Extensive afforestation is currently being widely promoted as a key nature-based solution for climate change mitigation. Fundamental to this strategy is the sequestration of carbon into long-term stable storage, either in wood products or the soil. However, the long-term effects of tree planting on soil carbon, or other soil properties, has rarely been examined. Importantly, afforestation can take many different forms, with differing effects on soil properties. Here, we evaluate how the historical afforestation of sandy heathland adopting a range of management options – including different combinations of conifers and broadleaves in monocultures and mixtures – have affected soil pH, total carbon and nitrogen concentrations, the C:N ratio, and carbon and nitrogen stocks almost a century later. We analyse these properties at a range of soil depths through the organic (litter, F and grass layers) and upper mineral (0–5 cm, 5–10 cm and 10–20 cm depth) soil layers. In comparison to the historical heathland sites, afforestation decreased soil pH, most dramatically under conifers, and increased the C:N ratio. However, there was overall little difference in carbon and nitrogen concentrations between alternative management options. While the total carbon and nitrogen concentrations were much higher in the organic layers of the forest options compared to the open sites, this did not translate into differences in the mineral layers. Furthermore, although we found some evidence of the transferral of carbon and nitrogen into the uppermost soil mineral layers, this was minimal in comparison to the concentrations of the organic layers. The soils at our study site are low quality and sandy, and are therefore unfavourable for incorporating organic matter, but it is still notable how little was incorporated after nearly a century of afforestation. Given the current emphasis on tree planting as a means to tackle climate change, these results demonstrate the fundamental importance of the appropriate consideration of both the afforestation management option and underlying soil type.

目前，广泛推广造林作为缓解气候变化的基于自然的关键解决方案。该策略的基础是将碳隔离在木材产品或土壤中的长期稳定存储中。但是，很少检查植树对土壤碳或其他土壤特性的长期影响。重要的是，绿化可以采取多种形式，对土壤特性的影响也不同。在这里，我们评估了采用一系列管理方案（包括针叶树和阔叶树在单一栽培和混合物中的不同组合）的沙质荒地的历史绿化如何影响土壤的pH值，总碳和氮浓度，C：N比以及碳和氮。近一个世纪后氮库存。我们通过有机层（凋落物，F和草层）和上部矿物层（0-5厘米，5-10厘米和10-20厘米深度）在土壤深度范围内分析这些特性。与历史上的欧石南丛生地相比，植树造林降低了土壤的pH值，在针叶树下最为明显，并增加了C：N比率。但是，替代管理方案之间的碳和氮浓度总体上几乎没有差异。尽管森林林木的有机层中的总碳和氮浓度比空地高得多，但这并没有转化为矿物质层的差异。此外，尽管我们发现了一些证据表明碳和氮转移到了最上层的土壤矿物层中，但是与有机层的浓度相比，这是最小的。我们研究地点的土壤质量低下且沙质，因此不利于有机物的掺入，但值得注意的是，经过近一个世纪的造林，土壤中的掺入量很少。考虑到当前重视植树作为应对气候变化的一种手段，这些结果证明了适当考虑造林管理方案和土壤类型的根本重要性。