應用競爭指數推估楓香人工幼齡林單木生長之效果評估

Assessment of individual tree growth in a juvenile Fragrant Maple (Liquidambar formosana) plantation based on competition indices

競爭作用為影響林木生長的重要因子之一，人工林競爭作用主要發生在林木之間。本研究目的在於應用競爭指數評估競爭作用對楓香人工幼齡林單木生長影響。研究地點位於臺灣中部地區國立中興大學所屬之惠蓀林場第1林班，本研究於2018年進行調查，對象為7年生楓香人工林，林分除了楓香樹種外，尚包括其他闊葉樹種，而本研究主要對象為楓香樹種，為瞭解林木間的競爭作用，採用距離獨立和距離相依指數量化林木的競爭作用，前者包括：Lorimer和Daniels競爭指數；後者包括：Hegyi、Biging和Rouvinen競爭指數。而競爭木的判定則採用距離相依競爭指數搭配搜尋半徑和最近林木株數兩種方式。本研究以Pearson相關分析探討林木生長和競爭指數的關係。結果顯示，不論距離獨立或距離相依兩類競爭指數與平均生長量皆具顯著的相關性。此外也發現使用距離相依競爭指數時，相關係數並不會隨著搜尋半徑或林木株數的增加而上升。本研究以Hegyi競爭指數為例，採用非線性模式分析競爭指數與胸徑生長量的關係，不論使用搜尋半徑或最近林木株數法，非線性模式皆具有良好的解釋能力。

Competition is a key factor influences tree growth that mainly occurred among trees in plantations. The purpose of this study was to assess the competition factor affecting tree growth in a juvenile Fragrant Maple (Liquidambar formosana) plantation based on the competition indices. The study area was a 7-year-old L. formosana plantation mixed with other broad-leaf trees located at the compartment no.1 of Huisun Experimental Forest Station, National Chung Hsing University. This study mainly addressed L. formosana trees surveyed in 2018. Both distance dependent (DD) and distance independent (DI) competition indices were simultaneously employed to measure competition factor. DD competition indices included the Lorimer and Daniels indices, whereas DI competition indices included the Hegyi, Biging and Rouvinen indices. The competition trees were selected based on the DI competition indices combined with search radius and number of trees. Pearson correlation analysis were used to examine the relationships between tree growth and competition indices. The results showed that both DD and DI competition indices were significantly correlated with tree growth. However, either increasing search radius or number of trees failed to improve the correlation coefficients between competition indices and tree growth in the DD competition indices. We used the Hegyi competition index as an example to illustrate the relationships between competition index and DBH growth of trees by nonlinear regression models. Regardless of the approaches using either search radius or number of trees, nonlinear regression model were able to explain the relationship well.