Akselsson Cecilia, Westling Olle, Alveteg Mattias, Thelin Gunnar, Fransson Ann-Mari, Hellsten Sofie
IVL Swedish Environmental Research Institute, Göteborg, Sweden.
Sci Total Environ. 2008 Oct 15;404(2-3):284-9. doi: 10.1016/j.scitotenv.2007.11.017. Epub 2007 Dec 26.
Nitrogen (N) is often considered to be the major factor limiting tree growth in northern forest ecosystems. An increased N availability, however, increases the demand for other nutrients such as base cations and phosphorous (P) which in turn may change which nutrient is the limiting factor. If P or base cations become limiting, N will start to leach which means a risk of increased eutrophication of surface waters. As many studies focus on base cations, this study instead aims at estimating P budgets on a regional scale for different harvesting scenarios relevant for Swedish conditions. P budget calculations were carried out for 14,550 coniferous sites from the Swedish National Forest Inventory, as weathering+deposition-harvesting-leaching. Three scenarios with different harvest intensities were used: 1) no harvesting, 2) stem harvesting and 3) whole-tree harvesting. The input data were derived from measurements and model results. The P budget estimates indicate that harvesting, especially whole-tree harvesting, result in net losses of P in large parts of Sweden. The highest losses were found in southern Sweden due to high growth rate in this area. In the whole-tree harvesting scenario the losses exceeded 1 kg ha(-1) y(-1) on many sites. N budget calculations on the same sites indicate that N generally accumulates in the whole country and especially in the southern parts. Consequently, the N and P budget calculations indicate that the forests in southern Sweden are in a transition phase from N-to P-limitation to growth. This transition will proceed as long as the accumulation of N continues. These results are important in a sustainable forestry context, as a basis for assessing the risk of future N leaching, and in designing recommendations for abatement strategies of N deposition and for application of wood ash recycling and N fertilization.
氮（N）通常被认为是北方森林生态系统中限制树木生长的主要因素。然而，氮供应量的增加会增加对其他养分（如碱性阳离子和磷（P））的需求，这反过来可能会改变限制因素是哪种养分。如果磷或碱性阳离子成为限制因素，氮将开始淋失，这意味着地表水富营养化加剧的风险。由于许多研究关注碱性阳离子，本研究旨在针对与瑞典情况相关的不同采伐情景，在区域尺度上估算磷预算。对瑞典国家森林资源清查中的14550个针叶林站点进行了磷预算计算，计算方法为风化+沉积-采伐-淋失。使用了三种不同采伐强度的情景：1）不采伐，2）树干采伐，3）全树采伐。输入数据来自测量和模型结果。磷预算估计表明，采伐，尤其是全树采伐，导致瑞典大部分地区的磷净损失。由于该地区生长速度高，瑞典南部的损失最大。在全树采伐情景下，许多站点的损失超过1千克·公顷⁻¹·年⁻¹。对相同站点的氮预算计算表明，氮在全国范围内普遍积累，尤其是在南部地区。因此，氮和磷预算计算表明，瑞典南部的森林正处于从氮限制到磷限制再到生长的过渡阶段。只要氮的积累继续，这种过渡就会持续。这些结果在可持续林业背景下很重要，可作为评估未来氮淋失风险的基础，并为设计氮沉降减排策略、木灰回收利用和氮肥施用的建议提供依据。
