In European forests, plant N supply varies from regions where N deposition is negligible and a low natural N supply limits production to regions where high N deposition adds to a high natural N supply. Here, we ask if the differences in N supply are too large to make one system of management for wood production, continuous–cover forestry or rotational forestry, optimal across these conditions.

We analyzed the C/N ratio in c. 8400 samples of surficial soil layers along a 2400 km long transect through Sweden and Germany to obtain a quantitative description of differences in plant N supply. We discuss the differences in relation to forest management, especially evidence that soil C/N ratios below 25 are associated with higher N supply, risks of leaching of nitrate, and gaseous losses of N₂O, whereas ratios above 25 are associated with a tighter N cycle and an N limitation to tree growth.

The percent soil with C/N ratios above 25 declines from 91 in N. Norrland in Sweden to 26 in Germany. Simultaneously, mor soils (with a distinct organic layer on top of the mineral soil) decline from 95% to 16%, while mull soils (in which organic matter and mineral particles are mixed) increase from 1% to 40%. However, low C/N ratios also occur in the north, where we find the largest width in C/N ratios from 16 in mull soils to 36 in mor soils, which compares with a variation in Germany from 17 to 27. Soils under conifers generally have higher C/N ratios than soils under broadleaves, but our survey data cannot support that the trees are the sole cause of this pattern. Very low C/N ratios occur in conifer–dominated forests in the north.

The high incidence (74%) of C/N ratios below 25 indicates that forest management in Germany should use methods, which minimize the risk of N losses. Continuous–cover forestry may fulfill that objective. In the north with 9% of the soils below this threshold, risks of N losses are small. There, rotational forestry involving clear–felling alleviates the competition for soil N from larger trees allowing successful regeneration of tree seedlings. From the perspective of interactions between plant N supply and management of forests for wood production, no single management system seems optimal along this large gradient. We propose that research on forest management systems should address the importance of N supply.

在欧洲森林中，植物的氮供应因氮沉积量可忽略不计的地区而不同，自然氮供应量低限制了氮素沉积量增加而自然氮供应量高的地区的产量。在这里，我们要问氮供应的差异是否太大，以至于无法在这些条件下使木材生产，连续覆盖林或轮作林的管理体系达到最佳。

我们分析了c中的C / N比。通过瑞典和德国，在一条2400公里长的样带上，对8400个表层土壤层进行了采样，以定量描述植物氮素供应的差异。我们讨论了与森林经营有关的差异，特别是证据表明低于25的土壤C / N比与更高的氮供应，硝酸盐浸出的风险和N ₂ O的气态损失有关，而高于25的比与紧密管理有关。 N个循环和N个对树木生长的限制。

碳氮比高于25的土壤百分比从瑞典北诺兰郡的91％下降到德国的26％。同时，铁道土壤（在矿质土壤上有明显的有机层）从95％下降到16％，而泥土（混合了有机质和矿物质颗粒的土壤）从1％增加到40％。但是，北部的C / N比也很低，在这里，我们发现C / N比的最大宽度从泥土中的16到mor土壤中的36，与德国的17/27相比有所变化。针叶树下的土壤通常，其C / N比值比宽叶下的土壤高，但是我们的调查数据不能支持树木是造成这种模式的唯一原因。北部针叶林为主的森林中，C / N比非常低。

C / N比低于25的高发生率（74％）表明德国的森林经营应采用使N损失风险最小化的方法。连续覆盖林业可以实现这一目标。在北部，有9％的土壤低于此阈值，氮素流失的风险很小。在那里，涉及清除伐木的轮伐林业减轻了大树对土壤氮的竞争，使树苗得以成功再生。从植物氮的供应与木材生产森林的管理之间的相互作用的角度来看，在这个大梯度上似乎没有单一的管理系统是最佳的。我们建议对森林管理系统的研究应解决氮供应的重要性。