Abstract
Cassia abbreviata and Senegalia nigrescens are indigenous trees found in North and Central regions of Botswana. However, inadequate knowledge of their silviculture and decline in population due to deforestation, expanding settlements, infrastructure and agriculture are major threats to most indigenous tree species in Botswana. Like many indigenous tree species, Cassia abbreviata and Senegalia nigrescens are slow-growing and are threatened by overexploitation for numerous uses. Because of the increased demand for medicinal uses, medicinal species such Cassia abbreviata are rapidly disappearing in many habitats and threatened to extinction. This study assessed the response of pre-sowing treatment methods on quiescency and germination of seeds of Cassia abbreviata and Senegalia nigrescens tree species found in semiarid Savanna Ecozone of Botswana. Pre-sowing treatment included immersion in 98% undiluted sulfuric acid (H2SO4) for 15, 30, 45 and 60 minutes, submergence in boiling water for one, two, three minutes and submerged in warm water for 24 hours, mechanical scarification of the seed coat and control. ANOVA showed that there is a highly significant difference (P < 0.0001) among the treatments of C. abbreviata in seed germination and no significant difference among the treatments of S. nigrescens. The highest germination percentage of C. abbreviata seeds was 81%, which was found from seeds immersed in H2SO4 for 30 minutes, while for S. nigrescens seeds, the highest germination percentage was 99%, which was found from seeds treated with mechanical scarification and those immersed in H2SO4 for 15 and 45 minutes. The objective of this study is to determine the effect of pretreatment methods on germination of C. abbreviata and S. nigrescens seeds. Based on these results, we recommend sulphuric acid and mechanical scarification as suitable seed pre-sowing treatments for enhancing the germination of C. abbreviata and S. nigrescens, respectively.
Highlights
Forests and rangelands are the fundamental constituents of arid zone ecosystems which come up with sustentation for satisfactory conditions for agriculture and human livelihoods
Germination Percentages The results indicated that percent germination was affected by pre-sowing treatments in the two species [C.abbreviata-One Way ANOVA: F (9,39) = 54.91, P = 0.00001 and S. nigrescens - One Way ANOVA: F (9, 39) =5.5, P=0.0002)] (Table 2)
For C. abbreviata, the highest mean percent germination was documented in seeds exposed to sulfuric acid for 30 and 15 minutes (81 and 80%), respectively, followed by those subjected to the acid for 45 minutes (77%) and nicking (72%) (Table 2)
Summary
Forests and rangelands are the fundamental constituents of arid zone ecosystems which come up with sustentation for satisfactory conditions for agriculture and human livelihoods. They provide numerous goods and ecosystem services. They are essential habitat for many other organisms.[1] Globally, forests and tree resources have been declining over the past few decades due to deforestation, which threatens othertree dependent organisms.[2] Deforestation has been credited to humanexercises, such as cutting down trees for construction or manufacturing timber and fuelwood, clearing land for cropping or grazing and human settlement.[3] Deforestation has been exacerbated by climate change, drought and forest fires.there is crucial need to reclaim degraded land in arid environments using multipurpose indigenous trees and shrubs These trees and shrubs are adaptable and have evolved to withstand harsh environmental conditions
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