Early Selection of Tree Species for Regeneration in Degraded Woodland of Southeastern Congo Basin

Miombo woodland (MW) has several multi-purpose forest species, which are over-exploited for agriculture, charcoal and logging. Industrial plantations are among the promising solutions for sustainable management of MW, but high-yielding MW species are still lacking in the forestry sector. In this context, the present study assessed the growth of MW species, with respect to their early (ES) or late (LS) successional status. Seedling development was assessed for eight tree species, which were ES (Combretum collinum, Pterocarpus tinctorius) and LS (Brachystegia boehmii, B. longifolia, B. spiciformis, B. wangermeana, Julbernardia globiflora, J. paniculata), 1, 2 and 4 years after planting. Germination and survival varied in relation to ontogenetic traits of the species, but not the successional status, as was the case for growth and productivity. Seed germination was 60% to 88% for all species (except C. collinum). Seedling survivorship was greater than 70% for most species, except for J. paniculata (36%). ES species have greater growth compared to LS, due to the allocation of biomass to diameter and the length of the root, respectively, from the early stage of seedling development. These two strategies of biomass allocation are positively correlated with height. We further observed two distinct phases of seedling development (0–2 and 2–4 years) for all species. Growth differences among LS species were identified 4 years after planting. Based on seedling biomass, B. spiciformis, C. collinum and P. tinctorius are the most productive potential candidates for reforestation of degraded MW. We concluded that seedling growth and productivity varied according to strategies of biomass allocation that were related to successional status (ES (Chipya group) versus LS (Miombo group)) and to age following planting.

Towards Conservation of Genetic Variation of Tropical Tree Species With Differing Successional Status: The Case of Mansonia altissima A. Chev and Triplochiton scleroxylon K. Schum

Two important West African timber tree species with differing successional status, Mansonia altissima A. Chev and Triplochiton scleroxylon K. Schum were investigated in this study. Triplochiton scleroxylon is a pioneer species found in open forests, whereas Mansonia altissima is a nonpioneer light-demanding tree species occurring in closed forests. Amplified fragment length polymorphism markers were used to compare the genetic diversities of these two timber species in stands with different degrees of human impact (isolated forest patch, logged forest, farmland, plantation, and primary forest). Contrasting effects of human impact on genetic diversity were detected for these two timber species. The results suggested severe effects of human impact on the genetic diversity of Mansonia altissima, a nonpioneer species. However, no adverse effect was recorded in Triplochiton scleroxylon, a pioneer species. These findings indicate that nonpioneer tree species could be more prone to genetic erosion than pioneer tree species as a result of adverse human impacts. Therefore, conservation of genetic diversity in both pioneer and nonpioneer tree species populations would likely necessitate different measures.