Bush encroachment affects ~45 million ha of Namibia and, without appropriate restoration measures, it negatively affects rangeland productivity and biodiversity. Thinning is a common method to counteract bush encroachment. The thinning strategy applied in north-central Namibia was assessed to examine how effective it has been in reducing bush encroachment. Trees/shrubs were selectively thinned manually, targeting all height classes, except individuals with stem diameters ≥18 cm. We investigated the effects on the vegetation and soil properties using surveys on three freehold farms (in 2016 and 2017) in bush-encroached and previously thinned habitats. Our results revealed significant differences in the mean total nitrogen (TN) content between the treatments; thinned areas had higher TN content which would be beneficial for fast-growing grasses. In the thinned plots, the occurrence probability of red umbrella thorn (Vachellia reficiens Warwa) was significantly reduced, indicating that it was the most harvested species; and umbrella thorn (Vachellia tortilis (Burch.) Brenan spp. heteracantha) was increased, indicating that it favoured reduced densities of dominant species. Natural regeneration was rapid; the tree/shrub abundance in the 0–1-m height class in the thinned area surpassed those in the non-thinned by 34 per cent, ~7.2 years since thinning. Thinning significantly reduced tree/shrub abundances of the 1–3- and >3-m height classes, which was still evident 7.2 years since thinning. Based upon the generalized linear mixed-effects model, tree/shrub counts between treatments may equalize in ~14 and 15 years for the 1–3- and >3-m height classes, respectively. Thinning was effective in reducing tree/shrub abundances and can be used to restore wildlife habitat on the Namibian farmland: however, post-thinning management is required to maintain an open savannah vegetation structure as the 0–1-m height class cohort will eventually grow into mature trees/shrubs.

中文翻译：

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恢复稀疏减少了对纳米比亚中北部永久业权农田的灌木侵占

灌木侵占影响了约 4500 万公顷的纳米比亚，如果没有适当的恢复措施，它会对牧场生产力和生物多样性产生负面影响。疏伐是对抗灌木侵占的常用方法。对纳米比亚中北部应用的疏伐策略进行了评估，以检查其在减少灌木侵占方面的有效性。树木/灌木被人工选择性地细化，针对所有高度等级，茎直径≥18 cm 的个体除外。我们通过调查三个永久业权农场（2016 年和 2017 年）在灌木侵占和先前稀疏的栖息地中调查了对植被和土壤特性的影响。我们的结果显示处理之间的平均总氮 (TN) 含量存在显着差异。间伐区的 TN 含量较高，有利于草的快速生长。间伐地块中，红伞刺（Vachellia reficiens Warwa）的出现概率显着降低，表明它是收获最多的品种；和伞刺（Vachellia tortilis (Burch.) Brenan spp. heteracantha）增加，表明它有利于降低优势物种的密度。自然再生迅速；间伐区 0-1 米高度级别的树木/灌木丰度超过非间伐区 34%，距间伐约 7.2 年。间伐显着降低了 1-3 米和大于 3 米高度等级的树木/灌木丰度，这在间伐后 7.2 年仍然很明显。根据广义线性混合效应模型，对于 1-3 米和＞3 米的高度等级，处理之间的树木/灌木数量可能分别在约 14 年和 15 年内达到平衡。