, with the view to providing the database necessary for their sustainable management. Materials and Methods Study Areas The study was carried out in the arboretum of the Forestry Research Institute of Nigeria. The institute lies between Longitude 3°53’ and 3°9’E and between latitudes 7°25’ and 7°55’N. The region is characterized with a bimodal pattern of rainfall with peaks in July and September with mean annual rainfall of about 1420.106mm. The area is within the tropical rainforest zone of Nigeria. Mean annual temperature varies between 18.07°C and 34.4°C, while the mean relative humidity in the area is about 82% between June and September, and about 60% between December and February (Ugwu and Ojo, 2015). The Nauclea diderrichii stands occupy 0.99ha while Terminalia ivorensis stands have an area of about 0.35ha. Both Nauclea diderrichii and Terminalia ivorensis plots were established in the year 2010 with espacement of 5m x 5m. Data Collection and Analysis Data were collected through direct enumeration and measurement of trees in the Nauclea diderrichii and Terminalia ivorensis plots. The method used for data collection was total enumeration. All the trees in the plots of the two species were counted in order to determine the number of trees in each of the areas. Tree variables collected included DBH, diameter at base, middle and top, and total height of all the trees. JAFE 6(2): 1-5, 2019 2 Journal of Agriculture and Food Environment Volume 6(2): 1-5, 2019 Onilude, 2019 Stand density was determined for each species using estimated number of trees and basal areas of the species per hectare. The estimated number of trees of each species per hectare was obtained by extrapolating the total number of trees enumerated in the respective stands as shown in Equation 1. Diameter growth rates of the species were obtained by calculating the Mean Annual Increment (MAI) in diameter at breast height (DBH) for each of the species. Firstly, MAI in DBH was determined for each tree by dividing the DBH of each tree by its age. The MAI in DBH of each species was then estimated by adding the MAIs of all the individuals of a species, and dividing the total by the number of individuals of the species. ℎ 푁 = × 푛…………………Equation 1 푎 N = Trees per hectare h = one hectare a = area of plot in hectare n = number of trees enumerated in the stands The Basal Area (BA) of individual trees sampled was estimated using the formula in the equation given by Husch et al, (2003) as shown in Equation 2. However, total basal area of each species was obtained by adding the basal areas of the individuals of the species. 휋푑2 BA = ……………………………..……….Equation 2 4 Where: BA = Basal area (m2) D = dbh (cm) Π = 3.142 (constant) Results and Discussion Stand Density Table 1: Tree Density and Basal area (BA) for the Nauclea diderrichii and Terminalia ivorensis species Number of trees Variables/Tree species Nauclea diderrichii Terminalia ivorensis Per Stand Per hectare Per Stand Per hectare Frequency 426 430 140 400 Total BA (m2) 4.28 4.32 9.39 26.83 In the arboretum of FRIN, a total number of 426 Nauclea diderrichii trees species were counted, which had a density of 430 trees per hectare with a total basal area of 4.32m2ha-1 as shown in Table 1. The Terminalia ivorensis species had a stand density of 400 trees per hectare, with a total basal area of 26.83m2ha-1 as shown in Table 1. JAFE 6(2): 1-5, 2019 3 Journal of Agriculture and Food Environment Volume 6(2): 1-5, 2019 Onilude, 2019 Diameter Growth Rate In this study, in the Nauclea diderrichii stands, the DBH range of the measured trees was 19.2cm, with an average of 10.98cm (Table 2) while Terminalia ivorensis trees had average and range of DBH were 24.31cm and 70.1cm respectively (Table 2). Table 2: Mean Annual Increment (MAI) and Diameter at Breast Height (DBH) of Nauclea diderrichii and Termanalia ivorensis species Variables/ Tree species Nauclea diderrichii Terminalia ivorensis Mean DBH (cm) 10.98 24.31 DBH Range (cm) 19.2 70.1 Total MAI (cmyr-1) 467.61 340.28 Mean MAI (cmyr-1) 1.10 2.43 MAI Range (cmyr-1) 1.92 7.01 The total value of MAI in DBH calculated for Nauclea diderrichii stands was 467.61cmyr-1, while the mean and range were 1.10cmyr-1 and 1.92cmyr-1 respectively (Table 2). However, for Terminalia ivorensis stands, total value of MAI in DBH was 340.28cmyr-1, while the mean and -1 -1 range of MAI in DBH were 2.43cmyr and 7.01cmyr respectively as shown in Table 2. Comparing the stand or population densities with the average growth rates recorded for the two tree species in the study, it was observed that the two parameters varied in opposite directions. Nauclea diderrichii had the highest population density of about 430 trees per hectare as shown in Table 1, but recorded the least mean growth rate of about 1.10cm yr-1 when compared with that of Terminalia ivorensis as shown in Table 2. Also, despite having the least frequency per hectare (Table 1) and total DBH, Terminalia ivorensis had the highest mean MAI but lower total MAI (Table 2). The trees were planted at the espacement of 3m x 3m, the initial stocking of 1089 trees per hectare.