This study is designed to develop the site index curves based on the most appropriate height growth models which are also developed in the study, to each species; Cryptomeria japonica, Pinus koraiensis, Liriodendron tulipifera, and Betula platyphylla. In addition, it was intended to compare and analyze the index curve developed in the study and the index curve developed by the national policy. If the index curves following the national policy has not produced, the site index curves of Pinus koraiensis and Quercus mongolica were used as comparison and analysis of the curves. The study is conducted to provide basic data on sustainable forest management and maintenance for the stands in Jeolla-do province.
The basic data of the study is the survey for ‘Customized Afforestation Map’ by Korea Forestry Promotion Institute which is measured age, height and diameter at breast height of dominant trees on 410 plots and 2,365 volumes of Cryptomeria japonica, 473 plots and 2,365 volumes of Pinus koraiensis, 94 plots and 2,365 volumes of Liriodendron tulipifera and 179 plots and 417 volumes of Betula platyphylla.
Based on the basic data, the height growth model was developed using Chapman-Richards growth function, Gompertz function, and Schumacher function, and the most suitable height growth model for each species was induced into the site index curve of the base age of 30 years. In addition, the developed site index curve was compared and analyzed with the site index curve used at the national site index.
The results of this study are as follows. The model of the height growth model by the species Cryptomeria japonica, Pinus koraiensis, Liriodendron tulipifera, and Betula platyphylla in Jeolla-do was developed by selecting the model with the lowest MSE value, with the limit section of 95% confidence level of each coefficient not containing zero through nonlinear least-symmetric regression analysis. The results showed that the Gompertz function was suitable to Cryptomeria japonica, Liriodendron tulipifera, and Betula platyphylla, and to the Pinus koraiensis, Chapman-Richards growth function is the most suitable to develop the height growth models. As result of schematization of residual pattern of the analysis showed statistical suitability and rationality with homoscedasticity on the basis.
The site index curve of the species in Jeolla-do was developed using the anamorphic method after selecting the model of the height growth developed by each species. The variables to develop the curves are the dominant tree height, the stand age and the reference age which is 30 years. As a result, the site index of Cryptomeria japonica developed a total of seven curves in the range of 8, 10, 12, 14, 16, 18, 20, while the site index of Pinus koraiensis developed a total of eight curves in the range of 8, 10, 12, 14, 16, 18, 20, 22. In addition, the site index of Liriodendron tulipifera developed a total of eight curves in the range of 8, 10, 12, 14, 16, 18, 20, 22, and the site index of Betula platyphylla developed a total of seven curves in the range of 8, 10, 12, 14, 16, 18, and 20.
The site index for the species in the Jeolla-do province was shown as a Sigmoid curve in which the annual capacity gradually falls as the age increases. In the case of Cryptomeria japonica, it is considered that early height growth rate is larger than middle and late height growth rate, focusing on height growth than diameter growth in order to avoid weeding out caused by the failure of the early photosynthesis for growth. In the case of Pinus koraiensis, the physiological nature which is shade tolerant tree suggests that the rapid height growth caused by light competition in initial stage has changed into a pattern of diameter growth when a certain age has been reached. For Liriodendron tulipifera, the slope for each of the same age was found to be greater than for other species in this study. It is considered that Liriodendron tulipifera has a relatively faster rate of growth than other species because it is rapid growth tree. As for Betula platyphylla, the extent to which the height growth decreased significantly as the age increased compared to other species in the study. It is expected to focus on diameter growth rather than height growth as it is extremely intolerant tree, young trees lose from the early light competition were eliminated and the survived trees tried to take over the ground.
Comparing and analyzing the site index curve by the study with the site index curve developed by national site index, it showed that the curves of site index developed in the study vary more than that of the national site index. In addition, the site index curve by the study is significant because it includes geographical, ecological, and environmental effects on the Jeolla-do province, for that reason it could be applied to the present stand grown in the Jeolla-do province of South Korea.
The site index curves of Cryptomeria japonica and Pinus koraiensis developed in this study were compared and analyzed with the site index curves of the Pinus Koraiensis at the national site index, and the status index curves of Liriodendron tulipifera developed in this study were compared with those of the national site index of Liriodendron tulipifera and Quercus mongolica. In addition, the site index curves of Betula Platyphylla developed in this study were compared with Betula Platyphylla and Quercus mongolica developed by the country. As a result, the comparison of the site index curves between Cryptomeria Japonica and Pinus Koraiensis, Betula Platyphylla and Betula Platyphylla was analyzed to reject the null hypothesis in the F-test at a significant level of 10%, with p-value of 0.1 or less, making it statistically significant, which is not applicable to site index curve at the national site index; In the comparison between the trees, the curve of the tree came first is developed by the study and the curve came later is developed nationally and it is applied to the later descriptions. In addition, the comparison of the site index curves of Pinus Koraiensis and Pinus Koraiensis, Liriodendron tulipifera and Liriodendron tulipifera, Liriodendron tulipifera and Quercus mongolica, Betula Platyphylla and Quercus mongolica were analyzed as having p-value of 0.1 or more in the F-test, which was not statistically significant and it was analyzed that it could be applied to the site index curve of the national site index.
