Management of Vitellaria paradoxa in Guinea savanna rangelands in Ghana
From 1993-1994, a study of Vitellaria paradoxa was carried out. This study involved an in-depth review of biological and ecological information on Vitellatia throughout its range. Stand studies and an analysis of the climate in relation to fire risk. There were also experimental investigations of germination and pollination. All field studies were at the site of the Cocoa Research Institute outstation at Bole. Stand characteristics of Vitellaria (>10 cm dbh) at the 68 kM2 plot of the Cocoa Research Institute's Sheanut Research Station, Bole were examined in two strata distinguished on the basis of distance from the nearest village: >3.0 km and <3.0 km. Regeneration (<10 cm dbh) was assessed and recorded for height, root collar diameter and mode of regeneration. Analysis of variance indicated higher stocking of individuals > 10 cm dbh further from villages but significantly more Vitellaria trees >10 m tall close to villages. Suckers accounted for > 86% of regenerating individuals, and more than 90% of regenerating plants were < 50 cm high. Analysis of climatic data indicated a mean drought index (1990-1994) of 514 ± 61 points. However, the fire danger index never reached an extreme value. The germination response of depulped, cracked and intact seeds of Vitellaria sown under- and outside the canopy of mature Vitellatia trees (> 30 cm dbh), showed a significant association between germination and seed treatment: a higher proportion of depulped than intact seeds germinated. Open pollinated flowers, gave significantly lower fruit set than hand-pollinated flowers. There was no difference, however, in the amount of fruit set achieved with pollen from sources 50 m, 500 m and 1000 m away or from flowers of two different style lengths. It is concluded that fires are adversely affecting the population structure and natural regeneration of stands at Bole, and that low fruit set in Vitellaria is due at least in part, to low vector activity. Suggestions are made for future research on the species.