Schrumpf Marion, Axmacher Jan C, Zech Wolfgang, Lehmann Johannes, Lyaruu Herbert V C
Department of Soil Science, University of Bayreuth, D-95440 Bayreuth, Germany.
Sci Total Environ. 2007 Apr 15;376(1-3):241-54. doi: 10.1016/j.scitotenv.2007.01.076. Epub 2007 Mar 1.
At the lower parts of the forest belt at Mt. Kilimanjaro, selective logging has led to a mosaic of mature forest, old secondary forests ( approximately 60 years), and old clearings ( approximately 10 years) covered by shrub vegetation. These variations in the vegetation are reflected by differences in nutrient leaching from the canopy and in both amount and quality of litter reaching the ground, thereby also influencing mineralization rates and the composition of seepage water in litter percolate and soil solution. The aim of this study was to investigate how above- and belowground nutrient dynamics vary between regeneration stages, and if forest regeneration at the clearings is hampered by a deterioration of abiotic site conditions. K, Mg, Ca, Na and N compounds were analysed in rainfall, throughfall, organic layer percolate and the soil solution to a depth of 1.00 m at three clearings, three secondary forest and four mature forest sites. Element fluxes via throughfall showed only small variations among regeneration stages except for K and NO(3)-N. With 57-83 kg ha(-1) a(-1)and 2.6-4.1 kg ha(-1) a(-1) respectively, K and NO(3)-N fluxes via throughfall were significantly higher at the clearings than at the mature forest sites (32-37 and 0.7-1.0 kg ha(-1) a(-1) for K and NO(3)-N). In organic layer percolate and in soil solution at 0.15-m soil depth, concentrations of K, Mg, Ca and N were highest at the clearings. In the organic layer percolate, median K concentrations were e.g. 7.4 mg l(-1) for the clearings but only 1.4 mg l(-1) for the mature forests, and for NO(3)-N, median concentrations were 3.1 mg l(-1) for the clearings but only 0.92 mg l(-1) for the mature forest sites. Still, differences in annual means between clearings and mature forests were not always significant due to a high variability within the clearings. With the exception of NO(3)-N, belowground nutrient concentrations in secondary forests ranged between concentrations in mature forests and clearings. Vegetation type-specific differences decreased with increasing soil depths in the soil solution. Overall, the opening of the forest led to a higher spatial and seasonal variation of nutrient concentrations in the seepage water. These results suggest differences in both mineralization rates and in nutrient budgeting at different regeneration stages. Since nutrient availability was highest at the clearings and no compaction of the soil was observed, deterioration of soil properties did not seem to be the main reason for the impeded regeneration on the clearings.
在乞力马扎罗山森林带的较低区域，选择性采伐导致形成了由成熟森林、老龄次生林（约60年树龄）和老龄林中空地（约10年树龄）组成的镶嵌景观，林中空地被灌木植被覆盖。植被的这些差异反映在树冠层养分淋溶以及落到地面的凋落物数量和质量的差异上，进而也影响了矿化速率以及凋落物渗滤液和土壤溶液中渗流水的成分。本研究的目的是调查地上和地下养分动态在不同更新阶段之间如何变化，以及林中空地的森林更新是否受到非生物立地条件恶化的阻碍。在三个林中空地、三个次生林和四个成熟林样地，对降雨、穿透雨、有机层渗滤液和深度达1.00米的土壤溶液中的钾、镁、钙、钠和氮化合物进行了分析。除了钾和硝酸根 - 氮外，穿透雨的元素通量在不同更新阶段之间仅显示出微小差异。钾和硝酸根 - 氮通过穿透雨的通量分别为57 - 83千克·公顷⁻¹·年⁻¹和2.6 - 4.1千克·公顷⁻¹·年⁻¹，林中空地的通量显著高于成熟林样地（钾和硝酸根 - 氮分别为32 - 37千克·公顷⁻¹·年⁻¹和0.7 - 1.0千克·公顷⁻¹·年⁻¹）。在有机层渗滤液和0.15米土壤深度的土壤溶液中，钾、镁、钙和氮的浓度在林中空地最高。例如，在有机层渗滤液中，林中空地钾的中位浓度为7.4毫克·升⁻¹，而成熟林仅为1.4毫克·升⁻¹；对于硝酸根 - 氮，林中空地的中位浓度为3.1毫克·升⁻¹，而成熟林样地仅为0.92毫克·升⁻¹。不过，由于林中空地内变化较大，林中空地和成熟林之间的年平均值差异并不总是显著。除了硝酸根 - 氮外，次生林地下养分浓度介于成熟林和林中空地之间。土壤溶液中特定植被类型的差异随着土壤深度增加而减小。总体而言，森林的砍伐导致渗流水养分浓度在空间和季节上有更高的变化。这些结果表明不同更新阶段在矿化速率和养分收支方面存在差异。由于养分有效性在林中空地最高且未观察到土壤压实，土壤性质恶化似乎不是林中空地更新受阻的主要原因。
