(2023) Enhancing Weed Management in a Young Cedar Plantation by Leveraging High-performing Cedar Varieties and Soil Topographical Conditions

This study aimed to investigate an active central Shikoku Island forestry site to assess the growth performance of cedar saplings in the presence of weed competition. By examining the potential of using high-performing cedar varieties, we tried to identify opportunities for reducing weeding efforts. Furthermore, we evaluated the influence of soil layer thickness and terrain ruggedness index (TRI) on the development of randomly selected cedar saplings and discussed the feasibility of selectively targeting weeding efforts in part of a forest compartment. The results showed that the selected variety ‘Takaoka#1’ exhibited superior sapling height, stem diameter, and crown width compared with the common variety ‘Tanoaka’ three years after plantation. Although the advantage of Takaoka#1 in terms of sapling height was somewhat mitigated by the lanceolate tree form of Tanoaka, logistic regression analysis revealed that using Takaoka#1 increased the likelihood of cedar saplings outcompeting weeds for sunlight. Moreover, cedar saplings were found to perform better at sites with thicker soil layers and lower TRI, indicating the need for a gentler terrain. Conversely, weed height was not associated with soil layer thickness or TRI. Logistic regression analyses incorporating soil layer thickness and TRI as explanatory variables confirmed their significant impact on the probability of cedar saplings thriving amidst weed competition. Overall, our study suggests that reducing weeding efforts in a young cedar plantation is possible when using high-performing varieties and strategically identifying sites characterized by thicker soil layers and lower TRI, thus enabling enhanced cedar sapling growth. © 2023 Nihon Ringakkai. All rights reserved.