Sclerocarya birrea, commonly known as Marula, has three subspecies with Tanzania being the only country where all subspecies co-exist. This study was done to assess and compare local knowledge, population status, phenology and propagation of the three subspecies. Three sites located north to south of the country were selected for the study. Each of the three sites namely Holili village (North), Kiegea village (East-Central) and Malinzanga village (South) represented one of the subspecies. Local knowledge was assessed by administering a total of 323 questionnaires to at least 20% of the household heads in each study villages. Direct Observations, Key Informants Interviews and PRA were also used to collect data. Study of population status and regeneration of
Sclerocarya birrea involved sampling of two landuse types at each village i.e. wild and on farm environment using the plotless sampling technique. Each plot consisted of 100 nearest neighbour Sclerocarya trees from which dendrometric variables (height, dbh, height to first branch and crown diameter) were measured. At each plot, 10% of 20m x 20m plots were used to assess regeneration status. Species associated with Sclerocarya were also identified and counted at each site. Ten female and ten male trees randomly selected from each site were used for the phenology study from which detailed events of
leafing, flowering and fruiting onsets and durations were recorded. Fruits were counted from under the 10 female trees and diameter and weight of 50 fruits selected randomly from each of the 10 female trees were measured. Cuttings, marcoting and grafting experiments were conducted to test for the most practical and cost-efective propagation method to farmers under their local environmental realities. It was found that although farmers consider marula as an important species and own it on their farms, the species is underutilized in Tanzania due to some institutional barriers. Results from the population
study revealed that the on farm population for subspecies caffra was denser than all other populations. For the other two subspecies the wild populations were denser than their respective on-farm population. Abundance of male trees was higher than female trees for all subspecies and environments. Spatial distribution for all the populations was random with R values close to 1.0, meaning that observed distribution (r_o) was close to the expected distribution (r_e). Male trees were significantly bigger than females. Coppicing from stumps and sprouting from roots were the main form which the population of Sclerocarya birrea is recruited. All aspects of phenology varied by subspecies, land-use, gender and weather with the exception of flowering and fruiting
which did not vary with land-use. Results showed that subspecies multifoliolata had significantly heavier fruits and more yield than subspecies birrea and caffra (p < 0.001). Fruits from subspecies birrea were significantly larger than those from the other two subspecies (p < 0.001).Trees from the wild population yielded more fruits that were also heavier than those from on-farm but the difference was only significant for subspecies multifoliolata (p < 0.001). Results showed that fruit physical properties and yield have allometric relationship with tree size structure and they vary with rainfall and type of subspecies but not with farmers' selection pressure and intervention. Propagation by cuttings and air layering of Sclerocarya birrea failed. Grafting at the beginning of the rain seasons using wild root stock resulted into 99% success and fruiting after just two years. This study concludes that, if Sclerocarya birrea is domesticated in Tanzania it can contribute to food security, income generation and environmental conservation. The government, NGOs and researchers have a key role to play in helping farmers toimprove the management and utilization of marula.