Effects of frequent veld fires on the seed bank of Herbaceous species at different soil depths in Matopos Research Institute, a semi-arid part of Zimbabwe.

Abstract

Veld fires are very common in the semi-arid tropics, in Zimbabwe alone they frequently occur causing damage to the environment and infrastructure in hence their effect was investigated. The project was carried out in Mahiye a farm in Matopos Research Institute (MRI) and Tshabalala game sanctuary with the aim of investigating the effect of the frequent veld fires on the soil seed bank of herbaceous species. The effect of fire was investigated on three depth levels these being the0-3cm, 3-6cm and 6-9cm. Twelve 100m2 plots were marked in the two sites, 6 in burnt site (Mahiye) and the other 6 in unburnt site (Tshabalala). A species composition survey was done in the plots and identified 32 species. The Mahiye site was burnt before soil sampling, and collected in sequence at soil depths of 0-3cm, 3-6cm and 6-9cm. The soil samples were then germinated on heat sterilised sand in a greenhouse. A total of 1472 plants emerged but only 477 (32.4%) managed to survive up to species identification stage. A total of 21 and 18 species, including forbs and sage, germinated from the burnt and unbumt sit respectively. Grasses dominated both sites and there were no significant differences (P>0.05) in the germination frequencies of the plants between burnt and unbunrt site meaning fire did not affect seed bank in the burnt site. Amongst the species that emerged in the germination trials there were new species like Disitariaveluting. Digitaiia tenatta and sorehumversicolor while other species did not grow in the germination trials. This meant there were significant differences (P<0.05 between species emergence between the in-situ and ex-situ species emergence. The results of the trial also showed that viable seed are mostly found in the upper horizon, the 03cm, while the 3-6 and 69cm did not show significant differences according to the Duncan’s multiple range test.. However when comparing germination frequencies between the three depth levels they showed significant differences (P<0.05). The frequency of increasers, decreasers and invaders did differ significantly between the sites. The burnt and unbumt sites were dominated by decreaser species in the 0-3cm, followed by increaser species in the burnt site and invaders in the unbent site.