Seed weight patterns of Acacia tortilis from seven seed provenances of Botswana

Abstract

Laboratory-based seed storage systems have been developed as an alternative to in situ conservation for indigenous woody plant species. However, interactions between seed quality and environmental variables must be known for each species prior to seed collection, storage and sowing to ensure effective conservation. This study investigated Acacia tortilis seed weight/quality patterns across seven Botswana seed provenances in relation to: soil nutrient status, altitude; latitude; slope angle; % grass cover; height and density of other woody plants nearby. The higher rainfall and relatively eutrophic seed provenances of northwestern Botswana (Chobe, Okavango and Makgadikgadi) were associated with large A. tortilis species and seeds, as well as higher densities of woody plants. Spatial variation in seed weights of A. tortilis was principally a function of rainfall and soil organic carbon. Although more work is required to establish the relationship between seed weight and germination rates for A. tortilis, this research suggests that seed collection should focus on sites with high levels of rainfall and soil organic carbon.