Social Sciences, Sunyani, Ghana. Corresponding author s ABSTRACT

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1 AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , doi:.21/abjna , ScienceHuβ, Assessment of diameter-height relationships of Pycnanthus angolensis, Heritiera utilis, Ceiba pentandra and Terminalia superba at Fure River Forest Reserve of Ghana 1 Alexander Baffour Afrifa and 2 anthony Albert Adomako 2 University of Energy and Natural Resource, School of Natural Resources, Department of Social Sciences, Sunyani, Ghana. 2 Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. Corresponding author s alexafrifa4@yahoo.com ABSTRACT Tree height measurements of indigenous species are expensive and time consuming. The development of a relationship between total tree height and diameter at breast height (dbh) is, therefore, considered crucial in forest inventories. The objective was to develop equations for estimating tree heights as a function of dbh of 12-year indigenous species; Ceiba pentandra, Terminalia superba, Pycnanthus angolensis and Heritiera utilis at Fure River Forest Reserve (FRFR). A study was conducted in a -hectare mixed stand at FRFR at Asankragwa Forest District. The m by m plot was demarcated and divided into three strata based on species compositions. Randomized Complete Block Design was used to ensure that variation within the blocks is minimized and variation among blocks is maximized. The results were analyzed with Microsoft Excel. Positive correlations between dbh and total height were observed in all the four species with the following relationships: y = 69.3x for Heritiera utilis, y = 26.8x for Ceiba pentandra, y = 29.99x for Terminalia superba and y = 1.611x for Pycnanthus angolensis. This intervention would be highly appreciated for reducing the high cost of determining tree height in forest inventories but highly site specific. Key Words: Pycnanthus angolensis, Heritiera utilis, Ceiba pentandra, Terminalia superba, Diameter, Height. INTRODUCTION Ghana s natural forest is left with about 1.6 million hectares by the close of 11 as against 8.2 million hectares in 19 and at the moment the rate of deforestation is about 6, hectares per annum (Forestry Commission, 11). Plantation development is therefore a key to sustainable forest management in Ghana. However, plantation development in Ghana is mostly dominated by exotic homogeneous species. In effect, the structure and the composition of Ghana s tropical heterogeneous forest is fast becoming exotic monoculture plantations leading to loss of ecological and environmental benefits derived from the nation s natural forest. Stem diameter at breast height (dbh) and tree height are commonly used parameters of tree growth and the relationships between them are the most commonly used measurement of tree size and they are frequently required for both routine forest management activities and for research purposes. Consequently, accurate data on these two variables are quite important especially for reliable future management plans (Osman, et al. 13). Dominant plants have linear diameter-height trajectories while suppressed plants have curved trajectories, with diameter growth declining more than height growth (Sumida, et al, 13). The factors influencing the relationships are attributed to the characteristics of the species, the site and the age of the stand. Tree height measurements are expensive and time consuming and often they are carried out only on a small portion of sampled trees. The development of a

2 Agric. Biol. J. N. Am., 14, (4): relationship between total tree height and diameter at breast height (dbh) is considered crucial in forest inventories - they have been used for a variety of practical purposes in the realm of forestry. The relationship between dbh (1.3 m) and total height is a structural characteristic of a tree that describes key elements of stem form, and thus the volume of the harvestable stem (Osman, et al. 13). Many growth and yield-projection systems also use height and diameter as the two basic input variables, with all or part of the tree heights predicted from measured diameters (Hanus et al., ). The relationship between tree height and stem diameter is modified by the environment. The height diameter relationship varies from stand to stand (Hanus et al, ).Diameter is easier to measure but the total height of trees of interlocking crowns is difficult to measure due to the difficulty to locate the topmost point of the tree crown, height of leaning trees. A model developed between dbh and the total height can be used to determine the total height of trees that could increase knowledge and enhance proper management of forest plantations. The height and diameter relationship when established can be used to predict the productivity levels of the soil on which the plantation is established. The high forest ecological zone of Ghana accounts for most of the biological diversity of the country. The research plot established by the Forestry Commission is a classic example of how to mimic nature in the right way. This research work will therefore underscore the possibility of establishing and managing indigenous heterogeneous plantations and also serve as baseline information for future comparison of Plantation development in the district. The objective was to develop equations for estimating tree heights as a function of dbh of 12- year indigenous species; Ceiba pentandra, Terminalia superba, Pycnanthus angolensis and Heritiera utilis at Fure River Forest Reserve (FRFR). MATERIALS AND METHODS The study was conducted at Fure River Forest Reserve at Asankragwa Forest District in Ghana where a fivehectare mixed indigenous stand had been established in the year in compartment 72 of the reserve. The reserve is in the Wet Evergreen (WE) forest type and the rainfall pattern is bimodal with mean annual rainfall ranging between 1 mm and 1 mm The mean temperature ranges between 21.3 o C and 2.6 o C. The Soils of the study area are mainly ochrosol/oxysol intergrades and the altitude varies from 9m to 1m with the highest point in the eastern portion (Brammer, 1962). After the reconnaissance survey, the five-hectare plot of m by m was demarcated and stratified into three blocks based on species composition. Each stratum was sub-divided into sub-plots of m 2 (i.e..2 ha) each by using Prismatic Compass and a 3 meter linear tape. The first stratum represents 12 sub-plots containing all the four indigenous species, Terminalia superba, Ceiba pentandra, Heritiera utilis and Pycnanthus angolensis (coloured green) The second stratum (coloured red) comprises five subplots containing three indigenous species, Terminalia superba, Ceiba pentandra, and Pycnanthus angolensis whilst the third one (coloured yellow) consists of three sub-plots with only two species, Terminalia superba and Ceiba pentandra. Simple Random Sampling was used to select 4% of the sub-plots from each stratum and this resulted five, two and one sub-plot(s) from the first, second and third strata respectively. Figure 1 represents the composition of the species and the species selected (#) for the study. As different proportions of the species were planted in the various sub-plots, Randomized Complete Block Design was used to ensure that variation within the sub-plots is minimized. Four trees each of C. pentandra, T. superba, P. angolensis and/or H. utilis were randomly selected for measurement in each of the eight selected sub-plots. Total height and diameter at breast height were the parameters taken from the selected trees with Vertex VI Hypsometer and Diameter tape respectively. The information obtained from the selected trees in the eight selected sub-plots were analysed with Microsoft Excel computer application software and presented on graphs. 14

