1. Developing criteria for identifying suitable plantation forest sites for underplanting of Callerya speciosa

Abstract

This study aims to develop a scientific set of criteria for identifying suitable plantation forests for the underplanting of Callerya speciosa, addressing the urgent need arising from the rapid depletion of the species’ natural resources. The research conducted surveys and assessed the growth and tuber yield of naturally occurring and plantation-grown Stemona tuberosa in four representative provinces (Hoa Binh (now Phu Tho), Lao Cai, Bac Giang (now Bac Ninh), and Quang Ninh) and several other northern provinces. Principal Component Analysis (PCA) was applied to determine the influence of site factors on tuber yield. Results showed that tuber yield depends on site conditions. PCA identified six primary factors affecting yield: canopy cover, soil compaction, soil depth, rock content, slope gradient, and topography, with canopy cover being the most influential factor. Based on these findings, the study established classification criteria dividing plantation suitability into three categories: highly suitable, suitable, and unsuitable. Sites with canopy cover ≤ 0.4, low mountain terrain, slope <10 degrees, soil depth >100 cm, loose to slightly compact soil, and rock content < 3 % were classified as highly suitable, while sites with canopy cover ≥ 0.6 or rock content >8 % were deemed unsuitable. These criteria provide forest managers with a foundation for selecting appropriate sites, thereby enhancing the plantation.