Seed Scarification Reduces Seedling Survival And Tree Growth And Longevity In Senegalia Polyacantha At A Site In Central Zambia, Southern Africa

One of the impediments to artificially regenerating forests is seed dormancy and seed scarification improves germination rate. However, the majority of studies on seed treatment to break dormancy in dry tropical woody species have focussed on the seedling stage and little is known about the effects of seed treatment on saplings and trees. This study, conducted at a permanent site in central Zambia, aimed at determining the effects of seed scarification on seedling emergence and survival and growth and longevity of Senegalia polyacantha, a fast growing and nitrogen-fixing species that is widely distributed in Sub-Saharan Africa. Seedling emergence from scarified and untreated seeds was monitored and first-year survival assessed. Enrichment planting with nursery transplants and direct sowing of scarified seed was undertaken and the survival and growth of planted and non-planted trees monitored for 17 years. Seed scarification increased seedling emergence but seedling survival was significantly reduced. Planted trees from scarified seeds had lower radial growth (0.22 cm yr-1) compared to non-planted trees (0.56 cm yr-1). Planted trees also had a shorter lifespan than non-planted trees. Seed scarification in S. polyacantha should be applied with caution to avoid significant negative effects on seedling survival and growth and longevity of trees.