Agroforestry Systems 59: 289–294, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. 289 Population status and gender imbalance of the marula tree, Sclerocarya birrea subsp. caffra in northern Namibia Elizabeth Nghitoolwa, John B. Hall ∗ and Fergus L. Sinclair School of Agricultural and Forest Sciences, University of Wales, Bangor, UK; ∗ Author for correspondence (e-mail: j.b.hall@bangor.ac.uk; fax: 44 1248 382832) Key words: Diameter class distribution, Parkland, Sex ratio, Wooded farmland Abstract The population status of many wild fruit trees that support rural people in Africa remains poorly understood despite its importance for their management. Here, we establish a baseline for size class distribution and gender ratios for marula (Sclerocarya birrea subsp. caffra), a widespread but sparsely distributed species of wooded farmland, that has both traditional importance to rural communities and an emerging commercial potential. A population of marula trees around two neighbouring villages in northern Namibia was surveyed in August 2001. The stem diameter at 1.3 m height (dbh) of all individuals ≥1 cm dbh in 40 fields, totalling 286 ha in area, was measured and their gender was recorded as female, male or unknown. Over 400 trees were enumerated, the largest >100 cm dbh. Despite the low threshold (1 cm dbh) for inclusion, relatively few trees (around 40%) were <20 cm dbh, suggesting the population may not be self-sustaining. The area was nevertheless well-stocked, with ca 1 tree ha −1 ≥ 20 cm dbh – an unusually high density for Sclerocarya. Tree gender becomes evident when individuals reach about 15 cm dbh. In one village, the sex ratio of larger trees (40–80 cm dbh) was significantly skewed in favour of females. This was attributed to selective elimination of individuals that have failed to fruit and was much less pronounced in the second village. The sparse distribution and gender imbalance of trees have implications in relation to management requirements for ensuring adequate pollen flow. Introduction As for many of the wild fruit trees that support rural populations in Africa (Leakey 1999), the population status of Sclerocarya birrea remains poorly under- stood. Here, we present data on size class distribution and gender ratios for sparse tree populations around villages. We use this information to address vital management issues for dioecious trees in parklands. Sclerocarya birrea (A.Rich.) Hochst. (Anacardi- aceae) is a deciduous tree with a short (to 4 m) bole, frequently 80 cm or more in diameter, and a rounded or spreading crown. This dioecious, mammal- dispersed, species is a widely utilized wild African fruit source, and its natural geographic range is par- ticularly extensive – from Namibia east to the Indian Ocean, through eastern Africa, north to Eritrea and Ethiopia and west to Senegal and Mauritania. It is also remarkable for its bulky main roots, which store water (Van Wyk 1972–1974; Soumaré et al. 1994), and its capacity to thrive under mean annual rainfall as low as 500 to 600 mm. Mature individuals in dry areas may rise as much as 4 m above the woody plants around them to reach heights of 10 to 12 m. There has been archaeological confirmation of exploitation for at least the last 1000 years (Palmer and Pitman 1972–1974; Neumann et al. 1998). Being one of the largest of African dryland trees it has, by virtue of the wide crown spread of mature individuals, long been accorded significance as a shade tree and a venue for meetings in various cultures (Goosen 1985). Three subspecies are recognized. Subsp. birrea, occurs in western Africa and south to Tanzania in east- ern Africa. Subsp. multifoliolata is restricted to Tan- zania, and possibly the neighbouring part of Kenya. Subsp. caffra occurs south of the equator, span- ning the continent from the Atlantic to the Indian