3 Height (m) Agric. Biol. J. N. Am., 14, (4): # # # m # # # # # m Fig. 3.3 Diagram showing layout of plots 3 RESULTS Determine of the relationships of diameters and heights of Terminalia superba, Ceiba pentandra, Heritiera utilis and Pycnanthus angolensis in a mixed stand at Fure River Forest Reserve. 2 1 y = 26.88x R² =.47 Four Linear equations representing the diameterheight relationships of the four indigenous species in the mixed stand were determined from their respective scatter diagrams. The relationships between diameter and height of the selected four indigenous species; Ceiba pentandra, Terminalia superba, Pycnanthus angolensis and Heritiera utilis were y = 26.8x , y = 29.99x , y = 1.61x , y = 69.3x and coefficient of determinations; R 2 = 46%, R 2 = 23%, R 2 = %, and R 2 = 3% respectively (Figures 1-4) Fig. 1 Diameter Height Relationship of Ceiba pentandra at age

4 Height (m) Height (m) Height (m) Agric. Biol. J. N. Am., 14, (4): y = x R² =.228 Fig. 2 Diameter Height Relationship of Terminalia superba at age y = 1.611x R² =.3 Fig. 3 Diameter Height Relationship of Pycnanthus angolensis at age y = 69.31x R² = Fig. 4 Diameter Height Relationship of Heritiera utilis at age 12 DISCUSSION Development of equations for estimating tree heights as a function of dbh of 12-year indigenous species; Ceiba pentandra, Terminalia superba, Pycnanthus angolensis and Heritiera utilis at Fure River Forest Reserve (FRFR). Diameter and height determination is closely related to the quality and quantity of the wood in the bole of the tree and may be used to indicate site quality, tree vigour and growth. It is also an assessment of the productive capacity of the site, influencing the timing and the type of silvicultural treatments that may be applied to an area. The linear regression models developed under the study for the diameter at breast height and the total height relationships of the four indigenous species, Terminalia superba, Ceiba pentandra, Heritiera utilis and Pycnanthus angolensis, planted at the same site in the same year under the same silvicultural treatments show various degrees of positive correlations. The linear models are classified as good, fair, weak, and very poor with coefficient of determinations (R 2 ) of 3.1%, 4.7%, 22.9% and.3% respectively. This implies that 3.1%, 4.7%, 22.9% and.3% respectively of variations of the heights of the four indigenous species in a mixed stand at FRFR is attributed to the changes in the diameter at breast height. In other words, 46.9%, 4.3%, 77.1% and 99.7% respectively of the changes in the relationships cannot be accounted for by the relationships between diameter and height measurements and this could be due to such factors as genetic, soil, competition, disease or pest attacks, inaccurate planting distances and errors arising from inaccurate height estimation. The poor fit could be probably due to greater difficulty in measuring the total heights of the trees (Hanus et al, ). This situation might also have occurred due to poor silvicultural treatments given to the stand. For instance, no tending operation had been carried out for the past eight years and the trees had never been thinned since its establishment twelve years ago. The initial planting distance of 4 metres by 4 metres had been maintained up to date and this could probably have led to competition for nutrients, water, light, space and other unfavourable factors. 147

5 Agric. Biol. J. N. Am., 14, (4): CONCLUSION The diameter-height linear regression models developed for the four indigenous species gave reasonable estimates of tree heights with R 2 range of.3 3%. The best model is that of Heritiera utilis which has a linear equation, y = 69.3x and R2 = 3%. The models could be used to predict the heights of the species under consideration. The poor fit could be probably due to greater difficulty in measuring the total heights of the trees. This unfortunate situation might also have occurred due to poor silvicultural treatments given to the stand. These results could be used as a tool in making both silvicultural and management decisions. Further studies are required at well managed plantations to improve the prediction quality of the species. Acknowledgement : I am very appreciative of the advice, criticisms, and suggestions of the reviewers, who provided detailed and insightful comments to strengthen the paper REFERENCES Brammer, H. (1962). Soils: In Agriculture and Land use in Ghana. J.B. Wills ed., Oxford University Press, London, Accra, New York pp. Forestry Commission, (11). Ghana Forest and Wildlife Policy. 11, Revised Edition. Ministry of lands and Natural Resources. Accra, Ghana. Osman, E.H., Idris, E.A., and Ibrahim, E.M. (13). Modelling Height-Diameter Relationships of Selected Economically Important Natural Forests Species. Journal of Forest Products & Industries, 13, 2(1), Sumida, A., Miyaura, T., and Torii, H. (13). Relationships of tree height and diameter at breast height revisited: analyses of stem growth using -year data of an even-aged Chamaecyparis obtusa stand. Oxford Journals, Life Sciences, Tree Physiollogy, 33(1), Hanus, M.L., Hann, D.W., and Marshall, D.D. (). Predicting height to Crown Base for Undamaged and Damaged Trees in Southwest Oregon, Oregon State University, Forest Research Laboratory, Corvallis. 148