| Summary: | 碩士 === 國立中興大學 === 森林學系所 === 98 === This study aimed to understand the relationships between the crown characteristics and crown shape and to evaluate thinning effects of a Japanese cedar (Cryptomeria japonica D. Don) plantation in the Luan-Da Working Circle of central Taiwan.
I employed stratified sampling method by utilizing the diameter class. The stand was divided into five stratifies, with 4 trees in each diameter class, respectively. That is, 20 trees were sampled in total. Six crown parameters were analyzed including crown radius (RB), length (CL), relative crown height (RCH), diameter at breast height (DBH), and live crown ratio (CR). Using stepwise regression analysis, I found out crown radius (OCR) model best estimated the crown shape, with R2 equaled to 0.92. The equation was illustrated as below:
OCRi=(0.32+13.77×CR) ×[(RCHi-1) ÷(RCHi+1)]+(-3.75-0.04×DBH-8.98×CR) ×(RCHi-1)
In addition, the Mean Absolute Percentage Error (MAPE) showed good forecasting to the OCR model, with the range of MAPE was 14.97-27.15%. The findings revealed that the OCR model can be used to effectively assess the crown shape.
The study investigated the stand 5 years after thinned. The results showed that thinning had positive effects on the growth rate (%) and crown development. The findings revealed that 35% of above thinning treatment increased the growth rate of DBH, basal area, volume, and carbon storage, while 45% of below thinning treatment has effects on space that crown projection area was significant larger than stands of other thinning treatments. The results can also provide foundation regarding the thinning information for Japanese cedar plantation management.
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