In the comparison of the site index curves of the Cryptomeria Japonica and Pinus Koraiensis, at the curves of Cryptomeria Japonica, the dominant tree height is larger than the dominant trees height of Pinus Koraiensis at the curves until 30 years of the reference age. However, after the reference age, the dominant trees of Pinus Koraiensis are taller than that of Cryptomeria Japonica. This is because the reactivity of intolerant tree Cryptomeria Japonica against the initial light competition for growth which is positive is higher than the reactivity of shade tolerant tree Pinus Koraiensis, which is negative, and the growth pattern is different due to the difference in growth environment.
In the comparison of the curves of Pinus Koraiensis, it showed a difference in asymptotic lines after the early growth to about 33 years of age, although the value to the age of 33 years was not different. The difference is because the national Pinus Koraiensis site index curve was developed by integrating the geographical and environmental effects of various ecological areas in South Korea but the curve of Pinus Koraiensis by the study, is developed to reflect the different from the geographical and environmental effects of Jeolla-do province.
In the comparison of the site index curves of Liriodendron tulipifera, the curves of Liriodendron tulipifera developed in the study showed shorter height than the nationally developed curves until the reference age which is 30 years, but height level of the curve by the study goes higher when it passes the reference age. This is due to the difference in the degree of precision due to the provisional development of the national site index curve of Liriodendron tulipifera and the difference in the traits and environment of the local plantation because Liriodendron tulipifera is a trend of carrying out a lot of new plantations as rapid growth tree.
Comparing the site index curves of Liriodendron tulipifera and Quercus mongolica, the value was similar from the initial growth to the reference age of 30 years, but after 30 years, the height of the dominant tree of Liriodendron tulipifera were taller than Quercus mongolica. Especially, in F-test, p-value was 2.5 times higher than that of nationally developed index of Liriodendron tulipifera, so it is appropriate to apply the curve of Quercus mongolica than the curve of Liriodendron tulipifera developed by the country to Liriodendron tulipifera growing in Jeolla-do province. The result is reflecting the ecological characteristics of Quercus mongolica, deciduous tree distributed throughout South Korea, and it is important in that it is possible to apply result actually to forest management.
In the comparison of the site index curves of Betula Platyphylla, the curve by the study showed the lower values to the height of the dominant tree until 30 years of age, but after 30 years, the curve by the study showed higher values of the dominant tree height than the value on the curve by country. It shows the difference in the precision because the national Betula Platyphylla site index curve is currently developing, and Betula Platyphylla which is a fast growing tree specie has the different characteristics by the region and the environment of growth.
Comparing the curves of Betula Platyphylla and Quercus mongolica, the site index curve of Betula Platyphylla developed in this study showed a higher value to the height of the dominant tree until about 25 years of age, and it was matched for about 10 years from about 27 to about 37 years and then the values of the height went higher again. The result reflected the characteristic of Betula Platyphylla that it grows fast in the early stage. In addition, the result of comparing the six site indices, p-value was the highest in the F-test and the national site index curve of Quercus mongolica is applicable to the middle-aged Betula Platyphylla stand in Jeolla-do province with high precision. Even though there is the national site index curve of Betula Platuphylla, it is inapplicable to the species in Jeolla-do province.
As a result, it is considered unreasonable to apply the site index curve of a Pinus Koraiensis if the status index curve of the coniferous tree does not exist, and it is reasonable to apply the site index curve of Quercus mongolica if the site index curve of the deciduous tree does not exist.
Therefore, the site index curves developed by the study could estimate the high level of site for stands of Cryptomeria Japonica, Pinus Koraiensis, Liriodendron tulipifera, Betula Platyphylla in Jeolla-do province, and it is important to identify the possibility of applying the national of site index in Jeolla-do and the difference of regional site index through comparison with the nationwide indices. Furthermore, based on the results of the study, it is expected that it will provide basic data for sustainable forest management and maintenance, and it provides the needs to develop the site index curve suitable for present stand grown by the region in South Korea.