Parkia biglobosa (Jasq.) benth. in Nigeria : a resource assessment
Parkid higlohosa, an important indigenous fruit tree of West Affican Sudanian woodland, was studied with respect to natural population distribution and structure, regeneration, reproductive biology and phytosociology in Nigeria. As relevant background, a comprehensive range-wide monographic account of the species was assembled. An ecological survey covering the range of Parkia in Nigeria was undertaken between 1994-1995. The survey involved four ecological zones ranging from derived to Sudan/Sahel zone transition. In each ecological zone there were two sample sites within each of which there were two land use types. The survey showed that nearest mature con-specific neighbour distance and corresponding stocking for all individuals ý: 10 cm dbh ranged from 25.5 m and 15 tree ha-I in the north down to 91.5 m and I tree ha-I in the south. A gradual increase in stocking from the lowland forest zone boundary to the Sudan savanna was observed. Parkia populations are significantly more concentrated in cultivated fields than in less intensively used areas of the bush fallow. Natural regeneration in Parkia in Nigeria was sparse overall - 9.80 individuals ha-I and coppice shoot regeneration was the main form. Bush fallow conditions favour more regeneration than intense cultivation, and to the south there is more regeneration than in the north. Tree morphological appraisal showed that there tended to be taller trees in the south of the Nigerian range (with a moister climate) but with smaller diameter than in the north. A broader crown diameter typified populations in the northern part of Nigeria range compared with the south. Branching height ranged from 1.7 m in the north to 3.9 m in the south. The tree rarely branched below Im anywhere. Two was the most frequent number of primary branches. Individuals with more than two primary branches per tree occur more frequently in the north of the range. For all morphological parameters except the number of primary branches a significant land use effect was detected. In the survey 136 associated woody species were recorded. More woody tree species were associated with Parkia biglobosa in the south than in the north of its range in Nigeria. A reproductive cycle of 135 days was observed at Saki, Nigeria. Capitulum abortion rate was more than 30% and not related to the tree diameter or crown position. Capitulum, podding efficiency was about 67%. Open pollinated capitula had the highest number of pods per treatment. Parkid displays some degree of self-compatibility. Capitula located >5 m above the ground are more likely to be pollinated than those below.