This research aims to establish a technique for regional stand density control by distinguishing region-specific local forms of Pinus densiflora in South Korea based on the relationship between height and DBH growth, and compose a stand density management diagram.
Firstly, in order to represent the typical characteristics of Pinus densiflora forests, pure forests were extracted with a Pinus densiflora occupancy ratio of 75% by basal area at breast height. To minimize the impact of stand density on DBH growth, the dominant trees were extracted, pertaining to the top 30% of trees by height within the considered region, and these were analyzed. The residuals of each considered region were calculated relative to the estimated height-DBH growth model, which used a Weibull growth model, and according to the spatial distribution characteristics of the extracted residuals, the Gi* of Getis and Ord was used to classify colonies.
As a result of the analysis, colonies were classified into Gangwon region, central region, and southern region. The height and DBH growth of Gangwon region was superior, whereas relatively smaller trees were distributing in the southern region, excluding the Jirisan-Deogyusan areas. In the case of the central region, overall poor growth of Pinus densiflora was observed.
Using survey data for 1,886 plots of actual pine tree stands, a model was produced to develop a stand density control diagram. The total of 1,624 plots were included in the final selection based on the definition of pure pine forests as those with an occupancy ratio exceeding 75% by basal area at breast height. From the results, an optimum stand density control diagram was created for the actual Pinus densiflora stands.
In order to verify the fit of estimated values for stand volume, the χ2 value was calculated for the equivalent height curve with a significance level of 5%, and the acceptable error rate was found to be approximately 20%. The minimum acceptable error rates for estimations of stand volume and DBH are 16.11% and 6.67%, respectively, and so the accuracy of stand volume estimation was somewhat low.
An analysis to set the standard stand density control line revealed that the proper management method used a maximum Ry (relative yield index) of 0.8. Based on this, a method to determine thinning periods and a standard table of survival by DBH were constructed.
Stand production limits were estimated using the regional site index curve, and these were used to set production targets. Gangwon region were determined to be suitable for production of large diameter logs (special wood), large diameter logs, and heavy logs, while the Pinus densiflora in central and southern regions are suitable for large diameter logs and heavy logs. Based on such log productions, a thinning control methods and diagrams were compiled.
Since the stand density control diagram created in this research allows the prediction of yield and thinning process by density control route, it is expected to enable the establishment of management plans according to the quantity and characteristic of the logs being targeted for forest management. It is also expected to help determine thinning times and establish logical, appropriate management plans by ascertaining the state of actual stands.