Dioecious Allanblackia stuhlmannii, in East Usambara Mountains becomes a farmland tree when farmers leave the species after clearing the forests. This study examined the process of continuous thinning on sex ratio. Density in natural forest was estimated to be 34–74 mature trees per hectare with an average male:female ratio among reproducing trees observed to be 1:0.59. Density in farmland was 0.5–20 trees per hectare with male:female ratio ranging from 1:0.48 on recent farmland to 1:2 on old farmland. Our results suggest that the reduction of Allanblackia trees in new clearings was not sex biased; however, subsequent cutting targeted mainly males leaving farmland to be populated predominantly with females. Initial sex segregation of A. stuhlmannii is not known, but a 10-year old gene bank of related Allanblackia parviflora in Ghana suggests an even segregation. Allanblackia is gender stable albeit there are few observations of plants changing from male to female during the first year’s flowering and occasional fruit production in males. Average diameter at breast height for first flowering of 44 males was 13.3 cm and that of 17 females 16.3 cm. Decline in Allanblackia trees in farmland from 2011 to 2016 was estimated at about 13% (range from 0 to 23% in monitoring plots) and most of these were male trees.

中文翻译：

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雌雄异株的 Allanblackia stuhlmannii (Engl.) 的性别比例。在坦桑尼亚乌桑巴拉森林和农田

东乌桑巴拉山脉的雌雄异株 Allanblackia stuhlmannii 当农民在清除森林后离开该物种时成为农田树。本研究考察了性别比持续变薄的过程。天然林中的密度估计为每公顷 34-74 棵成熟树木，观察到的繁殖树木之间的平均雄性：雌性比为 1：0.59。农田密度为每公顷0.5-20棵树，男女比例从新农田的1：0.48到旧农田的1：2不等。我们的结果表明，新空地中 Allanblackia 树的减少没有性别偏见；然而，随后的砍伐主要针对离开农田的男性，主要是女性。尚不清楚 A. stuhlmannii 的初始性别隔离，但是加纳一个 10 年前的相关 Allanblackia parviflora 基因库表明了一种均匀的分离。Allanblackia 是性别稳定的，尽管在第一年开花期间很少观察到植物从雄性变为雌性，并且雄性偶尔会产生果实。44 只雄性首次开花的胸高平均直径为 13.3 厘米，17 只雌性的平均胸高为 16.3 厘米。2011 年至 2016 年农田 Allanblackia 树的下降估计约为 13%（监测地块的范围为 0 至 23%），其中大部分是雄树。